CN112769114A - Method for selecting parameters of thyristor valve in controllable arrester - Google Patents
Method for selecting parameters of thyristor valve in controllable arrester Download PDFInfo
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Abstract
本发明提供一种选择可控避雷器中晶闸管阀参数的方法，避雷器本体分为受控元件MOA1和固定元件MOA2，控制单元CU由晶闸管阀K和触发控制系统组成，受控元件MOA1和控制单元CU并联；关键参数选择是晶闸管阀型可控避雷器的研制基础，只有确定了系统对其具体参数要求，才能进行选择合适的晶闸管元件，晶闸管阀型可控避雷器可限制任何形式的操作过电压，给出了持续运行电压、工频过电压、操作过电压和雷电过电压四种电压应力下，确定晶闸管阀参数选择方法和选择结果，其中断态重复峰值电压VDRM可取8kV，电压上升率dU/dt为0.038kV/μs，浪涌电流ITSM不小于24.6kA，电流上升率di/dt为22.0kA/μs，漏电流IL中全电流不超过5mA，其中阻性电流应不超过1mA，选择KP1900A/8500V型号晶闸管。
The invention provides a method for selecting parameters of a thyristor valve in a controllable arrester. The arrester body is divided into a controlled element MOA1 and a fixed element MOA2, a control unit CU consists of a thyristor valve K and a trigger control system, the controlled element MOA1 and the control unit CU Parallel connection; the selection of key parameters is the basis for the development of thyristor valve controllable arresters. Only after the specific parameter requirements of the system can be determined, the appropriate thyristor components can be selected. The parameter selection method and selection result of the thyristor valve are determined under the four voltage stresses of continuous operating voltage, power frequency overvoltage, operating overvoltage and lightning overvoltage. The dt is 0.038kV/μs, the surge current I TSM is not less than 24.6kA, the current rise rate di/dt is 22.0kA/μs, the total current in the leakage current I L is not more than 5mA, and the resistive current should not exceed 1mA, choose KP1900A/8500V type thyristor.
Description
Technical Field
The invention relates to a method for selecting key parameters of an extra-high voltage alternating current thyristor valve type controllable arrester, and provides a method for selecting key parameters of an extra-high voltage alternating current thyristor valve type controllable arresterUnder four kinds of voltage stress of continuous operation voltage, power frequency overvoltage, operation overvoltage and thunder and lightning overvoltage, the parameter selection method and the selection result of the thyristor valve are adopted, the key parameter selection is the development basis of the thyristor valve type controllable arrester, and only the system is determined to meet the specific parameter requirements, so that the patent is the basis and the premise for developing the thyristor valve type controllable arrester, and the method specifically comprises the following steps: off-state repetitive peak voltage VDRMVoltage rise rate du/dt, on-state current ITAVSurge current ITSMCurrent rise rate di/dt, leakage current, etc.
Background
In an ultra-high voltage transmission system, the saturation characteristic of air gap operation impulse discharge voltage is more obvious, and the deep reduction of the operation overvoltage level plays a crucial role in reducing the air gap of a line. When the operating overvoltage is reduced from 1.7pu to 1.6pu, the air gap of the transmission line is reduced by 0.6m on average. In addition, the operation overvoltage level also has a certain influence on the manufacturing difficulty of the power transmission and transformation equipment, so that it is necessary to reduce the operation overvoltage multiple deeply.
At present, 2 schemes are mainly adopted for reducing the operation overvoltage:
(1) the 2 measures of the metal oxide arrester and the breaker additionally provided with the closing resistor are jointly used. The two combined actions can limit the maximum relative 2% statistical operation overvoltage of the system to 1.6-1.7 pu. However, the closing resistor still has great defects in the aspects of operational reliability and economy, a mechanism is complex after the closing resistor is added to the circuit breaker, the operational risk of the circuit breaker is greatly increased, the cost of the circuit breaker is increased more after the closing resistor is added to the circuit breaker, and the circuit breaker does not adopt the closing resistor when the system conditions allow the circuit breaker to be operated by power system operation departments and manufacturers.
(2) When the line between 2 extra-high voltage transformer substations is short, the rated voltage of the lightning arrester is reduced, and the system operation overvoltage can be limited to 1.6-1.7 pu. For example, the length of the shortest line section from Suzhou to Shanghai in Huainan-Nanjing-Shanghai alternating current extra-high voltage transmission engineering is only 60km, if a breaker is not adopted and a closing resistor is added, only a metal oxide arrester is adopted, the rated voltage of the metal oxide arrester needs to be reduced from 828kV to 804kV (the rated voltage is reduced by 3%), and the chargeability of the arrester is increased from 0.77 to 0.79 at present. However, the longer line can not meet the requirement even if the rated voltage of the lightning arrester is reduced to 804 kV. For example, when the length of the extra-high voltage alternating current transmission line is 85.5km, the lightning arrester with 804kV can only reduce the overvoltage along the line to 1.74pu, and still cannot meet the requirement, and the rated voltage of the lightning arrester must be reduced to be lower, and even 762kV (the rated voltage is reduced by 8%) is required to meet the requirement. At the moment, the long-term operation chargeability of the lightning arrester is increased from the current 0.77 to 0.83, so that the aging speed of the lightning arrester resistance card under the normal operation condition is accelerated, and the reliability margin is greatly reduced. And the prerequisite condition for using the 762kV lightning arrester is to limit the system power frequency overvoltage to the bus side 1.2pu and the line side 1.3pu, so that the use condition is extremely limited.
The concept of the controllable lightning arrester is provided according to the urgent need of an extra-high voltage alternating current transmission system for deeply reducing the level of the operating overvoltage and the defects of the conventional operating overvoltage limiting method in the aspects of economy and operation reliability.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for confirming the parameters of a thyristor valve in a controllable arrester, wherein the thyristor valve has high response speed to overvoltage, can be quickly switched on under the condition of operating overvoltage and can be quickly switched off when the current passes zero; compared to a switching type controllable arrester, a thyristor valve type controllable arrester can limit any form of operating overvoltage. Therefore, the flexible limiting method for the operating overvoltage adaptive to the change of the operating condition is researched, and the method has the core content that a controllable lightning arrester is installed on the side of a transformer substation line and a conventional lightning arrester is installed in the middle of the line, so that the operating overvoltage is reduced deeply, and the closing resistance of a breaker is eliminated. The controllable arrester technology is the core of the flexible limiting method for operating overvoltage. Regarding the controllable arrester technology, the key parameter selection is the development foundation of the thyristor valve type controllable arrester, and only if the specific parameter requirements of the system are determined, the proper thyristor element can be selected, the strict serial and parallel structure design is carried out, and the feasible integrated structure design is further carried out.
The continuous operation voltage of the arrester is an effective value of power frequency voltage which is allowed to be applied between the arrester terminals for a long time. The operating voltage is related to the grounding mode and duration of the system. The temperature of the lightning arrester rises when absorbing the overvoltage energy, and the lightning arrester can be normally cooled under the voltage without thermal breakdown after the voltage limiting is finished. The continuous operation voltage of the lightning arrester is generally equal to or higher than the highest operation phase voltage of the system.
In an extra-high voltage alternating current system, the continuous operation voltage of the controllable lightning arrester is the maximum phase voltage of the system, and can be calculated according to the formula (1).
And finally, selecting the continuous operation voltage of the controllable lightning arrester to be 638kV according to GBZ 24842 and 20091000 kV extra-high voltage alternating current transmission and transformation project overvoltage and insulation matching.
According to UcAnd the controllable ratio alpha can be 15 percent, so that the rated voltage of the lightning arrester of the controllable part and the fixed part can be calculated, as shown in the formula (2). The thyristor switch and the controllable part of the lightning arrester are in parallel connection structure, and the voltages of the thyristor switch and the controllable part of the lightning arrester are equal.
Under the continuous operation voltage of the system, the thyristor valve is not conducted, the controllable part in the controllable arrester and the valve plate of the fixed part bear the system voltage together, and the repeated peak voltage U of the disconnected state required to be borne by the thyristor valve can be determinedKAs shown in formula (3).
In addition, the national standard GBT 24845 states in 2018 technical Specification for gapless metal oxide arresters for 1000kV alternating current systems: the resistive current (fundamental current peak value) of the lightning arrester adopting the four-column valve plate parallel structure in the extra-high voltage alternating current system under the continuous operation voltage should not exceed 3mA, and the total current (effective value) should not exceed 20 mA. As shown by lightning arrester type test data and project group test tests, the total current of the single-column valve plate is about 1.4mA under the AC continuous operation voltage, the resistive current (four columns are connected in parallel) of the lightning arrester body is about 1mA, and the leakage current of the lightning arrester is about 6mA under the AC continuous operation voltage after the four columns are connected in parallel.
According to standard and measured data, considering a certain safety margin, in order to reduce the influence of leakage current introduced by the parallel thyristor switch on the fixed part of the lightning arrester, the size of the leakage current of the thyristor switch is reduced as much as possible, and the leakage current I of the thyristor switch connected in parallel with the controllable lightning arrester under the AC continuous operation voltageLThe resistive current should not exceed 1mA, as long as it does not exceed 5mA (full current).
In a power system, a voltage rise whose amplitude exceeds the maximum working phase voltage and frequency is power frequency or close to the power frequency may occur during normal or fault, which is collectively called power frequency voltage rise or power frequency overvoltage. Such overvoltages are generally not dangerous for the electrical equipment normally insulated by the system, but play an important role in determining the insulation level in ultra-high voltage long-distance transmission, for the following reasons:
(1) the amplitude of the operation overvoltage is directly influenced by the increase of the power frequency voltage;
(2) the working conditions and the effect of the protection electric appliance are influenced by the increase of the power frequency voltage. For example, the rated voltage of the lightning arrester must be greater than the power frequency voltage rise value of the connection point, and under the same protection ratio, the higher the rated voltage of the lightning arrester is, the higher the residual voltage value is, and the higher the insulation level of the required electrical equipment is.
(3) The power frequency voltage is long in rising duration, and has great influence on equipment insulation and operation performance, such as free inside oil paper insulation, pollution insulator flashover, iron core overheating, corona and interference thereof and the like.
Three reasons of no-load long line capacitance effect, asymmetric grounding and sudden load shedding are all the reasons of increasing the power frequency voltage of the power system. According to the specification of GBZ 24842 once 20091000 kV extra-high voltage alternating current transmission and transformation project overvoltage and insulation coordination, in an extra-high voltage system in China, the power frequency overvoltage at the transformer substation side of the circuit breaker is not more than 1.3p.u., and the power frequency overvoltage at the line side of the circuit breaker is not more than 1.4p.u.
