CN109980602B - Digital self-adaptive protection device and method for transformer based on pressure characteristics - Google Patents
Digital self-adaptive protection device and method for transformer based on pressure characteristics Download PDFInfo
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- CN109980602B CN109980602B CN201910376457.5A CN201910376457A CN109980602B CN 109980602 B CN109980602 B CN 109980602B CN 201910376457 A CN201910376457 A CN 201910376457A CN 109980602 B CN109980602 B CN 109980602B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/04—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for transformers
Abstract
A digital self-adaptive protection device and method for a transformer based on pressure characteristics comprises the following steps: the device comprises a transient oil pressure characteristic quantity measuring module, a switching quantity input module, a signal conditioning and collecting module and a digital core module; the transient oil pressure characteristic quantity measuring module is connected with the signal conditioning and collecting module, and the signal conditioning and collecting module and the switching value input module are connected with the digital core module. The method obtains the transient oil pressure digital information of a plurality of measuring points in the oil tank in real time, calculates to obtain the action pressure value representing the oil pressure amplitude, and constructs the protection criterion and the threshold value setting method by utilizing the obvious difference of the characteristic quantity under different operating conditions of the transformer, thereby realizing the reliable, quick and sensitive discrimination and removal of the internal fault of the transformer oil tank without being influenced by the excitation surge current. Meanwhile, the invention designs a protection scheme with self-adaption of fault states and self-adaption of threshold values so as to improve the action speed of protection.
Description
Technical Field
The invention belongs to the field of power systems, and relates to a digital self-adaptive protection device and method for a transformer based on pressure characteristics, which are used for reliably, quickly and sensitively discriminating internal faults of an oil tank of an oil-immersed power transformer.
Background
The power transformer is an important element for power transmission, and once a fault occurs, the power transformer can have a serious influence on the power supply reliability and the operation stability of a power system. Especially, the large power transformer installed at the system hub has high voltage level, large capacity, complex structure and high cost, and thus, the damage caused by the fault will cause huge economic loss. Therefore, a relay protection device with good performance and reliable operation must be installed according to the capacity and importance of the transformer.
The development of the relay protection technology depends on the knowledge of fault characteristics, and generally, the internal fault of the transformer is considered to have three main characteristics, namely, the phase current is increased, the differential current is increased, and the fault gas is formed. Corresponding to the first two electrical quantity characteristics, widely applied protection measures include overcurrent protection and current differential protection, and the latter is one of the main protection modes for the internal short circuit fault of the current transformer. However, the current differential protection of the transformer has two main defects in principle: firstly, excitation inrush current existing in an excitation loop when a transformer is switched on in a no-load state may cause differential protection maloperation; second, when a weak fault such as a short circuit of a single turn or a small number of turns is encountered, the differential protection may fail due to insufficient sensitivity. In view of this, in the last 20 years, scholars invented transformer gas protection to make up for the shortage of electric quantity protection. Compared with electric quantity protection, the non-electric quantity protection generated by reacting to the fault gas can more comprehensively and directly react to the running state of the protected object, and has unique advantages in the aspects of sensitivity and the like. Although tens of thousands of oil-immersed transformers are successfully protected in the traditional mechanical non-electric quantity protection in the use process of nearly one hundred years, the higher requirements of the current high-capacity and high-voltage-level power transformers are more and more difficult to meet due to the problems of difficult theoretical modeling, principle defects, adoption of threshold values by experience, insufficient mechanical structure action performance and the like. The system power failure and transformer explosion accidents caused by protection failure and misoperation accidents happen, the safe and reliable operation of a power system is seriously influenced, and the safety of transformer substation operators and the life and property safety of people around the transformer substation are seriously threatened.
When serious overheating or arc fault occurs inside the oil-immersed power transformer, the liquid insulating oil is instantly vaporized and decomposed to form high internal energy bubbles with a certain volume. Under the continuous injection of fault electric energy, the internal pressure of a fault bubble is also increased continuously, and meanwhile, due to the expansion inertia of the liquid insulating oil near a fault point, a gas-liquid phase interface between the fault bubble and the surrounding liquid insulating oil inevitably generates obvious pressure increase and propagates in the transformer oil tank in the form of pressure waves, so that the integral sudden increase of the internal oil pressure of the oil tank is caused. In addition, since the transformer tank is not a pressure vessel, the tank is often deformed or cracked under the impact of internal pressure waves. On the other hand, when the transformer has an external short-circuit fault, the fault point is positioned at the outlet of the transformer, and the influence on the internal pressure of the oil tank is only reflected on the vibration of the winding caused by the short-circuit through current. At the same time, the process causes limited variation in oil pressure, since the mechanical strain of the windings will consume a large amount of energy. Similar to an external fault, the normal operation of the transformer and the magnetizing inrush current are all caused by vibration generated by current flowing through a winding to cause oil pressure change. Therefore, the internal fault state of the transformer can be effectively discriminated by using the difference of the oil pressure characteristics in the transformer under different operating conditions.
