A method for phase checking of a self-shunt generator PT by using excitation variable current

Abstract

The present application belongs to the technical field of power application, and particularly relates to a method for phase checking of a self-shunt generator PT by using a field-changing current. The present application solves the technical problem of the existing reverse phase checking by determining the trigger angle of a three-phase full-bridge rectifier circuit and the same nature of the current change of the high-voltage side or the low-voltage side of a field-changing transformer and the voltage change of the same phase of a generator terminal, and uses the same nature as the basis for phase checking of the self-shunt generator PT. Meanwhile, the present application is simple in method, convenient in operation, accurate in phase checking, and suitable for large-scale popularization and use.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric power application, and in particular relates to a method for performing phase checking on a self-shunt excited generator PT by utilizing an excitation variable current. Background Art

[0002] In a generator set, a phase check test must be performed after the generator body and voltage transformer (PT) have been overhauled. Similarly, a phase check should also be performed after overhauling or changing the secondary circuit associated with the parallel connection of the generator set. If AC power sources with different phases and phase sequences are asynchronously paralleled or closed, large inrush currents and overvoltages can be generated, damaging primary equipment such as generators and transformers. Incorrect phase sequence of the terminal voltage can cause secondary equipment protection to malfunction or fail to operate, causing serious damage to the power grid. Therefore, after overhauling equipment such as the generator, main transformer, and PT, a phase check test should be performed on the generator outlet PT.

[0003] Take the common 220kV system wiring diagram as an example. Figure 1 As shown, it features a dual-bus, dual-section wiring configuration with a total of 10 outgoing lines. Station A is equipped with six outgoing lines, two main transformers, and one standby transformer bay. The main transformer bays are connected to the generators of units #9 and #10, which use self-parallel excitation. Units #7 and #8 use a three-machine excitation system.

[0004] When the generator outlet PT of unit #9 or #10 needs to be phase-checked, the IA or IIA busbar needs to be left blank. After the generator is zero-voltage-boosted, it is connected to the blanked busbar, again zero-voltage-boosted. The busbar PT voltage and the corresponding phase generator outlet PT voltage are then used for phase checking. If the phase sequence is correct and the generator terminal voltage at the corresponding phase leads the busbar voltage by 30°, the generator outlet PT and primary circuit connections are correct.

[0005] There are a total of 11 bays connected to the 220kV A station busbar, evenly distributed on the IA and IIA busbars. Therefore, the reverse discharge process required to empty the busbar is very complicated.

[0006] After the generator primary equipment or PT body / secondary circuit work is completed, the PT phase verification test is required. Since the 220kV busbar has been in long-term operation, the busbar PT of station A has not performed any work. Therefore, the voltage phase sequence of the PT of station A busbar is used as the reference.

[0007] Taking the #10 generator outlet PT phase check as an example, the operator must clear the 220kV busbar VIIA and close the #10 generator's 2102 switch on the IIA busbar. Then, close the 210 switch and ramp up the #10 generator from zero. After ramping up the #10 generator, the maintenance personnel check the #10 generator outlet PT secondary voltage and compare it with the phase sequence of the PT voltage on the IIA busbar. Because the #10 main transformer is connected in a Yd-11 configuration, the generator terminal voltage should lead the busbar voltage by 30°. Therefore, a vector analyzer is used to check the phase and sequence of the generator terminal PT secondary voltage with the 220kV busbar VIIA PT secondary voltage. The generator terminal voltages UA, UB, and UC lead the corresponding busbar voltages by 30°, respectively.