Power frequency overvoltage caused by no-load long line capacitance effect
Due to power frequency capacitive reactance XCInductive reactance X greater than power frequencyLSo that the capacitive current in the line drops U over the inductive reactance under the influence of the supply potential ELWill make the voltage U on the capacitive reactanceCAbove the supply potential, UC＝E+ULThat is, the voltage on the no-load transmission line is higher than the power supply voltage, which is the increase of the power frequency voltage caused by the inductance-capacitance effect of the no-load line.
Power frequency overvoltage caused by asymmetric grounding
Asymmetric short-circuiting is the most common fault form in a power transmission line, and the voltage of a non-fault phase generally rises when a single phase or two phases are asymmetrically short-circuited to the ground, wherein the voltage of the non-fault phase rises more seriously when the single phase is grounded. The non-fault phase electricity calculation formulas are shown in formulas (4) to (5).
In the formula, X0Is a zero sequence reactance;
X1is a positive sequence reactance;
UAfor faulty phase voltage, UB、UCA non-faulted phase voltage;
and alpha is a grounding coefficient.
In ungrounded neutral systems, X0Is a line to ground capacitive reactance with a large value, X1It is inductive reactance, so the K value must be negative. Power frequency voltage rise in case of single-phase earth faultHigh voltage up to 1.1 times of rated voltage.
For systems in which the neutral point is grounded via an arc suppression coil, the arc suppression coil is used to compensate for the zero sequence capacitance. Whether under-compensated or over-compensated, there is always k → ∞ or k → - ∞. It follows that the non-faulted phase voltage will rise to the line voltage. The grounding mode is adopted by a 35-70 kV system generally.
When the neutral point is directly grounded, the zero sequence reactance is inductive reactance, so the K value is a positive value. When a single-phase earth fault occurs, the voltage of a non-fault phase rises along with the increase of the K value, and the power frequency voltage rises by not more than 1.4 times of phase voltage, namely 0.8 times of rated voltage. Generally, the operation mode is adopted by the system of 110kV and above.
Power frequency overvoltage caused by load shedding
When the power transmission line runs under heavy load, the power frequency voltage is also increased due to sudden load shedding of a certain fault. In this case, the power frequency voltage rise is influenced by many factors, such as the size of the transmission load before the circuit breaker trips, the capacitance effect of the power frequency long line, the characteristics of the generator excitation system and the voltage regulation period, and the inertia of the prime mover speed regulator and the brake equipment.
By analyzing the characteristics of various power frequency overvoltage, the power frequency voltage rise amplitude is relatively small, but the duration is long. According to relevant regulations in GBZ 24842-20091000 kV extra-high voltage alternating current transmission and transformation project overvoltage and insulation coordination, the power frequency overvoltage at the transformer station side of the circuit breaker should not exceed 1.3p.u., and the power frequency overvoltage at the line side of the circuit breaker should not exceed 1.4p.u. Calculated, the maximum U that the system voltage and thyristor switch need to withstand under various operating overvoltagesKAs shown in equation (7).
UK＝U×α＝1257.3×0.15＝188.6kV (7)
When the thyristor valve body is conducted when the voltage is lower than 1.4p.u., the controlled part is short-circuited, the system voltage is completely applied to two ends of the fixed part, the voltage peak value is 1257kV at the moment and is far larger than the rated voltage of the fixed part, and the fixed part acts. Meanwhile, because the power frequency voltage is increased for a long time, if the power frequency overvoltage is limited only by the fixed part, the fixed part of the lightning arrester bears heat generated by heating in the state for a long time, and potential safety hazards exist. Therefore, it can be seen from the above analysis that the thyristor valve body operating voltage should be increased to ensure that the thyristor valve body is in a reliable off state when the system has a power frequency overvoltage, and the controlled portion and the fixed portion together bear the system power frequency overvoltage.
During operation of an electrical power system, sudden changes in operating conditions, such as normal operation or fault operation, may cause interconversion of electromagnetic energy between inductive and capacitive elements within the system, causing oscillatory transients, which may cause overvoltage, i.e., operating overvoltage, on certain equipment or local power networks.
In a direct neutral grounding system, common operating overvoltages are: closing the no-load line overvoltage, cutting off the no-load transformer overvoltage, splitting off the overvoltage and the like. Due to the improved performance of circuit breakers and other equipment, the removal of dead lines and the removal of dead transformer overvoltages has become less severe. The probability of generating high-amplitude splitting overvoltage is very small in practice, so that the no-load circuit switching-on overvoltage is the most serious for an extra-high voltage system, wherein the conditions comprise normal switching-on and automatic reclosing.
The closing operation performed due to normal operation needs is called normal closing, which is also called planned closing. For example, the line is put into normal operation after being overhauled, and the power transmission line is switched on according to the scheduling requirement. Under the condition, no abnormity exists on the circuit before switching on, after switching on, the voltage of each point of the circuit is transited from zero value to the power frequency steady state voltage value considering the capacitance effect, and switching on overvoltage can occur in the transition process. When the power supply voltage is the peak value, the normal switching-on overvoltage is the maximum, and the voltage calculation formula is shown as the formula (8).
Ut＝Em(1-cosω0t)＝Em-Emcosω0t (8)
From the above formula, when t ═ pi/ω0While, UtThe maximum value can be obtained to be 2Em. Since there is always damping in the actual line, UtThe waveform of the normal no-load line closing overvoltage appears as a ringing waveform as shown in fig. 3 (a).
Automatic reclosing is a common operation in a system, wherein the automatic reclosing is controlled by a relay protection system to be tripped and then is closed again after a time delay. When a certain phase of the system is in short circuit with the ground, the circuit breaker trips, the circuit becomes a no-load circuit with ground fault, if the residual voltage on the non-fault phase circuit just reaches the peak value and the circuit breaker is switched on when the positive polarity maximum value of the non-fault phase power supply is about 0.5s later, the voltage of each point of the non-fault phase circuit can be switched on from-EmThe maximum value of the overvoltage amplitude is 3E according to the formula (8) after the transition to the power frequency steady state valuemThe waveform is shown in FIG. 3 (b).
By combining the characteristics of the operation overvoltage, the voltage peak value of the operation overvoltage is related to the type of the operation overvoltage, and if the voltage peak value of the operation overvoltage does not reach the action threshold value of the thyristor valve body, the thyristor valve body is ensured to be in a reliable turn-off state. The maximum voltage peak value U which needs to be borne by the thyristor valve body in the condition is calculatedKAnd (du/dt) K was 175.11kV and 0.234 kV/. mu.s, respectively.
When the operation overvoltage exceeds the action threshold of the thyristor valve body, the valve body is in a conducting state, and according to GBZ 24842-2009, the operation overvoltage is limited to be below 1.6-1.7 p.u., so that the valve body needs to be ensured to act before the voltage rises to the specified voltage. The maximum current passing through the thyristor in the operation overvoltage is 2.8kA and the wave front time is about 200 mus according to the simulation of relevant parameters of the ultra-high voltage transmission line 'Shijiazhuang-Beijing' during the valve body conduction period, so that the di/dt is about 14A/mus.
The accident caused by lightning striking the overhead transmission line accounts for 30-50% of the total accident of the power grid, and meanwhile, the lightning stroke overvoltage wave of the lightning stroke line invading the substation and the power plant from the line is a main factor influencing the safe operation of electrical equipment, and mainly comprises counterattack invasion wave overvoltage and shielding attack invasion wave overvoltage.
(1) Counterattack intrusion wave overvoltage
The lightning stroke of tower overvoltage can be divided into lightning stroke on the tower top without a lightning conductor and lightning stroke on the tower top with the lightning conductor.
When lightning strikes on the top of the tower without the lightning conductor, the lightning current i flows through the tower and the grounding resistor R thereofchThe current flows into the ground, and the amplitude U of the tower top potential is obtained by considering that the impedance of a lightning stroke point is low, so that the influence of the wave resistance of a lightning channel can be omitted in the calculationtdCan be calculated according to equation (9).
Wherein, ILIs the amplitude of the lightning current,
Rchis a resistance to ground, and is,
Lgtthe equivalent inductance of the tower.
When the line has the lightning conductor, the operation experience shows that the number of times of lightning striking the tower in the total number of the lightning falling of the line is related to the number of the lightning conductor and the terrain of the passing region. The ratio of the number of lightning strikes on the tower to the total number of lightning strikes on the line is called the strike rate.
When lightning strikes on the tower top, negative charges in the lightning channel and positive induced charges in the tower, the lightning conductor and the ground are quickly neutralized to form lightning current. On one hand, lightning impulse waves with negative polarity are transmitted downwards along a tower and downwards along a lightning conductor to two sides, so that the potential of the tower top is continuously raised, and the potential of a conducting wire is changed through electromagnetic coupling; on the other hand, the positive polarity lightning which rapidly develops from the tower top to thundercloud causes rapid change of a space electromagnetic field, and causes positive polarity induced lightning waves to appear on the conducting wire. The voltage applied to the line insulator string is the difference between the tower top potential and the conductor potential. Once this voltage exceeds the impulse discharge voltage of the insulator string, the insulator string flashover occurs, creating a counterattack.
(2) Surge intrusion overvoltage
Lightning stroke lead overvoltage can be divided into two situations of no lightning conductor and lightning conductor according to whether the line has the lightning conductor protection.
When lightning strikes on a wire without a lightning conductor, lightning current flows to two sides along the wire to form overvoltage waves and the overvoltage waves are transmitted to the two sides. Lightning current wave i that normally flows through a lightning strike pointzAnd voltage amplitude U on the wiredCan be calculated by the following equations (10) and (11).
High-voltage lines of 110kV and above in China are generally provided with lightning protection wires to prevent the wires from being directly struck by lightning. However, due to various random factors, such as failure of the shielding effect of the lightning conductor, it may also happen that the lightning strikes the conductor by-passing the lightning conductor, commonly referred to as strike-around. The probability of shielding failure in a lightning stroke line is called shielding failure rate PαFor plain and mountain areas, the detour rate can be generally calculated by equation (12).
Although the probability of the shielding failure is low, the amplitude of the lightning current is small when the shielding failure occurs, once the shielding failure occurs, high impact overvoltage is formed, and the line insulator can be subjected to flashover or invade the safety of the substation crisis electrical equipment. The overvoltage amplitude on the line after a shielding failure occurs can also be calculated by equation (12).
