JPS5850085B2 - Protective relay method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protective relay system that performs protective operations by digitally converting analog quantities obtained from current transformers and voltage transformers in the event of a failure in a power transmission line, distribution line, bus transformer, etc. .

Conventionally, power system protection and control were generally carried out using analog amounts of current and voltage, but in recent years, due to increases in power transmission voltage and capacity, as well as longer distances for power transmission, it has become possible to use information from multiple electrical stations. Digital processing of voltage and current is effective for comprehensive protection control, and there is a trend toward the realization of this digital processing.

In view of this, it is an object of the present invention to provide a protective relay system that can perform protective operations by detecting voltage, current, phase angle, etc. using digital quantities in a short time and with highly accurate calculations. .

This will be explained below with reference to FIGS. 1 and 2.

FIG. 1 is for explaining the present invention in detail, and two alternating current electrical quantities a and b will be described as an example.

In Figure 1, the two electrical quantities are each a = As1nω
t b = Bs1n(0) t+θ) However, A and B are maximum values, and θ is the angle formed by a and b.

The digital quantity sampled at all times t1 is 22
, t)2, and if this is the second sampling digit amount, a 2 = As1nωt1 °----
−−°−(])b2=Bsin(ωt1+θ)・・・・
...It is expressed as (2).

Next, if the digital amount obtained by sampling at a sampling interval α before tl is the first sampling amount, and they are respectively designated as al and bl, the following is obtained.

a1=Asin(cc>tl-(X)-(3
)b 1= Bs1n (ωt1−α〇)・・・・・・
...(4) Also, the digital quantity obtained by sampling after the sampling interval α after tl is set as the third sampling digital quantity, and each is 23. l) If it is 3, it becomes as follows.

a3=As□.

(ωt1+α) ・・・・・・・・・ (5) b
3=Bsin(ωt1+θtenα) ・−・−・−(
6) Equation (3) - Equation (5) al-a3=A (sin(ωt1-α)-sin(ω
t1+α)−−2Acos(c) t sinα
・・・・・・・・・(7) Equation (4) - Equation (6) b 1-b3=B (sin(ωt, -α+θ)-si
n(ωt1+α+θ))=-2Bcos(ωt0+θ)
sin α ・・・・・・・・・(8) (1) formula × (2)
Formula a2X b2=ABsinωt16sin(ωt1+θ
)B m-(cosθ-cos(2ωt1+θ)) (9)
(7) Formula x (8) Formula (al a3)X(bl b3)""4ABS11]'
α(cosωt1”cos(ωt1+θ)) =2ABsin2α(cosθ+cos (2ωt1+θ))...(10) Multiply both sides of equation (9) by 4sin2α'4 a2 b2sin2α= 2AB 5in2α(
cosθ−cos(2ωt1+θ))・・・・・・・・・
・ 01) (10) Formula Juen type Ka2b2+(al-a3) (bl-b3)--A
B cos θ・(12) However, if K = 45in2α A/-, B/- one effective value, then VdVΣ Equation (12) is Ka2 b2+(al-a3) (bl-b3)=K
A'B' cos θ (13) Equation (13) subtracts the third sampling digital amount from the first sampling digital amount, multiplies it, multiplies it by the second sampling digital amount, and adds it. By doing (
13) As shown on the right side of the equation, it can be expressed by the effective value of two electrical quantities and the phase angle, and is a value that is independent of time t.

Note that K is a constant determined by the sampling interval α.

Furthermore, in equation (13), if a and b have exactly the same amount of electricity, a2=b2. a,=b,', a3=b3, so expression (13) can be expressed in terms of α as K a2”+
(al-33)2-A2, converting a single quantity of electricity, that is, the magnitude of voltage or current, into a value that is independent of time t,
A protective relay system that can determine the operation of a protective relay etc. can be obtained.

FIG. 2 shows an embodiment of the present invention based on the above principle, and the figure shows analog amounts of current and voltage obtained by the current transformer 2 and voltage transformer 3 provided on the power transmission line 1. A case of a direction discrimination relay method in which sampling is performed by analog digital converters 4 and 5, respectively, and analog digital conversion is performed to determine the direction of current with respect to voltage will be described.

The current obtained by the analog-to-digital converters 4 and 5
The voltages are 11+V1 for the first sampling digital amount and 12.V for the second sampling digital amount, respectively. V2, and the third sampling digital amount is 13tV3, the difference calculation circuit 6 in FIG. 2 calculates (1
113) and (V1V3), and the multiplier 10 calculates (113) and (V1V3).
t3) Find X(v1V3).

That is, the difference calculation circuit 6 is composed of two sets of shift registers and a subtracter for storing two samplings. For example, when the current sampling digital amount 11 is input, this i is stored in the shift register. It is also applied to the subtractor.

The subtracter inputs the input 11 and the digital quantity i3 two samplings ago, which was output from the shift register in response to the input of 11, and subtracts 11 by 13.

Voltage data ■1. (2) A similar difference calculation is performed on the third side and multiplied by the multiplier 10.

Furthermore, K X t 2
13) The following result expressed by equation 13) can be obtained.

K12v2+(il-i3)(vl-v3)=KIVc
osθ However, ■ is the effective value of the current ■ is the effective value of the voltage θ is the phase angle of the voltage and current By issuing a new command to the output terminal 11, it is possible to obtain a protective relay system that operates within a range of ±90° phase difference between voltage and current.

In this way, in the present invention, the AC difference is determined by the three sampling digital quantities, and after the third sampling, all (
13) If the formula holds and the fourth sampling digital quantity is found, a3b3+(a2-a4)(b2-b4)-ABCO3
All protective relaying methods protect transmission lines, distribution lines, busbars, etc. by knowing the magnitude of current, voltage, phase angle, etc. Needless to say, it can be applied to control, measurement, etc.

As described above, the present invention samples the instantaneous value of an electric quantity, converts it into a digital quantity, and performs arithmetic processing using this digital quantity. Based on equation (13), the voltage and current can be calculated using only three samplings of the digital quantity. Since the phase angle and the magnitude of the current are determined using direct current, calculation processing can be performed extremely stably in a short period of time.Moreover, this calculation requires only two multiplications and one subtraction, making the calculation simple. It is something.

In addition, the technical effects based on formula 03) are very limited, such as requiring less memory because it is only necessary to store the data for performing calculations on the sampling value two samples before the current sampling.

Therefore, according to the present invention, the capacity and distance of the power transmission system can be increased, and high-speed, high-precision protection that can sufficiently meet the accompanying demand for faster protection is possible.

[Brief explanation of drawings]

FIG. 1 is an AC waveform diagram for explaining the present invention in detail. FIG. 2 is a block diagram showing one embodiment of the present invention. 1 is a power transmission line, 6 is a difference calculation circuit, T, 10 is a multiplier, 8 is an adder, and 9 is a comparison judgment circuit.

Claims (1)

[Claims] 1. Current transformer and voltage transformer for detecting the electrical quantity of alternating voltage or alternating current. The analog quantity of alternating current voltage and current obtained from this transformer is sampled with a certain synchronized signal and converted from analog to digital. Analog-to-digital converter, voltage and current of each electrical quantity of three consecutive samples converted by this converter, current and current, voltage and voltage at the time of the second sampling of any combination of electrical quantity Means for calculating the product value and multiplying by a constant Means for subtracting the value at the time of the third sampling from the value at the time of the first sampling of each electric quantity for each of the combined electric quantities; By this means. Means for calculating the product value of the values obtained by subtracting the respective values; and means for adding the product value obtained by this means and the value obtained by multiplying the product value of the combined electrical quantities by a constant. Features a protective relay system.