[0008] During this period, operators must perform complex and complex operations to maintain the empty busbar. Single-busbar operation presents significant safety risks. If any fault is discovered during the reverse flow process, Station A will be operating on a single busbar, as the busbars are interconnected during the reverse flow. Any fault on this busbar will cause a complete power outage at Station A, leading to a major power production accident. The reverse flow process requires operators to perform multiple operations both remotely and locally, creating a complex set of procedures with a significant risk of misoperation. Summary of the Invention

[0009] In view of the technical problems existing in the above-mentioned conventional generator outlet PT phase checking, the present invention proposes a method for performing phase checking on the self-shunt generator PT by using excitation variable current, which has reasonable design, convenient operation and can realize rapid phase checking.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is to provide a method for performing phase checking on a self-shunt-excited generator PT by using an excitation variable current, comprising the following steps:

[0011] a. First determine the connection group of the excitation transformer;

[0012] b. Then, determine how many degrees the low-voltage side voltage of the excitation transformer leads the A, B, and C phases of the generator terminal according to the connection group of the excitation transformer;

[0013] c. Divide an operating cycle into 6 periods based on the trigger angle. When a phase current on the low side of the excitation transformer rises, the voltage of the same phase at the generator end before grid connection should be close to the peak value.

[0014] d. Observe the startup waveforms before grid connection in the fault recorder to determine the trigger angle;

[0015] e. After the generator starts to raise the voltage from zero, use the current waveform on the low-voltage side of the generator excitation transformer or the current waveform on the high-voltage side of the excitation transformer as a reference in the fault recorder to check the generator terminal voltage phase sequence according to the phase relationship in step c and the trigger angle determined in step d.

[0016] Preferably, in step c, if the trigger angle divides one operating cycle into 6 time periods on average, then Ia, Ib, and Ic in the secondary current of the excitation transformer are each conducted for 120° at intervals of 60° during the positive and negative half-wave cycles, and when a rising edge occurs in a phase current on the low side of the excitation transformer, the corresponding voltage of the same phase at the generator end before grid connection should be close to the peak value.

[0017] Compared with the prior art, the advantages and positive effects of the present invention are:

[0018] 1. The present invention provides a method for performing phase checking on a self-shunt generator (PT) using an excitation variable current. This method solves the technical problems associated with existing inverted phase checking by determining the trigger angle in a three-phase fully controlled bridge rectifier circuit, the current changes on the high-voltage or low-voltage side of the excitation transformer, and the voltage changes on the same phase at the generator end as the basis for performing phase checking on the self-shunt generator PT. Furthermore, the method is simple, easy to operate, accurate in phase checking, and suitable for large-scale promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0020] Figure 1 This is the common 220kV system wiring diagram introduced in the background technology;

[0021] Figure 2 A diagram of a common existing generator-transformer system provided in Example 1;

[0022] Figure 3 A three-phase bridge rectifier circuit diagram provided in Example 1;

[0023] Figure 4 The waveform diagram provided in Example 1 when the trigger angle α=0°;

[0024] Figure 5 The waveform diagram of the trigger angle α=0°VT1 provided in Example 1;

[0025] Figure 6 The waveform diagram of the trigger angle α=30° provided in Example 1;

[0026] Figure 7 The load waveform diagram provided in Example 1 when the trigger angle α is 60°;

[0027] Figure 8The load waveform diagram provided in Example 1 with a trigger angle α=90°;

[0028] Figure 9 A three-phase fully controlled bridge circuit diagram of a resistive-inductive load provided in Example 1;

[0029] Figure 10 The waveform diagram of the resistive-inductive load when the trigger angle α is 30° provided in Example 1;

[0030] Figure 11 The waveform diagram of the resistive-inductive load when the trigger angle α is 60° provided in Example 1;

[0031] Figure 12 The waveform diagram of the resistive-inductive load when the trigger angle α is 90° provided in Example 1;

[0032] Figure 13 This is a waveform diagram of the resistive-inductive load triggering process when the trigger angle α is 90° provided in Example 1. DETAILED DESCRIPTION

[0033] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways than those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Example 1: This example provides a method for performing phase correction on a self-excited generator PT using an excitation variable current.

