CN114818567A - Modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 harmonic current - Google Patents
Modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 harmonic current Download PDFInfo
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Abstract
The invention discloses a modeling simulation method based on series-resistance arc turn-to-turn short circuit excitation 3, 5-order harmonic current, which is characterized by comprising the following steps of establishing a digital circuit simulation model according to a current arcing process and a circuit principle during series-resistance arc turn-to-turn short circuit; and outputting analog electrical quantity by using the digital circuit simulation model, and performing circuit equivalent simulation according to a proportional step unit or a non-equal proportional step unit combination in the digital circuit simulation model according to a fault development process to complete dynamic simulation of series arc resistance turn-to-turn short circuit and display and reduction of electrical characteristic change of the series arc resistance turn-to-turn short circuit. The monitoring principle and function of the related fault monitoring and protecting device are verified by utilizing the dynamic real-time waveform data of the computational simulation, the reliability and accuracy of the monitoring technology and the device thereof are tested and checked, and turn-to-turn short circuit fault monitoring or the principle and performance simulation test of the protecting device can be carried out in a laboratory environment.
Description
Technical Field
The invention relates to the technical field of power fault simulation, in particular to a modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3 and 5 harmonic currents.
Background
In a reactive compensation system of a power transmission and distribution network, a parallel compensation capacitor bank (hereinafter referred to as parallel capacitor) which can be switched in groups is adopted. A1000 kV ultrahigh voltage transformer substation is generally provided with a parallel capacitor of about 180Mvar to 240Mvar in a 110kV voltage class configuration grouping mode in a third winding of a transformer, a 500kV ultrahigh voltage transformer substation is generally provided with a parallel capacitor of about 45Mvar to 60Mvar in a 66kV or 35kV voltage class configuration grouping mode in a third winding of a transformer, and 220kV and 110kV transformer substations are also provided with a parallel capacitor of a proper capacity in a low-voltage winding of the transformer according to an in-situ compensation principle to compensate reactive power flow, improve power factor and control and stabilize voltage level. A series reactor with a series reactance rate of 12% is arranged in a part of groups of parallel capacitors, and a series current limiting reactor with a series reactance rate of 5-6% is arranged in the other part of the groups. The current limiting series reactance is used for limiting the parallel-capacitance inrush current of frequent switching, a parallel-capacitance group of a series reactor with the series reactance rate of 12% is configured, and meanwhile, the amplification effect of the parallel-capacitance group with the series reactance rate of 5-6% on 3-order harmonics of a power system is restrained, so that the parallel-capacitance group with the series reactance rate of 12% always is thrown first and quit finally in the switching sequence, and the amplification of the 3-order harmonics caused by the independent operation of the parallel-capacitance group with the series reactance rate of 5-6% is prevented. The series reactance of the parallel capacity of the outdoor transformer substation is generally a dry air core reactor. The main faults of the dry-type air-core reactor, whether parallel reactance or series reactance, are inter-strand short circuit, inter-turn short circuit, surface flashover discharge and the like.
In order to avoid the fault of the transformer or the reactor in the using process, the simulation is carried out on the fault generation reason and the fault generation process of the reactor and the transformer, so that the working personnel can be assisted to judge the fault generation reason in time, the fault source is cut off, the fault generation trend is known, and the larger loss is avoided.
Disclosure of Invention
Therefore, the invention aims to provide a modeling simulation method based on series arc interturn short circuit excitation 3, 5-order harmonic current, which simulates the arc combustion discharge characteristic at a wire turn short circuit position during interturn fault and has the repeated process characteristics of short circuit arc combustion, zero-cross cut-off, arc extinction, delayed opening and arc reignition along with a power frequency period. A computer digital analog circuit model is established, analog calculation is carried out by utilizing the model, dynamic characteristic reduction and reappearance of related fault processes are carried out, particularly, unique characteristics and mechanism of stable 3 and 5-order harmonic current after parallel-group serial resistance turn-to-turn short circuit are reduced and disclosed, monitoring principles and functions of related fault monitoring and protecting devices are verified by utilizing dynamic real-time waveform data of calculation simulation, reliability and accuracy of monitoring technology and devices are tested and checked, and turn-to-turn short circuit fault monitoring or principle and performance simulation test of the protecting devices can be carried out in a laboratory environment.
In order to achieve the purpose, the modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 times of harmonic current comprises the following steps:
s1, establishing a digital circuit simulation model according to the current arcing process and the circuit principle when series arc resistance turn-to-turn short circuit occurs;
and S2, simulating a fault development process by using the digital circuit simulation model, and performing circuit equivalent simulation according to the combination of proportional stepped units or non-proportional stepped units in the digital circuit simulation model according to the fault development process to complete the dynamic process of series arc resistance turn-to-turn short circuit, the display of electrical characteristic change and the reduction simulation of fault cases.
Preferably, the digital circuit simulation model comprises an equivalent simulation part of the power system, an equivalent simulation part of the transformer substation and the capacitor bank and an equivalent simulation part of a filter bank of an alternating current system of the direct current conversion station, wherein the equivalent simulation part of the filter bank influences the harmonic characteristics of the system; the equivalent simulation part of the power system comprises a generator and an ideal double-winding boosting transformer; the transformer substation equivalent simulation part comprises a step-down transformer and a switchable parallel capacitor bank; the generator is used for providing stable voltage, and the ideal double-winding boosting transformer is used for boosting the stable voltage to reach a power supply standard;
the step-down transformer is used for reducing the high voltage input by the step-up transformer in the power system, and the switchable parallel capacitor bank comprises a series reactor and a capacitor; and setting an interturn short-circuit fault simulation with an expanded number of turns of a developmental fault on a coil of the series reactor, and carrying out equivalence according to a proportional step unit or a non-equal proportional step unit combination equivalent value during short-circuit simulation to realize the simulation of the initial stage, the middle stage and the later stage of the development of the short-circuit fault.