Disclosure of Invention
The invention aims to provide a digital self-adaptive protection device and a digital self-adaptive protection method for a transformer based on pressure characteristics, wherein the method can be used for reliably, sensitively and quickly identifying internal faults of an oil-immersed power transformer and is not influenced by magnetizing inrush current.
In order to achieve the purpose, the invention adopts the following technical scheme:
a digital self-adaptive protection device of a transformer based on pressure characteristics comprises: the device comprises a transient oil pressure characteristic quantity measuring module, a switching quantity input module, a signal conditioning and collecting module and a digital core module; the system comprises a digital core module, a transient oil pressure characteristic quantity measuring module, a signal conditioning and collecting module, a switching value input module and a signal conditioning and collecting module, wherein the transient oil pressure characteristic quantity measuring module is connected with the signal conditioning and collecting module;
the transient oil pressure characteristic quantity measuring module is used for measuring oil pressure change characteristics of different positions in the transformer and outputting corresponding analog voltage/current signals;
the signal conditioning and acquisition module is used for receiving the analog voltage/current signal output by the transient oil pressure characteristic quantity measuring module, converting the analog voltage/current signal into a standard digital signal which can be identified by the digital core module, and outputting the standard digital signal;
the switching value input module is used for acquiring relevant switching value signals needing to be known, outputting the relevant switching value signals as high level 1 or low level 0, and using the high level 1 or low level 0 as input digital signals of the digital core module;
the digital core module is used for executing protection operation on the received standard digital signal and the input digital signal to complete a standard digital signal processing task, and further realizing a relay protection function.
The invention has the further improvement that the transient oil pressure characteristic quantity measuring module consists of a plurality of high-frequency dynamic oil pressure sensors and communication cables thereof; the high-frequency dynamic oil pressure sensor is arranged on the transformer body, and a probe at the end part of the high-frequency dynamic oil pressure sensor is in contact with the transformer insulating oil to measure the oil pressure change characteristics of different positions in the transformer.
The invention has the further improvement that the measuring frequency of the high-frequency dynamic oil pressure sensor is 20kHz, the measuring error is less than 1 percent, the working temperature is-45-120 ℃, and the measuring range is-0.1-6 MPa.
The invention has the further improvement that the signal conditioning and collecting module consists of a wiring terminal, a signal conditioning circuit, a low-pass filter, a signal sampling circuit and an analog-digital A/D conversion circuit; the wiring terminal is connected with the signal conditioning circuit, the signal conditioning circuit is connected with the low-pass filter, the low-pass filter is connected with the signal sampling circuit, and the signal sampling circuit is connected with the analog-to-digital A/D conversion circuit; the wiring terminal is further connected with the transient oil pressure characteristic quantity measuring module, and the analog-to-digital A/D conversion circuit is further connected with the digital core module.
The invention has the further improvement that the digital core module consists of a bus, a central processing unit, a timer/counter, a random access memory and a control circuit; the bus comprises a data bus, an address bus and a control bus, and realizes data exchange and operation control; the central processing unit realizes digital signal processing in real time by utilizing a single chip microprocessor, a general microprocessor or a digital signal processor; the timer/counter is used for providing a timing sampling trigger signal, forming interruption and protecting delayed action timing; the random access memory is used for temporarily storing temporary data, including data information input by the signal conditioning and acquisition module and intermediate results in the calculation processing process; the control circuit realizes the connection and coordination work of the whole digital circuit through a complex programmable logic device or a field programmable gate array.
The invention has the further improvement that the invention also comprises an external communication interface module, a man-machine conversation module and a switching value output module which are connected with the digital core module;
the external communication interface module is used for providing an information channel with a computer communication network and a remote communication network;
the man-machine conversation module is used for establishing information relation between the digital protection device and a user;
the switching value output module controls the on or off of the trip circuit through the output 0 or 1 state.
