CN102646958B - Asynchronous self-oscillating protection method and protection device of generator - Google Patents

Abstract

The invention provides an asynchronous self-oscillating protection method of a generator, comprising the following steps of: receiving a three-phase current signal of a current transformer at a machine end of the generator by an alternating current input plug-in; after carrying out analog-to-digital conversion on a signal received by the alternating current input plug-in, simultaneously using a fixed sampling frequency to collect the three-phase current signal at the machine end of the generator by a DSP (Digital Signal Processor) plug-in; carrying out low-pass filtering and band-pass filtering to obtain a signal with a sub-synchronous modal frequency; obtaining the sub-synchronous modal frequency by using a zero-crossing algorithm; adopting a Fourier calculation method of a variable data window to obtain an amplitude of a three-phase current sub-synchronous modal signal; and carrying out definite time lag and inverse time lag protection judgments by phases, so as to send out an alarming signal or a tripping signal to reflect asynchronous self-oscillating relay protection of overdosed sub-synchronous current in armature current of the generator. A CPU (Central Processing Unit) plug-in is responsible for functions of bottom layer driving software, bus control, communication, man-machine interaction treatment, message treatment, fault wave recording and the like. The whole device realizes the asynchronous self-oscillating protection of the generator.

Description

The asynchronous self-oscillation protection device of generator and guard method

Technical field

The present invention relates to field of power, relate more specifically to the asynchronous self-oscillatory protective relaying device of generator and guard method.

Background technology

Some large thermal power plants are away from load center, using long distance powedr transmission, and configure the equipment such as series capacitor compensation in transmission line of electricity, and direct current transportation mode is also used sometimes.When parameter coordination not at that time, may occur the asynchronous self-excitation magnetic phenomenon (referred to as asynchronous self-excitation) of generator, there is the electric current for the subsynchronous frequency for being slightly below synchronizing frequency (power frequency) in armature supply among generator unit stator winding, subsynchronous electric current can produce pulsating torque, make unit heating, vibration aggravation, can injury device when serious.Sub-synchronous oscillation frequency is mostly between 10Hz~45Hz.

Such as, China Inner Mongol Datang Tuoketuo Power Plant, installed capacity is 8 × 600MW, is delivered to Huiyuan transformer station through the loop line of support source four, then pacifies double loop, source through source and seizes by force double loop to Beijing-Tianjin-Tangshan Grid power transmission.8 sets of fixed capacity string benefits are mounted with the circuit of Huiyuan transformer station.Static block filter (SBF) is installed in the high-pressure side of generator main transformer.SBF is by one group of inductance, electric capacity mutually series-parallel circuit.In April, 2008, during Tuoketuo Power Plant carries out main transformer high-pressure side short circuit up-flow, because SBF parameters are improper, generating set occurs in that obvious asynchronous self-excitation, and electric current is in divergent trend, prevents generating set from being normally incorporated into the power networks.SBF design parameter is have adjusted afterwards, and after 2 years, SBF just formally puts into effect, and asynchronous self-excitation is inhibited.Equipment is damaged for the asynchronous self-excitation that prevents similar, asynchronous self-oscillation protection device should be installed.

For the asynchronous self-oscillation of generator, there is patent in the past《The method and monitor of monitoring subsynchronous oscillation of electrical power system》(ZL94100918.1) a kind of method is proposed, this method is extracted the subsynchronous component in transient power, be compared with the definite value of setting by measuring transient power, during more than definite value, alarm or tripping operation.The corresponding monitor of the Patent design simultaneously.The patent Shortcomings, the asynchronous self-excitation occurred during carrying out main transformer high-pressure side short circuit up-flow than Tuoketuo Power Plant as mentioned above, voltage very little during due to short circuit, transient power can not possibly be big, and this method is hard to work.In addition, being limited by technical conditions at that time, single CPU pattern is also simply employed on digital hardware circuits, reliability is not high.

The content of the invention

The purpose of the present invention is：Propose a kind of asynchronous self-oscillation relay protecting method for reflecting in generator armature electric current and there is excessive subsynchronous electric current.When there is asynchronous self-oscillation in generator, existing power frequency (50Hz) component in the three-phase current of generator unit stator winding, subsynchronous (10Hz~45Hz) component is included again, sometimes multiple subsynchronous components be may occur in which, the modal components of each subsynchronous component, referred to as respective frequencies.Relay protection is carried out to the asynchronous self-oscillation of subsynchronous electric current with this criterion.

