CN109001587B - Method for verifying main transformer high-voltage side CT polarity by utilizing excitation inrush current - Google Patents

Method for verifying main transformer high-voltage side CT polarity by utilizing excitation inrush current Download PDF

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CN109001587B
CN109001587B CN201810723723.2A CN201810723723A CN109001587B CN 109001587 B CN109001587 B CN 109001587B CN 201810723723 A CN201810723723 A CN 201810723723A CN 109001587 B CN109001587 B CN 109001587B
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voltage
voltage side
main transformer
phase
current
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CN109001587A (en
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李本瑜
王冰清
赵明
刘宏君
游昊
石磊
石恒初
张琳波
方毅
陈剑平
杨远航
张鑫
李源辉
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Yunnan Power Grid Co Ltd
CYG Sunri Co Ltd
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Yunnan Power Grid Co Ltd
CYG Sunri Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/72—Testing of electric windings

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Abstract

The invention discloses a method for checking the polarity of a main transformer high-voltage side CT (current transformer) by utilizing an excitation inrush current, which aims to solve the technical problem of conveniently checking whether the polarity of the main transformer high-voltage side CT wiring is correct or not. The method comprises the steps of collecting three-phase secondary voltage and three-phase secondary current of a high-voltage side bus of a main transformer, calculating three-phase instantaneous reactive power, calculating the reactive power average value of one period, and judging that the CT wiring of the current transformer is correct, wherein the reactive power average value is more than 0. Compared with the prior art, the method has the advantages that the instantaneous reactive power is calculated by utilizing the magnetizing inrush current generated by the transformer and the voltage of the high-voltage side of the main transformer, the average value of the instantaneous reactive power in a unit period is obtained through calculation, the average value of the reactive power is larger than zero, CT wiring is considered to be correct, otherwise, CT wiring is considered to be wrong, and a circuit breaker of the high-voltage side of the main transformer is tripped, so that the aim of checking the polarity of the CT on the high-voltage side of the main transformer is fulfilled, the misoperation or the rejection of protection equipment caused by the CT wiring mistake is.

Description

Method for verifying main transformer high-voltage side CT polarity by utilizing excitation inrush current
Technical Field
The invention relates to a relay protection method of a power system, in particular to a method for checking the polarity of a current transformer at the high-voltage side of a main transformer of a transformer substation.
Background
The current transformer CT is a main device in an electric power system, and mainly has the functions of converting large current of a primary system into small current of a secondary system for use by loop devices such as measurement, protection and the like, timely and accurately reflecting the operation condition of the primary system, facilitating protection, control and monitoring of the electric power system by an operation department, and playing an important role in preventing the fault range from being expanded and ensuring the reliable operation of the system. If the CT polarity of the high-voltage side of the transformer is connected incorrectly, the transformer protection equipment is very easy to malfunction or refuse, the power supply reliability of the transformer substation is reduced while primary equipment is damaged, and even a power grid may be damaged greatly. Therefore, before power transmission of a transformer substation with a newly built or expanded main transformer interval or in a situation involving change of a main transformer high-voltage side CT secondary circuit, detailed inspection and test on the main transformer high-voltage side CT secondary circuit are required to ensure the wiring correctness of the secondary circuit.
According to the CT polarity correctness checking regulation, in the work that a circuit such as new operation, major repair or technical improvement and the like is greatly changed, before the operation of newly added or changed primary and secondary equipment of electric power, the CT polarity correctness needs to be checked by primary current. And if the polarity of the head and tail outlet terminals of the CT primary winding is the same as that of the head and tail outlet terminals of the secondary winding, the CT wiring is considered to be correct, otherwise, the CT wiring is considered to be wrong.
In the conventional test method in the prior art, an independent power supply is generally adopted to perform a through-current test on the primary side of the CT, a phase table is used to measure the current phase of the secondary side, the correctness of the polarity of the CT is judged according to the angle relationship between the voltage and the current displayed by the phase table, if the voltage leads the current and the angle difference is less than 90 degrees, the CT wiring is considered to be correct, otherwise, the CT wiring is considered to be wrong. Because the transformer high-voltage side CT transformation ratio is large and limited by the capacity of an independent power supply, the current generated by a primary side through-flow test on a secondary side is extremely small, even only 2-5 mA, most phase meters cannot meet the precision, the obtained main transformer (main transformer) high-voltage side CT polarity check result is low in reliability, a certain risk exists when the main transformer is put into operation, and the protection device can be mistakenly operated or refused to operate seriously, so that the safe and stable operation of an electric power system is influenced.
Disclosure of Invention
The invention aims to provide a method for checking the polarity of a main transformer high-voltage side CT by using an excitation inrush current, and the technical problem to be solved is to conveniently check whether the polarity of the main transformer high-voltage side CT connection is correct.
