WO2014173132A1

WO2014173132A1 - Method for monitoring unbalanced current at stator side after inter-turn short circuit in hydro-generator rotor

Info

Publication number: WO2014173132A1
Application number: PCT/CN2013/088470
Authority: WO
Inventors: 郭宝甫; 刘志文; 陈海龙; 孙宇光; 肖志刚; 王威; 李俊霞; 刘艳东; 郭玉宝
Original assignee: 国家电网公司; 许继集团有限公司; 许继电气股份有限公司
Priority date: 2013-04-27
Filing date: 2013-12-03
Publication date: 2014-10-30
Also published as: CN103245820A

Abstract

A method for monitoring an unbalanced current at a stator side after inter-turn short circuit in a hydro-generator rotor. The method adopts a super-long data window technology, and automatically adjusts the length of a data window according to the number of pole-pairs of a generator, thereby achieving an accurate calculation of fractional harmonic of different units. In this method, an effective value of a fault circulating current is calculated accurately, and fundamental waves, third harmonic waves, and fifth harmonic waves in the unbalanced current during normal operation are filtered out effectively, thereby improving the sensitivity of monitoring the inter-turn short circuit fault in generator rotor windings.

Description

Hydrogenerator rotor inter-turn short-circuit stator side unbalance current monitoring method

The invention relates to a method for monitoring unbalanced current of a stator-side short-circuit stator of a hydro-generator rotor.

Background technique

Many scholars in domestic universities have made many theoretical studies on the inter-turn short-circuit fault of generator rotor windings. However, in terms of the inter-turn short-circuit fault of the rotor winding of the motor, there are relevant standards for offline detection only, and in terms of online monitoring. There is no clear technical specification. On-line monitoring, early prevention and diagnosis of generator rotor winding turn-to-turn short-circuit faults are necessary, but generator rotor inter-turn short-circuit fault monitoring devices are currently not mature and reliable related products at home and abroad, most power plants consider generator rotors Due to the difficulty in signal acquisition, the short-circuit fault monitoring device is unlikely to be a practical product. After the inter-turn short-circuit fault occurs in the rotor winding of the hydro-generator, the branch currents at the neutral point of the stator will generate unbalanced current dominated by fractional harmonics, and the complete split-phase cross-section protection and zero-sequence current type cross-section protection will not The equilibrium current is theoretically dominated by fractional harmonics and does not contain the fundamental component. The resulting fractional harmonics are mainly related to the pole pair P of the generator, and harmonics such as 1/P, 2/P... N/P (N is a natural number) appear. Accurately detecting the unbalanced current dominated by fractional harmonics is a necessary guarantee for on-line monitoring of the inter-turn short-circuit fault of the generator rotor winding. Taking the sampling of N=32 points per power frequency cycle and the pole pair P=30 of the generator as an example, the partial fractional harmonics included in the simulated measured current are: 5Hz, 10Hz, 20Hz, 30Hz, 40Hz, integer harmonics are: 50Hz, 150Hz, 250Hz, each harmonic current peak is 10mA, Figure 1 is the use of power frequency as the basic data window for the fault current containing the above harmonics The value is calculated and simulated. It can be seen that the conventional microcomputer protection sampling data window length cannot accurately calculate the unbalanced current mainly composed of fractional harmonics.

In order to calculate the RMS effective value of the fractional harmonics more accurately, Figure 2 uses NXP as the basic data window length, and also N=32 points per power frequency cycle, and the generator pole pairs P=30. For example, the effective value of the fault current is calculated and simulated. It can be seen from Fig. 2 that the method can accurately calculate the total effective value of the unbalanced current including the fundamental wave and the like (including the harmonics of each harmonic). The theoretical value of the total effective value of the balanced current is 20 mA, and the theoretical value of the fractional harmonic unbalanced current RMS is 15.81 mA), but the fundamental wave, the third harmonic, the fifth harmonic, etc. in the unbalanced current cannot be filtered out. It has a serious impact on the sensitivity of monitoring the fault of the generator rotor winding turn-to-turn short circuit.

Summary of the invention

The object of the present invention is to provide a method for detecting unbalanced current of a stator-side short-circuit of a hydro-generator rotor, which is used to solve the problem that the fundamental wave, the third harmonic and the fifth harmonic in the unbalanced current cannot be filtered by the prior art. This has the problem of affecting the sensitivity of fault monitoring.