The technical scheme is that：The asynchronous self-oscillation relay protecting method of generator, exchange input plug-in unit (AI) receives the current signal of generator generator terminal current transformer (CT)；After modulus (AD) conversion; DSP plug-in units gather the three-phase current signal of generator using fixed sampling frequency simultaneously; by LPF and bandpass filtering; obtain the signal of subsynchronous modal frequency; the frequency of subsynchronous mode is obtained using zero crossing algorithm; the amplitude of the subsynchronous mode signals of three-phase is obtained using the fourier computational methods of changing data window, split-phase is timed limit and inverse time-lag protection differentiates, sends alarm signal or trip signal；Signal output plug-in unit (DO) output alarm signal relay idle contact；Trip output inserter (TRIP_OUT) output tripping relay idle contact.Main CPU plug-in is responsible for the functions such as bottom layer driving software, bus marco, communication, man-machine dialogue system, Message processing, failure wave-recording.Whole device realizes the asynchronous self-oscillation protection of generator.Receive the three-phase current signal of generator generator terminal current transformer by exchange input plug-in unit；The signal that exchange input plug-in unit is received is after analog-to-digital conversion; gather the three-phase current signal of generator generator terminal using fixed sampling frequency simultaneously by DSP plug-in units; and pass through LPF and bandpass filtering; obtain the signal of subsynchronous modal frequency; the frequency of subsynchronous mode is obtained using zero crossing algorithm; the amplitude of the subsynchronous mode signals of three-phase current is obtained using the fourier computational methods of changing data window, split-phase is timed limit and inverse time-lag protection differentiates, sends alarm signal or trip signal.

Using the system configurations of " CPU+ two CSTRs ", the three-phase current signal of generator is gathered using fixed sampling frequency, only two pieces DSP determine asynchronous self-excitation simultaneously, just output alarm or trip signal.

Gather the three-phase current signal i of generator using fixed sampling frequency simultaneously using two blocks of DSP plug-in units_A、i_B、i_C, by low pass filtered waves 1 and bandpass filtering formula 2, obtain the signal i " of subsynchronous modal frequency_{M, A}、i″_{M, B}、i″_{M, C},

$\left[\begin{array}{c}{i^{\′}}_A\\ {i^{\′}}_B\\ {i^{\′}}_C\end{array}\right]=H_L\left(s\right)\left[\begin{array}{c}{i}_A\\ i_B\\ i_C\end{array}\right]$ Formula 1

$\begin{array}{cc}\left[\begin{array}{c}{i^{\′\′}}_{m,A}\\ {i^{\′\′}}_{m,B}\\ {i^{\′\′}}_{m,C}\end{array}\right]=H_{B,m}\left(s\right)\left[\begin{array}{c}{i^{\′}}_A\\ {i^{\′}}_B\\ {i^{\′}}_C\end{array}\right]& m=\mathrm{1,2},\·\·\·\end{array}$ Formula 2

Wherein, H_L(S) it is low pass filter, cut-off frequency is in the range of 43Hz~48Hz, and LPF parameter is fixed in the definite value of protection device, it is not necessary to adjusted；H_{B, m}(s) it is m-th of bandpass filter, bandpass filtering parameter is also secured in protection device, according to the demand of protected generator, it is determined that needing the number of high-order band-pass filterses.

Two blocks of DSP plug-in units handle the signal i " of subsynchronous modal frequency using zero crossing algorithm simultaneously_{M, A}、i″_{M, B}、i″_{M, C}, m=1 2 ..., draws signal i "_{M, A}、i″_{M, B}、i″_{M, C}Frequency, the frequency of phase current is averaged and is used as final modal frequency f_m；Then calculated using the fourier of changing data window and obtain subsynchronous mode signals i "_{M, A}、i″_{M, B}、i″_{M, C}Amplitude sequence I_{M, i}(n) with corresponding phasor

The formula that the fourier that uses is calculated for：

$\left\{\begin{array}{cc}{\stackrel{\→}{I}}_{m,i}\left(n\right)=g_m(a_{m,i}\left(n\right)-j\·b_{m,i}\left(n\right))& \\ I_{m,i}\left(n\right)=g_m\sqrt{a_{m,i}^2\left(n\right)+b_{m,i}^2\left(n\right)}& \\ a_{m,i}\left(n\right)=\frac{2}{N_m}\left[\underset{k=0}{\overset{N_m-1}{\mathrm{\Σ}}}{i^{\′\′}}_{m,i}(n-N_m+k)\cos (k\·\frac{2\mathrm{\π}}{N_m})\right]& i=A,B,C,m=\mathrm{1,2},\·\·\·\\ b_{m,i}\left(n\right)=\frac{2}{N_m}\left[\underset{k=0}{\overset{N_m-1}{\mathrm{\Σ}}}{i^{\′\′}}_{m,i}(n-N_m+k)\sin (k\·\frac{2\mathrm{\π}}{N_m})\right]& \\ N_m=\mathrm{round}(f_s/f_m)& \end{array}\right.$ Formula 3

Wherein, g_mFor gain correction coefficient, f_sFor protection device or the sample frequency of monitoring device, f_mFor subsynchronous modal frequency, N_mFor correspondence f_mData window length, I_{M, i}(n) be subsynchronous electric current amplitude sequence,Corresponding phasor, if before twice filtering cause signal attenuation, gain correction coefficient g is added in formula 3_m, amplitude rectification is carried out, correction coefficient is the function of modal frequency, is determined in advance by the amplitude versus frequency characte of wave filter.