[0036] like Figure 2 As shown, the high-voltage side voltage of the excitation transformer is derived from the generator terminal, stepped down by a 20kV / 890V Yd-11 transformer, and then fed to a thyristor three-phase fully controlled bridge rectifier circuit. Because the excitation transformer utilizes a Yd-11 connection, the voltage waveform on the high-voltage side of the excitation transformer lags behind the low-voltage side of the excitation transformer by 30°. Similarly, the high-voltage side voltage of the excitation transformer is derived from the generator terminal, so the terminal voltage lags behind the low-voltage side voltage of the excitation transformer by 30°. Of course, another common excitation transformer connection is the Yd-01 connection. This connection type is crucial in determining how much the low-voltage side voltage of the excitation transformer leads the A, B, and C phases of the generator terminal. In this embodiment, the common Yd-11 connection is used as an example.

[0037] For a three-phase bridge rectifier circuit, such as Figure 3As shown, we are accustomed to calling the three thyristors with cathodes connected together a common cathode group (VT1, VT3, VT5), and the three thyristors with anodes connected together a common anode group (VT2, VT4, VT6). According to the amplitude and phase sequence of the AC voltages A, B, and C, the thyristors are turned on in the order of VT1-VT6.

[0038] Therefore, in a three-phase bridge fully controlled rectifier circuit, the thyristor triggering order is VT1-VT6. When the trigger angle α = 0°, for the three thyristors in the common cathode group (VT1, VT3, VT5), the phase with the highest AC voltage connected to the anode is turned on; for the three thyristors in the common anode group (VT2, VT4, VT6), the phase with the lowest AC voltage connected to the cathode is turned on. Therefore, at any time, one thyristor in each of the common anode and common cathode groups is in the on state. Therefore, when α = 0°, thyristor conduction can be called natural commutation, and the commutation point is the intersection of the phase voltages.

[0039] Depend on Figure 4 From the three-phase voltage waveforms of A, B, and C, we can see that when the common cathode group thyristors are conducting, the actual secondary voltage waveform Ud1 (positive half-wave) is the envelope of the three-phase voltage in the positive half-wave. Similarly, when the common anode group thyristors are conducting, the actual secondary voltage waveform Ud2 (negative half-wave) is the envelope of the three-phase voltage in the negative half-wave. Therefore, within a single three-phase AC cycle, we can decompose a single AC cycle into six time periods based on the conduction order.

[0040] The detailed triggering process is as follows:

[0041] When the trigger angle α = 0°, it is the first period. The intersection of the positive half-wave voltage of phase A and the voltage of phase C occurs at the trigger angle α = 0°. At this time, the conduction angle is triggered, and the phase with the highest positive half-wave voltage is phase A, so VT1 is turned on. Similarly, the negative half-wave voltage of phase B has the highest amplitude and gradually decreases. At this time, VT6 continues to conduct and gradually turns off.

[0042] When the second period arrives, the negative half-wave voltage is at the intersection of UB and UC. A trigger pulse arrives, and the amplitude of the negative half-wave voltage Uc gradually increases, turning on VT2 in the common anode group. Similarly, VT1 on phase A in the positive half-wave continues to conduct and gradually moves toward the end of the second period. At this point, the voltages UA and UB intersect, and UB continues to increase. When the next trigger pulse arrives, VT1 on phase A in the common cathode group turns off, and VT3 on phase UB is triggered.

[0043] Therefore, at the beginning of the third period, VT3 conducts during the positive half-wave, while VT2 conducts continuously during the negative half-wave. At the end of the third period, at the start of the fourth period, the positive half-wave, Ub, is still at its highest amplitude, so VT3, connected to UB, conducts continuously during the positive half-wave. During the negative half-wave, it is at the intersection of Uc and Ua, after which the amplitude of ua gradually increases. Therefore, when the trigger pulse arrives, VT2, connected to uc, turns off, and VT4, whose cathode is connected to Ua, conducts.

[0044] At the end of the fourth period and the beginning of the fifth period, the positive half-wave is the intersection of the Ub and Uc voltage amplitudes, and the penalty pulse arrives. In the positive half-wave, VT5 connected to the anode and uc is turned on, and VT3 connected to ub is turned off; in the negative half-wave, VT4 connected to the cathode and ua is continuously turned on.