By integrating the characteristics of the lightning overvoltage, the lightning overvoltage wave front time is short, the overvoltage amplitude caused by lightning stroke is large, and the lightning current peak value is large. Simulation work is carried out according to relevant parameters of the ultra-high voltage transmission line of Shijiazhuang-Beijing West, and simulation settlement results are shown in a table 1.
TABLE 1 lightning overvoltage requirements on thyristor valve body parameters
According to the simulation calculation result, if the thyristor valve body is not conducted under the lightning overvoltage, the maximum U which the valve body needs to bear is obtainedK、(du/dt)K243kV and 103 kV/mu s respectively, if the thyristor valve body is conducted, the maximum I born by the valve bodyKAnd (di/dt)K24.6kA and 22 kA/. mu.s, respectively.
The various working conditions of continuous operation voltage, power frequency overvoltage, operation overvoltage and lightning overvoltage are comprehensively analyzed, various parameters which need to be borne by the thyristor valve body under various working conditions are obtained, and the summary statistics are shown in table 2.
TABLE 2 requirements of multiple operating conditions on thyristor valve parameters
Note: (1) the two states of turn-off and turn-on of the operation overvoltage exist because the operation overvoltage can have the condition that the voltage peak value does not reach the action threshold value; (2) the reason why the lightning overvoltage has two states of turn-off and turn-on is that two design ideas exist considering that the thyristor valve body is difficult to endure huge di/dt.
As can be seen from the statistical parameters, the thyristor valve operation threshold is set to 190kV so as to avoid the maximum power frequency overvoltage peak and be lower than the lightning overvoltage limit. Meanwhile, the thyristor valve body is ensured to have the total current less than 5mA during continuous operation, otherwise, the leakage current flowing through the upper end fixing part of the lightning arrester is overlarge. Because the thyristor valve body adopts BOD self-triggering action, the conduction time is fast, and the waveform identification is difficult to realize only by taking the voltage at two ends of the thyristor as a criterion, the thyristor valve body is conducted under lightning overvoltage, and the di/dt in the conduction process of the thyristor needs to be restrained. By combining the above analysis, parameters of the thyristor valve body in the controllable arrester can be obtained, as shown in table 3.
TABLE 3 thyristor valve switching parameter requirements
Result of parameter selection
(1) Off-state repetitive peak voltage VDRM
The thyristor switch operating voltage is 190kV, namely the thyristor valve body is ensured to be in a reliable turn-off state no matter under any working condition when the voltage of the two ends of the thyristor valve body is lower than 190 kV. Therefore, the maximum voltage to be borne by the thyristor switch under various working conditions is 190kV, the withstand voltage of a single thyristor cannot meet the requirement, and the thyristor series connection technology must be adopted. The voltage across a single thyristor can be calculated as in equation (13).
Wherein f is the safe use coefficient of the thyristor device;
and m is the serial number of the thyristor devices.
If f is 1.3 and m is temporarily selected by the number of series-connected resistor chips of MOA1, V isDRMAt least 7.8kV, with reference to the highest voltage parameter, V, of the current thyristor deviceDRM8kV can be taken. By consulting thyristor manufacturers, the current thyristor production capacity can meet the requirement of the off-state repeated peak value.
(2)du/dt
According to the analysis of the various working conditions, the thyristor needs to be reliably turned off under the most severe power frequency overvoltage, and the du/dt which the thyristor needs to bear under the maximum power frequency overvoltage is 0.038 kV/mu s through calculation.
(3) On-state current ITAV
Under the continuous operation voltage of the system, the thyristor switch is always in an off state, and only when the overvoltage of the system occurs and reaches a control threshold value, the thyristor switch is switched on for a short time, so that no special requirement is imposed on the on-state rated current of the thyristor switch.
(4) Surge current ITSM
Maximum surge current I to be borne by thyristor switchK24.6kA, the maximum surge current I of the thyristor device is requiredTSMShould not be less than 24.6 kA.
(5)di/dt
According to the calculation, the maximum on-state current increasing rate (di/dt) which is required to be borne by the thyristor switch of the extra-high voltage thyristor valve type controllable arrester under the lightning stroke working conditionKThe concentration was 22.0 kA/. mu.s. In terms of the current production process level of the thyristor device, the prior art is not enough to support the thyristor to meet the requirement of di/dt, so that a di/dt limiting measure needs to be adopted in the design.
(6) Leakage current
The technical specification of the gapless metal oxide arrester for the GB/Z24845 and 20091000 kV alternating current system stipulates that: the resistive current (fundamental current peak value) of the lightning arrester adopting the four-column valve plate parallel structure in the extra-high voltage alternating current system under the continuous operation voltage should not exceed 3mA, and the total current (effective value) should not exceed 20 mA. As shown by lightning arrester type test data and project group test tests, the total current of the single-column valve plate is about 1.4mA under the AC continuous operation voltage, the resistive current (four columns are connected in parallel) of the lightning arrester body is about 1mA, and the leakage current of the lightning arrester is about 6mA under the AC continuous operation voltage after the four columns are connected in parallel.
According to standard and measured data, a certain safety margin is considered to be left, in order to reduce the influence of leakage current introduced by the parallel thyristor switches on the lightning arrester body, the size of the leakage current of the thyristor switches is reduced as much as possible, and the leakage current I of the thyristor switches connected in parallel with the controllable lightning arrester under the alternating current continuous operation voltageLThe preliminary press does not exceed 5mA (full current), where the resistive current should not exceed 1 mA.
In summary, the statistics of the key parameter requirements that the thyristor needs to meet under various working conditions in the extra-high voltage ac thyristor valve type controllable arrester are shown in table 4. Because the existing thyristor devices can not meet the di/dt parameter requirements of the project, the limitation of the parameters on the performance is not considered during model selection, and a KP1900A/8500V type thyristor is selected according to other parameters and comprehensively considering the market application condition.
Table 4 controllable arrester thyristor device parameter requirements
And selecting the device type according to the parameter requirements of the controllable arrester thyristor device in the table 4. And (5) investigating thyristor devices of the Parry, the south vehicle and the ABB.
Under the same voltage withstanding level, the KP1900A/8500V type thyristor has the following key parameters: indexes such as surge current, di/dt tolerance and cost performance are outstanding, other indexes such as on-state current and holding current have small performance difference, and finally the type of the thyristor device is selected to be KP1900A/8500V of Pi Rui.
And carrying out test detection on the selected KP1900A/8500V thyristor. The test results were as follows:
1) the number of the thyristors in series connection can be calculated to be 32 according to the system requirements and the parameters of the thyristors; and in an anti-parallel structure, 64 thyristors are used in total. The continuous operation voltage of each layer of thyristor is 96/32 kVrms, and du/dt is 3 kV/mus. The lightning resistance and the operation impact can reach more than 9kV, du/dt can endure more than 9 kV/mus, and the requirements are met.
2) Through tests, the KP1900A/8500V thyristor allows the maximum di/dt: practical requirements of 2.3 kA/mus, much less than 22 kA/mus, require saturable reactor suppression.
3) The leakage current of the KP1900A/8500V thyristor device has positive temperature characteristics, the leakage current increases along with the temperature rise, the higher the temperature is, the faster the leakage current increases, and the leakage current of the anti-parallel thyristor is in the range of 1.25 mA-2.2 mA and <5mA under the continuous operation voltage within the range of-40 to +60 ℃, so that the requirement is met.
Technical effects
The invention flexibly controls the input quantity of the resistor discs of the lightning arrester, changes the volt-ampere characteristic curve of the lightning arrester, ensures that the lightning arrester has high reliability when the system normally operates, can deeply reduce the operation overvoltage under the transient condition, cancels the closing resistance of a circuit breaker, is more economical than the conventional limiting method, and has great theoretical and engineering innovation significance on an ultra-high voltage alternating current transmission system.
A method of selecting thyristor valve parameters in a controllable arrester, the method comprising:
the lightning arrester body is divided into a controlled element MOA1 and a fixed element MOA2, a control unit CU consists of a thyristor valve K and a trigger control system, and the controlled element MOA1 is connected with the control unit CU in parallel;
under the continuous operation voltage of the system, the thyristor valve K is in a closed state, the control unit CU is switched off, the controlled element MOA1 and the valve plate of the fixed element MOA2 in the controllable lightning arrester jointly bear the continuous operation voltage of the system, and the maximum voltage peak value U required to be borne by the thyristor valve can be obtained according to the maximum phase voltage of the systemK135kV, and the voltage rise rate dU/dt is 0.027 kV/mus;
under the power frequency overvoltage of the system, the thyristor valve K is in a turn-off state, the control unit CU is turned off, the controlled element MOA1 in the controllable lightning arrester has no potential safety hazard, the valve plates of the controlled element MOA1 and the fixed element MOA2 bear the system voltage together, and the maximum voltage peak value U required to be borne by the thyristor valve K can be determinedK188kV, the voltage rise rate dU/dt is 0.038 kV/mus;
under the operation overvoltage of the system, if the peak value of the operation overvoltage does not reach the action threshold value of the thyristor valve body, the thyristor valve K is ensured to be in a reliable turn-off state, and the control unit CU is disconnected; maximum voltage peak value U that thyristor valve body needs to bearKAnd the voltage rise rate dU/dt is 219kV and 0.55 kV/mu s respectively; when the operation overvoltage reaches or exceeds the action threshold value of the thyristor valve body, the thyristor valve K is in a conducting state, the control unit CU is closed, the maximum current passing through the thyristor is 2.8kA, and the current rise rate di/dt is 0.014 kA/mus;
in-systemUnder the lightning overvoltage, if the thyristor valve body K is not conducted under the lightning overvoltage, the control unit CU is disconnected, and then the maximum U which needs to be borne by the valve body is obtainedK243kV, the voltage rise rate dU/dt is 103 kV/mus, if the thyristor valve body K is conducted and the control unit CU is closed, the maximum current peak value I born by the valve body is requiredK24.6kA, and the current rise rate di/dt is 22 kA/mus;
the action voltage of the thyristor valve body should avoid the maximum peak value of the power frequency overvoltage and be lower than the lightning overvoltage limit value, so the action threshold value of the thyristor valve body is set to 190kV, and the repeated peak voltage V of the thyristor device in the off state can be confirmedDRM8kV can be taken;
the main parameters of the required thyristor device can be confirmed through simulation calculation of the extra-high voltage power transmission system under various overvoltage working conditions, wherein the off-state repeated peak voltage VDRM8kV can be taken, the voltage rise rate dU/dt is 0.038 kV/mu s, and the surge current ITSMNot less than 24.6kA, current rise rate di/dt of 22.0 kA/mus, and leakage current ILThe middle and full current does not exceed 5mA, wherein the resistance current should not exceed 1mA, and a KP1900A/8500V model thyristor is selected.