The amplitude I of two blocks of DSP plug-in units simultaneously to calculating_{M, i}It is timed limit and inverse time-lag protection differentiates, criterion is：

Definite time-lag criterion：I_{M, i}＞ I_{Set, m}And t_{M, i}＞ t_{Set, m}Formula 4

Inverse time lag criterion： $t_{m,i}=\frac{80T_{p,m}}{I_{m,\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="HDA0000149517570000021.png"\; state="\{\{state\}\}">i</figure-callout>}}^2/I_n^2-1}$ And I_{M, i}＞ I_{Pk, m}And t_{M, i}＞ t_{Min, m}Formula 5

Wherein, I_{Set, m}For the specified time current ration of m-th of subsynchronous mode, span 0.1A~5.0A；t_mjAnd t_{Set, m}The time of respectively m-th subsynchronous mode and the definite time protection delay value of m-th of subsynchronous mode, t_{Set, m}0.01~60s of span；t_{Min, m}For the inverse time-lag protection minimum movements delay of m-th of subsynchronous mode, 0.01~60s of span；T_{P, m}For the time constant of the inverse time-lag protection of m-th of subsynchronous mode, 0.01~60s of span；I_{M, i}For the subsynchronous current amplitude calculated using formula 3；I_nFor rated current of generator value；I_{Pk, m}For the inverse time-lag protection current start value of m-th of subsynchronous mode, all current values are the sub-values of CT bis-.

1) result of logic discrimination is alarm or tripping operation；

2) alarm signal is exported, and two blocks of DSP plug-in units send out the result that alarming logic differentiates, pass through core bus, signal output plug-in unit is given by alarm signal, by signal output plug-in unit output alarm signal relay idle contact, if the result that two pieces of DSP differentiate is different, device locking output；

3) trip signal is exported, and two blocks of DSP plug-in units send out the result that Trip Logic differentiates, pass through core bus, tripping operation output inserter is given by trip signal, tripping relay idle contact is exported by tripping operation output inserter, if the result that two pieces of DSP differentiate is different, device locking output.

CPU card provides bottom layer driving software, possesses the control module of bus marco, communication, man-machine dialogue system, Message processing, failure wave-recording.

The asynchronous self-oscillation relay protection protection device of generator, including main CPU plug-in, exchange input plug-in unit (AI), two blocks of DSP plug-in units, modulus (AD) change-over circuit, one block signal output inserter (DO) and one piece of tripping operation output inserter (TRIP_OUT), wherein exchange input plug-in unit (AI) connects and receives the current signal of generator generator terminal current transformer (CT), two blocks of DSP plug-in units are followed by by modulus (AD) change-over circuit, two blocks of DSP plug-in units gather the three-phase current signal and low-pass filtered and bandpass filtering of generator using fixed sampling frequency, through zero crossing frequency measurement and Fourtier integral, carry out logic discrimination, two pieces of DSP plug-in units outputs of output signal connect signal output plug-in unit (DO) and tripping operation output inserter (TRIP_OUT).Alarm signal is connect signal output plug-in unit by the result that two blocks of DSP plug-in units differentiate alarming logic by core bus, by signal output plug-in unit output alarm signal relay idle contact, if the result that two pieces of DSP differentiate is different, device locking output.

The beneficial effects of the invention are as follows：By the LPF and bandpass filtering of high-order, the instantaneous value of subsynchronous mode electric current can be obtained；The amplitude and phasor of each mode signals can be accurately calculated using fourier algorithm, by specified time, inverse time over-current protection, the protection of the asynchronous self-excitation excitation of generator is realized.Protection device only needs to measure generator generator terminal three-phase current, and method is simple and reliable；While if there is asynchronous self-excitation during solving generating set short circuit experiment, the problem of transient power method fails；In addition, using the hardware configuration form of " CPU+ two CSTRs ", only two pieces DSP determine asynchronous self-excitation simultaneously, and just output alarm or trip signal, improve the reliability of protection device.

Brief description of the drawings

Fig. 1 is hardware system block diagram of the present invention.

Fig. 2 is the amplitude versus frequency characte figure for the 8 rank Chebyshev II type low pass filters that the present invention is designed.

Fig. 3 is the amplitude versus frequency characte figure for 28 rank Chebyshev II type bandpass filters that the present invention is designed.

Fig. 4 is present invention specified time, inverse time-lag protection logic chart.