The invention has the further improvement that the switching value output module consists of a photoelectric isolation device and an outlet relay, wherein one end of the photoelectric isolation device is connected with the digital core module, and the other end of the photoelectric isolation device is connected with the outlet relay;
the man-machine conversation module comprises a compact keyboard, a display screen, an indicator light, a button, a printer interface and a debugging communication interface.
A protection method of a digital self-adaptive protection device of a transformer based on the pressure characteristics comprises the following steps:
(1) the transient oil pressure characteristic quantity measuring module measures oil pressure change characteristics of different positions in the transformer and outputs and simulates voltage/current signals, and the signal conditioning and collecting module receives the simulated voltage/current signals output by the transient oil pressure characteristic quantity measuring module, converts the simulated voltage/current signals into standard digital signals which can be identified by the digital core module and outputs the standard digital signals; the switching value input module is used for acquiring relevant switching value signals needing to be known, outputting the relevant switching value signals as high level 1 or low level 0, and using the high level 1 or low level 0 as input digital signals of the digital core module; comparing the transient oil pressure value p of each measuring point at the current t moment after the input digital signal received by the digital core module and the standard digital signalms.i(t) whether a predetermined protection start threshold p is reachedstDetermining whether the transformer self-adaptive protection based on the pressure characteristics is started, if the formula ① is satisfied, setting a starting flag, and entering the step (2);
pms.i(t)≥pst①
in formula ①, pms.i(t) represents the transient oil pressure value of the ith measuring point in the transformer at the time t, wherein i is 1,2, …, N; p is a radical ofstIndicating a protection activation threshold;
(2) judging whether the transformer is in a no-load closing state at present, if so, performing the step (3), and otherwise, performing the step (5);
(3) calculating no-load closing action pressure p by using formula ②op.k；
In formula ②, TkThe length of a no-load closing data window;
(4) if the calculated no-load closing action pressure p is obtainedop.kGreater than or equal to a preset no-load closing protection action threshold value pth.kIf the formula ③ is satisfied, the protection action is performed, the trip is performed to remove the fault, the whole device is reset, and the manual reset is waited;
pop.k≥pth.k③
under the condition of magnetizing inrush current of the transformer, the action pressure pop.kIs an unbalance amount p different from 0ub.kIs less than a protection threshold value pth.k(ii) a Once the air drop is in the internal short-circuit fault, the fault gas generation and the pressure wave propagation can cause the internal pressure of the oil tank to suddenly rise, and at the moment pop.kWill be greater than the threshold value pth.kTherefore, the action behavior of protection is determined by judging whether the formula ③ is established;
(5) the operating pressure p at the current time t is calculated by equation ④op.i：
In the formula IV, T is the length of the data window;
(6) comparing the calculated operating pressure pop.iAnd a predetermined pressure protection action threshold value pthIf the calculated operating pressure p is greater than or equal toop.iGreater than or equal to a preset pressure protection action threshold value pthIf the formula ⑤ is satisfied, the protection action is performed, the trip is performed to remove the fault, the whole device is reset, and the manual reset is waited;
pop.i≥pth⑤。
in a further development of the invention, in step (1), the protection activation threshold p is setstIs defined as:
pst＝krelpnm·max⑥
in formula ⑥, krelAs a reliability factor, a reliability factor krelIs 1.2; p is a radical ofnm.maxThe maximum value of the transient oil pressure value under the normal operation condition of the transformer is obtained;
in the step (3), the length T of the no-load closing data windowkThe length of the data window is the same as that of a data window selected when a preset no-load closing action threshold value is set; no-load closing data window length TkSet to 5ms, 10ms or 20 ms.