Further, preferably, in the digital circuit simulation model, a real-time electromagnetic induction ampere-turn balance equation shown in the following is established according to a relationship between the number of short-circuit loop current ampere-turn balance magnetic fluxes caused by the number of short-circuit turns and the total ampere-turn number of the whole coil:
N12*I1(t)+N2*I2(t)＝0
wherein N12 is a normal turn with a certain number of turns, namely a primary turn, and I1(t) is a real-time current passed by a coil, namely a primary current; n2 is the number of short circuit turns, namely secondary turns, and I2(t) is the real-time current of the short circuit ring, namely the secondary current.
Preferably, in any one of the above embodiments, according to the fact that when the arc is burned, the local coil inductance disappears after the real-time ampere-turn balance, and when the arc is extinguished, the local coil inductance recovers in real time; and (3) equating the equivalent circuit parameters from the two ports on the primary side, wherein the equivalent resistance has the following expression formula:
wherein: rs is a single-turn resistor, R12 is a port primary side equivalent resistor, I1 is coil through current, I2 is short-circuit loop current, and N2 is the number of short-circuit turns.
Preferably, in any one of the above embodiments, the proportional stepped unit or the non-equal proportional stepped unit includes a plurality of sets of fault series reactance equivalent circuits connected in series, where the fault series reactance equivalent circuits include turn-to-turn short circuit loss series reactance inductance, adjustable turn-to-turn short circuit circulating current loss equivalent resistance, and a bidirectional short circuit arc control thyristor simulating an arc extinguishing reignition process; and the bidirectional short circuit arc control thyristor is connected in series with the turn-to-turn short circuit circulation loss equivalent resistor and then is connected in parallel at two ends of the turn-to-turn short circuit loss equivalent inductor as a whole.
In any of the above embodiments, preferably, the duration and duration of the respective on and off of the positive and negative half-waves are controlled by using different triggering angles of the bidirectional short-circuit arc control thyristor for simulating the arc extinguishing and reignition process, so as to simulate the reignition characteristic change after the arc extinguishing of the positive and negative half-wave arc short circuit; the adjustable turn-to-turn short circuit circulating current loss equivalent resistor is used for simulating the characteristic that the circulating current generates active loss equivalent resistor after turn-to-turn short circuit, and the turn-to-turn short circuit loss series reactance equivalent inductance simulates the characteristic that the inductance loss is increased after the turn-to-turn short circuit is continuously enlarged.
Preferably, in any one of the above embodiments, in S2, the combination of the proportional stepped units or the non-proportional stepped units with equal values completes a dynamic simulation test of series arc resistance inter-turn short circuit, including that the series reactor is simulated by using dry hollow series reactors, the triggering and conduction angles of the bidirectional thyristors are controlled by using stepped timing control, and the process of nonlinear expansion of the short circuit turns of the dry hollow series reactors after a fault is simulated; the method specifically comprises the following steps:
s201, according to data when short-circuit faults actually occur, when 100% of inductance loss occurs, the number of short-circuit turns is 40, and the turn-to-turn short-circuit loss series reactance equivalent inductance and the adjustable turn-to-turn short-circuit circulation loss equivalent resistance are subjected to equal proportion or non-equal proportion gradient reduction according to preset step times;
s202, when turn-to-turn short circuit loss series reactance equivalent inductance and adjustable turn-to-turn short circuit circulation loss equivalent resistance are reduced according to gradient, the current of each stage of series equivalent resistance is increased to about 15-30 times of rated current according to short circuit circulation.
Preferably, in any one of the above embodiments, in S201, when the turn-to-turn short circuit loss series reactance equivalent inductance and the adjustable turn-to-turn short circuit circulating current loss equivalent resistance are reduced proportionally or non-proportionally according to a preset step number; the method also comprises the steps that the preset step frequency is 5 times, the inductance loss gradient is an unequal proportion gradient, and the reignition time of the delayed short-circuit discharge arc after the voltage-resisting peak value is connected in a power frequency cycle is simulated according to different trigger angles.
In any of the above embodiments, preferably, the method further includes the content ratio of 3 rd order harmonic and 5 th order harmonic in the digital circuit simulation model under different inductance loss degrees; and the content of 3 rd order harmonics and 5 th order harmonics at different triggering angles.
In any of the above embodiments, preferably, the content of the 3 rd order harmonic and the 5 th order harmonic obtained in the digital circuit simulation model is compared with the actual parameters of the actual dry type air core reactance interturn fault case, and the parameters in the digital circuit simulation model are adjusted according to the comparison result.
The modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3 and 5 harmonic currents is characterized in that a digital circuit simulation model is built, simulation calculation is carried out by utilizing the model, dynamic characteristic reduction and reproduction of related fault processes are carried out, unique characteristics and mechanism of stable 3 and 5 harmonic currents are restored and disclosed after parallel-combined series arc resistance turn-to-turn short circuit occurs, monitoring principles and functions of related fault monitoring and protecting devices are verified by utilizing dynamic real-time waveform data of calculation simulation, reliability and accuracy of monitoring technologies and devices are tested and checked, and turn-to-turn short circuit fault monitoring or protecting device principle and performance simulation tests can be carried out in a laboratory environment; the fault model and the simulation method are used for calculation and simulation, a power system digital simulation platform such as an RTDS real-time digital simulation system is used for generating fault characteristics and characteristics, and the fault electrical characteristic output of converting output digital quantity into physical analog quantity is used for conveniently verifying the technical principle and the functional correctness of the fault monitoring or protection technology.
Drawings
FIG. 1 is a flow chart of a modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 harmonic currents.