The invention adopts the following technical scheme: a method for verifying the polarity of a main transformer high-voltage side CT by using an excitation inrush current comprises the following steps:
the protection device collects three-phase secondary voltage u of a main transformer high-voltage side busa、ub、ucAnd three-phase secondary current ia、ib、icCalculating three-phase instantaneous reactive power q:
Figure BDA0001719170010000021
wherein u isaIs an instantaneous second-order value of A phase voltage, ubIs the instantaneous secondary value of the B-phase voltage ucIs an instantaneous secondary value of the C-phase voltage iaIs an instantaneous secondary value of the A-phase current, ibIs an instantaneous secondary value of the B-phase current, icThe instantaneous secondary value of the C-phase current;
secondly, calculating the reactive power average value of one period:
Figure BDA0001719170010000022
wherein T is a voltage period;
and thirdly, the reactive power average value Q is larger than 0, and the protection device judges that the CT wiring of the current transformer is correct.
In the third step of the method, the average value Q of the reactive power is less than 0, and the CT wiring of the current transformer is considered to be wrong.
According to the method, the CT of the current transformer is in wrong wiring, and the protection device acts on tripping of the circuit breaker on the high-voltage side of the main transformer.
The protection device of the method of the invention checks the CT polarity of the main transformer high-voltage side current transformer, and firstly, the following three conditions are simultaneously met:
the method comprises the following steps that firstly, a protection device collects position information of a circuit breaker on the high-voltage side of a main transformer and judges that the high-voltage side of the main transformer is in a charging state;
secondly, the protection device collects current information of the high-voltage side of the main transformer and judges that the main transformer has current according to the current amplitude;
and thirdly, the protection device acquires bus voltage information corresponding to the high-voltage side of the main transformer and judges whether the voltage of the high-voltage side is normal according to the voltage amplitude and the phase.
The judgment basis for judging that the high-voltage side of the main transformer is in a charging state under the first condition of the method is as follows: from the jump moment of the main transformer high-voltage side circuit breaker from the branch TW to the closing HW, the time t is 200ms from the time t when the main transformer high-voltage side circuit breaker is operated to the time t from the closing HW.
The judgment basis for judging the current of the main transformer by the second condition of the method is the logic or of the following conditions:
Ia＞0.05In，Ib＞0.05In，Ic＞0.05In
wherein, IaA secondary value of the effective value of the A-phase current, IbA secondary value of the effective value of the phase B current, IcIs a secondary value of the effective value of the C-phase current, InTo protect the secondary rating of the current transformer CT.
The judgment basis for judging the high-voltage side voltage to be normal under the condition three of the method is the logical AND of the following conditions:
Uab＞70，Ubc＞70，Uca＞70
Ua-Ub＜2，Ub-Uc＜2，Uc-Ua＜2
118＜UaAng-UbAng＜122
118＜UbAng-UcAng＜122
118＜UcAng-UaAng＜122
wherein, UabIs A, B two-phase line voltage effective value secondary value, UbcIs B, C two-phase line voltage effective value secondary value, UcaIs C, A two-phase line voltage effective value secondary value, UaIs the second order value of A phase voltage, UbIs the second order value of the effective value of the B phase voltage, UcIs a secondary value of the effective value of the C phase voltage, UaAngIs the phase angle of A phase voltage, UbAngPhase angle of B phase voltage, UcAngIs the phase angle of the C-phase voltage.
In the method, a voltage transformer PT is arranged on a bus connected with the high-voltage side of a main transformer, and a current transformer CT is arranged on the high-voltage side of the main transformer.
The method of the invention is characterized in that a protection device arranged at the high-voltage side of a main transformer acquires three-phase secondary voltage u of a corresponding bus at the high-voltage side of the main transformer through a voltage transformer PTa、ub、uc(ii) a The protection device collects three-phase secondary current i at the high-voltage side of the main transformer through the current transformer CTa、ib、ic。
The protection device of the method acquires the position of the switch through the auxiliary contact of the circuit breaker on the high-voltage side of the main transformer.
Compared with the prior art, in the process of charging the main transformer, the transformer can generate excitation inrush current under the action of hysteresis characteristics of an iron core, instantaneous reactive power is calculated by utilizing the excitation inrush current generated by the transformer and the voltage of the high-voltage side of the main transformer, the average value of the instantaneous reactive power in a unit period is obtained by calculation, the CT wiring is considered to be correct if the average value of the reactive power is greater than zero, otherwise, the CT wiring is considered to be wrong, and a circuit breaker on the high-voltage side of the main transformer is tripped, so that the aim of checking the CT polarity on the high-voltage side of the main transformer is fulfilled, the misoperation or the rejection of protection equipment caused by the CT wiring error is prevented, and.
