CN1154219C - Earthing protection method for stator of power generator - Google Patents

Abstract

The present invention relates to a stator earthing protection method for a generator. An earthing resistor at the secondary side of an earthing transformer is connected with an electric reactor in parallel, resonance frequency signals are sent to the electric reactor, or the resonance frequency signals are sent from a voltage inductor in an extinguishing coil, the voltage /current ratio of the signals are measured, and then, the method carries out protection. When resonance frequency f<i> is close to industrial frequency, signals of 0.7 f<i> to 0.95 f<i> or 1.05 f<i> to 1.3 f<i> are sent, the voltage and current phase difference of the signals is measured, and the method carries out the protection. Stator windings always compensate an earthing capacitor, and the protection sensitivity is enhanced. The method is suitable for large hydraulic generator stator earthing protection and is suitable for rotor earthing protection.

Description

Earthing protection method for stator of power generator

Technical field

The present invention relates to the not directly ground connection generator stator ground protection of relay protection of power system technology, particularly neutral point.

Background technology

Generator accounts for more than 60% of generator failure due to earth fault, and the stator grounding fault as untimely removing, may cause the fault of other types, and directly influence the safe operation of generator after taking place.The domestic and international at present double frequency type residual voltage stator ground fault protection of developing; the power frequency residual voltage and the triple-frequency harmonics residual voltage that adopt generator itself to produce; has the certain protection function; but be subjected to the influence of stator winding direct-to-ground capacitance, be difficult to satisfy the requirement of high-rating generator stator high sensitivity ground protection.Authors such as Zhou Qiang are in Automation of Electric Systems 1999; in 23 (11) 22～25 " the Three Gorges Left Bank Hydropower Station generator one transformer group resist technology schemes " literary composition; introduce to adopt and directly inject constant frequency signal, measurement signal voltages, electric current and power etc. carry out the method for ground protection.But neutral point is through the high resistance ground generator, injecting signal during fault-free directly flows back to through the stator winding direct-to-ground capacitance, when earth fault takes place, with respect to injecting signal frequency, the stator winding capacitance to earth is less than earth resistance, inject the signal major part and still flow back to, have only a very little part to flow back to by fault resstance by the stator winding direct-to-ground capacitance.Owing to influenced by the stator winding direct-to-ground capacitance, during high resistance earthing fault, signal code, voltage and measurement impedance variation are less, are difficult to detect.The neutral by arc extinction coil grounding generator, owing to adopt the low frequency or the high-frequency signal that inject constant frequency, signal frequency is away from the generator resonance frequency, and with respect to injecting signal, arc suppression coil induction reactance or less than half of stator winding capacitance to earth, or surpass the twice of stator winding capacitance to earth.Be subjected to this generator unit stator winding-to-earth capacity influence equally, during high resistance earthing fault, signal code, voltage and measurement impedance variation are less, are difficult to detect, and do not satisfy the requirement of high-rating generator high resistance earthing protecting.

Summary of the invention

The purpose of this invention is to provide a kind of earthing protection method for stator of power generator, neutral point adopts through the high resistance ground generator and adds reactor compensation stator capacitance current, and injects resonant frequency signal; To be convenient for measuring relevant data, improve generator stator ground protection sensitivity.

A kind of earthing protection method for stator of power generator of the present invention, stator winding neutral point inject low frequency signal through high resistance ground on grounding transformer secondary side and earth resistance thereof, it is characterized by:

(1) reactor in parallel on the described grounding transformer secondary side earth resistance, its inductance value is

$L=\frac{1}{{3W_s^2\mathrm{CN}}^2}$

Wherein N is the grounding transformer no-load voltage ratio, and C is the single-phase stator winding-to-earth capacity, W _sBe injection signal angular frequency,

(2) inject low frequency signal from the earth resistance two ends, its angular frequency is W _s,

(3) measure described reactor two ends and inject the voltage U that signal produces _BAnd the signal code I of injection grounding transformer secondary side and described reactor _i,

(4) calculate stator winding resistance to earth R _f

$L=\frac{1}{{{3W}_s}^2{\mathrm{CN}}^2}$

Work as R _fLess than setting value R _SetThe time, the circuit protection mechanism action.