FIG. 2 is a diagram of a short-circuit circulating current waveform for computer simulation according to the principles of actual short-circuit failure in accordance with the present invention;
FIG. 3 is a typical current waveform of a fault phase in an lc loop of a parallel capacitor bank after turn-to-turn short circuit according to the present invention;
FIG. 4 is a schematic view of a turn-to-turn short circuit in a branch of a layer of the coil of the present invention;
FIG. 5 is a schematic diagram of the electromagnetic induction principle of turn-to-turn short circuit of the air-core coil;
FIG. 6 is a schematic diagram of a circuit model of the bidirectional thyristor valve series equivalent resistor and inductor parallel connection for fault turn fault characteristics of the present invention;
FIG. 7 is a diagram of an arc current waveform at the middle stage of development of an air core coil turn-to-turn short circuit fault (about 50% of inductance loss) according to the present invention;
FIG. 8 is a diagram of the current waveform of the coil at the later stage of the turn-to-turn short circuit fault development (about 90% of the inductance loss) of the air-core coil of the present invention;
FIG. 9 is a case wave recording diagram of a 35kV3X20Mvar group 12% series reactance turn-to-turn short circuit fault;
FIG. 10 is a diagram of the electrical wiring of the power system of the digital circuit simulation model of the present invention;
FIG. 11 is a diagram of a fixed-scale unit steady-state model fault phase series reactance equivalent circuit model of the present invention;
FIG. 12 is a case computer simulation model of a 35kV3 × 20Mvar set 12% series reactance turn-to-turn short circuit fault of the present invention;
FIG. 13(a) is a fault phase waveform of inter-turn short circuit fault simulation in a simulation experiment of the present invention;
FIG. 13(b) is a schematic diagram of the 3, 5 harmonic current content values of the fault simulation shown in FIG. 13 (a);
FIG. 14 is a waveform diagram of the wave-recording fault phase current of the case of the 35kV3X20Mvar set 12% series reactance turn-to-turn short circuit fault of the present invention;
FIG. 15 is a voltage waveform of a neutral point of a computer simulation result of the turn-to-turn short circuit fault case of the present invention;
FIG. 16 is the three-phase current waveform and its harmonic content in the corner of the transformer for the turn-to-turn short circuit fault case of the present invention;
FIG. 17 shows the 3 rd/5 th harmonic content at 90% inductance loss in the simulation test of the present invention;
FIG. 18 shows the 3 rd/5 th harmonic content at 80% inductance loss in the simulation test of the present invention;
FIG. 19 shows the 3 rd/5 th harmonic content at 50% inductance loss in the simulation test of the present invention;
FIG. 20 shows the 3 rd order/5 th order harmonic content at 20% inductance loss in the simulation test of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the detailed description.
As shown in fig. 1, an embodiment of the invention provides a modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 th harmonic current, which includes the following steps:
s1, establishing a digital circuit simulation model according to the current arcing process and the circuit principle when series arc resistance turn-to-turn short circuit occurs;
and S2, simulating a fault development process by using the digital circuit simulation model, and performing circuit equivalent simulation in the digital circuit simulation model according to the combination of proportional stepped units or non-proportional stepped units to complete the dynamic process of series arc resistance turn-to-turn short circuit, the display of electrical characteristic change and the reduction simulation of a fault case.
It should be noted that, when a digital circuit simulation model is established, firstly, statistical analysis shows that, according to actual fault cases, because turn-to-turn short-circuit loop current is relatively small (large and short-circuit loop current resistance is about 150-300 times of normal turn current), the speed of expansion of the number of fault turns caused by short-circuit turn high temperature and arc combustion in series-to-turn short-circuit is relatively slow, and after development and expansion for several minutes, the number of short-circuit turns of turn-to-turn short-circuit fault is continuously developed and expanded by about 30-40 turns (inductance loss caused by 1 turn is about 3%), equivalent inductance of series-to-turn short-circuit is reduced to completely disappear. Since the series reactance equivalent inductance and reactance are reduced, the impedance of the whole loop is increased on the contrary, and therefore the current of the loop cannot be increased but is reduced on the contrary.
In an actual fault case, the fault tolerant series reactance is a 500kV ultrahigh voltage transformer substation, the fault rate of a dry type hollow series reactance with 12% series reactance rate is high, and the following fault rule is found according to the analysis and statistical research results of all cases which are close to 10 cases and can start wave recording to record fault waveforms after the fault:
(1) the turn-to-turn short circuit of the series reactance is slow in development and can last for a period from several minutes (1-5 minutes) to dozens of minutes (1-5 minutes or 30 minutes).
(2) The continuous development of turn-to-turn short circuits causes the continuous nonlinear reduction of equivalent reactance.
(3) And stable 3 and 5 harmonics can be excited and generated in the turn-to-turn fault process.
(4) And finally, the dry-type air-core reactor is ignited and spontaneously combusted due to the fault.
Research shows that in the case of turn-to-turn short circuit, on one hand, the equivalent reactance is reduced and the equivalent resistance is increased along with the continuous expansion of the number of turns. On the other hand, because turn-to-turn short circuit exists in the form of arc arcing in each power frequency cycle, an insulating film residue still exists at a high-temperature damage or damage part generated by short-circuit circular arc at the short circuit part of a lead at the early stage of a fault, more importantly, the short circuit part is subjected to continuous arc burning ablation and electric power breaking and the like along with the heating and melting of a short-circuit turn aluminum lead under the short-circuit circular current of 15-30 times, a developmental arc ablation gap and a groove can be formed, meanwhile, because the turn-to-turn potential is in the level of tens of volts to tens of volts, when the electric arc burns in the gap, because the maintaining voltage (recovery voltage) is low, after the short-circuit current crosses zero, the air insulation in the gap with the width of several millimeters to tens of millimeters can be recovered for a short time, the electric arc cannot reignite immediately, and the electric arc is reignited after being extinguished for about 2-6 mS. Therefore, the short-circuit circulating current waveform is shown in fig. 2 below, the short-circuit circulating current is not a continuous sine wave but an intermittent wave, the continuous sine wave with high amplitude in fig. 2 is a normal series resistance terminal voltage waveform, and the intermittent waveform with low amplitude is an analog simulation turn-to-turn short-circuit ring and arc current waveform (the current in the short-circuit ring cannot be directly recorded in the actual fault process); fig. 3 is a waveform diagram of an lc loop with significant 3, 5 harmonic currents excited by an arcing turn-to-turn short circuit fault.
