JPS5922446B2 - Protective relay device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protective relay device that protects a power system through digital processing.

Many proposals have been made for this type of protective relay device, but in the past, Kirchhoff's first law was applied to power transmission line protection, and changes in the sum of instantaneous values of data sampled at the same time at each electrical station were used. It was a so-called current differential system that controlled the circuit breaker.

However, if the power transmission line in the protected area is long distance, cable system, etc., the distribution constant of the line (inductance, ground capacitance C
etc.), the current waveform and voltage waveform at the power transmitting end and the power receiving end are different, and the current differential method has a limit in protection performance.

That is, when the power transmission line is a long distance, and an accident such as a short circuit occurs outside the protected area of the cable system, the inductance of the line and the resonance current due to the ground capacitance C cause the current waveform to include high-order harmonics.

Further, harmonics are generated from the propagation delay of the waveform determined by L, C and line length l.

For this reason, the current waveform at the transmitting end and that at the receiving end rarely match, and the current differential method, which simply compares the current waveforms at the transmitting end and the receiving end, can detect faults in power systems with high accuracy. was difficult.

Note that harmonics generated by resonance due to line inductance and ground capacitance C have no particular effect in internal faults, but in external faults most of the harmonics pass through the transmitting end and receiving end, so differential relays are There is no particular problem in this case.

The present invention has been made in view of the above-mentioned problems, and provides a protective relay device that compensates for the influence that harmonics generated due to line propagation delays have on current waveforms, and can highly accurately detect faults in power systems. It is something to do.

The protective relay device according to the present invention treats the transmission line in the self-protected section as a distributed constant circuit, mutually transmits and receives digital quantities sampled and converted at the same time at each electric station, and calculates the difference between the instantaneous values. Obtain the value at each sampling time, add these differential values with the differential value before the waveform propagation time τ to 2τ in the self-protection section, and use the minimum value of the added value as the control signal for the circuit breaker, or use the differential value as the control signal for the circuit breaker. A signal integrated over a 4τ interval is used as a control signal for the circuit breaker.

First, the principle of the protective relay device according to the present invention will be explained.

In Figure 1a, the distance from the transmitting end S to the receiving end R is 6 (m), and the inductance per unit length of the power transmission line is
As an LC distributed constant circuit with ground capacitance C, when expressed in the frequency domain by the Laplace operator S using four-terminal constants as the sending end voltage Vs, sending end current is, receiving end voltage ■R1 receiving end current iR, In the above formula, surge impedance Z and propagation time τ are 25
*, the above equations (1) and (2) become V S (S
) = cosh (S r ) V R (S) + Zsi
nh (ST) i R(S)”
・” ”・”・= ”・・・・(3) Here, if the receiving end is terminated with a resistor r, V R(S)−r i R(S) ・・・・・・
・・・・・・・・・From (5), the formula (5) is converted into (3),
Substituting into equation (4), Vs(S)=(rcosh
(Sr)+Zsinh(Sr月i□(S)・・・・・・
・・・・・・・・・・・・・・・(6)

By the above equations (6) and (7), i B(S) and 1R(
S) can be obtained by rearranging the above equations (8) and (9) from the hyperbolic sine and cosine formulas.

Here, when a step voltage of E is applied to the power transmission end S, since the step voltage E can be expressed as iE/S in the complex frequency domain, the above equations (10) and (11) are expressed as Vs(S).
When /S is substituted and rearranged, the sending end current is and the receiving end current iR become the following formulas.

Figure 1 shows that r-Oo in equation (12) and α3) above.
This diagram shows the temporal change in the propagation current when the power receiving end R is open. For i 3 (t) and i B (t), the above α2) and r-■ are substituted into equation (13). The calculations shown in Figure 1C are obtained.

As is clear from this figure, the sending end current 1s(t) is 4
It becomes a rectangular wave with a period of τ, and the receiving end current 1B(t) becomes zero.

Note that the current i 5(t
), t The waveform of B(t) can be obtained from equations (12) and (13) as follows.

When r-(9), r=■ in equations (12) and (13)
By substituting and rearranging, ■R(S)=0 ・・・・・・・・・・・・・・・
(15) According to the formula for inversely converting ■R(S) into the time domain, it becomes (C in Figure 1).

Similarly, when r=O, r=Z/3, and the respective time domain waveforms are as shown in FIGS. 2b and 3a.

Then, by sampling the waveform shown in Figure C at intervals of at least 2τ or less, and performing the differential value t5(t)-1R(t) for each sample value, the waveform shown in Figure 1D can be obtained. .

Similarly, FIG. 2a shows the temporal change of the propagation current when r=o, and the current increases with time.

In this case, i 5 (t) and i R (t) have step-like waveforms as shown in FIG.