[0045] Time comes to the end of the fifth period and the beginning of the sixth period. At this time, in the positive half-wave, UC still continues to be the phase with the highest voltage amplitude. Therefore, VT5 connected to the anode and uc continues to be turned on; in the negative half-wave, the voltage reaches the intersection of Ua and Ub voltage amplitudes, and then the Ub amplitude continues to increase. At this time, the negative half-wave trigger pulse arrives, VT4 connected to the cathode and ua is turned off, and VT6 connected to ub is turned on.

[0046] When the time comes to the end of the sixth period, the first period starts, at this time, in the positive half wave, the UC amplitude is still the largest, so the VT5 connected to the anode and UC is continuously turned on; in the negative half wave, the VT6 connected to the cathode and UB is continuously turned on. Finally, the sixth period ends, as shown in the figure below. Figure 5 shown.

[0047] At this point, the first trigger cycle of the three-phase sine wave ends and the next cycle begins. Similarly, regardless of how the trigger angle changes, the basic principle of the conduction process of the three-phase fully controlled rectifier bridge is as shown above.

[0048] From this, we can see that at each moment, two thyristors are turned on to form a power supply circuit, one of which is a common cathode group and the other is a common anode group. The thyristors that are turned on are both the phase with the highest amplitude in the half-wave, and they are not the thyristors of the same phase.

[0049] According to the trigger sequence, the thyristors conduct in the order VT1-VT6, with the conduction phases differing by 60°. Each thyristor conducts for 120°. The trigger pulses for the common cathode groups VT1, VT3, and VT5 differ by 120°, and the trigger pulses for the common anode groups VT2, VT4, and VT6 also differ by 120°. The trigger pulses for the upper and lower arms of the same phase—VT1 and VT4, VT3 and VT6, and VT5 and VT2—differ by 180°. Based on the conduction period, it can be calculated that a thyristor is in the on state for 120° and in the off state for 240° during a cycle.

[0050] Table 1 Thyristor conduction sequence table

[0051]

[0052] like Figure 6 As shown in the figure, the operating conditions of a three-phase fully-controlled bridge rectifier circuit change when the trigger angle α changes. For example, when the trigger angle α = 30°, the contact timing moves 30° back from the voltage intersection point. Dividing a cycle into six equal segments, each 60°, the thyristor's turn-on time is delayed by 30° compared to a trigger angle of α = 0°. Similarly, the turn-off time is also delayed by 30°.

[0053] Therefore, the current flowing through the low-voltage side of the transformer, taking phase A as an example, the ia waveform is that when VT1 is turned on for 120 degrees, ia is positive, and the waveform axis of ia is the same as the secondary voltage Ud in the same period; during the 120 degrees when VT4 is turned on, ia is negative, and the waveform axis is the same as the ud load in the same period.

[0054] Similarly, if Figure 7 As shown in the figure, when the trigger angle α = 60°, the voltage waveform of the three-phase fully controlled bridge rectifier circuit continues to shift backward by 30°. At this time, the conduction angle of each thyristor is still 120°, and the waveform of the rectified output voltage Ud is still as shown in the table above, which is the voltage difference between UA, Ub, and Uc. Therefore, as the trigger angle progresses, the waveform of the secondary load voltage Ud passes through the zero point, and the average voltage continues to decrease.

[0055] When the trigger angle α exceeds 60°, the thyristor's trigger angle continues to shift backward. Therefore, theoretically, the secondary voltage Ud continues to decrease and will become negative. However, in reality, when the secondary load is a purely resistive load, the waveform of the current id flowing through the load is consistent with ud. Once ud decreases to 0, id also decreases to 0, and the current flowing through the thyristor also decreases to 0, causing the thyristor to turn off and the output rectified voltage ud to be 0. Therefore, the waveform of ud cannot have negative values. For example, when α = 90°, in a purely resistive load electrical circuit, the order in which the thyristors conduct remains as shown in the table above.