In Fig. 1：

A. generator.

B. generator generator terminal threephase current transformer.

C. asynchronous self-oscillation protection device.

In Fig. 4：

A. the electric current decision logic element in formula 4, exports 1, otherwise exports 0 when condition is met.

B. " delay " logic element in formula 4, when input becomes 1 by 0, by the t that is delayed_setOutput 1, when input is constant or when being changed into 0 from 1 for 0, is output as 0.

C. definite time protection alarm or tripping operation result output.

D. the current start logic element in formula 5, exports 1, otherwise exports 0 when condition is met.

E. " delay " logic element related to current value in formula 5.Time t is determined by formula 5, is electric current I_{Eq, 2}Function.

When input becomes 1 by 0, timer starts timing, when delay reaches t, logic output 1；When input is constant or when being changed into 0 from 1 for 0, timer starts to successively decrease until for 0, now logic output 0.

F. the minimum time t in formula 5_min" delay " logic element.When input becomes 1 by 0, by the t that is delayed_minOutput 1, when input is constant or when being changed into 0 from 1 for 0, is output as 0.

G. AND gate operation logic.

H. inverse time-lag protection alarm or tripping operation result output.

Embodiment

(1) exchange input plug-in unit (AI).Generator generator terminal three-phase current is input to the exchange input plug-in unit (AI) of protection device, is then sent through by core bus on two blocks of DSP plug-in units after current transformer (CT) pick-up.

(2) current signal is sampled.Two blocks of DSP plug-in units carry out modulus (AD) to ac input signal simultaneously and changed, while using fixed sampling frequency, being sampled to generator generator terminal Current Transmit secondary side current, obtaining three-phase current i_A、i_B、i_C。

(3) LPF.LPF parameter is fixed in the definite value of protection device, it is not necessary to adjusted.Dsp chip calculation procedure calculates three-phase current, by i_A、i_B、i_CBy the LPF of a high-order, as a result for：

$\left[\begin{array}{c}{i^{\&prime;}}_A\\ {i^{\&prime;}}_B\\ {i^{\&prime;}}_C\end{array}\right]=H_L\left(s\right)\left[\begin{array}{c}{i}_A\\ i_B\\ i_C\end{array}\right]$ Formula 1

Wherein, H_L(s) it is low pass filter, cut-off frequency is in the range of 43Hz~48Hz.

(4) bandpass filtering.Bandpass filtering parameter is fixed in protection device.According to the demand of protected generator, it is determined that needing how many groups of high-order band-pass filterses, general 2~4, such as the subsynchronous electric current of two modal frequencies is only concerned, then need to only design 2 bandpass filters.Dsp chip calculation procedure further filters above-mentioned signal, obtains subsynchronous mode electric current：

$\begin{array}{cc}\left[\begin{array}{c}{i^{\&prime;\&prime;}}_{m,A}\\ {i^{\&prime;\&prime;}}_{m,B}\\ {i^{\&prime;\&prime;}}_{m,C}\end{array}\right]=H_{B,m}\left(s\right)\left[\begin{array}{c}{i^{\&prime;}}_A\\ {i^{\&prime;}}_B\\ {i^{\&prime;}}_C\end{array}\right]& m=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;\end{array}$ Formula 2

Wherein, H_{B, m}(S) it is m-th of bandpass filter.

(5) zero crossing frequency measurement and Fourtier integral：The signal obtained after above-mentioned processing is all the relatively good sine wave of sine degree.Signal i " can be calculated using zero crossing algorithm_{M, A}、i″_{M, B}、i″_{M, C}Frequency, the frequency of three-phase current averages as final modal frequency f_m.Dsp chip calculation procedure calculates subsynchronous mode signals i " using fourier algorithm_{M, A}、i″_{M, B}、i″_{M, C}Amplitude sequence I_{M, i}(n) with corresponding phasor

Obtain：

Formula 3

Wherein, g_mFor gain correction coefficient, f_sFor protection device or the sample frequency of monitoring device, f_mFor subsynchronous modal frequency, N_mFor correspondence f_mData window length, I_{M, i}(n) be subsynchronous electric current amplitude sequence,

It is corresponding phasor.Because above filtering is likely to cause signal attenuation twice, so adding gain correction coefficient g in formula 3_m, carry out amplitude rectification.Correction coefficient is the function of modal frequency, is determined in advance by the amplitude versus frequency characte of wave filter；