Drawings
Fig. 1 is a transformer primary side equivalent circuit diagram.
Fig. 2 is a schematic diagram of the basic magnetization curve and hysteresis loop of the transformer core.
FIG. 3-1 shows the magnetic flux at α with the magnetic flux flowing through the excitation branch0＝00，φrHysteresis loop diagram of 0.5.
FIG. 3-2 shows the magnetic flux at α with the magnetic flux flowing through the excitation branch0＝00，φrCurrent dependence graph of 0.5.
FIGS. 3-3 show the magnetic flux at α with the magnetic flux flowing through the excitation branch0＝1800，φrHysteresis loop schematic of-0.5.
FIGS. 3-4 show the magnetic flux at α with the magnetic flux flowing through the excitation branch0＝1800，φr-0.5 current dependence.
FIGS. 3-5 show the magnetic flux at α with the magnetic flux flowing through the excitation branch0＝900，φrHysteresis loop diagram of 0.
FIGS. 3-6 show the magnetic flux at α with the magnetic flux flowing through the excitation branch0＝900，φrCurrent dependence graph of 0.
Fig. 4-1 is a simulation waveform diagram of the three-phase voltage on the high-voltage side of the transformer in the case of correct wiring of the CT in embodiment 1 of the present invention.
Fig. 4-2 is a simulation waveform diagram of three-phase current on the high-voltage side of the transformer in the case of correct CT wiring in embodiment 1 of the present invention.
Fig. 4-3 are simulation waveforms of the instantaneous reactive power at the high-voltage side of the transformer in the case of correct CT wiring in embodiment 1 of the present invention.
Fig. 4-4 are simulated waveforms of the reactive power on the high-voltage side of the transformer in the case of correct CT wiring in embodiment 1 of the present invention.
Fig. 5-1 is a simulation waveform diagram of the instantaneous reactive power at the high-voltage side of the transformer in the case of the polarity reversal of the phase-a CT in embodiment 1 of the present invention.
Fig. 5-2 is a simulation waveform diagram of the reactive power at the high-voltage side of the transformer in the case of the polarity reversal of the phase-a CT in embodiment 1 of the present invention.
FIG. 6-1 is a waveform diagram of three-phase current at the high-voltage side of the transformer in the case of correct CT wiring in embodiment 2 of the present invention.
Fig. 6-2 is a waveform diagram of the three-phase current on the high-voltage side of the on-site transformer in the case of correct wiring of the CT in embodiment 2 of the present invention.
Fig. 6-3 are the waveform diagrams of the instantaneous reactive power at the high-voltage side of the on-site transformer in the case of correct CT wiring in embodiment 2 of the present invention.
Fig. 6-4 are waveform diagrams of reactive power at the high-voltage side of the on-site transformer in the case of correct CT wiring in embodiment 2 of the present invention.
Fig. 7-1 is a waveform diagram of instantaneous reactive power on the high-voltage side of the transformer in the case of A, C-phase CT phase reversal in the embodiment 2 of the present invention.
Fig. 7-2 is a waveform diagram of reactive power on the high-voltage side of the transformer in the case of A, C-phase CT phase reversal in the embodiment 2 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
The method for verifying the main transformer high-voltage side CT polarity by using the magnetizing inrush current judges the CT polarity by using the magnetizing inrush current generated on the primary side when the transformer is switched on in a no-load state, so that the method is based on the analysis of the generation reason and the characteristics of the magnetizing inrush current.
As shown in fig. 1, on the primary side, R, when the transformer is unloadedlAnd LlRespectively representing the conductor equivalent resistance (resistance) and leakage inductance, L, of the transformer windingmRepresenting the excitation inductance, RhThe equivalent resistance of the hysteresis loss (hysteresis resistance) is shown. The equivalent circuit (equivalent circuit) on the primary side of the transformer when no load exists can be expressed as a series-connected wire equivalent resistor RlAnd leakage inductance LlExcitation inductance L in parallelmAnd a hysteresis resistance RhAnd (4) connecting in series. In the equivalent circuit, i denotes a current flowing into the primary side of the transformer, i.e., an exciting current (magnetizing inrush current), imRepresenting the current through the excitation inductance LmMagnetizing current of branch ihRepresenting the hysteresis resistance R flowing throughhThe current of (2).