[0056] Therefore, in the first period, if Figure 8 As shown, when α=90°, VT1 is turned on, the secondary voltage ud=Ud1-Ud2=ua-uc, and VT1 continues to conduct to the intersection of UA and ub voltages. At this time, Ua-Ub=0, and the current id flowing through the secondary load is 0. Therefore, the thyristor VT1 is turned off.

[0057] After VT1 turns off, no other thyristors turn on until the second period arrives. At this time, the α = 90° trigger pulse arrives, and the uc voltage amplitude is the highest in the negative half-wave. Therefore, VT2, whose cathode is connected to uc, is triggered to turn on. The rectified voltage ud = ub - uc = ubc. When the voltage reaches the intersection of uc and ua, the voltage of ud is equal to 0, so the current flowing through the secondary resistance load is 0, so thyristor CT2 turns off. After that, no thyristor turns on within the 30° range.

[0058] Until the time comes to the third period, at this time the α=90° pulse arrives, the working cathode group VT3 is turned on, at this time ud=ub-ua=uba, VT3 continues to conduct to the voltage intersection of Ub and Uc, at this time the ud voltage is 0, VT3 is turned off.

[0059] After that, no thyristor conducts until the fourth period. At this time, the trigger pulse arrives, and the Ua phase with the largest negative half-wave amplitude of the voltage cycle, that is, the thyristor VT4 connected to the cathode of phase A, conducts. At this time, the load voltage Ud = Uc-Ua = Uca. VT4 continues to conduct until the voltage Ub and Ua meet, at which point Ud = 0, so the thyristor VT4 is turned off.

[0060] At this time, no thyristor is turned on until the fifth period. At this time, the positive half-wave trigger angle α = 90° arrives, and the thyristor VT5 connected to the anode of Uc is turned on. The load voltage Ud = Uc-Ub = Ucb. VT5 continues to conduct until the voltage intersection of Uc and Ua, at which time the voltage of Ud is 0 and VT5 is turned off.

[0061] Before the sixth period arrives, no thyristors are conducting. When the sixth period arrives, the negative half-wave trigger angle α = 90°. At this point, the Ub phase has the largest amplitude in the negative half-wave. Therefore, thyristor VT6, whose cathode is connected to Ub, conducts. This conduction continues until the intersection of Ub and Uc voltages, at which point Ud = 0, and VT6 turns off.

[0062] After that, no thyristor is turned on until the next trigger cycle comes.

[0063] In the rectified voltage waveform Ud, 30° out of every 60° is zero. Therefore, when α = 90°, only one thyristor conducts in each cycle. Similarly, when the trigger angle continues to increase to 120°, the rectified output voltage Ud will all be zero, and its average voltage will also be zero. This shows that the phase shift range of the trigger angle α for a three-phase bridge-type fully controlled rectifier circuit with a purely resistive load is 120°.

[0064] Since in the excitation circuit, Figure 9 As shown, the generator rotor is equivalent to a resistive-inductive load, which will generate a back electromotive force in the circuit, thus preventing the voltage and current of the load from changing suddenly.

[0065] When α ≤ 60°, since the rectified voltage Ud only passes through the zero point and there is no reverse voltage, the on-off state of each thyristor, the waveform of the output rectified voltage Ud, and the voltage borne by each thyristor remain essentially unchanged compared to a purely resistive load. The difference is that the back EMF provided by the resistive-inductive load is superimposed on the rectified output voltage Ud, resulting in a different load current waveform Id. With a purely resistive load, the waveform change trend of Id is the same as that of Ud. However, with a resistive-inductive load, the back EMF in the inductor causes the current waveform flowing through the load to become straight. When the inductance is large enough, the load current waveform can approach a straight line. Similarly, the current flowing through each thyristor also approaches a straight line.