$\left\{\begin{array}{cc}{\stackrel{\&RightArrow;}{I}}_{m,i}\left(n\right)=g_m(a_{m,i}\left(n\right)-j\&CenterDot;b_{m,i}\left(n\right))& \\ I_{m,i}\left(n\right)=g_m\sqrt{a_{m,i}^2\left(n\right)+b_{m,i}^2\left(n\right)}& \\ a_{m,i}\left(n\right)=\frac{2}{N_m}\left[\underset{k=0}{\overset{N_m-1}{\mathrm{\&Sigma;}}}{i^{\&prime;\&prime;}}_{m,i}(n-N_m+k)\cos (k\&CenterDot;\frac{2\mathrm{\&pi;}}{N_m})\right]& i=A,B,C,m=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;\\ b_{m,i}\left(n\right)=\frac{2}{N_m}\left[\underset{k=0}{\overset{N_m-1}{\mathrm{\&Sigma;}}}{i^{\&prime;\&prime;}}_{m,i}(n-N_m+k)\sin (k\&CenterDot;\frac{2\mathrm{\&pi;}}{N_m})\right]& \\ N_m=\mathrm{round}(f_s/f_m)& \end{array}\right.$ Formula 4

(6) specified time and inverse time-lag protection of subsynchronous electric current differentiate, the amplitude I of two blocks of DSP plug-in units simultaneously to calculating_{M, i}It is timed limit and inverse time-lag protection differentiates, criterion is：

Definite time-lag criterion：I_{M, i}＞ I_{Set, m}And t_{M, i}＞ t_{Set, m}Formula 5

Inverse time lag criterion： $t_{m,i}=\frac{80T_{p,m}}{I_{m,\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="HDA0000149517570000021.png"\; state="\{\{state\}\}">i</figure-callout>}}^2/I_n^2-1}$ And I_{M, i}＞ I_{Pk, m}And t_{M, i}＞ t_{Min, m}Formula 6

Wherein, I_{Set, m}For the specified time current ration of m-th of subsynchronous mode, span 0.1A~5.0A；t_{Set, m}For the definite time protection delay of m-th of subsynchronous mode, 0.01~60s of span；t_{Min, m}For the inverse time-lag protection minimum movements delay of m-th of subsynchronous mode, 0.01~60s of span；T_{P, m}For the time constant of the inverse time-lag protection of m-th of subsynchronous mode, 0.01~60s of span；I_{M, i}For the subsynchronous current amplitude calculated using formula 3；I_nFor rated current of generator value, I_{Pk, m}For the inverse time-lag protection current start value of m-th of subsynchronous mode.All current values are the sub-values of CT bis-.

(7) result of logic discrimination can be alarm or tripping operation.

Alarm signal is exported, and two blocks of DSP plug-in units send out the result that alarming logic differentiates, by core bus, signal output plug-in unit (DO) are given by alarm signal, by signal output plug-in unit (DO) output alarm signal relay idle contact.If the result that two pieces of DSP differentiate is different, device locking output.

Trip signal is exported, two blocks of DSP plug-in units send out the result that Trip Logic differentiates, by core bus, tripping operation output inserter (TRIP_OUT) is given by trip signal, tripping relay idle contact is exported by tripping operation output inserter (TRIP_OUT).If the result that two pieces of DSP differentiate is different, device locking output.

(8) main CPU plug-in.Main CPU plug-in is responsible for the functions such as bottom layer driving software, bus marco, communication, man-machine dialogue system, Message processing, failure wave-recording.

The embodiment of the present invention：Design is a kind of to reflect in generator armature electric current asynchronous self-oscillation protective relaying device and the guard method that there is excessive subsynchronous electric current.With reference to the concrete condition of certain one 600MW steam turbine generator of power plant, illustrate the embodiment of this method.

The generating set is mounted with that static block filter SBF, SBF are some inductance and electric capacity mutually series-parallel circuit in main transformer high-pressure side.Field test shows, after SBF inputs, and the two subsynchronous modal components that frequency near 27.0Hz and 39.0Hz is included in asynchronous self-excitation phenomena, generator three-phase current once occurred in generator；Afterwards after adjustment SBF parameter, asynchronous self-excitation obtains a certain degree of suppression.To prevent asynchronous self-oscillation from damaging generating set, asynchronous self-oscillation protection device is installed.Specific method for convenience of description, it is assumed here that illustrated exemplified by the subsynchronous electric current for occurring in that the two modal frequencies of 27.0Hz and 39.0Hz.

Concrete scheme is as follows：

(1) core texture of protection device is " CPU+ two CSTRs "; there is one piece of CPU card; two blocks of DSP plug-in units; two blocks of DSP plug-in units carry out the calculating of subsynchronous electric current and the differentiation of relay protective scheme simultaneously; constitute " dual "; only two pieces DSP, which sentence, asynchronous self-oscillation, and protection device is just alarmed or tripped.Protection device further comprises exchange input plug-in unit (AI), signal output plug-in unit (DO) and tripping operation output inserter (TRIP_OUT).

