CN-121983915-A - Method for reducing neutral point displacement voltage of generator

CN121983915ACN 121983915 ACN121983915 ACN 121983915ACN-121983915-A

Abstract

The invention provides a method for reducing the displacement voltage of a neutral point of a generator, and relates to the technical field of relay protection of power systems. The method is carried out under the condition of no-load operation or grid-connected operation of the generator and comprises Step1, actually measuring the A-phase fundamental wave voltage of the generator Neutral displacement voltage Step2, measuring or calculating fundamental current of generator neutral point grounding device Step3, calculate the capacitance current Step4, obtained by the preceding steps 、、 And Further calculating to obtain capacitance pre-solution parameters C x and C y , and determining the two phases of the external capacitor and the external capacitor value according to the positive-negative relationship and the magnitude relationship of the capacitance pre-solution parameters C x and C y . Under the condition that the displacement voltage exists in normal operation of the generator, the proper capacitance of the external numerical value of a certain two phases at the machine end is determined through conventional measurement and simple calculation, so that the displacement voltage is reduced, and the problem that the prior art depends on a quasi-distributed capacitance parameter model or a machine end simulation ground fault experiment is solved.

Inventors

LV XIAOYONG
LI MING
SANG XITAO
CHEN AO
LEI FENGLING
NIU XIUYING

Assignees

中国长江电力股份有限公司

Dates

Publication Date: 20260505
Application Date: 20260129

Claims (10)

1. A method for reducing the neutral point displacement voltage of a generator, which is characterized in that the method is carried out under the condition of no-load operation or grid-connected operation of the generator, and comprises the following steps: step1, actually measuring the A-phase fundamental voltage of the generator Neutral displacement voltage ; Step2, measuring or calculating fundamental current of generator neutral point grounding device ; Step3, calculating the capacitance current ; Step4, obtained by the preceding steps 、、 And Further calculating to obtain capacitance pre-solution parameters C x and C y ; Step5, determining the external capacitor and the external capacitor value at which two phases according to the positive-negative relationship and the magnitude relationship of the capacitor pre-solution parameters C x and C y .
2. The method for reducing neutral point displacement voltage of generator according to claim 1, wherein in Step1, a fault recorder or a relay protection device is used to measure three-phase voltage of a generator-side voltage transformer and open-delta voltage of the transformer, thereby obtaining a-phase fundamental wave voltage Neutral displacement voltage 。
3. The method for reducing neutral point displacement voltage of generator according to claim 1, wherein Step2, when adopting the actual measurement method, uses a fault recorder or relay protection device to measure the current of the current transformer on the primary side winding grounding loop of the generator neutral point grounding device, thereby obtaining the fundamental current When the calculation method is adopted, the equivalent parameters of the neutral point grounding equipment are firstly obtained, and then the formula is adopted Calculating to obtain fundamental wave current Where R is the equivalent series resistance of the neutral grounding device, L is the equivalent series inductance, Is the fundamental angular frequency.
4. A method of reducing generator neutral point displacement voltage according to claim 1, the characteristic is that in Step3, the capacitance current The calculation formula of (2) is as follows: ;(1) Wherein, the 、、 Respectively the actually measured capacitance to ground of the stator windings of the A phase, the B phase and the C phase of the generator under the static condition, Is the fundamental angular frequency.
5. The method for reducing generator neutral point displacement voltage according to claim 1, wherein in Step4, the capacitance pre-solution parameters C x and C y are obtained by solving the following equation: ;(2) Wherein, the The three-phase unbalance current defined for the method of the invention, Is the modulus of the three-phase unbalanced current, Is a current Is used for the phase angle of (a), For the phase a potential of the generator, Is the modulus of the phase a potential, Is the phase angle of the a-phase potential.
6. The method for reducing generator neutral point displacement voltage according to claim 1, wherein Step5 determines the two phases of the external capacitor and the external capacitor value according to the rule in the following table: Capacitance pre-solution parameters C x and C y externally-hung capacitance compensation rule Wherein, C a+ 、C b+ 、C c+ represents the externally-hung capacitors at the machine end of the A phase, the B phase and the C phase respectively, and the result shows that the externally-hung capacitors at the machine end three phases are not needed.
7. The method of claim 1, wherein during steps 1 to 5, the terminal voltage, stator current, rotor current and winding temperature of the generator are monitored in real time, and when any parameter exceeds ±10% of the rated value, the capacitor configuration operation is suspended and an alarm signal is sent.
8. The method for reducing generator neutral point displacement voltage according to claim 4, wherein the actual measurement of the capacitance to ground of the generator stator winding is performed by using a power frequency alternating current withstand voltage test in combination with a capacitance measuring instrument, and the measuring error is not more than +/-1%.
9. The method for reducing the neutral point displacement voltage of the generator according to claim 1, wherein the externally hung capacitor is a metallized polypropylene film capacitor, the capacitance deviation is not more than +/-2%, the rated voltage is not less than 1.5 times of the rated voltage of the generator, and the rated current is not less than 1.2 times of the corresponding capacitance current.
10. A method for reducing generator neutral point displacement voltage according to claim 3, wherein the fundamental wave angular frequency ω has a value of 2Ω, where f is the generator rated frequency and the range of values is 50Hz or 60Hz.