[0066] like Figure 10 、 Figure 11 As shown in the figure, when the trigger angle α>60°, the presence of inductance L and the back electromotive force provided by the resistive-inductive load will cause Ud to have a negative half-wave component. Therefore, taking the trigger angle α=90° as an example, if the inductance L is large enough, the positive and negative half-wave areas in Ud are essentially equal, so the average value of Ud is approximately 0. Therefore, this shows that in a three-phase fully controlled bridge rectifier circuit with a resistive-inductive load, the phase shift range of the α trigger angle is 90°.

[0067] The following describes in detail the trigger angle α = 90°. Figure 12 、 Figure 13 Figure 1 shows the trigger waveform of a three-phase fully controlled bridge rectifier circuit under resistive and inductive load conditions. The trigger angle still divides one operating cycle into six equal time periods. The waveform of the secondary voltage Ud pulsates six times within one cycle, and the waveform of each pulsation is the same.

[0068] During the first period, a trigger pulse α = 90° arrives. At this point, the amplitude of Ua in the positive half-wave is maximum. VT1, whose anode is connected to Ua, conducts, and Ud = UA - Uc = Uac, conducting for 30°. The voltage then reaches the intersection of Ua and Ub, where Ud = 0. At this point, due to the back electromotive force provided by the inductor L, Ud can become negative, allowing the thyristor to continue conducting for 120° until the next positive half-wave trigger angle α arrives.

[0069] Similarly, when the time comes to the second period, the negative half-wave trigger angle α=90° arrives. At this time, the voltage with the largest amplitude in the negative half-wave is the Uc phase, so VT2, whose cathode is connected to Uc, is turned on. After 30 degrees of conduction, it reaches the voltage intersection point of Uc and Ua. At this time, the amplitude of Ud passes through 0. Due to the effect of the inductor L, the current Id is not allowed to change suddenly, thus providing reverse electromotive force, and VT2 continues to conduct until the arrival of the trigger angle in the next negative half-wave.

[0070] When the time comes to the third period, the phase with the largest amplitude in the positive half-wave is Ub phase. Therefore, VT3, whose anode is connected to Ub, is turned on for 120° until the next positive half-wave trigger pulse arrives.

[0071] Similarly, when the time comes to the fourth period, the negative half-wave Ua voltage amplitude is the largest. Therefore, the thyristor VT4 whose cathode is connected to Ua is turned on, and the conduction time is 120° until the next negative half-wave trigger angle arrives.

[0072] When the time reaches the fifth period, the positive half-wave trigger angle arrives, and the phase with the highest amplitude is Uc. Therefore, VT5 whose anode is connected to Uc is turned on, and the conduction lasts for 120°.

[0073] Until the sixth period arrives, the Ub phase has the largest amplitude in the negative half-wave, so the trigger angle α in the negative half-wave causes the thyristor VT6 connected to the cathode and Uc to turn on. At this point, the triggering in one cycle ends and enters the next cycle.

[0074] Because under the condition of resistive-inductive load, the voltage waveform of Ud can have a negative half-wave, and the amplitudes of the positive and negative half-waves are equal, the average voltage of Ud is 0.

[0075] When the trigger angle α is less than 90°, the positive half-wave voltage accounts for a larger proportion than the negative half-wave voltage in the Ud voltage, and the average value of Ud is greater than 0.

[0076] In the generator excitation system, the excitation transformer uses a Y / d-11 connection. The high voltage of the excitation transformer is drawn from the generator terminals, and the low-side voltage leads the generator terminal voltage by 30°. The triggering process shows that the excitation transformer secondary currents Ia, Ib, and Ic conduct for 120° every 60° during the positive and negative half-wave cycles.

[0077] As can be seen from the trigger waveforms of the three-phase fully controlled bridge rectifier circuit, taking phase A as an example, thyristor VT1, whose anode is connected to phase A, conducts at a trigger angle α = 90°. At this time, current flows through phase A on the low-voltage side of the excitation transformer, resulting in a rising edge of current Ia. Similarly, during the negative half-wave, VT, whose cathode is connected to the phase A voltage, conducts. At this time, current flows through the negative half-wave of the excitation transformer, resulting in a falling edge of current Ia on the negative half-wave.