Therefore, based on the short-circuit current arcing process of the arc short circuit in the ablation slit and the groove and the circuit principle thereof, the repeated processes of turn-on short circuit, arc burning, zero-crossing turn-off, arc extinguishing, delayed turn-on and arc reignition of turn-to-turn short circuit are synchronously controlled by an ideal switch or a thyristor, so that the characteristics and the fault development change process of continuous, stable and obvious quantity and 3, 5 and 7 times of main harmonic current in the parallel LC loop current can be simulated in the series-reactance turn-to-turn short circuit process generated or caused by the excitation of the arc short circuit, a digital circuit model with consistent principle and same mechanism is established by using a digital circuit simulation technology, a reasonable simulation method is set, the fault mechanism and the characteristics are revealed, a specific fault case is reduced, the special electrical characteristics and the characteristics appearing in the fault are explained, and the fault monitoring, the inspection and the arc reignition are carried out to monitor the fault and inspect, The method comprises the steps of checking the fault characteristics of a monitoring technology and a device consistent with real faults, for example, establishing a modeling simulation method based on 12% and 5-6% common series reactance rate current-limiting series arc-resistance turn-to-turn short circuit excitation 3 and 5 harmonic currents of a parallel capacitor bank by using an RTDS real-time digital simulation system, establishing a digital circuit model, outputting analog electric quantity by using the digital analog physical conversion capacity of the RTDS real-time digital simulation system, carrying out a dynamic analog test of series arc-resistance turn-to-turn short circuit, and checking the monitoring technology related to monitoring the series arc-resistance turn-to-turn short circuit faults and the monitoring correctness and the functionality of a monitoring device thereof.
In another embodiment of the present invention, as shown in fig. 4-6, when calculating the parameters of the digital circuit simulation model, the turn-to-turn short circuit fault of the inductance coil is a breakdown discharge in which the insulation of some adjacent turn is reduced or damaged and a non-metallic direct short circuit (discharge is through damaged or failed polyester film) occurs, when an arc burns at the short circuit, the arc circulating current Ic1 is Ic2+ Ic, and the short-circuit circulating current Ic2 exists between the turns of the short circuit. The current in the short-circuit ring is dozens of times to dozens of times of the coil current Ic, and the current direction is opposite to the coil current.
When a part of turns in the hollow coil are in short circuit between adjacent turns, the short circuit turns and the normal turns are hinged through an alternating current magnetic field, and the electromagnetic induction principle of the short circuit turns and the normal turns on a certain small scale close to the space is in the induction relationship between the two primary and secondary independent coils with good magnetic field coupling. As shown in fig. 6, the whole coil is divided into 3 serial parts, i.e., L11, L12 and L13 parts, corresponding to inductances k11 × L, k12 × L and k13 × L, corresponding to turns N11, N12 and N13, wherein turns of the coil L12 are inter-turn short-circuited, the number of short-circuited turns is N2, corresponding to a secondary coil L2 of the coil L12, and the coils L2 and L12 have a complete flux coupling relationship as in an ideal transformer. A magnetic flux ampere-turn balance relation based on an electromagnetic induction principle is formed between the short-circuit turn and a normal turn of the magnetic flux tight hinge in a certain surrounding space size range.
In the digital circuit simulation model, according to the relationship between the number of short-circuit loop current ampere-turn balance magnetic flux caused by the number of short-circuit turns and the total ampere-turn number of the whole coil, a real-time electromagnetic induction ampere-turn balance equation is established as follows:
n12 × I1(t) + N2 × I2(t) ═ 0 formula 1
Wherein, N12 is a normal turn with a certain number of turns, namely a primary turn, and I1(t) is a real-time current passed by a coil, namely a primary current; n2 is the number of short circuit turns, i.e. secondary side turns, and I2(t) is the real-time current of the short circuit loop, i.e. secondary side current.
According to the fact that when the arc burns, the local coil inductance disappears after the ampere turns are balanced in real time, and L12 is equal to 0; when the arc is extinguished, the real-time local coil inductance recovers, and L12 is k 12L; and (3) equating the equivalent circuit parameters from the two ports on the primary side, wherein the equivalent resistance has the following expression formula:
wherein: rs is a single-turn resistor, R12 is a port primary side equivalent resistor, I1 is coil through current, I2 is short-circuit loop current, and N2 is the number of short-circuit turns.
According to actual measurement and theoretical calculation, 12% series resistance short circuit is commonly used, and when the short circuit turns are in the scale of 1-10 turns, the short circuit loop current is about 30-40 times of the coil current, namely I 2 /I 1 The ratio is (30-40) times. 5-6% of the series short-circuit ring current is about 15-30 times of the coil current.
Because the ampere-turns of the 6% and 12% common series reactance are far less than the parallel reactance, the short-circuit loop current of the short-circuit turn is about 15-40 times of the normal current (the large parallel short-circuit loop current is 150-300 times), the fault at the short-circuit position of the practical lead wire turn still has insulation film residue at the high-temperature damage or damage position generated by the short-circuit loop current at the short-circuit position of the initial lead wire, the short-circuit position can form a developmental arc ablation gap and a groove under the actions of continuous arc burning ablation, electric power snapping and the like along with the temperature rise and melting of the short-circuit turn aluminum lead wire under the short-circuit loop current of 15-30 times, the short-circuit position can be extinguished due to the transient recovery of air insulation at a distance of several millimeters to approximately 10 millimeters after the zero crossing of the arc current, the short-circuit loop current can be extinguished due to the delay of 1-3 mS after the turn potential is reapplied in the next half-frequency period after the open circuit is extinguished, the process is equivalent to the restrike/turn-on and turn-off/turn-off process of turn-to-turn short circuit electric arc after the inductor of the bypass part is short-circuited under the synchronous control of an ideal switch or a thyristor.