When the transformer is switched on in no-load, leakage inductance L is ignoredmAccording to kirchhoff's voltage law, current law and electromagnetic induction law, the voltage and current expressions of the primary side loop are as follows:
Figure BDA0001719170010000071
in the formula (1), UmRepresents the peak voltage value applied by the power supply to the high-voltage side of the main transformer, omega represents the angular frequency of the voltage on the high-voltage side of the main transformer, t represents the time, alpha0Denotes an initial phase angle of a voltage when the power supply is switched on, phi denotes a total magnetic flux (magnetic flux) linked with the primary winding, and N denotes the number of turns of the primary winding of the transformer. Due to the resistance RlThe pressure drop is small and negligible in the initial phase of the analytical transition, i.e. it is
Figure BDA0001719170010000072
Solving the differential equation (2) to obtain a magnetic flux phi:
Figure BDA0001719170010000073
in the formula (3), C represents a constant term in the general solution of a differential equation, and the residual magnetism of the iron core at the moment of closing the transformer is assumed to be phirBecause the magnetic flux can not be suddenly changed, at the moment of switching on the transformer, namely when t is equal to 0, the magnetic flux phi is equal to the residual magnetism phirThus, there are:
Figure BDA0001719170010000074
at the moment of power failure of the transformer, under the influence of a hysteresis loop, when the current is 0, the magnetic flux is not 0, and residual magnetism phi is generatedrThe magnetic hysteresis loop of which the polarity and the numerical value are located by the magnetic circuit at the moment of power failureThe location of the operating point.
Bringing formula (4) into formula (3) can obtain a magnetic flux phi of:
Figure BDA0001719170010000075
in the formula (5), phimRepresents the magnitude of the steady state flux, which is:
Figure BDA0001719170010000081
as can be seen from the equation (1), the magnetizing inrush current i flows through the hysteresis resistor RhCurrent i of the branchhAnd current through the excitation inductor LmCurrent i ofmComposition of wherein ihThe relative relationship with the magnetic flux phi can be obtained by the formula (1). To describe the magnetic flux phi and the current flowing through the excitation inductor LmCurrent i ofmThe relationship (c) is explained by the basic magnetization curve of the transformer core.
The basic magnetization curve of the transformer core is a B-H curve of magnetic field intensity H and induced magnetic induction intensity B, the magnetic induction intensity B and magnetic flux phi, the magnetic field intensity H and magnetization current imThe following relationships exist:
φ＝BS (7)
Figure BDA0001719170010000082
in the formulas (7) and (8), S represents the sectional area of the transformer core, l represents the length of the transformer core, and N represents the number of turns of the transformer coil, so that the B-H curve can be converted into phi-i according to the geometric size of the transformer coremCurve line. As shown in FIG. 2, the magnetization curve of the transformer is non-linear when φ<φsWhen the transformer core is not saturated, its magnetic conductivity is higher, excitation electric resistance is large, imAre small; when phi is>φsWhen the transformer works in a saturation region, the magnetic permeability of the transformer is small, and small increase of magnetic flux can cause imIs increasing sharply. Phi is asThe saturation magnetic flux is the product of saturation magnetic induction and the sectional area of the transformer core, the saturation magnetic induction is determined by the material composition of the transformer core, and a transformer manufacturer can provide a technical manual of the transformer when the transformer leaves a factory, wherein the specific value of the saturation magnetic induction of the transformer can be determined.
Initial phase angle alpha when power supply is switched on0＝00Remanence phirAs can be seen from equation (5), the magnetic flux Φ of the transformer core becomes 2 Φ half a cycle after the power supply is turned onm+φr>>φsAt this time, the transformer core is heavily saturated. As shown in FIG. 3-1,. phi and imThe waveform of (a) constitutes a magnetization curve when phi<φsWhen i ismSmall, increasing slowly with increasing magnetic flux; when phi is>φsTime, transformer flux is saturated, imIncreases sharply with increasing magnetic flux. As shown in fig. 3-2, the waveforms of the magnetic flux phi and the magnetizing inrush current i changing with the angle (time) are deviated above the time axis, the magnetic flux phi and the magnetizing inrush current i change periodically with time, the magnetic flux slowly increases with time in the initial stage, i is extremely small and can be ignored, the magnetic flux changes rapidly with time, when phi changes rapidly with time>φsDuring the process, the current is increased sharply, after a half period, the current reaches a positive peak value and then decays, and the waveform is in a symmetrical shape.
When alpha is0＝1800，φrAnd when the power supply is switched on for a half period, the magnetic flux of the transformer core reaches the maximum reverse value, and the negative direction of the transformer core is seriously saturated at the moment. As shown in FIGS. 3-3, phi and imThe waveform of (a) constitutes a magnetization curve when phi<φsWhen i ismSmall, increasing slowly with increasing magnetic flux; when phi is>φsTime, transformer flux is saturated, imIncreases sharply with increasing magnetic flux. As shown in fig. 3 to 4, the waveforms of the magnetic flux phi and the magnetizing inrush current i, which vary with the angle (time), are biased to be below the time axis, the magnetic flux phi and the magnetizing inrush current i vary periodically with time, and in the initial stage, the magnetic flux increases slowly with time, i is extremely small (negligible), and with the passage of time, the magnetic flux changes rapidly with the passage of time,when phi is>φsDuring the period, the current increases sharply, reaches the peak value after half a period, then decays, and the waveform is symmetrical.