Described earthing protection method for stator of power generator, it further is characterized as: described injection low frequency signal frequency f _s=10～40Hz is behind the described reactor in parallel, with adaptive mode fine setting f _sNumerical value, the feasible U that measures _BAnd I _iPhase place is consistent, to guarantee

$L=\frac{1}{{3W_s^2\mathrm{CN}}^2}$ Equation is set up

The present invention adopts and adds reactor compensation stator winding capacitance to earth; and follow the tracks of the ageing of insulation of stator winding, the variation of direct-to-ground capacitance; adjust and inject signal frequency; the stator winding capacitance to earth is compensated all the time; eliminate or weaken of the influence of stator winding direct-to-ground capacitance greatly signal measurement; improved generator stator ground protection sensitivity, be particularly useful for large-sized water turbine generator stator winding high resistance earthing protecting, also protected applicable to generator rotor ground.

Description of drawings

Fig. 1 injects signal ground guard method wiring schematic diagram for the stator winding neutral point adds reactance through the high resistance ground generator.

Fig. 2 is the equivalent electric circuit of Fig. 1.

Embodiment

Below in conjunction with accompanying drawing method of the present invention is further specified.

Among Fig. 1 and Fig. 2, stator winding A, B, C phase neutral point are through grounding transformer D ground connection, and for remedying the influence of stator winding direct-to-ground capacitance 3C, at grounding transformer D secondary side earth resistance Ro two ends parallel connection one reactor L, its inductance value size is:

$L=\frac{1}{{3W_s^2\mathrm{CN}}^2}=\frac{1}{{12\mathrm{\&pi;}}^2{f_s^2\mathrm{CN}}^2}----\left(1\right)$

Wherein 3C is the stator winding direct-to-ground capacitance, W _sFor injecting signal angular frequency, f _sFor injecting signal frequency, N is the grounding transformer no-load voltage ratio.By signal source E _sInject signal, its frequency range f _s=10～40Hz is with respect to power frequency component (f ₀=50Hz), add the induction reactance of reactor and the ratio of stator winding capacitance to earth:

$\frac{X_L}{X_C}={3N}^2{W}_0^2\mathrm{LC}=\frac{W_0^2}{W_s^2}=\frac{f_0^2}{f_s^2}-----\left(2\right)$

Found out by (2) formula: it is low more to inject signal frequency, and the two ratio is big more, and it is more little to the influence of the normal operation of system to add reactor.Consider signal source making, reactor choose common desirable injection signal frequency f _sBe 10～20Hz.Stator winding loop resistance to earth R _fCan measure the L two ends through divider resistance R by computer CPU and inject the voltage U that signal produces _B, measure injection current I through current transformer TA _i, through calculating:

$R_f=N^2\frac{U_B}{I_i}-------\left(3\right)$

Among Fig. 2, R _eBe signal source E _sInternal resistance, 3C is the stator winding direct-to-ground capacitance, other identify same Fig. 1.

Claims (2)

1. earthing protection method for stator of power generator, the stator winding neutral point injects low frequency signal through high resistance ground on grounding transformer secondary side and earth resistance thereof, it is characterized by:

(1) reactor in parallel on the described grounding transformer secondary side earth resistance, its inductance value is

$L=\frac{1}{3W_s^{2}C{N}^2}$

Wherein N is the grounding transformer no-load voltage ratio, and C is the single-phase stator winding-to-earth capacity, W _sBe injection signal angular frequency,

(2) inject low frequency signal from the earth resistance two ends, its angular frequency is W _s,

(3) measure described reactor two ends and inject the voltage U that signal produces _BAnd the signal code I of injection grounding transformer secondary side and described reactor _i,

(4) calculate stator winding resistance to earth R _f

$R_f=N^2\frac{U_B}{I_i}$

Work as R _fLess than setting value R _SetThe time, the circuit protection mechanism action.

2. earthing protection method for stator of power generator as claimed in claim 1 is characterized by: described injection low frequency signal frequency f _s=10～40Hz is behind the described reactor in parallel, with adaptive mode fine setting f _sNumerical value, the feasible U that measures _BAnd I _iPhase place is consistent, to guarantee

$L=\frac{1}{3W_s^2{\mathrm{CN}}^2}$ Equation is set up.

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