On the other hand, in order to verify the rationality of the circuit control simulation using the thyristor, it is necessary to further study the relationship between the thyristor trigger angle and the discontinuous waveform of the short-circuit loop current, and 3 rd harmonic and 5 th harmonic, as shown in fig. 7, the relationship between the c-phase series reactance fault in the three-phase parallel capacitor bank and the short-circuit loop current and the coil current (inductance loss 50%, arc restrike 2 milliseconds after the peak value of the analog voltage, short-circuit loop current discontinuous waveform diagram with the thyristor trigger angle of 36 degrees) when the c-phase series reactance fault develops into the middle-phase turn-to-turn short-circuit current arc burning and goes through the zero-crossing extinction-restrike cycle, the curve with the peak value high in the diagram is the reference Uc voltage (kv), and the curve with the peak value low in the diagram is the amplified ten-time current Ic1 (ka) 10 (ka), as shown in fig. 8, the simulated c-phase series reactance fault development later stage has a large inductance loss (90%), and the arc extinction time is long, that the thyristor is controlled after being triggered under the condition of a large corresponding trigger angle (65 degrees) The current (Ic) oscillogram of the coil and the LC loop, wherein the 3 rd harmonic current content at the cursor time exceeds 22 percent, and the 5 th harmonic current content reaches about 13 percent; fig. 9 shows the waveform of the recording current of the fault reactor after about 5 minutes of actual occurrence of the 35kv parallel series-reactance fault case of the 500kv substation, in which the 3 rd harmonic current content exceeds 20% and the 5 th harmonic current content reaches above about 10%, and it can be seen that the waveforms and the harmonic current characteristics of the two have high similarity. The actual recording diagram of the fault case (the inductance loss reaches 80-90% after the fault is developed for about 5 minutes) is consistent with the simulation result. Therefore, the digital circuit simulation model can be constructed by adopting the following structure.
As shown in fig. 10, in an embodiment of the present invention, the digital circuit simulation model includes an equivalent simulation part of the power system, an equivalent simulation part of the transformer substation and the capacitor bank, and an equivalent simulation part of the filter bank of the ac system of the dc converting station that affects the harmonic characteristics of the system; the equivalent simulation part of the power system comprises a generator and an ideal double-winding boosting transformer; wherein G is a constant voltage source of an infinite generator, T is an ideal non-short-circuit impedance and lossless double-winding step-up transformer, and X is S Is an equivalent system inductive reactance, R S Is an equivalent system resistance. The transformer substation equivalent simulation part comprises a step-down transformer and a switchable parallel capacitor bank; the generator is used for providing stable voltage, and the ideal double-winding boosting transformer is used for boosting the stable voltage to reach a power supply standard;
the step-down transformer is used for reducing the high voltage input by the step-up transformer in the power system, and the switchable parallel capacitor bank comprises a series reactor and a capacitor; in which STB is step-down transformer, SC is switchable parallel capacitor bank (composed of series reactance X) L And a capacitor X C Composition (c); and setting turn-to-turn short circuit fault simulation with expanded turn number of developmental fault on a coil of the series reactor, and carrying out equivalence according to the equivalent of a proportional step unit or a non-equal proportional step unit combination during short circuit simulation so as to realize the simulation of the initial stage, the middle stage and the later stage of the development of the short circuit fault. Other power systems may affect parts of the 3, 5 and 7 th harmonic absorption amplification characteristics such as the dc converter station lines and their filter banks: including line equivalent reactance X L AC field filter and compensation capacitor bank (including switched capacitor SC, 3-time and 12/24-time filter bank) and shunt reactor X for balancing industrial frequency capacitive compensation capacity g (calculation simulation requirement, actual AC field without shunt reactor)
The electrical wiring of the parallel capacitor bank unit in the figure is connected in a star connection mode according to a three-phase group, and is formed by 12% (or 5-6%) of current limiting series reactance and parallel capacitors.
As shown in fig. 11, therefore, in an embodiment of the present application, a thyristor is used to implement series-reactance short-circuit fault simulation by arranging a proportional stepped unit or a non-equal-proportion stepped unit as a fault series-reactance equivalent circuit, where the proportional stepped unit or the non-equal-proportion stepped unit includes a plurality of sets of fault series-reactance equivalent circuits connected in series together, where the fault series-reactance equivalent circuit includes an inter-turn short-circuit loss series-equivalent inductor, an adjustable inter-turn short-circuit circulating current loss equivalent resistor, and a bidirectional short-circuit arc control thyristor that simulates arc arcing and extinguishes a reignition process; and the bidirectional short circuit arc control thyristor is connected in series with the turn-to-turn short circuit circulation loss equivalent resistor and then is connected in parallel at two ends of the turn-to-turn short circuit loss equivalent inductor as a whole. In the figure, C is a parallel capacitor, R is series reactance equivalent normal loss resistance, L1-L5 are series reactance inductance with equal proportion or non-equal proportion turn-to-turn short circuit loss, Delta R is turn-to-turn short circuit circulation loss equivalent resistance, and V1-V5 are bidirectional thyristor valves simulating short circuit arc extinction-restrike characteristics.
Further, the difference of the trigger angle of the bidirectional short circuit electric arc control thyristor is adopted to control the on and off duration and duration of the positive and negative half-waves respectively, and the change of the reignition characteristic after the electric arc of the positive and negative half-wave electric arc short circuit is extinguished is simulated; the adjustable turn-to-turn short circuit circulating current loss equivalent resistor is used for simulating the characteristic that the circulating current generates active loss equivalent resistor after turn-to-turn short circuit, and the turn-to-turn short circuit loss series reactance equivalent inductance simulates the characteristic that the inductance loss is increased after the turn-to-turn short circuit is continuously enlarged.
Further, in S2, the step units or the step units with unequal proportions are combined to be equivalent to complete a dynamic simulation test of series arc resistance turn-to-turn short circuit, including that the series reactor adopts dry hollow series reactor to simulate, adopts step time sequence control to control the trigger and conduction angle of the bidirectional thyristor, and simulates the process of nonlinear expansion of the short circuit turn of the dry hollow series reactor after a fault; the method specifically comprises the following steps:
s201, according to data when short-circuit faults actually occur, when 100% of inductance loss occurs, the number of short-circuit turns is 40, and the turn-to-turn short-circuit loss series reactance equivalent inductance and the adjustable turn-to-turn short-circuit circulation loss equivalent resistance are subjected to equal proportion or non-equal proportion gradient reduction according to preset step times;
s202, when turn-to-turn short circuit loss series reactance equivalent inductance and adjustable turn-to-turn short circuit circulation loss equivalent resistance are reduced according to gradient, the current of each stage of series equivalent resistance is increased to about 15-30 times of rated current according to short circuit circulation.
Preferably, in any one of the above embodiments, in S201, when the turn-to-turn short circuit loss series reactance equivalent inductance and the adjustable turn-to-turn short circuit circulating current loss equivalent resistance are reduced proportionally or non-proportionally according to a preset step number; the method also comprises the steps that the preset step frequency is 5 times, the inductance loss gradient is an unequal proportion gradient, and the reignition time of the delayed short-circuit discharge arc after the voltage-resisting peak value is connected in a power frequency cycle is simulated according to different trigger angles.