When alpha is0＝900，φrWhen the instantaneous voltage of the power supply is the maximum value, a steady-state magnetic flux is established once the power supply is switched on, so that the corresponding switching-on current reaches a steady-state no-load current without a transition state. As shown in FIGS. 3-5, [ phi ] and imThe waveform of (a) constitutes a magnetization curve when phi<φsWhen i ismSmall, increasing slowly with increasing magnetic flux; when phi is>φsTime, transformer flux is saturated, imIncreases sharply with increasing magnetic flux. As shown in fig. 3-6, the waveforms of the magnetic flux phi and the magnetizing inrush current i changing with the angle (time) are located on both sides of the time axis, the magnetic flux phi and the magnetizing inrush current i change periodically with time, the initial magnetic flux phi is 0, the initial current is 0, and phi is 0 in the whole process<φsThe current i is small.
It can be seen that the magnitude of the magnetizing inrush current is greatly influenced by the saturation degree of the iron core of the transformer, and the saturation degree of the iron core is related to the remanence of the transformer and the initial phase angle when the transformer is switched on. Aiming at an ideal power generation system with infinite capacity, the voltage amplitude, the frequency and the phase sequence are stable, and the three-phase closing angle difference is 1200If the closing angle of a certain phase is 900When no excitation surge current is generated near the closing, the closing angle of the other two phases is-1500、-300And excitation inrush current of a certain degree can be generated, so that at least two phases of the transformer can generate excitation inrush current of different degrees when the transformer is switched on. Simulation research shows that (document 1, research on magnetizing inrush current problems and identification methods of transformers, liu jian li, thesis of studios of Jiangsu university, 2010, page 14-20), the magnetizing inrush current of the transformers can reach 6-8 times of rated current, and under the influence of a B-H curve, the magnetizing inrush current contains a large amount of non-periodic components, mainly secondary harmonics, and the content of the non-periodic components is related to the saturation degree of an iron core.
The above analysis shows that the transformer generates a sufficiently large magnetizing inrush current during charging, but the magnetizing inrush current of the transformer contains a large amount of non-periodic components, and the method for determining the current direction in the prior art is based on the current being a sinusoidal periodic function, so that the method for determining the current direction by using the magnetizing inrush current in the prior art has the defect of unreliability. Therefore, the method introduces the concept of instantaneous reactive power as the judgment basis of the current direction.
Let ua、ub、ucSecondary value, i, representing instantaneous value of three-phase voltage on high-voltage side of main transformera、ib、icExpressing the secondary value of the instantaneous value of the three-phase current at the high-voltage side of the main transformer, and converting u by Clark for convenient calculation and controla、ub、ucAnd ia、ib、icTransformed into the alpha beta 0 coordinate system, having
Figure BDA0001719170010000101
Figure BDA0001719170010000111
In the α β 0 coordinate system, the voltage vector u and the current vector i may be represented by u, respectivelyα、uβ、iα、iβSynthesis, namely:
Figure BDA0001719170010000112
defining three-phase instantaneous active power (instantaneous active power) p and three-phase instantaneous reactive power (instantaneous reactive power) q as:
Figure BDA0001719170010000113
in expression (12), the symbol dot product represents the vector inner product operation, and the symbol cross product x represents the vector outer product operation.
The formula (11) is introduced into the formula (12):
Figure BDA0001719170010000114
substituting the formula (9) and the formula (10) into the formula (13) to obtain instantaneous active power p and instantaneous reactive power q:
p＝uaia+ubib+ucic (14)
Figure BDA0001719170010000115
integral calculation is carried out on the instantaneous active power and the instantaneous reactive power in a voltage period T, then the average value of the instantaneous active power and the instantaneous reactive power in a unit period after integral is obtained, and the active power average value P and the reactive power average value Q of the transformer in a period are obtained:
Figure BDA0001719170010000121
in the equation (16), the active power average value P represents energy consumption of a load of the main transformer, and the reactive power average value Q represents reactive power absorbed by the main transformer.