Then, by sampling at intervals of at least τ and finding the differential value 1s(t)-iR(t), the waveform shown in C in the figure can be obtained as the differential value.

i R(t), and the differential value i 3(t)-
A waveform of i R(t) is obtained.

Furthermore, if we substitute various values for r, we get 1s(t).

1B(t) has a different waveform, but even in the case of collapse, the period of the differential value i3(t)-iB(t) is 2τ or 4τ.

Differential value i 5 (t) - i R (t) = i (t), and in Figure 1 d, 1 (t) + i (t - 2τ)3ξ
By adding (t)a, that is, the instantaneous value 2τ before the current time, with the current data, ξ(t)a can be obtained.

Moreover, in FIG. 2C, the differential value i (t) + i (
t −r ) ξ(t)b, that is, by adding the instantaneous value τ before the current time with the current data, ξ(t)
b can be set to 0.

Furthermore, in Figure 3, 1(t)+i (t-r
)Eξ(t) If we perform the calculation of b, 0.5■ will remain between 0<1≧r, but simply 1(t)=t 5(t) t
The differential value can be made smaller than when calculating B(t).

On the other hand, as is clear from the waveforms in Figure 1 d and Figure 2 C,
i (t
)−i 8(t) i□(1) If all of them are added, that is, an operation equivalent to interval integration is performed, the result will be almost zero.

Up to this point, transient phenomena have been described when direct current is applied to the line, but harmonics having periods of 2τ and 4τ are similarly superimposed on the current when an alternating voltage E=Vsinωt is applied.

Then, the instantaneous value differential value 1(t) of this AC waveform is τ, 2
Adding the differential value before τ or integrating the 4τ interval (
(addition), it is possible to reduce errors in differential values due to harmonics.

[For example, the transmission end current l5(S) in the case of r=0 at the alternating voltage V: E CO3ωt is as follows, and l3(t) in the time domain is as follows.

I 3(t)=f(t)+2 f(t-2r)+2
f (t −4r )+ ... The current I 5 (t) waveform for this alternating voltage is = 12×1O−2 (SeC
) and ω=2πf=100π, for example, the current s(τ) at t2τ becomes as shown in FIG. 6a.

The broken line in the figure indicates the receiving end current I R(t).

The difference between IB(t) and l8(t) becomes a rectangular wave as shown in FIG.

Similarly, the currents I 5 (t), I □ (t) and ξ (t) = I3 IB when r=■ are as shown in FIGS. 6c and d.

As is clear from the above explanation, the instantaneous differential value i (t
) is obtained, and this i (t) is given τ, and the instantaneous differential value i(
-τ) and 1(t-2τ), respectively, ξ(t)a,
By obtaining ξ(t)b and detecting the minimum value among them, the minimum error of the differential value is always obtained regardless of r shown in Figure 1a, and this signal is used as a breaker. By using a control signal of

In Figure 1 d1 Figure 2 C, ξ(t)a, ξ(t
) b becomes zero and becomes 0.75 for the first 4τ in Figure 3.
It can be made very small by further dividing 0.5I between I and the next 4τ.

Conversely, in the event of an internal accident, the differential value has a large commercial frequency component, and this period is 20m5 or 16.66m5,
For example, in a 200Km, 500Kv overhead line, τ is approximately 66
At 0 μs and 4τ, it becomes 2640 μS, and when integrating over a 4τ interval, there is no adverse effect of attenuating the commercial frequency even when obtaining ξ(t)a and ξ(t)b.

From the above theoretical explanation, the present invention is different from the conventional current differential method in which the control signal for the circuit breaker is obtained by simply finding the differential value of the instantaneous value. By adding the waveform propagation time τ and the previous differential value by 2τ and minimizing the differential value from these added values, the differential value in the event of an external fault can be reduced, so the minimum value is detected. or add the instantaneous differential values for a 4τ interval to use as the control signal for the breaker, to avoid large errors in the differential value due to harmonics generated by the propagation time τ of the current wave. prevent becoming.

FIG. 4 is a block diagram showing one embodiment of the present invention,
This is a case where the differential value 2τ before is added to the differential value.

At electric stations S and R, analog quantities of current obtained through current transformers 1s and 1R are sampled and converted into digital quantities at the same time by A-D converters 2s and 2R, respectively, and the obtained digital quantities are are transmitted and received between electrical stations S and R using optical cables 3s and 3R as transmission lines, respectively.

Here, the optical cable 3s, 3□ is used as the transmission line because
Since the present invention performs sampling at a relatively high frequency in order to remove harmonics, this is to be able to sufficiently cope with the increase in the amount of data transmitted and received at each end, and it is also possible to use a coaxial cable as an equivalent. can.