For simple simulation, equivalent inductance and equivalent resistance can be reduced by 20% in an equal proportion by adopting turn-to-turn short circuit development scale steps, and progressive equivalent inductance reduction is accumulated. The control sequence is set according to 5-level steps of 20%, 40%, 60%, 80% and 100%, the corresponding series equivalent resistance of each level is calculated according to rated current of which the short-circuit loop current is increased to about 15-30 times (the average value can be set to be 25 times), the number of short-circuit turns is about 40 turns when 100% inductance loss occurs, and the total equivalent short-circuit loop current thermal effect resistance is 40 turns x25 times x25 times/1000 turns 25 times.
The equivalent resistance is connected in series after each 20% inductance loss proportional unit thyristor valve block according to the relation that 25/5 is equal to 5 times, the equivalent resistance is assigned according to 4-6 times of series resistance normal total loss, when the inductance loss is less than 50% of faults, the equivalent resistance can be assigned with 6 times of value, and when the inductance loss is more than 80% of faults, the equivalent resistance can be assigned with 4 times of value.
According to the research analysis and fitting of a plurality of fault cases, the fault series reactance is found to be mostly cut under the actions of arc high-temperature ablation, aluminum wire melting and electric power snapping from the initial fault point, and an air gap and a groove which are continuously developed along with turn-to-turn short circuit fault and continuously developed and lengthened along with the increase of the number of fault turns are formed, as shown in a real post-fault anatomical photograph of FIG. 11, thereby causing the short-circuit arc burning discharge to be temporarily extinguished after the zero crossing of the arc current, and then the short-circuit wire turns induce the inter-turn potential, under the action of power frequency voltage of tens of volts to tens of volts, the arc discharge between the short circuit wire turns and between the burnt wire turns is recovered again, the arc is reignited, therefore, the short-circuit arc has the characteristics of discharge arc burning, arc current zero-crossing extinguishing and delayed reignition (which are equivalent to the controlled triggering and current zero-crossing natural turn-off characteristics of the bidirectional thyristor valve in fig. 6 and 10) which are periodic along with the power frequency voltage.
In any of the above embodiments, preferably, the method further includes the content ratio of 3 rd order harmonic and 5 th order harmonic in the digital circuit simulation model under different inductance loss degrees; and the content of 3 rd order harmonics and 5 th order harmonics at different triggering angles.
In any of the above embodiments, preferably, the content of the 3 rd order harmonic and the 5 th order harmonic obtained in the digital circuit simulation model is compared with the actual parameters of the actual dry type air core reactance interturn fault case, and the parameters in the digital circuit simulation model are adjusted according to the comparison result.
The application is described below by taking a three-phase group of 35kV3X20Mvar and 12% of series reactance rate as an example, wherein the three-phase group is commonly used and common faults are:
(1) transformer substation and power system operation condition collection parameters thereof
I, collecting the type, the wiring group, the transformation ratio, the capacity and the short-circuit impedance percentage value of the step-down transformer.
And II, collecting equivalent short-circuit impedance in a large mode and a small mode according to the high-voltage side and medium-voltage side equivalent power supply systems of the step-down transformer, wherein the equivalent short-circuit impedance comprises impedance characteristics (namely reactance and resistance proportion), and modeling a power supply system generator according to an infinite system.
And III, collecting filter parameters of an alternating current system with a direct current change station and impedance parameters of a connecting circuit of the alternating current system within a 50km distance range of the fault station. (harmonic impedance characteristics of ac filter banks (typically configured with 3 rd order, 11/13 th order, etc. filter banks) of a dc converter station will have an effect on inter-turn short faults and the resulting 3 rd, 5 th, 7 th, and 11 th harmonics).
(2) Calculating the value of the equivalent inductance and the equivalent resistance of the step with equal proportion (20 percent, 5 percent and equal proportion)
As shown in tables 1 and 2.
TABLE 1-35kV3 × 20Mvar, three-phase group parameter table of 12% string resistance
| Parallel capacitance parameter | 3X20Mvar, 12% group | Parameter of series inductance | Series reactance with 12% series reactance rate |
| Capacitive reactance (omega) | 28.801 | Inductive reactance (omega) | 3.46 |
| Capacitor (mu F) | 110.52 | Inductor (H) | 0.011 |
| Equivalent resistance (omega) | 0.035 (approximately 1% Ganzhi value) | / | / |
TABLE 2-35kV3 × 20Mvar, 12% series rate turn-to-turn fault 5 series stage equal proportion inductance and equivalent resistance table
Note: all the above calculations are based on a power frequency 50Hz power system.
Selecting system parameters, and establishing a simulation model by using PSCAD (power system computer aided design) to form a 12% series reactance turn-to-turn short circuit fault case computer simulation model shown in figure 12; the method comprises the steps of utilizing real fault case parameters to carry out nonlinear expansion based on short circuit turns, leading to nonlinear equivalent inductance and equivalent resistance change, simulating simulation of extinguishing and reigniting characteristics based on arc combustion discharge characteristics at turn short circuit positions during turn-to-turn fault of a series reactor, simulating arc extinguishing interruption, and then delaying the reigniting arc short circuit process after a certain time (angle). The simulation can reproduce the stable 3 and 5 harmonic currents after parallel-capacitor series anti-turn-to-turn short circuit in the fault case, the inductance loss after the turn-to-turn short circuit and the special characteristics and characteristics of the neutral point voltage under the condition that the 3, 5 and 7 harmonic currents are obvious.
FIG. 13(a) is a computer simulation result-fault phase current waveform, and FIG. 13(b) is a schematic diagram showing the values of 3, 5 harmonic current contents; (current unit kA in the figure), table 3 shows data of current statistics and neutral offset voltage of each frequency of the thyristor valve group at different trigger angles (simulating c-phase fault, and scanning possible thyristor trigger angles by using a-phase voltage as a reference angle of 0 degree).