From the above analysis, it can be seen that when the transformer is in the inrush current state, the magnetizing reactance decreases rapidly, the inrush current increases rapidly, and the magnetic field energy storage of the transformer changes rapidly, that is, the transformer performs a large amount of rapid energy exchange with the outside, which is indicated as an increase in the reactive loss of the transformer. From another perspective, the magnetizing inrush current flows only through the primary winding and the core. Flux lag voltage 900Combining ohm's law in magnetic circuit, it can be known that current and magnetic flux are in phase, i.e. current lag voltage 900Namely, the leakage reactance and the excitation reactance of the primary side winding absorb reactive power. Therefore, for the high-voltage side of the transformer, if the CT polarity is correctly connected, the head and tail outgoing line ends of the CT primary winding have the same polarity as the head and tail outgoing line ends of the secondary winding, primary current flows in from the head outgoing line end of the CT primary winding and flows out from the tail outgoing line end, and secondary current flows out from the CT from the tail outgoing line endLeading-out wire ends of the secondary winding flow in and leading-out wire ends flow out, and the detected reactive power average value should meet Q>0。
According to the method, instantaneous reactive power is calculated by means of excitation inrush current generated when the transformer is charged, then the average value of the integrated instantaneous reactive power in a unit period is calculated to obtain the average value of the reactive power, and finally the correctness of the CT polarity of the high-voltage side of the main transformer is judged according to the size of the average value of the reactive power, so that reliable guarantee is provided for the reliable operation of the transformer substation.
The invention adopts the technical scheme that a voltage transformer PT is arranged on a bus connected with the high-voltage side of a main transformer, and a protection device arranged on the high-voltage side of the main transformer acquires three-phase secondary voltage u of the bus corresponding to the high-voltage side of the main transformer through the PTa、ub、uc. A current transformer CT is arranged on a bus connected with the high-voltage side of the main transformer, and a protection device collects three-phase secondary current i of the high-voltage side of the main transformer through the CTa、ib、ic. The protection device collects the switch position through the auxiliary contact of the main transformer high-voltage side circuit breaker, and closes HW and jumps TW (separated TW).
The method comprises the following steps:
the protection device has a CT polarity check function and checks the CT polarity on the high-voltage side of the main transformer.
The method comprises the steps of acquiring position information of a circuit breaker on the high-voltage side of a main transformer to judge the running state of the main transformer, and judging whether the high-voltage side of the main transformer is in a charging state or not as one of necessary conditions for inputting a CT polarity checking function. The judgment basis is as follows: from the jump moment of the main transformer high-voltage side circuit breaker from the branch TW to the closing HW, the main transformer is considered to be in a charging state within the time from the closing HW to the moment t of the main transformer high-voltage side circuit breaker. Outside this time period, the CT polarity check function exits. The method t of the present invention is set to 200ms. The time t is less than the duration time of the magnetizing inrush current, so that the transformer can be ensured to continuously generate the magnetizing inrush current within the time t, and the correctness of CT wiring is effectively judged.
And secondly, acquiring current information of the high-voltage side of the main transformer by the protection device, judging whether the main transformer has current according to the current amplitude, wherein the judgment is a logical OR according to the following conditions as one of necessary conditions for the CT polarity check function:
Ia＞0.05In，Ib＞0.05In，Ic＞0.05In (17)
in the formula (17), IaA secondary value of the effective value of the A-phase current, IbA secondary value of the effective value of the phase B current, IcIs a secondary value of the effective value of the C-phase current, InTo protect the CT quadratic rating (intrinsic parameter of CT).
And thirdly, acquiring bus voltage information corresponding to the high-voltage side of the main transformer by the protection device, judging whether the voltage of the high-voltage side is normal according to the voltage amplitude and the phase, wherein the judgment is based on the logic AND of the following conditions as one of necessary conditions for the input of the CT polarity check function:
Uab＞70，Ubc＞70，Uca＞70
Ua-Ub＜2，Ub-Uc＜2，Uc-Ua＜2
118＜UaAng-UbAng＜122
118＜UbAng-UcAng＜122
118＜UcAng-UaAng＜122 (18)
in formula (18), UabIs A, B two-phase line voltage effective value secondary value, UbcIs B, C two-phase line voltage effective value secondary value, UcaIs C, A two-phase line voltage effective value secondary value, UaIs the second order value of A phase voltage, UbIs the second order value of the effective value of the B phase voltage, UcIs a secondary value of the effective value of the C phase voltage, UaAngIs the phase angle of A phase voltage, UbAngPhase angle of B phase voltage, UcAngIs the phase angle of the C-phase voltage.
II, collecting u by a protection devicea、ub、uc，ia、ib、icCalculating instantaneous reactive power using equation (15)，
Figure BDA0001719170010000141
In the formula (15), uaIs a second order value of instantaneous value of A phase voltage ubIs a second order value of the instantaneous value of the B phase voltage ucIs a secondary value of C phase voltage instantaneous value iaIs a second order value of instantaneous value of A phase current, ibIs a second order value of instantaneous value of B-phase current, icThe instantaneous value of the C-phase current is the second order value.