(2) exchange input plug-in unit (AI) and current signal sampling.Generator generator terminal three-phase current is input to the exchange input plug-in unit (AI) of protection device, is then sent through by core bus on two blocks of DSP plug-in units after current transformer (CT) pick-up.Two blocks of DSP plug-in units carry out modulus (AD) to ac input signal simultaneously and changed, sampled simultaneously with fixed sampling frequency (being such as 1200Hz), generator generator terminal Current Transmit secondary side current is obtained, that is, obtains three-phase current signal i_A、i_B、i_C。

(3) LPF.Design a low pass filter H_L(s), its cut-off frequency is in the range of 43Hz~48Hz.The filter parameter that design is completed is fixed up as definite value, is stored in protection device.Here an example is given, using the Chebyshev II type low pass filters of 8 ranks, low pass filter H_L(s) transfer function is：

$H_L\left(s\right)=\left(\underset{i=0}{\overset{8}{\mathrm{\&Sigma;}}}{b}_i{s}^{(8-i)}\right)/\left(\underset{i=0}{\overset{8}{\mathrm{\&Sigma;}}}{a}_i{s}^{(8-i)}\right)$

Each parameter is in wave filter：

B0~b8 result (being represented with scientific notation) is respectively：0.01, -1.1910e-14,3.1583e4,4.3568e-9,1.5585e10,2.9148e-3,2.4612e15,2.9683e2,1.2145e20.

A0~a8 result (being represented with scientific notation) is respectively：1.0,1.5282e3,1.1680e6,5.8185e8,2.0770e11,5.4613e13,1.0651e16,1.4105e18,1.2145e20.

The parameter of low pass filter is unrelated with modal frequency, is fixed definite value.The amplitude versus frequency characte of wave filter is as shown in Figure 2.The pattern of wave filter is not limited to Chebyshev II types.Calculated by formula 1 and obtain filtered value i ' for the first time_A、i′_B、i′_C。

(4) bandpass filtering.For the two modal frequencies of 27.0Hz and 39.0Hz, 2 groups of high-order band-pass filterses are designed.The filter parameter that design is completed is fixed up as definite value, is stored in protection device.Here an example is given, the Chebyshev II type bandpass filters of 8 ranks are selected, form is：

The centre frequency of 2 groups of bandpass filters is respectively 27.0Hz and 39.0Hz, and specific filter parameter is as follows：

H_{B, 1}(s) parameter：

B0~b8 result (being represented with scientific notation) is respectively：0.01, -1.4043e-016,2.0466e3, -3.4929e-011,1.0471e8, -3.3800e-006,1.3394e12, -1.4832e-002,4.2829e15.

A0~a8 result (being represented with scientific notation) is respectively：1.0,152.84,1.1402e5,1.2258e7,4.5378e9,3.1359e11,7.4618e13,2.5588e15,4.2829e17.

H_{B, 2}(s) parameter：

B0~b8 result (being represented with scientific notation) is respectively：0.01,1.1199e-015,3.2972e3,2.5408e-010,3.2334e8,6.3763e-006,1.0656e13, -0.10984,1.0445e17.

A0~a8 result (being represented with scientific notation) is respectively：1.0,152.84,2.3909e5,2.6595e7,2.0733e10,1.5119e12,7.7268e14,2.8080e16,1.0445e19.

The pattern of wave filter is not limited to Chebyshev II types.The amplitude versus frequency characte of wave filter is as shown in Figure 3.Calculated by formula 2 and obtain two groups of subsynchronous current signals (m=1,2)：i″_{M, A}、i″_{M, B}、i″_{M, C}。

Sub-synchronous oscillation frequency can also be provided with the bandpass filter of other frequencies in 10Hz~27Hz.

(5) zero crossing frequency measurement is carried out to obtained subsynchronous current signal and fourier is calculated.

The signal obtained after above-mentioned processing is all the relatively good sine wave of sine degree.Modal frequency f can be calculated using zero crossing algorithm_m.Zero passage point methods frequency measurement：Measure sinusoidal waveform adjacent twice by the negative corresponding time span of zero crossing for becoming just (or being become just by negative), the inverse of time is exactly frequency, so as to obtain i "_{M, A}、i″_{M, B}、i″_{M, C}Frequency, three frequencies average as final modal frequency f_m.For a subsynchronous modal frequency, if there is a phase current signal too small in its three-phase current, it is not enough to accurately measure frequency, then takes the frequency of two-phase mode electric current to be averaged；Similar, if there is biphase current signal too small in its three-phase current, the frequency for taking the larger electric current of that remaining signal is frequency measurement result；If its three-phase current signal all very littles, the centre frequency (27.0Hz and 39.0Hz) of bandpass filter is taken as the measurement result of modal frequency.

If the 2 modal frequency respectively f measured_1,2=27.0Hz, 39.0Hz, the data window length for thus obtaining fourier calculating are N₁=round (1200Hz/27.0Hz)=round (44.4)=44, N₂=round (1200Hz/39.0Hz)=round (30.8)=31.