The invention is further improved in that in the step (4), a no-load closing action threshold value p is setth.kComprises the following steps:
pth.k＝krelpub.kmax⑦
in formula ⑦, pub.kmaxSubstituting the transient oil pressure value measured by the internal measuring point of the transformer during the magnetizing inrush current into the formula ② for the unbalance of the internal operating pressure of the oil tank under the condition of the maximum pressure fluctuation generated by the magnetizing inrush current, wherein the p is obtained by calculationth.kThe value is the unbalance p of the internal operating pressure of the oil tank under the condition of maximum pressure fluctuation generated by the excitation surge currentub.kmax；
Setting the length T of the data window in the step (5) to be 5ms, 10ms or 20 ms;
in step (6), defining a pressure protection action threshold value pthComprises the following steps:
pth＝krelpub.max⑧
in formula ⑧, pub.maxSubstituting the transient oil pressure value measured by the internal measuring point of the transformer in the external most serious short-circuit fault into the formula ④ for the maximum unbalance amount of the internal operating pressure of the oil tank under the external most serious short-circuit fault condition, wherein the p is obtained by calculationop.iThe value is the maximum unbalance p of the internal operating pressure of the oil tank under the condition of the external most serious short circuit faultub.max。
Compared with the prior art, the invention has the following beneficial effects:
compared with the prior mechanical non-electric quantity protection, the invention uses the digital oil pressure information to form protection to discriminate the internal fault of the transformer and has the following advantages: first, the internal pressure characteristics of the tank are completely different in the mechanisms of pressure generation and change under normal and abnormal conditions of the power transformer and internal faults. Once the transformer has internal fault, fault electric energy is rapidly released to generate fault bubbles with certain volume and internal energy, and the bubbles are continuously heated and boosted to cause single-side sudden rise of the internal pressure of the oil tank. When an external short circuit occurs, the fault point is positioned outside the transformer, the influence on the internal pressure of the oil tank is only reflected on the vibration of the winding caused by the short-circuit through current, and the pressure characteristic presents the characteristics of limited amplitude and positive and negative oscillation. Secondly, the propagation speed of the pressure wave in the insulating oil is as high as 1.26m/ms, and for a large power transformer with the geometric dimension of 10m, the pressure characteristic change caused by any reason is not considered, and the pressure change captured by the protection measuring device only needs a plurality of milliseconds. Therefore, the pressure characteristics are selected to construct the protection with sufficient rapidity. Third, compared with the problem that the electric quantity protection shows insufficient sensitivity when facing low-energy faults such as short circuit of single turn or small turn number, the non-electric quantity protection has the common advantage of higher sensitivity and weak response fault. From the analysis of energy conversion, the electrical network fault is accompanied by the conversion of fault electric energy, and the non-electrical physical quantity is often a direct representation of different forms of energy and has a cumulative effect in nature. The device can realize real-time digital measurement, acquisition and operation of the oil pressure characteristic information in the oil tank on the premise of not damaging the existing structural integrity of the transformer.
Furthermore, the high-frequency dynamic pressure sensor with the measuring frequency of 20kHz, the measuring error of less than 1 percent, the working temperature of-45-120 ℃ and the measuring range of-0.1-6 MPa is adopted, so that the high-frequency dynamic pressure sensor can meet the high-temperature, oil stain and strong electromagnetic environment in the power transformer no matter the precision or the use range; the high-frequency dynamic pressure sensor is independent of a power network, the interference on the measurement and transmission of pressure characteristics is small, and harmonic waves are not injected into a power system; the data acquisition and processing element can completely meet the requirements of processing multi-channel and high-frequency data rapidly and in real time.
Furthermore, the traditional gas relay can only sense the flow velocity of oil flow through a mechanical spring device and can only output switching value information, and the single flow velocity amplitude cannot correctly distinguish the inside and outside faults of the transformer, so that protection misoperation or operation failure is caused. The device consists of a transient oil pressure characteristic quantity measuring module, a switching value input module, a signal conditioning and collecting module, a digital core module, an external communication interface module, a man-machine conversation module and a switching value output module. The method comprises the steps of calculating the action pressure based on transient oil pressure values of a plurality of measuring points by utilizing the characteristics that the amplitude of oil pressure in an oil tank is increased when the transformer has an internal fault, and the oil pressure is limited in amplitude and periodically oscillates under the conditions of normal operation, external short circuit or excitation inrush current, and judging the operation state of the transformer by comparing the action pressure with a protection action threshold value. And when the internal fault is judged, a tripping signal is sent out, the fault transformer is cut off, and the whole set of protection device is reset.