The controlled element MOA1 and the fixed element MOA2 of the lightning arrester body are both composed of a lightning arrester resistance card, a porcelain bushing, a flange, an upper end bolt and a lower end bolt; the thyristor valve has high response speed to overvoltage, can be quickly conducted under the overvoltage operation and is switched off when the current crosses zero; compared with a switch type controllable arrester, the thyristor valve type controllable arrester can limit any form of operation overvoltage; the input quantity of the resistor discs of the lightning arrester is flexibly controlled, and the volt-ampere characteristic curve of the lightning arrester is changed, so that the lightning arrester has high reliability when a system operates normally, the operating overvoltage can be deeply reduced under the transient condition, and the closing resistor of the circuit breaker is cancelled.
The thyristor valve is formed by connecting anti-parallel thyristor pairs in series.
Tests prove that the invention provides a method for selecting parameters of a thyristor valve and a selection result under four voltage stresses of continuous operation voltage, power frequency overvoltage, operation overvoltage and lightning overvoltage, and the KP1900A/8500V thyristor allows the maximum di/dt: 2.3 kA/mus, which is less than 22 kA/mus, needs to be restrained by a saturable reactor, and in terms of the current production process level of the thyristor device, under lightning overvoltage, the prior art is not enough to support the thyristor to meet the di/dt requirement, so that a di/dt limiting measure needs to be adopted in the design; the thyristor needs to be reliably turned off under the most severe power frequency overvoltage, and the calculation shows that the du/dt which the thyristor needs to bear under the maximum power frequency overvoltage is 0.038 kV/mu s, so that the prior art conditions can meet the requirements.
The invention gives the repeated peak voltage V of the off stateDRMAccording to the selection method and the result, the thyristor switch action voltage is 190kV, namely, the thyristor valve body is ensured to be in a reliable turn-off state no matter under any working condition when the voltage of the two ends of the thyristor valve body is lower than 190 kV; therefore, the maximum voltage to be borne by the thyristor switch under various working conditions is 190kV, the withstand voltage of a single thyristor cannot meet the requirement, and the thyristor series connection technology is required; the voltage at two ends of the single thyristor can be calculated according to the formula (1);
wherein f is the safe use coefficient of the thyristor device; and m is the serial number of the thyristor devices. If f is 1.3 and m is selected as 32 series resistors of MOA1, then V isDRMAt least 7.8kV, with reference to the highest voltage parameter, V, of the current thyristor deviceDRMIs 8 kV.
The invention also provides a system for selecting parameters of a thyristor valve in a controllable arrester, which is characterized by comprising:
the control unit CU in the lightning arrester is composed of a thyristor valve K and a trigger control system, a controlled element MOA1 and the control unit CU are connected in parallel, the thyristor valve K is triggered and conducted under the action of an operation overvoltage, the control unit CU is closed, the thyristor valve K is in a turn-off state under the action of a system continuous operation voltage, a temporary overvoltage and a lightning overvoltage, and the CU is disconnected;
the controlled element MOA1 in the lightning arrester body is connected with the fixed element MOA2 in series, under the conditions of continuous operation voltage, power frequency overvoltage and lightning overvoltage, the controlled element MOA1 and the fixed element MOA2 bear system overvoltage together, under the condition of operation overvoltage, the thyristor valve K is triggered and conducted, the CU is closed, the MOA1 is in short circuit, the MOA2 has low residual voltage, and the system operation overvoltage can be deeply reduced;
the fixed element MOA2 in the lightning arrester body is connected with the controlled element MOA1 in series and connected with the control unit CU in parallel, and under the conditions of continuous operation voltage, power frequency overvoltage and lightning overvoltage, the fixed element MOA1 and the fixed element MOA are used for bearing system overvoltage together, under the condition of operation overvoltage, the MOA2 residual voltage is low, and the system operation overvoltage can be deeply reduced;
under the continuous operation voltage of the system, the maximum voltage peak value U which the thyristor valve needs to bear can be obtained according to the maximum phase voltage of the systemK135kV, and the voltage rise rate dU/dt is 0.027 kV/mus; under the power frequency overvoltage of the system, the maximum voltage peak value U born by the thyristor valve K can be determinedK188kV, the voltage rise rate dU/dt is 0.038 kV/mus; under the operation overvoltage of the system, if the peak value of the operation overvoltage does not reach the action threshold value of the thyristor valve body, the maximum voltage peak value U which needs to be born by the thyristor valve bodyKAnd the voltage rise rate dU/dt is 219kV and 0.55 kV/mu s respectively; when the operation overvoltage reaches or exceeds the action threshold of the thyristor valve body, the maximum current passing through the thyristor is 2.8kA, and the current rise rate di/dt is 0.014 kA/mus; under the lightning overvoltage of the system, if the thyristor valve body K is not conducted under the lightning overvoltage, the control unit CU is disconnected, and then the maximum U required to be borne by the valve body is obtainedK243kV, the voltage rise rate dU/dt is 103 kV/mus, if the thyristor valve body K is conducted and the control unit CU is closed, the maximum current peak value I born by the valve body is requiredK24.6kA, and the current rise rate di/dt is 22 kA/mus;
the action voltage of the thyristor valve body should avoid the maximum peak value of the power frequency overvoltage and be lower than the lightning overvoltage limit value, so the action threshold value of the thyristor valve body is set to 190kV, and the repeated peak voltage V of the thyristor device in the off state can be confirmedDRM8kV can be taken;
the required thyristor can be confirmed through simulation calculation of the extra-high voltage power transmission system under various overvoltage working conditionsMain parameter of the device, wherein the off-state repetitive peak voltage VDRM8kV can be taken, the voltage rise rate dU/dt is 0.038 kV/mu s, and the surge current ITSMNot less than 24.6kA, current rise rate di/dt of 22.0 kA/mus, and leakage current ILThe middle and full current does not exceed 5mA, wherein the resistance current should not exceed 1mA, and a KP1900A/8500V model thyristor is selected.
The controlled element MOA1 and the fixed element MOA2 of the lightning arrester body are both composed of a lightning arrester resistance card, a porcelain bushing, a flange, an upper end bolt and a lower end bolt; the thyristor valve has high response speed to overvoltage, can be quickly conducted under the overvoltage operation and is switched off when the current crosses zero; compared with a switch type controllable arrester, the thyristor valve type controllable arrester can limit any form of operation overvoltage; the input quantity of the resistor discs of the lightning arrester is flexibly controlled, and the volt-ampere characteristic curve of the lightning arrester is changed, so that the lightning arrester has high reliability when a system operates normally, the operating overvoltage can be deeply reduced under the transient condition, and the closing resistor of the circuit breaker is cancelled.
The thyristor valve is formed by connecting anti-parallel thyristor pairs in series.
Tests prove that the invention provides a method for selecting parameters of a thyristor valve and a selection result under four voltage stresses of continuous operation voltage, power frequency overvoltage, operation overvoltage and lightning overvoltage, and the KP1900A/8500V thyristor allows the maximum di/dt: 2.3 kA/mus, which is less than 22 kA/mus, needs to be restrained by a saturable reactor, and in terms of the current production process level of the thyristor device, under lightning overvoltage, the prior art is not enough to support the thyristor to meet the di/dt requirement, so that a di/dt limiting measure needs to be adopted in the design; the thyristor needs to be reliably turned off under the most severe power frequency overvoltage, and the calculation shows that the du/dt which the thyristor needs to bear under the maximum power frequency overvoltage is 0.038 kV/mu s, so that the prior art conditions can meet the requirements.
The invention gives the repeated peak voltage V of the off stateDRMAccording to the selection method and the result, the thyristor switch action voltage is 190kV, namely, the thyristor valve body is ensured to be in a reliable turn-off state no matter under any working condition when the voltage of the two ends of the thyristor valve body is lower than 190 kV; therefore, the thyristor switch is considered to be moreThe maximum voltage to be born under the working condition is 190kV, the withstand voltage of a single thyristor cannot meet the requirement, and the thyristor series connection technology must be adopted; the voltage at two ends of the single thyristor can be calculated according to the formula (1);
wherein f is the safe use coefficient of the thyristor device; and m is the serial number of the thyristor devices. If f is 1.3 and m is selected as 32 series resistors of MOA1, then V isDRMAt least 7.8kV, with reference to the highest voltage parameter, V, of the current thyristor deviceDRMIs 8 kV.
Drawings
A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:
FIG. 1 is a schematic view of a thyristor valve type controllable arrester;
FIG. 2 is a schematic diagram of the operation of the capacitive dynamic voltage limiter;
fig. 3 is a line voltage waveform diagram when an unloaded line is closed.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The concept of the controllable lightning arrester is provided according to the urgent need of an extra-high voltage alternating current transmission system for deeply reducing the level of the operating overvoltage and the defects of the conventional operating overvoltage limiting method in the aspects of economy and operation reliability.
In the late nineties of the twentieth century, american researchers proposed the concept of a reactive compensation capacitance Dynamic Voltage limiter (CDVS) consisting of a lightning arrester and a thyristor switch in segmented parallel connection for suppressing the operating overvoltage generated by the switching of a compensation Capacitor, the principle of which is shown in fig. 2.
When the capacitor is thrown, the breaker is switched on, the thyristor pair is conducted, the MOV2 is in short circuit, and the voltage at the two ends of the capacitor C is only the residual voltage of the MOV1, so that the overvoltage generated at the two ends of the capacitor due to switching-on is limited, and the dynamic process generated due to switching operation is quickly inhibited. When the capacitor is switched off, the breaker is opened, the thyristor switches are all conducted, the MOV 0-MOV 4 are in short circuit, and a quick discharge loop is provided for the capacitor so as to limit overvoltage caused by breakover of the breaker.
The dynamic voltage limiter adopts a thyristor switch to control the input and the exit of an arrester element, solves the problem that the response time of a mechanical switch cannot meet the requirement, but is only used for inhibiting the operation overvoltage generated by switching of a capacitor in a low-voltage system, and the effect of limiting the operation overvoltage of an ultra-high voltage power transmission system is not researched.