Subsynchronous mode signals i " is calculated using fourier algorithm (formula 3)_{M, A}、i″_{M, B}、i″_{M, C}Amplitude sequence I_{M, i}(n) with corresponding phasor

Wherein, because filtering causes signal attenuation twice, the gain correction coefficient g among formula 3 is also predefined_m.According to the result of measurement frequency, low pass filter and the corresponding amplitude versus frequency characte Fig. 2 and Fig. 3 of bandpass filter are looked into, signal is found and passes through the gain g filtered twice_L(f_m) and g_{B, m}(f_m), then modal frequency f₁=27.0Hz gain coefficient is：g₁=(1/1.0) × (1/1.0)=1.0, modal frequency f2=39.0Hz gain coefficient is：g₂=(1/0.8602) × (1/1.0)=1.1625.

(6) specified time and inverse time-lag protection of subsynchronous electric current differentiate.By each subsynchronous mode current amplitude I in each phase current of calculating_{M, i}Substitute into criterion formula 4 and formula 5.For example set forth herein：Definite value is identical under two subsynchronous modal frequencies, and specified time alarm setting value is I_{Set, 1}=I_{Set, 2}=0.18A, be delayed t_{Set, 1}=t_{Set, 2}=1.5s；Specified time trip rating is I_{Set, 1}=I_{Set, 2}=0.5A, is delayed as t_{Set, 1}=t_{Set, 2}=12s；Inverse time current initiation value is I_{Pk, 1}=I_{Pk, 2}=0.2A, inverse time lag time of fire alarming constant is T_{P, 1}=T_{P, 2}=0.05s, trip time inverse time lag constant is T_{P, 1}=T_{P, 2}=0.16s；Inverse time lag minimum movements delay is t_{Min, 1}=t_{Min, 2}=5s.In addition, rated current of generator I_n=3.5A (generator terminal CT two sub-values, CT no-load voltage ratio is 25kA/5A).After logic discrimination condition is met, corresponding warning mark or tripping operation mark are set to 1, are otherwise set to 0.

(7) alarm signal is exported.Two blocks of DSP plug-in units send out the result that alarming logic differentiates, by core bus, signal output plug-in unit (DO) are given by alarm signal, by signal output plug-in unit (DO) output alarm signal relay idle contact.If the result that two pieces of DSP differentiate is different, device locking output.

(8) trip signal is exported.Two blocks of DSP plug-in units send out the result that Trip Logic differentiates, by core bus, tripping operation output inserter (TRIP_OUT) is given by trip signal, tripping relay idle contact is exported by tripping operation output inserter (TRIP_OUT).If the result that two pieces of DSP differentiate is different, device locking output.

(9) function of protection device main CPU plug-in.Main CPU plug-in is responsible for the functions such as bottom layer driving software, bus marco, communication, man-machine dialogue system, Message processing, failure wave-recording.

Using the above method, you can the subsynchronous electric current of multiple mode in detection generator armature electric current, and realize the asynchronous self-oscillation protection of generator.

Claims (3)

1. the asynchronous self-oscillation relay protecting method of generator, it is characterized in that：Receive the current signal of generator generator terminal current transformer by exchange input plug-in unit；After analog-to-digital conversion; DSP plug-in units gather the three-phase current signal of generator using fixed sampling frequency simultaneously; by LPF and bandpass filtering; obtain subsynchronous mode signals; the frequency of subsynchronous mode signals is obtained using zero crossing algorithm; the amplitude of the subsynchronous mode signals of three-phase is obtained using the fourier computational methods of changing data window, split-phase is timed limit and inverse time-lag protection differentiates, sends alarm signal or trip signal；Using the system configurations of " CPU+ two CSTRs plug-in unit ", the three-phase current signal of generator is gathered using fixed sampling frequency, only two blocks DSP plug-in units determine asynchronous self-excitation simultaneously, just output alarm or trip signal；Two blocks of DSP plug-in units gather the three-phase current signal i of generator using fixed sampling frequency simultaneously_A、i_B、i_C, by low pass filtered waves 1 and bandpass filtering formula 2, obtain subsynchronous mode signals i "_m,A、i"_m,B、i"_m,C,

$\left[\begin{array}{c}{i^{\&prime;}}_A\\ {i^{\&prime;}}_B\\ {i^{\&prime;}}_C\end{array}\right]=H_L\left(s\right)\left[\begin{array}{c}{i}_A\\ i_B\\ i_C\end{array}\right]$ Formula 1

$\left[\begin{array}{c}{i^{\&prime;\&prime;}}_{m,A}\\ {i^{\&prime;\&prime;}}_{m,B}\\ {i^{\&prime;\&prime;}}_{m,C}\end{array}\right]=H_{B,m}\left(s\right)\left[\begin{array}{c}{i^{\&prime;}}_A\\ {i^{\&prime;}}_B\\ {i^{\&prime;}}_C\end{array}\right],m=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;$ Formula 2