According to the invention, the functions of monitoring, fault processing, man-machine conversation, communication, self-checking, accident recording and analysis reporting and debugging of the protection device are realized according to the protection principle and the functional requirements, and the internal faults of the transformer oil tank are quickly, sensitively and reliably discriminated by utilizing the transient oil pressure information in the oil tank and the pressure difference under different operating conditions, and are not influenced by excitation surge current. In addition, considering that the oil pressure amplitude under the condition of magnetizing inrush current is obviously smaller than that of an external short-circuit fault and the inherent time window influences the action speed of protection under the condition of no-load fault, the invention designs a protection scheme with self-adaption of fault states and self-adaption of threshold values so as to improve the action speed of protection when the protection is faced with the no-load fault. The invention has simple principle and easy realization of the device, and improves the mechanical non-electric quantity protection formed by experience and feeling in the past to a new stage of quantitative analysis, high reliability judgment and digital realization, thereby being suitable for the requirements of the current and future high-capacity and high-voltage grade power transformers on the four-property non-electric quantity protection.
Drawings
FIG. 1 is a schematic diagram of the structure of the device of the present invention.
FIG. 2 is a flow chart of the present invention.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
Referring to fig. 1, the adaptive protection device for a transformer based on pressure characteristics, which is used in the present invention, includes: the device comprises a transient oil pressure characteristic quantity measuring module, a switching quantity input module, a signal conditioning and collecting module, a digital core module, an external communication interface module, a man-machine conversation module and a switching quantity output module; the device comprises a transient oil pressure characteristic quantity measuring module, a signal conditioning and collecting module, a switching value input module, an external communication interface module, a man-machine dialogue module and a switching value output module, wherein the transient oil pressure characteristic quantity measuring module is connected with the signal conditioning and collecting module, and the signal conditioning and collecting module, the switching value input module, the external communication interface module, the man-machine dialogue module and the switching value output module are all connected.
The transient oil pressure characteristic quantity measuring module consists of a plurality of high-frequency dynamic oil pressure sensors and communication cables thereof, and is used for measuring the internal oil pressure change characteristics of different positions of the transformer and outputting analog voltage/current signals corresponding to the internal oil pressure change characteristics. The high-frequency dynamic oil pressure sensor is arranged on the transformer body, and a probe at the end part of the sensor is directly contacted with the transformer insulating oil to measure the internal oil pressure change characteristics of different positions of the transformer. The measuring frequency of the high-frequency dynamic oil pressure sensor is 20kHz, the measuring error is less than 1%, the working temperature is-45-120 ℃, and the measuring range is-0.1-6 MPa.
The signal conditioning and collecting module consists of a wiring terminal, a signal conditioning circuit, a low-pass filter, a signal sampling circuit and an analog-digital A/D conversion circuit; the wiring terminal is connected with the signal conditioning circuit, the signal conditioning circuit is connected with the low-pass filter, the low-pass filter is connected with the signal sampling circuit, and the signal sampling circuit is connected with the analog-to-digital A/D conversion circuit; the wiring terminal is also connected with a communication cable. The signal conditioning and acquisition module is used for receiving the analog voltage/current signal output by the transient oil pressure characteristic quantity measuring module, converting the analog voltage/current signal into a standard digital signal which can be identified by the digital core module, and outputting the standard digital signal;
the switching value input module is used for acquiring relevant switching value signals needing to be known, and outputting the relevant switching value signals to be high level 1 or low level 0 to be used as input digital signals of the digital core module.
The digital core module consists of a bus, a central processing unit, a timer/counter, a random access memory and a control circuit; the bus comprises a data bus, an address bus and a control bus, and realizes data exchange and operation control; the central processing unit utilizes a single chip microprocessor, a general microprocessor or a digital signal processor to quickly realize digital signal processing in real time; the timer/counter is used for providing a timing sampling trigger signal, forming interruption and protecting the accurate timing of the time delay action; the random access memory is used for temporarily storing a large amount of temporary data needing fast exchange, including data information input by the signal conditioning and acquisition module and intermediate results of the calculation processing process; the control circuit realizes the effective connection and coordination work of the whole digital circuit through a complex programmable logic device or a field programmable gate array.
The digital core module is used for executing protection operation on the received standard digital signal and the input digital signal, finishing a digital signal processing task, commanding the normal operation of the connected modules, and realizing data exchange and operation control, thereby realizing a relay protection function.
The external communication interface module is used for providing an information channel with a computer communication network and a remote communication network, and realizing information interaction, data sharing, remote operation and remote maintenance.
The man-machine conversation module comprises a compact keyboard, a display screen, an indicator light, a button, a printer interface, a debugging communication interface and the like, and is used for establishing information contact between the digital protection device and a user so as to facilitate the manual operation and debugging of an operator on the protection device and obtain information feedback.