The researches change the structure of the lightning arrester to improve the performance of the lightning arrester, and beneficial attempts and researches are carried out on a limiting method of system overvoltage, but the researches are only limited to theoretical analysis and simulation calculation of low voltage grade, model machine development and experimental research are not carried out, and actual engineering application is not available.
Aiming at the defects of the prior art, the invention provides a method for confirming the parameters of a thyristor valve in a controllable arrester, wherein the thyristor valve has high response speed to overvoltage, can be quickly switched on under the condition of operating overvoltage and can be quickly switched off when the current passes zero; compared to a switching type controllable arrester, a thyristor valve type controllable arrester can limit any form of operating overvoltage. Therefore, the flexible limiting method for the operating overvoltage adaptive to the change of the operating condition is researched, and the method has the core content that a controllable lightning arrester is installed on the side of a transformer substation line and a conventional lightning arrester is installed in the middle of the line, so that the operating overvoltage is reduced deeply, and the closing resistance of a breaker is eliminated. The controllable arrester technology is the core of the flexible limiting method for operating overvoltage. Regarding the controllable arrester technology, the key parameter selection is the development foundation of the thyristor valve type controllable arrester, and only if the specific parameter requirements of the system are determined, the proper thyristor element can be selected, the strict serial and parallel structure design is carried out, and the feasible integrated structure design is further carried out.
The continuous operation voltage of the arrester is an effective value of power frequency voltage which is allowed to be applied between the arrester terminals for a long time. The operating voltage is related to the grounding mode and duration of the system. The temperature of the lightning arrester rises when absorbing the overvoltage energy, and the lightning arrester can be normally cooled under the voltage without thermal breakdown after the voltage limiting is finished. The continuous operation voltage of the lightning arrester is generally equal to or higher than the highest operation phase voltage of the system.
In an extra-high voltage alternating current system, the continuous operation voltage of the controllable lightning arrester is the maximum phase voltage of the system, and can be calculated according to the formula (1).
And finally, selecting the continuous operation voltage of the controllable lightning arrester to be 638kV according to GBZ 24842 and 20091000 kV extra-high voltage alternating current transmission and transformation project overvoltage and insulation matching.
According to UcAnd a controllable ratio alpha, which can be 15%, to calculate the controllable part and the fixed partThe rated voltage of the lightning arrester is shown as the formula (2). The thyristor switch and the controllable part of the lightning arrester are in parallel connection structure, and the voltages of the thyristor switch and the controllable part of the lightning arrester are equal.
Under the continuous operation voltage of the system, the thyristor valve is not conducted, the controllable part in the controllable arrester and the valve plate of the fixed part bear the system voltage together, and the repeated peak voltage U of the disconnected state required to be borne by the thyristor valve can be determinedKAs shown in formula (3).
In addition, the national standard GBT 24845 states in 2018 technical Specification for gapless metal oxide arresters for 1000kV alternating current systems: the resistive current (fundamental current peak value) of the lightning arrester adopting the four-column valve plate parallel structure in the extra-high voltage alternating current system under the continuous operation voltage should not exceed 3mA, and the total current (effective value) should not exceed 20 mA. As shown by lightning arrester type test data and project group test tests, the total current of the single-column valve plate is about 1.4mA under the AC continuous operation voltage, the resistive current (four columns are connected in parallel) of the lightning arrester body is about 1mA, and the leakage current of the lightning arrester is about 6mA under the AC continuous operation voltage after the four columns are connected in parallel.
According to standard and measured data, considering a certain safety margin, in order to reduce the influence of leakage current introduced by the parallel thyristor switch on the fixed part of the lightning arrester, the size of the leakage current of the thyristor switch is reduced as much as possible, and the leakage current I of the thyristor switch connected in parallel with the controllable lightning arrester under the AC continuous operation voltageLThe resistive current should not exceed 1mA, as long as it does not exceed 5mA (full current).
In a power system, a voltage rise whose amplitude exceeds the maximum working phase voltage and frequency is power frequency or close to the power frequency may occur during normal or fault, which is collectively called power frequency voltage rise or power frequency overvoltage. Such overvoltages are generally not dangerous for the electrical equipment normally insulated by the system, but play an important role in determining the insulation level in ultra-high voltage long-distance transmission, for the following reasons:
(1) the amplitude of the operation overvoltage is directly influenced by the increase of the power frequency voltage;
(2) the working conditions and the effect of the protection electric appliance are influenced by the increase of the power frequency voltage. For example, the rated voltage of the lightning arrester must be greater than the power frequency voltage rise value of the connection point, and under the same protection ratio, the higher the rated voltage of the lightning arrester is, the higher the residual voltage value is, and the higher the insulation level of the required electrical equipment is.
(3) The power frequency voltage is long in rising duration, and has great influence on equipment insulation and operation performance, such as free inside oil paper insulation, pollution insulator flashover, iron core overheating, corona and interference thereof and the like.
Three reasons of no-load long line capacitance effect, asymmetric grounding and sudden load shedding are all the reasons of increasing the power frequency voltage of the power system. According to the specification of GBZ 24842 once 20091000 kV extra-high voltage alternating current transmission and transformation project overvoltage and insulation coordination, in an extra-high voltage system in China, the power frequency overvoltage at the transformer substation side of the circuit breaker is not more than 1.3p.u., and the power frequency overvoltage at the line side of the circuit breaker is not more than 1.4p.u.
Power frequency overvoltage caused by no-load long line capacitance effect
Due to power frequency capacitive reactance XCInductive reactance X greater than power frequencyLSo that the capacitive current in the line drops U over the inductive reactance under the influence of the supply potential ELWill make the voltage U on the capacitive reactanceCAbove the supply potential, UC＝E+ULThat is, the voltage on the no-load transmission line is higher than the power supply voltage, which is the increase of the power frequency voltage caused by the inductance-capacitance effect of the no-load line.
Power frequency overvoltage caused by asymmetric grounding
Asymmetric short-circuiting is the most common fault form in a power transmission line, and the voltage of a non-fault phase generally rises when a single phase or two phases are asymmetrically short-circuited to the ground, wherein the voltage of the non-fault phase rises more seriously when the single phase is grounded. The non-fault phase electricity calculation formulas are shown in formulas (4) to (5).
In the formula, X0Is a zero sequence reactance;
X1is a positive sequence reactance;
UAfor faulty phase voltage, UB、UCA non-faulted phase voltage;
and alpha is a grounding coefficient.
In ungrounded neutral systems, X0Is a line to ground capacitive reactance with a large value, X1It is inductive reactance, so the K value must be negative. When single-phase earth fault occurs, the power frequency voltage is increased and can reach 1.1 times of rated voltage.
For systems in which the neutral point is grounded via an arc suppression coil, the arc suppression coil is used to compensate for the zero sequence capacitance. Whether under-compensated or over-compensated, there is always k → ∞ or k → - ∞. It follows that the non-faulted phase voltage will rise to the line voltage. The grounding mode is adopted by a 35-70 kV system generally.
When the neutral point is directly grounded, the zero sequence reactance is inductive reactance, so the K value is a positive value. When a single-phase earth fault occurs, the voltage of a non-fault phase rises along with the increase of the K value, and the power frequency voltage rises by not more than 1.4 times of phase voltage, namely 0.8 times of rated voltage. Generally, the operation mode is adopted by the system of 110kV and above.
Power frequency overvoltage caused by load shedding
When the power transmission line runs under heavy load, the power frequency voltage is also increased due to sudden load shedding of a certain fault. In this case, the power frequency voltage rise is influenced by many factors, such as the size of the transmission load before the circuit breaker trips, the capacitance effect of the power frequency long line, the characteristics of the generator excitation system and the voltage regulation period, and the inertia of the prime mover speed regulator and the brake equipment.
By analyzing multiple types of power frequencyThe characteristics of the voltage show that the power frequency voltage has relatively small amplitude but long duration. According to relevant regulations in GBZ 24842-20091000 kV extra-high voltage alternating current transmission and transformation project overvoltage and insulation coordination, the power frequency overvoltage at the transformer station side of the circuit breaker should not exceed 1.3p.u., and the power frequency overvoltage at the line side of the circuit breaker should not exceed 1.4p.u. Calculated, the maximum U that the system voltage and thyristor switch need to withstand under various operating overvoltagesKAs shown in equation (7).
UK＝U×α＝1257.3×0.15＝188.6kV (7)
When the thyristor valve body is conducted when the voltage is lower than 1.4p.u., the controlled part is short-circuited, the system voltage is completely applied to two ends of the fixed part, the voltage peak value is 1257kV at the moment and is far larger than the rated voltage of the fixed part, and the fixed part acts. Meanwhile, because the power frequency voltage is increased for a long time, if the power frequency overvoltage is limited only by the fixed part, the fixed part of the lightning arrester bears heat generated by heating in the state for a long time, and potential safety hazards exist. Therefore, it can be seen from the above analysis that the thyristor valve body operating voltage should be increased to ensure that the thyristor valve body is in a reliable off state when the system has a power frequency overvoltage, and the controlled portion and the fixed portion together bear the system power frequency overvoltage.
During operation of an electrical power system, sudden changes in operating conditions, such as normal operation or fault operation, may cause interconversion of electromagnetic energy between inductive and capacitive elements within the system, causing oscillatory transients, which may cause overvoltage, i.e., operating overvoltage, on certain equipment or local power networks.
In a direct neutral grounding system, common operating overvoltages are: closing the no-load line overvoltage, cutting off the no-load transformer overvoltage, splitting off the overvoltage and the like. Due to the improved performance of circuit breakers and other equipment, the removal of dead lines and the removal of dead transformer overvoltages has become less severe. The probability of generating high-amplitude splitting overvoltage is very small in practice, so that the no-load circuit switching-on overvoltage is the most serious for an extra-high voltage system, wherein the conditions comprise normal switching-on and automatic reclosing.
The closing operation performed due to normal operation needs is called normal closing, which is also called planned closing. For example, the line is put into normal operation after being overhauled, and the power transmission line is switched on according to the scheduling requirement. Under the condition, no abnormity exists on the circuit before switching on, after switching on, the voltage of each point of the circuit is transited from zero value to the power frequency steady state voltage value considering the capacitance effect, and switching on overvoltage can occur in the transition process. When the power supply voltage is the peak value, the normal switching-on overvoltage is the maximum, and the voltage calculation formula is shown as the formula (8).