In order to achieve the above object, the solution of the present invention is: A method for detecting unbalanced current of a stator-side short-circuit stator of a hydro-generator rotor, the steps are as follows:

(1) According to the generator pole pairs, determine the basic data window according to the formula τ ₌ ^ ¹ - ^ =

( 1 50

X 50

P J

Length, and determine the number of sampling points of the basic data window according to the formula M=NXP, where T is the length of the data window, P is the pole logarithm, M is the number of sampling points of the basic data window, and N is the number of sampling points of the weekly wave; (2) calculating, according to the data window length T, a total effective value of the unbalanced current including the fundamental wave, each integer harmonic, and each fractional harmonic;

(3) Perform analog sampling and data storage according to the number of sampling points in the basic data window, and discretize the total effective value of the unbalanced current according to the sampling data, calculate each fractional harmonic and fundamental wave, third harmonic, five times Harmonic unbalanced current RMS;

(4) Subtracting the rms value of the fundamental wave, the third harmonic and the fifth harmonic unbalance current from the total rms value of the discrete unbalanced current, and obtaining the total effective value of the fractional harmonic unbalance current;

(5) According to the calculated total harmonic value of the fractional harmonic unbalance current and the effective value of each fractional harmonic unbalance current, the inter-turn short-circuit fault of the hydro-generator rotor is monitored.

Further, step (2) calculates a total effective value of the unbalanced current including each harmonic by using a root mean square value method,

Where / _λ is the unbalanced current discrete sample value, which is the unbalanced current instantaneous value <丄M

Using the Fourier algorithm based on the basic data window to calculate each

N.real n.imag where η is a natural number and is the real part of the η/Ρ harmonic

The effective value is the total effective value of the unbalanced current of each harmonic including the fundamental wave discretized, The invention achieves the beneficial effects: The invention adopts the ultra-long data window technology, automatically adjusts the data window length according to the number of generator pole pairs, realizes the accurate calculation of the RMS values of the fractional harmonics and the fault circulation of different units, and effectively filters out The fundamental wave, the third harmonic and the fifth harmonic of the unbalanced current in normal operation accurately measure the unbalanced current mainly composed of fractional harmonics, which greatly improves the sensitivity of the monitoring of the inter-turn short-circuit fault of the rotor winding of the generator. .

DRAWINGS

Fig. 1 is a simulation diagram of the calculation of the effective value of the fault circulation with the power frequency as the basic data window; Fig. 2 is a simulation diagram of the calculation of the effective value of the fault circulation with the NXP as the basic data window; Fig. 3 is effective for the fault circulation by the method of the invention The value is calculated by simulation.

detailed description

The present invention will be further described in detail below with reference to the accompanying drawings.

The invention adopts a novel method for monitoring the unbalanced current mainly composed of fractional harmonics, and can completely filter out the fundamental wave, the third harmonic and the fifth harmonic in the unbalanced current, and accurately measure the fractional harmonics. The main unbalanced current, the specific steps are as follows:

First, determine the data window length based on the generator pole pair P, ie:

1 p

T = _{7 τ} =- = 0.02 corpse

1 x 50 ⁵⁰

ρ ) Moreover, the system determines the number of sampling points of the basic data window Μ=Ν Χ 根据 according to the set value of the generator pole pair Ρ and the sampling frequency of the system itself, where Ν is the number of sampling points per power frequency cycle, Ρ For the generator pole logarithm, Μ is the basic data window sampling points, Τ is the basic data window length.

Secondly, analog sampling and data saving are performed according to the number of sampling points in the basic data window. Calculate the total rms value of the unbalanced current using the rms value method:

Using the sampled data, discretize the calculated total rms current of the unbalanced current, ie

/ , = - H ' where , is the instantaneous value of the unbalanced current, / _λ is the discrete sample of the unbalanced current. The total rms value of the unbalanced current calculated at this time contains the fractional harmonic unbalanced current RMS of the fault information. It also contains the rms current of the unbalanced current of the fundamental wave, the third harmonic, and the fifth harmonic in normal operation.

Third, a series of coefficients of the Fourier algorithm corresponding to k are calculated according to the number of sampling points of the basic data window corresponding to the generator pole pairs, namely: for( k = 0; k 〈 M; k ++)

Coefl[k] = (2.0/M) * cos (n * k *2^/M); coefl[k+M]= (2.0/M) * sin(n * k *2^/M);

and

} where k is a natural number and the value of k is determined based on the simulation of the stator windings of the generator.