The switching value output module consists of a photoelectric isolation device and an outlet relay, wherein the photoelectric isolation device is connected with the outlet relay and used for controlling and executing the on-off of a tripping circuit through the output 0 or 1 state so as to realize the reliable action of protection.
Referring to fig. 2, based on the protection method of the protection device, the protection device is controlled according to the protection principle and the function requirement, and various operations such as data acquisition, external communication, digital operation, logic judgment, and action instruction execution are sequentially completed, and the specific steps are as follows:
(1) after the protection device is powered on or reset by hardware (reset for short), firstly, system initialization is executed to ensure that the whole protection device is in a normal working state;
(2) executing comprehensive self-checking after power-on, carrying out correctness and integrity detection on the working state of the device, sending an alarm signal and locking the whole device if a defect of the device is found, and waiting for technical personnel to remove the fault and manually reset;
(3) if the data acquisition initialization is carried out through self-checking, and timing sampling interruption is started to carry out address allocation on a circularly stored sampling data buffer area, a dynamic address pointer for marking the current latest data is set, then an interruption timer for controlling circular sampling is assigned and started according to a specified sampling period, and sampling interruption is opened;
(4) the transient oil pressure characteristic quantity measuring module measures oil pressure change characteristics of different positions in the transformer and outputs corresponding analog voltage/current signals; the signal conditioning and acquisition module receives the analog voltage/current signal output by the transient oil pressure characteristic quantity measurement module, converts the analog voltage/current signal into a standard digital signal which can be identified by the digital core module, and then outputs the standard digital signal; the switching value input module acquires relevant switching value signals needing to be known, outputs the relevant switching value signals as high level 1 or low level 0 and uses the high level 1 or the low level 0 as input digital signals of the digital core module; after the standard digital signal and the input digital signal received by the digital core module are received, the protection function is temporarily locked, enough data (data of one to two cycles) are stored in the sampling data buffer area, and then the protection function is opened;
(5) initializing the whole group, carrying out operation self-checking in an operation state, sending an alarm signal and locking the whole device if a device defect is found, and waiting for a technician to remove a fault and manually reset;
(6) if the fault does not occur, executing communication task processing to prepare data for information sending and receiving; the method comprises the following steps: collecting related data according to data sending requests of other parts of the protection method, sorting and packaging communication information according to a communication protocol, sorting and classifying data in a data receiving buffer area and explaining a task;
(7) executing man-machine conversation processing, performing tasks of scanning a keyboard, controlling buttons and displaying data on a display screen, interpreting and classifying various operation commands, and delivering corresponding task processing according to task types;
(8) judging whether the protection device is in a working operation mode; if the operation mode is not the working operation mode, debugging task processing is carried out, and the step (5) is returned after the debugging task is completed; if the operation mode is in the working operation mode, entering the step (9);
(9) judging whether the starting mark is set or not, if so, indicating that the protection device detects possible accident disturbance, and entering the step (11); otherwise, entering the step (10);
(10) comparing the transient oil pressure value p of each measuring point at the current time tms.i(t) whether a predetermined protection start threshold p is reachedstDetermining whether the transformer self-adaptive protection based on the pressure characteristics is started, if the expression ① is not established, returning to the step (5), if the expression ① is established, setting a starting flag, and entering the step (11);
pms.i(t)≥pst①
in formula ①, pms.i(t) represents the transient oil pressure value of the ith measuring point in the transformer at the time t, wherein i is 1,2, …, N; p is a radical ofstIndicating a protection enable threshold.
To ensure that the pressure protection can start working under fault and abnormal disturbance conditions, the protection start threshold p is setstIs defined as:
pst＝krelpnm·max②
in formula ②, krelThe reliability coefficient is 1.2; p is a radical ofnm.maxThe maximum value of the transient oil pressure value under the normal operation condition of the transformer is obtained.
(11) Judging whether the transformer is in a no-load closing state at present, if so, performing the step (12), and otherwise, performing the step (14);
(12) calculating no-load closing action pressure p by using formula ③op.k
In formula ③, TkThe length of the no-load closing data window is the same as the length of the data window selected when the preset no-load closing action threshold value is set, and can be selected to be 5ms, 10ms or 20ms according to requirements.