Table 3-90% inductance loss coil current and neutral voltage excursion data after arc reignition at different arc-quenching times/trigger angles.
The 3-order harmonic current content is 215 degrees at a trigger angle (equivalent to delaying for 65 degrees after the voltage peak value of a C-phase inductance coil for triggering, and exceeding 22 percent), and the 5-order harmonic current content reaches about 10-13 percent, 150 degrees are equivalent to delaying for 0 degrees (corresponding to the highest peak value point of a C-phase series impedance voltage waveform), the reference voltage waveform moment of the trigger angle is the sine wave 0 degree point of a bus voltage A phase, the actual series impedance voltage is in a phase opposite to the bus voltage due to the relation that capacitive current is applied to reactance, and therefore when simulating the series impedance fault of a B phase, 30 degrees are equivalent to delaying for 0 degree after the voltage peak value of a phase, and when simulating the series impedance fault of the A phase, 270 degrees are equivalent to delaying for 0 degree after the voltage peak value.
Table 4-35kV3 × 20Mvar 12% series reactance turn-to-turn short circuit fault case recording harmonic current change table.
The actual fault case recording data (the inductance loss reaches 80-90% after the fault is developed for about 5 minutes) is very consistent with the simulation result table. Fig. 14 is an analysis of current waveform and harmonic content of an actual fault case, wherein the 3 rd harmonic current content is 11.3-33%, and the 5 th harmonic current content is 4.4-14%, after the fault develops for about 5 minutes, due to the expansion of short circuit turns and the formation of arc ablation cutting gaps and grooves, arc combustion is more unstable, reignition time after arc extinguishment is increased (the trigger angle is increased), so that the 3 rd harmonic and the 5 th harmonic are increased violently, and the characteristics of the 3 th harmonic and the 5 th harmonic accord with the simulation characteristic rule.
Fig. 15 shows the voltage waveform (voltage unit kV in the figure) of the neutral point of the case computer simulation result of the 35kV3 × 20Mvar group reactance turn-to-turn short circuit fault with 12% series reactance. Wherein the harmonics are mainly given in 5, 11, 13, and 3 orders.
Fig. 16 is a graph of the waveform of three-phase current in a transformer corner and the harmonic content thereof in another 35kV3x20Mvar set 12% series reactance turn-to-turn short circuit case (in the graph, the waveform of current in the middle column is a fault phase waveform, wherein the harmonic content at the time of cursor is converted to 8.2% for 3 times and 13% for 5 times of a capacitor bank branch out of the corner), and the harmonic current appears in the case that the harmonic current is greater than 3 times for 5 times.
From the harmonic contents calculated in table 3, it can be seen that, as the short-circuit circular arc combustion is unstable and the circular arc interruption time and angle are increased due to the occurrence of arc harmonics, the 3 rd harmonic content is increased non-linearly, while the 5 th harmonic current is increased non-linearly and then gradually decreased after a certain angle (205 degrees in table 1), and the current content of the previous 5 th harmonic is greater than that of the 3 rd harmonic.
The condition that the 5 th harmonic current exceeds 3 rd harmonic is also found in the actual fault case oscillogram (figure 16), and the correctness of the simulation characteristic is proved.
According to the principle that short circuit loop current based on the electromagnetic induction ampere-turn balance principle is inevitably and gradually reduced after the short circuit turns are enlarged, the turn-to-turn short circuit develops later, the larger the short circuit turns and the smaller the short circuit loop current, the larger the loss inductance at the moment, the whole series reactance characteristic tends to be noninductive resistance, the coil magnetic flux also tends to zero, and the coil turn induction potential becomes very small accordingly. Therefore, the time for extinguishing and reigniting the arc current after the zero crossing is prolonged, and thus, the content of the 3 rd harmonic current in the harmonic current reaches a level of 20-30% and the content of the 5 th harmonic current reaches a level of about 6-10% as the trend shown by the simulation results of fig. 13 and table 3 in the simulation case.
Fig. 17 to 20 are graphs showing harmonic content at different firing angles under different inductance losses. The horizontal axis of the coordinate is a trigger delay angle, and the vertical axis of the coordinate is the content rate of 3 and 5-order harmonic current in coil current (branch current). Table 5 shows the actual parameters of the case of 12% serial reactance rate dry-type air-core reactance interturn fault of C phase in accordance with the 35kV3 × 20Mvar set of fig. 13 and the simulation results based on the computer simulation model, and table 5 below simulates the reignition time of the delayed short-circuit discharge arc after the voltage peak of serial reactance in one power frequency cycle at different triggering angles in accordance with five cases of 90%, 80%, 50%, 40% and 20% of the inductive losses and the reignition characteristics of the delayed discharge arc after the discharge arc is extinguished, wherein 150 degrees is 0 delay time for C phase, 270 degrees is 0 delay time for a phase, and 30 degrees is 0 delay time for B phase.
Table 5 shows the actual parameters of the case of the C-phase 12% series reactance interturn fault of the 35kV3X20Mvar group according to FIG. 13 and the simulation results based on the computer simulation model
As can be seen from the comparison of the simulation test and the actual fault case, the simulation model realizes the characteristics of arc burning, arc extinguishing and delayed reignition along with the characteristics of arc short circuit and the change rule thereof; the method realizes the fault process of restoring the specific case, the fault characteristic analysis of the specific case, and the fault electrical characteristic and characteristic restoration demonstration.
Calculating and simulating by using fault model and simulation method, generating fault characteristics and characteristics by using power system digital simulation platform such as RTDS real-time digital simulation system, and outputting fault electrical characteristics output by converting output digital quantity into physical analog quantity for verifying technical principle and functional correctness of fault monitoring or protection technology
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (10)
1. A modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 times harmonic current is characterized by comprising the following steps:
s1, establishing a digital circuit simulation model according to the current arcing process and the circuit principle when series arc resistance turn-to-turn short circuit occurs;
and S2, simulating a fault development process by using the digital circuit simulation model, and performing circuit equivalent simulation in the digital circuit simulation model according to the combination of proportional stepped units or non-proportional stepped units to complete the dynamic process of series arc resistance turn-to-turn short circuit, the display of electrical characteristic change and the reduction simulation of a fault case.