Then, the reactive power average value is calculated by using the formula (16):
Figure BDA0001719170010000142
III, judging
And judging that the CT wiring is correct when the reactive power average value Q is larger than zero and is larger than 0 by the protection device, and considering that the CT wiring is wrong if the reactive power average value Q is smaller than zero and is smaller than 0, wherein the protection device acts on the tripping of a circuit breaker on the high-voltage side of the main transformer.
In embodiment 1, a simulation model is built by using a real-Time Digital simulator (rtds) (real Time Digital simulator), and the parameters are set as follows: the capacity is 180MVA, the voltage is three-coil transformer of 220kV/110kV/35kV, the wiring mode is YY delta, the initial closing angle alpha of the no-load closing of the high-voltage side of the transformer0Residual magnetism of 00 ═ 00
Figure BDA0001719170010000151
Under the condition that the CT wiring is correct, as shown in figure 4-1, the simulation waveform of the three-phase voltage at the high side of the transformer is a sine periodic function, the phase difference of the three phases is 1200, the period is 20ms, and the amplitude is 81.6V. As shown in fig. 4-2, the three-phase current simulation waveform on the high-voltage side of the transformer is a non-sinusoidal periodic function, and contains an attenuated direct-current component and multiple harmonics, the period is 20ms, and the A, B, C three-phase current amplitudes are 0.24A, 0.03A and 0.06A, respectively. As shown in fig. 4-3, the simulation waveform of the instantaneous reactive power at the high-voltage side of the transformer is a non-sinusoidal periodic function, and contains attenuated direct-current components and multiple harmonics, the period is 20ms, and the waveform is biased above the time axis. As shown in fig. 4-4, the simulated waveform of the reactive power average value on the high-voltage side of the transformer is biased to be above the time axis and decays along with the time. It can be seen that the three-phase magnetizing inrush current is different in size and waveform, the A, C-phase inrush current characteristic is obvious, and the main transformer reactive power Q is greater than 0 under the condition that the CT wiring is correct.
Under the condition that the polarity of the phase-A CT is reverse, as shown in figure 5-1, the instantaneous reactive power simulation waveform on the high-voltage side of the transformer is a non-sinusoidal periodic function and contains attenuated direct-current components and multiple harmonics, the period is 20ms, and the waveform is positioned on two sides of a time shaft. As shown in fig. 5-2, the simulation waveform of the reactive power average value on the high-voltage side of the transformer is deviated below the time axis and decays along with the time. And under the condition that the polarity of the A-phase CT is reversed, the main transformer reactive power Q is less than 0.
Example 2, in the case that the on-site CT wiring is correct when the on-site transformer is in the no-load charging mode in the transformer in korea county, shou yang county, jin, shan xi province, as shown in fig. 6-1, the voltage waveform of the high-voltage side of the transformer is a sine periodic function, and the phase difference of the three phases is 1200The period is 20ms and the amplitude is 81.6V. As shown in fig. 6-2, the waveform of the three-phase current at the high-voltage side of the transformer is a non-sinusoidal periodic function, and contains attenuated direct-current components and multiple harmonics, the period is 20ms, and the A, B, C three-phase current amplitudes are 12.2A, 7.8A and 14.9A, respectively. As shown in fig. 6-3, the instantaneous reactive power waveform at the high-voltage side of the transformer is a non-sinusoidal periodic function, and contains attenuated dc components and multiple harmonics, the period is 20ms, and the waveform is biased above the time axis. As shown in fig. 6-4, the transformer high side reactive power average waveform is biased above the time axis and decays with time. It can be seen that the three-phase excitation inrush current has different sizes and waveforms, the A, C-phase inrush current has obvious characteristics, and the main transformer reactive power Q is correct in CT wiring>0。
If the CT phase sequence of A, C two phases is reversed, as shown in fig. 7-1, the instantaneous reactive power waveform at the high-voltage side of the transformer is a non-sinusoidal periodic function, and contains attenuated dc component and multiple harmonics, the period is 20ms, and the waveform is located at both sides of the time axis. As shown in fig. 7-2, the simulation waveform of the reactive power average value on the high-voltage side of the transformer is deviated below the time axis and decays along with the time. At the moment, the main transformer reactive power Q < 0.
The simulation and field test results show that the method can verify the CT wiring of the high-voltage side of the transformer in the no-load closing stage of the transformer to obtain an ideal result, prevent the maloperation or the refusal operation of the protection equipment caused by the CT wiring error, and improve the operation reliability of the transformer substation.