(13) If the calculated no-load closing action pressure p is obtainedop.kGreater than or equal to a preset no-load closing protection action threshold value pth.kIf the formula ④ is true, the protection action is carried out, the trip is carried out to remove the fault, the whole device is reset, and the manual reset is waited, otherwise, the step (5) is returned;
pop.k≥pth.k④
under the condition of magnetizing inrush current of the transformer, the action pressure pop.kIs an unbalance amount p different from 0ub.kIs less than a protection threshold value pth.k(ii) a Once the air drop is in the internal short-circuit fault, the fault gas generation and the pressure wave propagation can cause the internal pressure of the oil tank to suddenly rise, and at the moment pop.kWill be greater than the threshold value pth.kTherefore, by determining whether or not expression ④ is satisfied, the operation behavior of protection can be determined.
In order to ensure that the transformer self-adaptive protection based on the pressure characteristics does not malfunction under the condition of the most serious pressure fluctuation generated by the excitation inrush current, a no-load closing action threshold value p is setth.kComprises the following steps:
pth.k＝krelpub.kmax⑤
in formula ⑤, pub.kmaxSubstituting the transient oil pressure value measured by the internal measuring point of the transformer during the magnetizing inrush current into the formula ③ for the unbalance of the internal operating pressure of the oil tank under the condition of the maximum pressure fluctuation generated by the magnetizing inrush current, wherein the p is obtained by calculationth.kThe value is the unbalance p of the internal operating pressure of the oil tank under the condition of maximum pressure fluctuation generated by the excitation surge currentub.kmax。
(14) The operating pressure p at the current time t is calculated by equation ⑥op.i：
In the formula, T is the length of a data window, is the same as the length of the data window selected when the preset protection action threshold value is set, and can be selected to be 5ms, 10ms or 20ms as required
(15) Comparing the calculated operating pressure pop.iAnd a predetermined pressure protection action threshold value pthIf the calculated operating pressure p is greater than or equal toop.iGreater than or equal to a preset pressure protection action threshold value pthIf the formula ⑦ is true, the protection action is carried out, the trip is carried out to remove the fault, the whole device is reset, and the manual reset is waited, otherwise, the step (5) is returned;
pop.i≥pth⑦
in order to ensure that the transformer self-adaptive protection based on the pressure characteristics does not malfunction under the condition of the most severe pressure fluctuation generated when the external most severe short circuit fault occurs, a pressure protection action threshold value p is definedthComprises the following steps:
pth＝krelpub.max⑧
in formula ⑧, pub.maxSubstituting the transient oil pressure value measured by the internal measuring point of the transformer in the external most serious short-circuit fault into the formula ⑥ for the maximum unbalance amount of the internal operating pressure of the oil tank under the external most serious short-circuit fault condition, wherein the p is obtained by calculationop.iThe value is the maximum unbalance p of the internal operating pressure of the oil tank under the condition of the external most serious short circuit faultub.max。
The effect of the present invention will be described below by taking an SFSZ8-40000/110 three-phase three-winding transformer as an example, and the main geometric structure and the nameplate parameters of the transformer are shown in table 1.
TABLE 1 SFSZ8-40000/110 Transformer principal geometry and nameplate parameters
Considering that the oscillation frequency of the internal pressure of the oil tank is mainly concentrated on 100Hz and 50Hz under the conditions of normal operation of the transformer, external short circuit and excitation inrush current, in order to take protection reliability and calculation time into consideration, the time window length is selected to be 20ms in the pressure protection element, and the time window length is selected to be 20ms in the no-load closing element. Therefore, the protection starting threshold is calculated to be 0.226kPa, the pressure protection element operation threshold is 11.974kPa, and the no-load closing element operation threshold is 1.832 kPa.
Table 2 shows the behavior of the adaptive protection under different operating conditions of the transformer, which can be seen as follows: 1) the self-adaptive protection strategy added with the no-load switching-on protection element also has higher reliability and sensitivity, can correctly discriminate a plurality of fault states including single-turn short-circuit faults, and is not influenced by excitation inrush current. 2) The time window of protection calculation is actively shortened under the condition of magnetizing inrush current, and the protection threshold value is calculated according to the maximum unbalanced pressure generated by the magnetizing inrush current, so that the action speed of the self-adaptive protection strategy is obviously improved when the fault type of air drop is faced. In summary, the transformer self-adaptive protection scheme based on the pressure characteristics has the characteristics of simple principle and easy realization, and simultaneously meets the requirement of relay protection on the fourteen property.