2. The modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 harmonic currents according to claim 1, wherein the digital circuit simulation model comprises an electric power system equivalent simulation part, a transformer substation and capacitor bank equivalent simulation part and a filter bank equivalent simulation part of a direct current conversion station alternating current system influencing harmonic characteristics of the system;
wherein, the equivalent analog part of the power system comprises a generator, an ideal double-winding step-up transformer,
The transformer substation equivalent simulation part comprises a step-down transformer and a switchable parallel capacitor bank; the generator is used for providing stable voltage, and the ideal double-winding boosting transformer is used for boosting the stable voltage to reach a power supply standard;
the step-down transformer is used for reducing the high voltage input by the step-up transformer in the power system, and the switchable parallel capacitor bank comprises a series reactor and a capacitor; and setting turn-to-turn short circuit fault simulation with expanded turn number of developmental fault on a coil of the series reactor, and carrying out equivalence according to the equivalent of a proportional step unit or a non-equal proportional step unit combination during short circuit simulation so as to realize the simulation of the initial stage, the middle stage and the later stage of the development of the short circuit fault.
3. The modeling and simulation method based on series-connected arc resistance turn-to-turn short circuit excitation 3, 5 harmonic currents is characterized in that in the digital circuit simulation model, according to the relation between the number of short circuit loop current ampere-turn balance magnetic flux caused by the number of short circuit turns and the total ampere-turn number of the whole coil, a real-time electromagnetic induction ampere-turn balance equation shown as follows is established:
N12*I1(t)+N2*I2(t)＝0
wherein N12 is a normal turn with a certain number of turns, namely a primary turn, and I1(t) is a real-time current passed by a coil, namely a primary current; n2 is the number of short circuit turns, i.e. secondary side turns, and I2(t) is the real-time current of the short circuit loop, i.e. secondary side current.
4. The modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 times harmonic current according to claim 3, characterized in that according to the fact that when an arc burns, local coil inductance disappears after real-time ampere-turn balance, and when the arc extinguishes, local coil inductance recovers in real time; and (3) equating the equivalent circuit parameters from the two ports on the primary side, wherein the equivalent resistance has the following expression formula:
wherein: rs is a single-turn resistor, R12 is a port primary side equivalent resistor, I1 is coil through current, I2 is short-circuit loop current, and N2 is the number of short-circuit turns.
5. The modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 harmonic currents according to claim 2, characterized in that the proportional step unit or the non-equal proportional step unit comprises a plurality of groups of fault series reactance equivalent circuits connected in series, wherein the fault series reactance equivalent circuits comprise turn-to-turn short circuit loss series equivalent inductors, adjustable turn-to-turn short circuit circulation loss equivalent resistors and bidirectional short circuit arc control thyristors simulating arc extinguishing reignition process; and after the bidirectional short circuit arc control thyristor for simulating the arc burning, extinguishing and reigniting process is connected in series with the turn-to-turn short circuit circulating current loss equivalent resistor, the bidirectional short circuit arc control thyristor is connected in parallel with two ends of the turn-to-turn short circuit loss equivalent inductor as a whole.
6. The modeling simulation method based on series arc interturn short circuit excitation 3, 5 harmonic current according to claim 5, characterized in that the difference of the trigger angle of the bidirectional short circuit arc control thyristor is adopted to control the on and off duration and duration of the positive and negative half-waves respectively, so as to simulate the re-ignition characteristic change after the arc of the positive and negative half-wave arc short circuit is extinguished; the adjustable turn-to-turn short circuit circulating current loss equivalent resistor is used for simulating the characteristic that the circulating current generates active loss equivalent resistor after turn-to-turn short circuit, and the turn-to-turn short circuit loss series reactance equivalent inductance simulates the characteristic that the inductance loss is increased after the turn-to-turn short circuit is continuously enlarged.
7. The modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 th harmonic current according to claim 5, characterized in that in S2, the combination of the equivalent values according to the proportional step unit or the non-equal proportional step unit completes the dynamic simulation test of the series arc resistance turn-to-turn short circuit, which comprises that the series reactor adopts a dry type hollow series reactor for simulation, adopts step type time sequence control to control the trigger and the conduction angle of the bidirectional thyristor, and simulates the process of nonlinear expansion of the short circuit turn of the dry type hollow series reactor after the fault; the method specifically comprises the following steps:
s201, according to data when short-circuit faults actually occur, when 100% of inductance loss occurs, the number of short-circuit turns is 40, and the turn-to-turn short-circuit loss series reactance equivalent inductance and the adjustable turn-to-turn short-circuit circulation loss equivalent resistance are subjected to equal proportion or non-equal proportion gradient reduction according to preset step times;
s202, when turn-to-turn short circuit loss series reactance equivalent inductance and adjustable turn-to-turn short circuit circulation loss equivalent resistance are reduced according to gradient, the current of each stage of series equivalent resistance is increased to about 15-30 times of rated current according to short circuit circulation.
8. The modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 harmonic currents according to claim 7, wherein in S201, when the turn-to-turn short circuit loss series reactance equivalent inductance and the adjustable turn-to-turn short circuit circulating current loss equivalent resistance are reduced in equal proportion or non-equal proportion according to preset step times; the method also comprises the steps of presetting 5 times, wherein the inductance loss gradient is an unequal proportion gradient, and simulating the reignition time of the delayed short circuit discharge arc after the voltage resistance peak value is connected in a power frequency cycle according to different trigger angles.
9. The modeling and simulation method based on series arc resistance turn-to-turn short circuit excitation 3, 5 harmonic currents according to claim 6, further comprising the content ratio of 3 harmonic and 5 harmonic under different inductance loss degrees in a digital circuit simulation model; and the content of 3 rd order harmonics and 5 th order harmonics at different triggering angles.
10. The modeling simulation method based on series arc resistance turn-to-turn short circuit excitation 3 and 5 harmonic currents as claimed in claim 5, characterized in that the content of the 3 rd harmonic and the 5 th harmonic obtained in the digital circuit simulation model are compared with the actual parameters of the dry-type air-core reactance turn-to-turn fault case, and the parameters in the digital circuit simulation model are adjusted according to the comparison result.
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