At the electric station S, the transmitted and received digital quantities are added by the instantaneous value difference current calculation circuit 4 (actually, the current transformers IS and IR are configured so that the current direction flowing into the section is positive as shown in Fig. 4). To connect, the polarities are opposite to each other, so subtract), and the instantaneous differential value 1(t) = i 3(t) -
i and fL(t), and add the differential value 1(t) to the differential value 1(t-2τ
), i(-τ), and the minimum value calculation/determination circuit 6 detects the minimum value among the outputs of the adder circuits 5a and 5b and compares and determines it with a certain level, thereby determining the breaker control signal. obtain.

Although not shown, there is also an instantaneous differential current circuit on the electric station R side.
It is equipped with an addition circuit and a minimum value calculation determination circuit.

Here, 7s and 7R28s shown by broken lines are low-pass filters.

In general power systems, as mentioned above, the self-protection interval τ
In addition to harmonics generated by Superimposed on the current.

Therefore, the low-pass filters 7s and 7R28s remove complex high-order harmonics from the current signal and improve the control accuracy of the circuit breaker.

Note that the low-pass filter 8s is composed of a digital filter.

FIG. 5 is a block diagram showing another embodiment of the present invention, in which integration is performed over a 4τ interval.

The difference between this figure and FIG. 4 is that the instantaneous value difference current calculation circuit 4
An integrator 9 integrates (adds) the instantaneous differential value i (t) over a 4τ interval, and a determination circuit 10 compares the integration result with a constant level to obtain a breaker control signal. At the point.

As explained above, according to the protective relay device according to the present invention, the difference between the instantaneous values of both digital values obtained from both electric stations and the instantaneous value before the propagation time τ, 2τ can be The minimum value of these values is used as a control signal, or the differential value of the instantaneous value is integrated (added) over a 4τ interval and used as a control signal. The differential value of the instantaneous value can be obtained by removing .

Furthermore, since a low-pass filter is provided for the detected analog or digital quantity, it is possible to prevent superimposition of high-order harmonics due to an accident outside the self-protection area, and it is possible to further improve control accuracy.

[Brief explanation of the drawing]

1 to 3 are diagrams for explaining the principle of the present invention, FIG. 4 is a block diagram showing one embodiment of the protective relay device according to the present invention, and FIG. 5 is a diagram showing another embodiment of the protective relay device according to the present invention. A block diagram showing an example, Fig. 6 shows the sending end current 1s(t) at an alternating voltage.
FIG. 3 is a diagram for explaining the receiving end current I B (t). S, R...Electric station, 181□...Current transformer, 2S2R...A-D converter, 3s, 3
R... Optical cable, 4... Instantaneous value difference current calculation circuit, 5a, 5b... Addition circuit, 6.
...Minimum value calculation judgment circuit, 7s. 7□, 88...Low pass filter, 9...
... Integrator, 10... Judgment circuit.

Claims (1)

[Scope of Claims] 1. Means for sampling the analog quantity of current obtained from the power system at the same time at each electric station and converting it into a digital quantity, and means for mutually transmitting and receiving the digital quantity between opposing electric stations. and the instantaneous difference between the digital quantity, which becomes the detected current flowing in the direction from the own electrical station toward the protected area, and the digital quantity, which becomes the detected current flowing in the direction towards the protected area, received from the opposing electrical station. 1 and 2 times the current wave propagation time determined by the differential value of the instantaneous value, the distance l of the self-protected section line, the inductance L per unit length, and the ground capacitance C. The circuit breaker is characterized by comprising means for adding the differential values of the instantaneous values from the previous time, and an output stage that detects the minimum value of the differential values of the added instantaneous values and uses it as a control signal for the circuit breaker. Protective relay device. 2. The protective relay device according to claim 1, wherein the analog amount of current obtained from the power system has high-order harmonics removed. 3. The protective relay device according to claim 1, wherein the digital quantity has high-order harmonics removed. 4. Means for sampling the analog amount of current obtained from the power system at the same time at each electric station and converting it into a digital amount, means for mutually transmitting and receiving the digital amount between opposing electric stations, and The differential value of the instantaneous value between the digital quantity, which becomes the detected current flowing in the direction toward the protected area, and the digital quantity, which becomes the detected current flowing in the direction flowing towards the protected area, received from the opposite electrical station. and the current wave propagation time determined by the distance l of the self-protection line, the inductance per unit length, and the ground capacitance C.
A protective relay device comprising: means for integrating a differential value of the instantaneous values obtained within twice the time; and means for controlling a breaker based on the differential value of the integrated instantaneous values. 5. The protective relay device according to claim 2, wherein the analog amount of current obtained from the power system has high-order harmonics removed. 6. The protection relay device according to claim 2, wherein the digital amount has high-order harmonics removed. Protective relay device as described.