TABLE 2 action situation of adaptive protection under different operation conditions of transformers
While the invention has been described in further detail with reference to specific preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (3)
1. A protection method of a digital self-adaptive protection device of a transformer based on pressure characteristics is characterized by comprising the following steps:
(1) the transient oil pressure characteristic quantity measuring module measures oil pressure change characteristics of different positions in the transformer and outputs an analog voltage/current signal, and the signal conditioning and collecting module receives the analog voltage/current signal output by the transient oil pressure characteristic quantity measuring module, converts the analog voltage/current signal into a standard digital signal which can be identified by the digital core module and then outputs the standard digital signal; the switching value input module is used for acquiring relevant switching value signals needing to be known, outputting the relevant switching value signals as high level 1 or low level 0, and using the high level 1 or low level 0 as input digital signals of the digital core module; after receiving the input digital signal and the standard digital signal, the digital core module compares the transient oil pressure value p of each measuring point at the current t momentms.i(t) whether a predetermined protection start threshold p is reachedstDetermining whether the transformer self-adaptive protection based on the pressure characteristics is started, if the formula ① is satisfied, setting a starting flag, and entering the step (2);
pms.i(t)≥pst①
in formula ①, pms.i(t) represents the transient oil pressure value of the ith measuring point in the transformer at the time t, wherein i is 1,2, …, N; p is a radical ofstIndicating a protection activation threshold;
(2) judging whether the transformer is in a no-load closing state at present, if so, performing the step (3), and otherwise, performing the step (5);
(3) calculating no-load closing action pressure p by using formula ②op.k；
In formula ②, TkThe length of a no-load closing data window;
(4) if the calculated no-load closing action pressure p is obtainedop.kGreater than or equal to a preset no-load closing protection action threshold value pth.kIf the formula ③ is satisfied, the protection action is performed, the trip is performed to remove the fault, the whole device is reset, and the manual reset is waited;
pop.k≥pth.k③
(5) the operating pressure p at the current time t is calculated by equation ④op.i：
In the formula IV, T is the length of the data window;
(6) comparing the calculated operating pressure pop.iAnd a predetermined pressure protection action threshold value pthIf the calculated operating pressure p is greater than or equal toop.iGreater than or equal to a preset pressure protection action threshold value pthIf the formula ⑤ is satisfied, the protection action is performed, the trip is performed to remove the fault, the whole device is reset, and the manual reset is waited;
pop.i≥pth⑤。
2. the protection method of the digital adaptive transformer protection device based on the pressure characteristics as claimed in claim 1, wherein in the step (1), the protection starting threshold p is setstIs defined as:
pst＝krelpnm·max⑥
in formula ⑥, krelAs a reliability factor, a reliability factor krelIs 1.2; p is a radical ofnm.maxThe maximum value of the transient oil pressure value under the normal operation condition of the transformer is obtained;
in the step (3), the length T of the no-load closing data windowkThe length of the data window is the same as that of a data window selected when a preset no-load closing action threshold value is set; no-load closing data window length TkSet to 5ms, 10ms or 20 ms.
3. The protection method of the digital adaptive protection device for the transformer based on the pressure characteristics as claimed in claim 1, wherein in the step (4), the no-load closing action threshold value p is setth.kComprises the following steps:
pth.k＝krelpub.kmax⑦
in formula ⑦, pub.kmaxSubstituting the transient oil pressure value measured by the internal measuring point of the transformer during the magnetizing inrush current into the formula ② for the unbalance of the internal operating pressure of the oil tank under the condition of the maximum pressure fluctuation generated by the magnetizing inrush current, wherein the p is obtained by calculationth.kThe value is the unbalance p of the internal operating pressure of the oil tank under the condition of maximum pressure fluctuation generated by the excitation surge currentub.kmax；
Setting the length T of the data window in the step (5) to be 5ms, 10ms or 20 ms;
in step (6), defining a pressure protection action threshold value pthComprises the following steps:
pth＝krelpub.max⑧
in formula ⑧, pub.maxSubstituting the transient oil pressure value measured by the internal measuring point of the transformer in the external most serious short-circuit fault into the formula ④ for the maximum unbalance amount of the internal operating pressure of the oil tank under the external most serious short-circuit fault condition, wherein the p is obtained by calculationop.iThe value is the maximum unbalance p of the internal operating pressure of the oil tank under the condition of the external most serious short circuit faultub.max。
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