Ut＝Em(1-cosω0t)＝Em-Emcosω0t (8)
From the above formula, when t ═ pi/ω0While, UtThe maximum value can be obtained to be 2Em. Since there is always damping in the actual line, UtThe waveform of the normal no-load line closing overvoltage appears as a ringing waveform as shown in fig. 3 (a).
Automatic reclosing is a common operation in a system, wherein the automatic reclosing is controlled by a relay protection system to be tripped and then is closed again after a time delay. When a certain phase of the system is in short circuit with the ground, the circuit breaker trips, the circuit becomes a no-load circuit with ground fault, if the residual voltage on the non-fault phase circuit just reaches the peak value and the circuit breaker is switched on when the positive polarity maximum value of the non-fault phase power supply is about 0.5s later, the voltage of each point of the non-fault phase circuit can be switched on from-EmThe maximum value of the overvoltage amplitude is 3E according to the formula (8) after the transition to the power frequency steady state valuemThe waveform is shown in FIG. 3 (b).
By combining the characteristics of the operation overvoltage, the voltage peak value of the operation overvoltage is related to the type of the operation overvoltage, and if the voltage peak value of the operation overvoltage does not reach the action threshold value of the thyristor valve body, the thyristor valve body is ensured to be in a reliable turn-off state. Calculated, in this case, the thyristor valve body has to withstand the mostLarge voltage peak UKAnd (du/dt) K was 175.11kV and 0.234 kV/. mu.s, respectively.
When the operation overvoltage exceeds the action threshold of the thyristor valve body, the valve body is in a conducting state, and according to GBZ 24842-2009, the operation overvoltage is limited to be below 1.6-1.7 p.u., so that the valve body needs to be ensured to act before the voltage rises to the specified voltage. The maximum current passing through the thyristor in the operation overvoltage is 2.8kA and the wave front time is about 200 mus according to the simulation of relevant parameters of the ultra-high voltage transmission line 'Shijiazhuang-Beijing' during the valve body conduction period, so that the di/dt is about 14A/mus.
The accident caused by lightning striking the overhead transmission line accounts for 30-50% of the total accident of the power grid, and meanwhile, the lightning stroke overvoltage wave of the lightning stroke line invading the substation and the power plant from the line is a main factor influencing the safe operation of electrical equipment, and mainly comprises counterattack invasion wave overvoltage and shielding attack invasion wave overvoltage.
(1) Counterattack intrusion wave overvoltage
The lightning stroke of tower overvoltage can be divided into lightning stroke on the tower top without a lightning conductor and lightning stroke on the tower top with the lightning conductor.
When lightning strikes on the top of the tower without the lightning conductor, the lightning current i flows through the tower and the grounding resistor R thereofchThe current flows into the ground, and the amplitude U of the tower top potential is obtained by considering that the impedance of a lightning stroke point is low, so that the influence of the wave resistance of a lightning channel can be omitted in the calculationtdCan be calculated according to equation (9).
Wherein, ILIs the amplitude of the lightning current,
Rchis a resistance to ground, and is,
Lgtthe equivalent inductance of the tower.
When the line has the lightning conductor, the operation experience shows that the number of times of lightning striking the tower in the total number of the lightning falling of the line is related to the number of the lightning conductor and the terrain of the passing region. The ratio of the number of lightning strikes on the tower to the total number of lightning strikes on the line is called the strike rate.
When lightning strikes on the tower top, negative charges in the lightning channel and positive induced charges in the tower, the lightning conductor and the ground are quickly neutralized to form lightning current. On one hand, lightning impulse waves with negative polarity are transmitted downwards along a tower and downwards along a lightning conductor to two sides, so that the potential of the tower top is continuously raised, and the potential of a conducting wire is changed through electromagnetic coupling; on the other hand, the positive polarity lightning which rapidly develops from the tower top to thundercloud causes rapid change of a space electromagnetic field, and causes positive polarity induced lightning waves to appear on the conducting wire. The voltage applied to the line insulator string is the difference between the tower top potential and the conductor potential. Once this voltage exceeds the impulse discharge voltage of the insulator string, the insulator string flashover occurs, creating a counterattack.
(2) Surge intrusion overvoltage
Lightning stroke lead overvoltage can be divided into two situations of no lightning conductor and lightning conductor according to whether the line has the lightning conductor protection.
When lightning strikes on a wire without a lightning conductor, lightning current flows to two sides along the wire to form overvoltage waves and the overvoltage waves are transmitted to the two sides. Lightning current wave i that normally flows through a lightning strike pointzAnd voltage amplitude U on the wiredCan be calculated by the following equations (10) and (11).
High-voltage lines of 110kV and above in China are generally provided with lightning protection wires to prevent the wires from being directly struck by lightning. However, due to various random factors, such as failure of the shielding effect of the lightning conductor, it may also happen that the lightning strikes the conductor by-passing the lightning conductor, commonly referred to as strike-around. The probability of shielding failure in a lightning stroke line is called shielding failure rate PαFor plain and mountain areas, the detour rate can be generally calculated by equation (12).
Although the probability of the shielding failure is low, the amplitude of the lightning current is small when the shielding failure occurs, once the shielding failure occurs, high impact overvoltage is formed, and the line insulator can be subjected to flashover or invade the safety of the substation crisis electrical equipment. The overvoltage amplitude on the line after a shielding failure occurs can also be calculated by equation (12).
By integrating the characteristics of the lightning overvoltage, the lightning overvoltage wave front time is short, the overvoltage amplitude caused by lightning stroke is large, and the lightning current peak value is large. Simulation work is carried out according to relevant parameters of the ultra-high voltage transmission line of Shijiazhuang-Beijing West, and simulation settlement results are shown in a table 1.
TABLE 1 lightning overvoltage requirements on thyristor valve body parameters
According to the simulation calculation result, if the thyristor valve body is not conducted under the lightning overvoltage, the maximum U which the valve body needs to bear is obtainedK、(du/dt)K243kV and 103 kV/mu s respectively, if the thyristor valve body is conducted, the maximum I born by the valve bodyKAnd (di/dt)K24.6kA and 22 kA/. mu.s, respectively.
The various working conditions of continuous operation voltage, power frequency overvoltage, operation overvoltage and lightning overvoltage are comprehensively analyzed, various parameters which need to be borne by the thyristor valve body under various working conditions are obtained, and the summary statistics are shown in table 2.
TABLE 2 requirements of multiple operating conditions on thyristor valve parameters
Note: (1) the two states of turn-off and turn-on of the operation overvoltage exist because the operation overvoltage can have the condition that the voltage peak value does not reach the action threshold value; (2) the reason why the lightning overvoltage has two states of turn-off and turn-on is that two design ideas exist considering that the thyristor valve body is difficult to endure huge di/dt.
As can be seen from the statistical parameters, the thyristor valve operation threshold is set to 190kV so as to avoid the maximum power frequency overvoltage peak and be lower than the lightning overvoltage limit. Meanwhile, the thyristor valve body is ensured to have the total current less than 5mA during continuous operation, otherwise, the leakage current flowing through the upper end fixing part of the lightning arrester is overlarge. Because the thyristor valve body adopts BOD self-triggering action, the conduction time is fast, and the waveform identification is difficult to realize only by taking the voltage at two ends of the thyristor as a criterion, the thyristor valve body is conducted under lightning overvoltage, and the di/dt in the conduction process of the thyristor needs to be restrained. By combining the above analysis, parameters of the thyristor valve body in the controllable arrester can be obtained, as shown in table 3.
TABLE 3 thyristor valve switching parameter requirements
Result of parameter selection
(1) Off-state repetitive peak voltage VDRM
The thyristor switch operating voltage is 190kV, namely the thyristor valve body is ensured to be in a reliable turn-off state no matter under any working condition when the voltage of the two ends of the thyristor valve body is lower than 190 kV. Therefore, the maximum voltage to be borne by the thyristor switch under various working conditions is 190kV, the withstand voltage of a single thyristor cannot meet the requirement, and the thyristor series connection technology must be adopted. The voltage across a single thyristor can be calculated as in equation (13).
Wherein f is the safe use coefficient of the thyristor device;
and m is the serial number of the thyristor devices.
If f is taken1.3, m is temporarily selected by the number of series resistor pieces of MOA1, VDRMAt least 7.8kV, with reference to the highest voltage parameter, V, of the current thyristor deviceDRM8kV can be taken. By consulting thyristor manufacturers, the current thyristor production capacity can meet the requirement of the off-state repeated peak value.
(2)du/dt
According to the analysis of the various working conditions, the thyristor needs to be reliably turned off under the most severe power frequency overvoltage, and the du/dt which the thyristor needs to bear under the maximum power frequency overvoltage is 0.038 kV/mu s through calculation.
(3) On-state current ITAV
Under the continuous operation voltage of the system, the thyristor switch is always in an off state, and only when the overvoltage of the system occurs and reaches a control threshold value, the thyristor switch is switched on for a short time, so that no special requirement is imposed on the on-state rated current of the thyristor switch.
(4) Surge current ITSM
Maximum surge current I to be borne by thyristor switchK24.6kA, the maximum surge current I of the thyristor device is requiredTSMShould not be less than 24.6 kA.
(5)di/dt
According to the calculation, the maximum on-state current increasing rate (di/dt) which is required to be borne by the thyristor switch of the extra-high voltage thyristor valve type controllable arrester under the lightning stroke working conditionKThe concentration was 22.0 kA/. mu.s. In terms of the current production process level of the thyristor device, the prior art is not enough to support the thyristor to meet the requirement of di/dt, so that a di/dt limiting measure needs to be adopted in the design.
(6) Leakage current
The technical specification of the gapless metal oxide arrester for the GB/Z24845 and 20091000 kV alternating current system stipulates that: the resistive current (fundamental current peak value) of the lightning arrester adopting the four-column valve plate parallel structure in the extra-high voltage alternating current system under the continuous operation voltage should not exceed 3mA, and the total current (effective value) should not exceed 20 mA. As shown by lightning arrester type test data and project group test tests, the total current of the single-column valve plate is about 1.4mA under the AC continuous operation voltage, the resistive current (four columns are connected in parallel) of the lightning arrester body is about 1mA, and the leakage current of the lightning arrester is about 6mA under the AC continuous operation voltage after the four columns are connected in parallel.
According to standard and measured data, a certain safety margin is considered to be left, in order to reduce the influence of leakage current introduced by the parallel thyristor switches on the lightning arrester body, the size of the leakage current of the thyristor switches is reduced as much as possible, and the leakage current I of the thyristor switches connected in parallel with the controllable lightning arrester under the alternating current continuous operation voltageLThe preliminary press does not exceed 5mA (full current), where the resistive current should not exceed 1 mA.