Claims (10)

1. A method for verifying the polarity of a main transformer high-voltage side CT by using an excitation inrush current comprises the following steps:
the protection device collects three-phase secondary voltage u of a main transformer high-voltage side busa、ub、ucAnd three-phase secondary current ia、ib、icCalculating three-phase instantaneous reactive power q:
Figure FDA0002758309640000011
wherein u isaIs an instantaneous second-order value of A phase voltage, ubIs the instantaneous secondary value of the B-phase voltage ucIs an instantaneous secondary value of the C-phase voltage iaIs an instantaneous secondary value of the A-phase current, ibIs an instantaneous secondary value of the B-phase current, icThe instantaneous secondary value of the C-phase current;
secondly, calculating the reactive power average value of one period:
Figure FDA0002758309640000012
wherein T is a voltage period;
thirdly, the reactive power average value Q is larger than 0, and the protection device judges that the wiring of the Current Transformer (CT) is correct.
2. The method for verifying the CT polarity on the high-voltage side of the main transformer by using the magnetizing inrush current as claimed in claim 1, wherein the average value Q of the reactive power in the step three is less than 0, and the Current Transformer (CT) is considered to be in wrong wiring.
3. The method for verifying the polarity of the high-voltage side CT of the main transformer by using the magnetizing inrush current as claimed in claim 2, wherein the Current Transformer (CT) is in a wrong wiring, and the protection device acts on the high-voltage side circuit breaker of the main transformer to trip the circuit breaker.
4. The method for verifying the polarity of the CT on the high-voltage side of the main transformer by using the magnetizing inrush current as claimed in claim 1, wherein the protection device verifies the polarity of the Current Transformer (CT) on the high-voltage side of the main transformer by simultaneously satisfying the following three conditions:
the method comprises the following steps that firstly, a protection device collects position information of a circuit breaker on the high-voltage side of a main transformer and judges that the high-voltage side of the main transformer is in a charging state;
secondly, the protection device collects current information of the high-voltage side of the main transformer and judges that the main transformer has current according to the current amplitude;
and thirdly, the protection device acquires bus voltage information corresponding to the high-voltage side of the main transformer and judges whether the voltage of the high-voltage side is normal according to the voltage amplitude and the phase.
5. The method for verifying the CT polarity of the high-voltage side of the main transformer by using the magnetizing inrush current as claimed in claim 4, wherein the time period for judging that the high-voltage side of the main transformer is in the charging state under the condition I is as follows: from the jump moment from the reposition (TW) to the close (HW) of the main transformer high-voltage side circuit breaker, the time from the close (HW) of the main transformer high-voltage side circuit breaker to the moment t is within the t, and t is 200ms.
6. The method for verifying the CT polarity on the high-voltage side of the main transformer by using the magnetizing inrush current as claimed in claim 4, wherein the judgment basis for judging the current of the main transformer under the second condition is the logical OR of the following conditions:
Ia＞0.05In，Ib＞0.05In，Ic＞0.05In
wherein, IaIs two of effective value of A phase currentOrder value, IbA secondary value of the effective value of the phase B current, IcIs a secondary value of the effective value of the C-phase current, InThe secondary rating of a Current Transformer (CT) on the high-voltage side of the main transformer is obtained.
7. The method for verifying the CT polarity of the high-voltage side of the main transformer by using the magnetizing inrush current as claimed in claim 4, wherein the judgment basis for judging the high-voltage side voltage to be normal under the condition three is the logical AND of the following conditions:
Uab>70V，Ubc>70V，Uca>70V，
Ua-Ub<2V，Ub-Uc<2V，Uc-Ua<2V
118°<UaAng-UbAng<122°
118°<UbAng-UcAng<122°
118°<UcAng-UaAng<122°
wherein, UabIs A, B two-phase line voltage effective value secondary value, UbcIs B, C two-phase line voltage effective value secondary value, UcaIs C, A two-phase line voltage effective value secondary value, UaIs the second order value of A phase voltage, UbIs the second order value of the effective value of the B phase voltage, UcIs a secondary value of the effective value of the C phase voltage, UaAngIs the phase angle of A phase voltage, UbAngPhase angle of B phase voltage, UcAngIs the phase angle of the C-phase voltage.
8. The method for verifying the polarity of the main transformer high-voltage side CT through the magnetizing inrush current as claimed in claim 1, wherein a voltage transformer (PT) is installed on a bus connected to the main transformer high-voltage side, and a Current Transformer (CT) is installed on the main transformer high-voltage side.
9. The method for verifying the CT polarity on the high-voltage side of the main transformer by using the magnetizing inrush current as claimed in claim 1, wherein the protection device arranged on the high-voltage side of the main transformer acquires the corresponding bus on the high-voltage side of the main transformer through a voltage transformer (PT)Three-phase secondary voltage u ofa、ub、uc(ii) a The protection device collects three-phase secondary current i at the high-voltage side of the main transformer through a Current Transformer (CT)a、ib、ic。
10. The method for verifying the CT polarity on the high-voltage side of the main transformer by using the magnetizing inrush current as claimed in claim 1, wherein the protection device acquires the position of the switch through an auxiliary contact of a breaker on the high-voltage side of the main transformer.
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