Fourth, the real and imaginary values of the fractional harmonic unbalance current required for the analog quantity are sequentially calculated by the Fourier algorithm.

2 ^ 2π

— 2^[1⁄2 -cos(/i · :·—)]

M Τ"ΐ Μ

2 ^ 2π

— 2^b _k -^(nk--)]

MM Where is the real part of the n/P harmonic unbalanced current, /„., is the imaginary part of the n/P harmonic unbalanced current, and n is a natural number.

According to the calculation method of the n/P harmonic unbalance current RMS value, when n takes different values, calculate 1/P, 2/P... n/P (n is a natural number) subharmonic imbalance. Current RMS, calculate P/P (fundamental), 3P/P (third harmonic), 5P/P (five times)

Fault circulation [ _{p 3 ρ} χ

L /p /p

Where /«« is the total effective value of the fractional harmonic unbalance current, which is the total effective value of the unbalanced current including the fundamental wave, etc., which is the fundamental wave, / _{3P /} is the third harmonic,

//P /P ι _5Ρ / _/ P is the fifth harmonic.

Finally, the generator rotor interturn short-circuit fault is monitored based on the fractional harmonic unbalance current total rms value and the fractional harmonic unbalance current rms value.

3 is a simulation diagram obtained by calculating the effective value of the fault circulation by using the method of the present invention, and the theoretical value of the total rms value of the unbalanced current including each harmonic is 20 mA, and the total effective value of the fractional harmonic unbalance current The theoretical value is 15.81 mA. As can be seen from FIG. 3, the method of the present invention can filter out the fundamental wave, the third harmonic and the fifth harmonic in the unbalanced current.

Claims

Interests

1. The method for monitoring the unbalanced current of the stator side of the hydro-generator rotor inter-turn short circuit is characterized by the following steps:

(1) According to the generator pole pairs, according to the formula

And according to the formula M=N X P, the number of sampling points of the basic data window is determined, where Τ is the length of the data window, Ρ is the pole logarithm, Μ is the number of sampling points of the basic data window, and Ν is the number of sampling points of the weekly wave;

(2) calculating a total effective value of the unbalanced current including the fundamental wave, each integer harmonic, and each fractional harmonic according to the data window length Τ;

(4) Subtracting the rms value of the unbalanced current of the fundamental wave, the third harmonic and the fifth harmonic by subtracting the total effective value of the unbalanced current from the discretization, and obtaining the total effective value of the fractional harmonic unbalance current;

(5) According to the calculated total harmonic value of the fractional harmonic unbalance current and the effective value of each fractional harmonic unbalance current, the inter-turn short circuit fault of the hydro-generator rotor is monitored.

2 . The method for monitoring unbalanced current of a stator-side short-circuit of a hydro-generator rotor according to claim 1 , wherein the step (2 ) calculates an imbalance balance including each harmonic by using a root mean square method. 3 . The current flow always has an effective value, §§ΡΡ _:: II -- , , of which

The unbalanced balance current flows away from the discrete sampled sample values, and ii _tt is the instantaneous instantaneous value of the current flow without unevenness. .

33. Root according to the rights and interests of the requirements of the 22 water water turbine generator motor rotor rotor inter-turn short-circuit short circuit stator side side non-unbalanced balance current flow The monitoring and monitoring method method, its special characteristics lies in, in the 歩歩((33)), the Fourier algorithm is used based on the basic basic data window. Calculate the non-uniform equilibrium balance current flow of each sub-fractional harmonic wave sum and base-base wave, three-three-order harmonic harmonic wave, and five-five harmonic harmonic wave Effective value, §§卩卩::

.real + 1 .imag where I^^ 'c .k^ I = -V[i _k -sin(nk-3⁄4] n is a natural number, ^^ is the real part of the n/P harmonic, I _n . _Iimg is the imaginary part of the n/P harmonic.

The unbalanced current monitoring method for a stator-side short-circuit of a hydro-generator rotor according to claim 3, wherein the method for calculating the total effective value of the fractional harmonic unbalance current is:

1 fault ring ^ Γ ^ 1∑' 1% ^A 3P / ^A 5P / where, the total rms value of the fractional harmonic unbalance current, is the total rms value of the unbalanced current including the fundamental wave and the like, which is discretized, 1 is the fundamental wave, I _{P /} is the third harmonic, and I ^ is the fifth harmonic