Description

Method for reducing neutral point displacement voltage of generator Technical Field The invention relates to the technical field of relay protection of power systems, in particular to a method for reducing the displacement voltage of a neutral point of a generator. Background The single generator has low single-machine capacity and usually operates in a neutral point non-grounding mode. With the development of economy and society, the power load demand rapidly rises, and the single-machine capacity of the generator increases. In order to cope with larger capacitance current generated by single-phase grounding faults of the stator winding, the existing part of large-sized generator sets operate in a mode that a neutral point passes through an arc suppression coil. However, the operation mode of grounding through the arc suppression coil also accompanies the problem of larger neutral point displacement voltage of the generator. The larger neutral point displacement voltage enlarges the dead zone of the grounding protection of the stator of the generator, which is not beneficial to the safe and stable operation of the generator. The plug-in capacitor at the generator end is a method for reducing the displacement voltage of the neutral point, and how to determine the configuration phase and capacity of the plug-in capacitor is always a key problem of direct attention in engineering. In the conventional method, under the static condition of the generator, the capacitance of each phase of the stator winding of the generator and the direct-connected outer loop of the generator is actually measured in a split-phase manner, the phase with the largest capacitance is taken as a reference, the capacitance deviation of other two phases and the reference is calculated, and the capacitance which needs to be increased is hung outside one or the other two phases, so that the displacement voltage can be reduced. The disadvantage of this method is evident that the statically measured capacitance does not reflect the actual distributed capacitance current. Some cases show that when the fundamental wave potential of the stator winding is not symmetrical, obvious displacement voltage exists during normal operation of the generator, three phases of static actual measurement are basically equal to each other at the moment, and as a result, the capacitor is not hung outside the machine end and the method fails. The second method is that three-phase earth capacitance parameters of the stator winding of the generator are actually measured under the dynamic condition, namely, the generator is enabled to work at rated rotation speed, proper voltage is established, single-phase earth faults of the machine end are actually measured under the condition, then equations are listed according to a simplified equivalent circuit, the equations are solved to obtain the three-phase earth capacitance parameters, and similarly, the capacitance deviation of other two phases is calculated by taking the phase with the largest capacitance as a reference, and the capacitance which needs to be increased is hung outside the two phases or one phase, so that displacement voltage can be reduced. This method does not fail as in the former method, but has the disadvantage that the simulation of the ground fault of the machine is required, the experimental difficulty is high, and the risk exists, so that the method is rarely adopted on site. The method also comprises the steps of knowing the parameters of the capacitance to ground of the stator winding and the parameters of the neutral point grounding equipment of the generator, establishing a quasi-distributed capacitance parameter model, obtaining a displacement voltage and a displacement voltage result obtained by simulation calculation when the generator actually operates, and considering that the quasi-distributed capacitance parameter model is basically accurate, calculating the capacitance again, and obtaining a capacitance with proper external value at the machine end of which two phases or one phase according to the calculation result, thereby reducing the displacement voltage. The method has the defects that a more complex quasi-distributed capacitance parameter model needs to be built, the model is accurate, the calculation is complex and the difficulty is high, and sometimes, the model cannot be built under the condition that the specific wiring of the stator winding of the generator is not known. Disclosure of Invention The invention aims to provide a method for reducing the neutral point displacement voltage of a generator, which solves the problem that the prior art relies on a quasi-distributed capacitance parameter model or a machine end simulation ground fault experiment. In order to solve the technical problems, the invention adopts the following technical scheme: A method for reducing the neutral point displacement voltage of a generator is carried out under the condition of no-load operatio