Wherein, H_L(s) it is low pass filter, cut-off frequency is in the range of 43Hz~48Hz, and LPF parameter is fixed in the definite value of protection device, it is not necessary to adjusted；H_B,m(s) it is m-th of bandpass filter, bandpass filtering parameter is also secured in protection device, according to the demand of protected generator, it is determined that needing the number of bandpass filter；Two blocks of DSP plug-in units handle subsynchronous mode signals i " simultaneously using zero crossing algorithm_m,A、i"_m,B、i"_m,C, m=1,2 ... draws signal i "_m,A、i"_m,B、i"_m,CFrequency, and averaged as final subsynchronous mode signals frequency f_m：Then calculated using the fourier of changing data window and obtain subsynchronous mode signals i "_m,A、i"_m,B、i"_m,CAmplitude sequence I_m,i(n) with corresponding phasor

The formula that the fourier that uses is calculated for：

$\left\{\begin{array}{c}{\stackrel{\&RightArrow;}{I}}_{m,i}\left(n\right)=g_m(a_{m,i}\left(n\right)-j\&CenterDot;b_{m,i}\left(n\right))\\ I_{m,i}\left(n\right)=g_m\sqrt{a_{m,i}^2\left(n\right)+b_{m,i}^2\left(n\right)}\\ a_{m,i}\left(n\right)=\frac{2}{N_m}\left[\underset{k=0}{\overset{N_m-1}{\mathrm{\&Sigma;}}}{i^{\&prime;\&prime;}}_{m,i}(n-N_m+k)\cos (k\&CenterDot;\frac{2\mathrm{\&pi;}}{N_m})\right]\\ b_{m,i}\left(n\right)=\frac{2}{N_m}\left[\underset{k=0}{\overset{N_m-1}{\mathrm{\&Sigma;}}}{i^{\&prime;\&prime;}}_{m,i}(n-N_m+k)\sin (k\&CenterDot;\frac{2\mathrm{\&pi;}}{N_m})\right]\\ N_m=\mathrm{round}(f_s/f_m)\end{array}\right.i=A,B,C,m=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;$ Formula 3

Wherein, g_mFor gain correction coefficient, f_sFor the sample frequency of protection device, f_mFor subsynchronous mode signals frequency, N_mFor correspondence f_mData window length, I_m,i(n) it is subsynchronous mode signals amplitude sequence,

It is corresponding phasor, when above filtering causes to add gain correction coefficient g in signal attenuation, formula 3 twice_mAmplitude rectification is carried out, gain correction coefficient is the function of subsynchronous mode signals frequency, is determined in advance by the amplitude versus frequency characte of bandpass filter；

The amplitude I of two blocks of DSP plug-in units simultaneously to calculating_m,iIt is timed limit and inverse time-lag protection differentiates, criterion is：

Definite time-lag criterion：I_m,i＞ I_set,mAnd t_m,i＞ t_set,mFormula 4

Inverse time lag criterion：

And I_m,i＞ I_pk,mAnd t_m,i＞ t_min,mFormula 5

Wherein, I_set,mFor the specified time current ration of m-th of subsynchronous mode signals, span 0.1A~5.0A；t_set,mFor the definite time protection delay of m-th of subsynchronous mode signals, 0.01~60s of span；t_min,mFor the inverse time-lag protection minimum movements delay of m-th of subsynchronous mode signals, 0.01~60s of span；T_p,mFor the time constant of the inverse time-lag protection of m-th of subsynchronous mode signals, 0.01~60s of span；I_m,iFor the I calculated using formula 3_m,i(n)；I_nFor rated current of generator value；I_pk,mFor the inverse time-lag protection current start value of m-th of subsynchronous mode signals, all current values are the sub-values of CT bis-.

2. the asynchronous self-oscillation relay protecting method of generator as claimed in claim 1, it is characterized in that：

1）The result of logic discrimination is alarm or tripping operation；

2）Alarm signal is exported, and two blocks of DSP plug-in units send out the result that alarming logic differentiates, pass through core bus; signal output plug-in unit is given by alarm signal; by signal output plug-in unit output alarm signal relay idle contact, if the result that two pieces of DSP differentiate is different, protection device locking output；

3）Trip signal is exported, and two blocks of DSP plug-in units send out the result that Trip Logic differentiates, pass through core bus; tripping operation output inserter is given by trip signal; tripping relay idle contact is exported by tripping operation output inserter, if the result that two pieces of DSP differentiate is different, protection device locking output.

3. the asynchronous self-oscillation relay protecting method of generator as claimed in claim 1, it is characterized in that：CPU card is responsible for bottom layer driving software, bus marco, communication, man-machine dialogue system, Message processing, failure wave-recording function.

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