In summary, the statistics of the key parameter requirements that the thyristor needs to meet under various working conditions in the extra-high voltage ac thyristor valve type controllable arrester are shown in table 4. Because the existing thyristor devices can not meet the di/dt parameter requirements of the project, the limitation of the parameters on the performance is not considered during model selection, and a KP1900A/8500V type thyristor is selected according to other parameters and comprehensively considering the market application condition.
Table 4 controllable arrester thyristor device parameter requirements
And selecting the device type according to the parameter requirements of the controllable arrester thyristor device in the table 4. And (5) investigating thyristor devices of the Parry, the south vehicle and the ABB.
Under the same voltage withstanding level, the KP1900A/8500V type thyristor has the following key parameters: indexes such as surge current, di/dt tolerance and cost performance are outstanding, other indexes such as on-state current and holding current have small performance difference, and finally the type of the thyristor device is selected to be KP1900A/8500V of Pi Rui.
And carrying out test detection on the selected KP1900A/8500V thyristor. The test results were as follows:
1) the number of the thyristors in series connection can be calculated to be 32 according to the system requirements and the parameters of the thyristors; and in an anti-parallel structure, 64 thyristors are used in total. The continuous operation voltage of each layer of thyristor is 96/32 kVrms, and du/dt is 3 kV/mus. The lightning resistance and the operation impact can reach more than 9kV, du/dt can endure more than 9 kV/mus, and the requirements are met.
2) Through tests, the KP1900A/8500V thyristor allows the maximum di/dt: practical requirements of 2.3 kA/mus, much less than 22 kA/mus, require saturable reactor suppression.
3) The leakage current of the KP1900A/8500V thyristor device has positive temperature characteristics, the leakage current increases along with the temperature rise, the higher the temperature is, the faster the leakage current increases, and the leakage current of the anti-parallel thyristor is in the range of 1.25 mA-2.2 mA and <5mA under the continuous operation voltage within the range of-40 to +60 ℃, so that the requirement is met.
Technical effects
The input quantity of the resistor discs of the lightning arrester is flexibly controlled, the volt-ampere characteristic curve of the lightning arrester is changed, so that the lightning arrester has high reliability when a system normally operates, the operating overvoltage can be deeply reduced under the transient condition, the closing resistance of a circuit breaker is cancelled, the method is more economical than a conventional limiting method, and the method has great theoretical and engineering innovation significance on an ultra-high voltage alternating current transmission system.
A method of selecting thyristor valve parameters in a controllable arrester, the method comprising:
the lightning arrester body is divided into a controlled element MOA1 and a fixed element MOA2, a control unit CU consists of a thyristor valve K and a trigger control system, and the controlled element MOA1 is connected with the control unit CU in parallel;
under the continuous operation voltage of the system, the thyristor valve K is in a closed state, the control unit CU is switched off, the controlled element MOA1 and the valve plate of the fixed element MOA2 in the controllable lightning arrester jointly bear the continuous operation voltage of the system, and the maximum voltage peak value U required to be borne by the thyristor valve can be obtained according to the maximum phase voltage of the systemK135kV, and the voltage rise rate dU/dt is 0.027 kV/mus;
under the power frequency overvoltage of the system, the thyristor valve K is in a cut-off state, the control unit CU is switched off, the controlled element MOA1 in the controllable lightning arrester has no potential safety hazard, and the valve plates of the controlled element MOA1 and the fixed element MOA2 bear the system voltage togetherThe maximum voltage peak value U born by the thyristor valve K can be determinedK188kV, the voltage rise rate dU/dt is 0.038 kV/mus;
under the operation overvoltage of the system, if the peak value of the operation overvoltage does not reach the action threshold value of the thyristor valve body, the thyristor valve K is ensured to be in a reliable turn-off state, and the control unit CU is disconnected; maximum voltage peak value U that thyristor valve body needs to bearKAnd the voltage rise rate dU/dt is 219kV and 0.55 kV/mu s respectively; when the operation overvoltage reaches or exceeds the action threshold value of the thyristor valve body, the thyristor valve K is in a conducting state, the control unit CU is closed, the maximum current passing through the thyristor is 2.8kA, and the current rise rate di/dt is 0.014 kA/mus;
under the lightning overvoltage of the system, if the thyristor valve body K is not conducted under the lightning overvoltage, the control unit CU is disconnected, and then the maximum U required to be borne by the valve body is obtainedK243kV, the voltage rise rate dU/dt is 103 kV/mus, if the thyristor valve body K is conducted and the control unit CU is closed, the maximum current peak value I born by the valve body is requiredK24.6kA, and the current rise rate di/dt is 22 kA/mus;
the action voltage of the thyristor valve body should avoid the maximum peak value of the power frequency overvoltage and be lower than the lightning overvoltage limit value, so the action threshold value of the thyristor valve body is set to 190kV, and the repeated peak voltage V of the thyristor device in the off state can be confirmedDRM8kV can be taken;
the main parameters of the required thyristor device can be confirmed through simulation calculation of the extra-high voltage power transmission system under various overvoltage working conditions, wherein the off-state repeated peak voltage VDRM8kV can be taken, the voltage rise rate dU/dt is 0.038 kV/mu s, and the surge current ITSMNot less than 24.6kA, current rise rate di/dt of 22.0 kA/mus, and leakage current ILThe middle and full current does not exceed 5mA, wherein the resistance current should not exceed 1mA, and a KP1900A/8500V model thyristor is selected.
The controlled element MOA1 and the fixed element MOA2 of the lightning arrester body are both composed of a lightning arrester resistance card, a porcelain bushing, a flange, an upper end bolt and a lower end bolt; the thyristor valve has high response speed to overvoltage, can be quickly conducted under the overvoltage operation and is switched off when the current crosses zero; compared with a switch type controllable arrester, the thyristor valve type controllable arrester can limit any form of operation overvoltage; the input quantity of the resistor discs of the lightning arrester is flexibly controlled, and the volt-ampere characteristic curve of the lightning arrester is changed, so that the lightning arrester has high reliability when a system operates normally, the operating overvoltage can be deeply reduced under the transient condition, and the closing resistor of the circuit breaker is cancelled.
The thyristor valve is formed by connecting anti-parallel thyristor pairs in series.
Tests prove that the invention provides a method for selecting parameters of a thyristor valve and a selection result under four voltage stresses of continuous operation voltage, power frequency overvoltage, operation overvoltage and lightning overvoltage, and the KP1900A/8500V thyristor allows the maximum di/dt: 2.3 kA/mus, which is less than 22 kA/mus, needs to be restrained by a saturable reactor, and in terms of the current production process level of the thyristor device, under lightning overvoltage, the prior art is not enough to support the thyristor to meet the di/dt requirement, so that a di/dt limiting measure needs to be adopted in the design; the thyristor needs to be reliably turned off under the most severe power frequency overvoltage, and the calculation shows that the du/dt which the thyristor needs to bear under the maximum power frequency overvoltage is 0.038 kV/mu s, so that the prior art conditions can meet the requirements.
The invention gives the repeated peak voltage V of the off stateDRMAccording to the selection method and the result, the thyristor switch action voltage is 190kV, namely, the thyristor valve body is ensured to be in a reliable turn-off state no matter under any working condition when the voltage of the two ends of the thyristor valve body is lower than 190 kV; therefore, the maximum voltage to be borne by the thyristor switch under various working conditions is 190kV, the withstand voltage of a single thyristor cannot meet the requirement, and the thyristor series connection technology is required; the voltage at two ends of the single thyristor can be calculated according to the formula (1);
wherein f is the safe use coefficient of the thyristor device; and m is the serial number of the thyristor devices. If f is 1.3 and m is selected as 32 series resistors of MOA1, then V isDRMAt least 7.8kV, referred to at presentMaximum voltage parameter, V, of thyristor deviceDRMIs 8 kV.
The invention also provides a system for selecting parameters of a thyristor valve in a controllable arrester, which is characterized by comprising:
the control unit CU in the lightning arrester is composed of a thyristor valve K and a trigger control system, a controlled element MOA1 and the control unit CU are connected in parallel, the thyristor valve K is triggered and conducted under the action of an operation overvoltage, the control unit CU is closed, the thyristor valve K is in a turn-off state under the action of a system continuous operation voltage, a temporary overvoltage and a lightning overvoltage, and the CU is disconnected;
the controlled element MOA1 in the lightning arrester body is connected with the fixed element MOA2 in series, under the conditions of continuous operation voltage, power frequency overvoltage and lightning overvoltage, the controlled element MOA1 and the fixed element MOA2 bear system overvoltage together, under the condition of operation overvoltage, the thyristor valve K is triggered and conducted, the CU is closed, the MOA1 is in short circuit, the MOA2 has low residual voltage, and the system operation overvoltage can be deeply reduced;
the fixed element MOA2 in the lightning arrester body is connected with the controlled element MOA1 in series and connected with the control unit CU in parallel, and under the conditions of continuous operation voltage, power frequency overvoltage and lightning overvoltage, the fixed element MOA1 and the fixed element MOA are used for bearing system overvoltage together, under the condition of operation overvoltage, the MOA2 residual voltage is low, and the system operation overvoltage can be deeply reduced;
under the continuous operation voltage of the system, the maximum voltage peak value U which the thyristor valve needs to bear can be obtained according to the maximum phase voltage of the systemK135kV, and the voltage rise rate dU/dt is 0.027 kV/mus; under the power frequency overvoltage of the system, the maximum voltage peak value U born by the thyristor valve K can be determinedK188kV, the voltage rise rate dU/dt is 0.038 kV/mus; under the operation overvoltage of the system, if the peak value of the operation overvoltage does not reach the action threshold value of the thyristor valve body, the maximum voltage peak value U which needs to be born by the thyristor valve bodyKAnd the voltage rise rate dU/dt is 219kV and 0.55 kV/mu s respectively; when the operation overvoltage reaches or exceeds the action threshold of the thyristor valve body, the maximum current passing through the thyristor is 2.8kA, and the current rise rate di/dt is 0.014 kA/mus; under the lightning overvoltage of the system and the lightning overvoltage, if the thyristor valve body K is not conducted, the controlWhen the control unit CU is disconnected, the maximum U which the valve body needs to bear is obtainedK243kV, the voltage rise rate dU/dt is 103 kV/mus, if the thyristor valve body K is conducted and the control unit CU is closed, the maximum current peak value I born by the valve body is requiredK24.6kA, and the current rise rate di/dt is 22 kA/mus;
the action voltage of the thyristor valve body should avoid the maximum peak value of the power frequency overvoltage and be lower than the lightning overvoltage limit value, so the action threshold value of the thyristor valve body is set to 190kV, and the repeated peak voltage V of the thyristor device in the off state can be confirmedDRM8kV can be taken;
the main parameters of the required thyristor device can be confirmed through simulation calculation of the extra-high voltage power transmission system under various overvoltage working conditions, wherein the off-state repeated peak voltage VDRM8kV can be taken, the voltage rise rate dU/dt is 0.038 kV/mu s, and the surge current ITSMNot less than 24.6kA, current rise rate di/dt of 22.0 kA/mus, and leakage current ILThe middle and full current does not exceed 5mA, wherein the resistance current should not exceed 1mA, and a KP1900A/8500V model thyristor is selected.