[0078] When the trigger angle α = 90°, the rising edges of the currents in phases A, B, and C on the low-voltage side of the excitation transformer correspond to the triggering moments of the fully controlled rectifier bridges +A / +B / +C, respectively. At this point, the generator terminal voltages corresponding to phases A, B, and C are at their respective positive half-wave peaks. Taking phase A as an example, the corresponding phase angle is approximately 90°. When the trigger angle α = 90°, the average values ​​of Ia, Ib, and Ic are approximately 0. However, after the generator is excited, the average values ​​of Ia, Ib, and Ic are greater than 0, so the trigger angle α is less than 90°.

[0079] Since the excitation transformer uses a Yd-11 connection, as shown in the system diagram, the high-voltage side of the Yd-11 transformer is connected to the generator terminal. The voltage waveform is the same as the generator terminal voltage, and the voltage on the low-voltage side of the excitation transformer should lead the high-voltage side by 30°. If the secondary connection of the generator terminal PT is correct, the terminal voltages A, B, and C will lag the voltage on the low-voltage side of the excitation transformer by 30°. Therefore, when the terminal voltage reaches its peak at 90° in the positive half-wave, VT1, whose anode is connected to Ua, should conduct, corresponding to the rising edge of the current Ia on the low-voltage side of the excitation transformer. The same applies to phases B and C.

[0080] Taking a certain plant as an example, by observing the startup waveforms before grid connection in the fault recorder, it can be found that the trigger angle before grid connection α≈84°.

[0081] After determining this phase relationship, the generator TV phase verification process does not need to be reversed. After the generator is started from zero, the generator terminal voltage phase sequence can be verified on the fault recorder using the waveform of the generator excitation transformer low-voltage side current (or the excitation transformer high-voltage side current) as a reference. Taking phase A as an example, when the excitation transformer low-side phase A current shows a rising edge, the corresponding generator terminal voltage A before grid connection is close to the peak value, approximately 84°.

[0082] Therefore, the phase check can be completed by simply comparing the phase relationship between the current on the low-voltage side of the excitation transformer and the voltage at the generator terminal with the historical records in the fault recorder.

[0083] Therefore, after the primary equipment or the generator-end PT is overhauled, the generator PT phase check work can be performed by using the rising edge of the current on the low-voltage side of the excitation transformer and the corresponding machine-end voltage phase check method.

[0084] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any person skilled in the art may utilize the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes for application in other fields. However, any simple modification, equivalent change, and modification of the above embodiments made in accordance with the technical essence of the present invention without departing from the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for phase checking of a self-shunt excited generator PT using excitation variable current, characterized in that: The following steps are involved: a. First determine the connection group of the excitation transformer; b. Then, determine how many degrees the low-voltage side voltage of the excitation transformer leads the A, B, and C phases of the generator terminal according to the connection group of the excitation transformer; c. Divide an operating cycle into 6 periods based on the trigger angle. When a phase current on the low side of the excitation transformer rises, the voltage of the same phase at the generator end before grid connection should be close to the peak value. d. Observe the startup waveforms before grid connection in the fault recorder to determine the trigger angle; e. After the generator is started from zero and the voltage is increased, the generator terminal voltage phase sequence can be checked in the fault recorder based on the current waveform on the low voltage side of the generator excitation transformer or the current waveform on the high voltage side of the excitation transformer, according to the phase relationship in step c and the trigger angle determined in step d.

2. The method for performing phase checking on a self-shunt generator PT by using excitation variable current according to claim 1, characterized in that: In step c, if the trigger angle divides one operating cycle into six equal time periods, then the secondary currents Ia, Ib, and Ic of the excitation transformer are each conducted for 120° at intervals of 60° during the positive and negative half-wave cycles, and when a phase current on the low side of the excitation transformer shows a rising edge, the corresponding voltage of the same phase at the generator end before grid connection should be close to the peak value.

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