The controlled element MOA1 and the fixed element MOA2 of the lightning arrester body are both composed of a lightning arrester resistance card, a porcelain bushing, a flange, an upper end bolt and a lower end bolt; the thyristor valve has high response speed to overvoltage, can be quickly conducted under the overvoltage operation and is switched off when the current crosses zero; compared with a switch type controllable arrester, the thyristor valve type controllable arrester can limit any form of operation overvoltage; the input quantity of the resistor discs of the lightning arrester is flexibly controlled, and the volt-ampere characteristic curve of the lightning arrester is changed, so that the lightning arrester has high reliability when a system operates normally, the operating overvoltage can be deeply reduced under the transient condition, and the closing resistor of the circuit breaker is cancelled.
The thyristor valve is formed by connecting anti-parallel thyristor pairs in series.
Tests prove that the invention provides a method for selecting parameters of a thyristor valve and a selection result under four voltage stresses of continuous operation voltage, power frequency overvoltage, operation overvoltage and lightning overvoltage, and the KP1900A/8500V thyristor allows the maximum di/dt: 2.3 kA/mus, which is less than 22 kA/mus, needs to be restrained by a saturable reactor, and in terms of the current production process level of the thyristor device, under lightning overvoltage, the prior art is not enough to support the thyristor to meet the di/dt requirement, so that a di/dt limiting measure needs to be adopted in the design; the thyristor needs to be reliably turned off under the most severe power frequency overvoltage, and the calculation shows that the du/dt which the thyristor needs to bear under the maximum power frequency overvoltage is 0.038 kV/mu s, so that the prior art conditions can meet the requirements.
The invention gives the repeated peak voltage V of the off stateDRMAccording to the selection method and the result, the thyristor switch action voltage is 190kV, namely, the thyristor valve body is ensured to be in a reliable turn-off state no matter under any working condition when the voltage of the two ends of the thyristor valve body is lower than 190 kV; therefore, the maximum voltage to be borne by the thyristor switch under various working conditions is 190kV, the withstand voltage of a single thyristor cannot meet the requirement, and the thyristor series connection technology is required; the voltage at two ends of the single thyristor can be calculated according to the formula (1);
wherein f is the safe use coefficient of the thyristor device; and m is the serial number of the thyristor devices. If f is 1.3 and m is selected as 32 series resistors of MOA1, then V isDRMAt least 7.8kV, with reference to the highest voltage parameter, V, of the current thyristor deviceDRMIs 8 kV.
Claims (5)
1. A method of selecting thyristor valve parameters in a controllable arrester, the method comprising:
the lightning arrester body is divided into a controlled element MOA1 and a fixed element MOA2, a control unit CU consists of a thyristor valve K and a trigger control system, and the controlled element MOA1 is connected with the control unit CU in parallel;
under the continuous operation voltage of the system, the thyristor valve K is in a closed state, the control unit CU is switched off, the controlled element MOA1 and the valve plate of the fixed element MOA2 in the controllable lightning arrester jointly bear the continuous operation voltage of the system, and the maximum voltage peak value required to be borne by the thyristor valve can be known according to the maximum phase voltage of the systemUK135kV, and the voltage rise rate dU/dt is 0.027 kV/mus;
under the power frequency overvoltage of the system, the thyristor valve K is in a turn-off state, the control unit CU is turned off, the controlled element MOA1 in the controllable lightning arrester has no potential safety hazard, the valve plates of the controlled element MOA1 and the fixed element MOA2 bear the system voltage together, and the maximum voltage peak value U required to be borne by the thyristor valve K can be determinedK188kV, the voltage rise rate dU/dt is 0.038 kV/mus;
under the operation overvoltage of the system, if the peak value of the operation overvoltage does not reach the action threshold value of the thyristor valve body, the thyristor valve K is ensured to be in a reliable turn-off state, and the control unit CU is disconnected; maximum voltage peak value U that thyristor valve body needs to bearKAnd the voltage rise rate dU/dt is 219kV and 0.55 kV/mu s respectively; when the operation overvoltage reaches or exceeds the action threshold value of the thyristor valve body, the thyristor valve K is in a conducting state, the control unit CU is closed, the maximum current passing through the thyristor is 2.8kA, and the current rise rate di/dt is 0.014 kA/mus;
under the lightning overvoltage of the system, if the thyristor valve body K is not conducted under the lightning overvoltage, the control unit CU is disconnected, and then the maximum U required to be borne by the valve body is obtainedK243kV, the voltage rise rate dU/dt is 103 kV/mus, if the thyristor valve body K is conducted and the control unit CU is closed, the maximum current peak value I born by the valve body is requiredK24.6kA, and the current rise rate di/dt is 22 kA/mus;
the action voltage of the thyristor valve body should avoid the maximum peak value of the power frequency overvoltage and be lower than the lightning overvoltage limit value, so the action threshold value of the thyristor valve body is set to 190kV, and the repeated peak voltage V of the thyristor device in the off state can be confirmedDRM8kV can be taken;
the main parameters of the required thyristor device can be confirmed through simulation calculation of the extra-high voltage power transmission system under various overvoltage working conditions, wherein the off-state repeated peak voltage VDRM8kV can be taken, the voltage rise rate dU/dt is 0.038 kV/mu s, and the surge current ITSMNot less than 24.6kA, current rise rate di/dt of 22.0 kA/mus, and leakage current ILThe middle and total current is not more than 5mA, wherein the resistive current is not more than 1mA,a KP1900A/8500V model thyristor is selected.
2. The method of claim 1, further comprising that the controlled element MOA1 and the fixed element MOA2 of the arrester body are each composed of arrester resistor disc, porcelain bushing, flange, and upper and lower end bolts; the thyristor valve has high response speed to overvoltage, can be quickly conducted under the overvoltage operation and is switched off when the current crosses zero; compared with a switch type controllable arrester, the thyristor valve type controllable arrester can limit any form of operation overvoltage; the input quantity of the resistor discs of the lightning arrester is flexibly controlled, and the volt-ampere characteristic curve of the lightning arrester is changed, so that the lightning arrester has high reliability when a system operates normally, the operating overvoltage can be deeply reduced under the transient condition, and the closing resistor of the circuit breaker is cancelled.
3. The method of claim 1, further comprising the thyristor valve being comprised of anti-parallel thyristor pairs connected in series.
4. The method of claim 1, further comprising, after testing, the invention provides a method for selecting parameters of a thyristor valve and a selection result under four voltage stresses of continuous operation voltage, power frequency overvoltage, operation overvoltage and lightning overvoltage, wherein the maximum di/dt allowed for a KP1900A/8500V thyristor is as follows: 2.3 kA/mus, which is less than 22 kA/mus, needs to be restrained by a saturable reactor, and in terms of the current production process level of the thyristor device, under lightning overvoltage, the prior art is not enough to support the thyristor to meet the di/dt requirement, so that a di/dt limiting measure needs to be adopted in the design; the thyristor needs to be reliably turned off under the most severe power frequency overvoltage, and the calculation shows that the du/dt which the thyristor needs to bear under the maximum power frequency overvoltage is 0.038 kV/mu s, so that the prior art conditions can meet the requirements.
5. The method of claim 1, further comprising providing an off-repeat peak voltage, VDRMSelection method and result of thyristorThe switching action voltage is 190kV, namely the thyristor valve body is ensured to be in a reliable turn-off state no matter under any working condition when the voltage of the two ends of the thyristor valve body is lower than 190 kV; therefore, the maximum voltage to be borne by the thyristor switch under various working conditions is 190kV, the withstand voltage of a single thyristor cannot meet the requirement, and the thyristor series connection technology is required; the voltage at two ends of the single thyristor can be calculated according to the formula (1);
wherein f is the safe use coefficient of the thyristor device; and m is the serial number of the thyristor devices. If f is 1.3 and m is selected as 32 series resistors of MOA1, then V isDRMAt least 7.8kV, with reference to the highest voltage parameter, V, of the current thyristor deviceDRMIs 8 kV.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113514744A (en) * | 2021-09-14 | 2021-10-19 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | Method and device for determining withstand voltage value of thyristor and storage medium |
| CN113612469A (en) * | 2021-07-27 | 2021-11-05 | 许继集团有限公司 | Impedance matching device of electronic switch controllable self-recovery circuit |
| CN114024297A (en) * | 2021-11-12 | 2022-02-08 | 广东电网有限责任公司 | Controllable lightning arrester and method and system for reducing operation overvoltage |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108667001A (en) * | 2018-05-18 | 2018-10-16 | 中国电力科学研究院有限公司 | A 110kV thyristor valve-type controllable arrester device and verification method |
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Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108667001A (en) * | 2018-05-18 | 2018-10-16 | 中国电力科学研究院有限公司 | A 110kV thyristor valve-type controllable arrester device and verification method |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113612469A (en) * | 2021-07-27 | 2021-11-05 | 许继集团有限公司 | Impedance matching device of electronic switch controllable self-recovery circuit |
| CN113612469B (en) * | 2021-07-27 | 2024-02-09 | 许继集团有限公司 | Impedance matching device of electronic switch controllable self-recovery circuit |
| CN113514744A (en) * | 2021-09-14 | 2021-10-19 | 中国南方电网有限责任公司超高压输电公司检修试验中心 | Method and device for determining withstand voltage value of thyristor and storage medium |
| CN114024297A (en) * | 2021-11-12 | 2022-02-08 | 广东电网有限责任公司 | Controllable lightning arrester and method and system for reducing operation overvoltage |
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