JPS6051330B2 - Distance relay method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a distance relay method that determines the distance to a short circuit or ground fault point on a power transmission line by calculating the impedance of the power transmission line through digital processing of voltage and current.

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

Therefore, the protection provided at each electrical station is also required to be processed digitally. In view of the above points, the present invention aims to provide a distance relay system with a mho characteristic that can be processed digitally, and will be described below. FIG. 1 shows a waveform diagram a, a vector diagram b, and an RX diagram c for explaining the principle of the present invention. In Figure 1a, the current i obtained from the current transformer is expressed as (1) (2) (3) with a constant synchronized period ψ.
Sample and convert to digital as shown below. Now, if the digital quantity of the current i at the sampling point in (1) is i, and if the digital quantity after ψ from t1 is I2, then (ωt1+ψ) is the current time, and for example, the digital quantity one sample before, that is, after ω, is Subtract.

(2) - If equation (1) is set to i1, now ψ = 301 and substituting COS ψ -1 into Tan - 1100 - of equation (3), that is, 900 Ichi = 90 - (= 75 - advance) .

Further, in FIG. 1a, if the digital amount at the sampling point (3) is I3, then the digital value at the sampling point (1) is subtracted from the sampling point (3) as the current time.

Equation (4) - If equation (1) is i'', it is the same as calculating equation (3) above - As is clear from equations (3) and (5), pay attention to the phase angle - 1'' The first line of the hikidari is an angle dance.

. 8.

ψ1, (where n is a positive integer indicating the number of samples before the current time n = 1, 2, 3, etc.).
In other words, the current 1″ shown in equation (3) is the current current 12
It is the amount obtained by subtracting the current 11 from one sampling ago,
The current 1'' shown in equation (5) is the amount obtained by subtracting the current 11 two samplings ago from the current current 13, and has a characteristic angle 0 shown in FIG. 1c.

Depending on the case, this i'' may be used. Now to explain the case where n = 1, i'' is (90 degrees 1 ψ/
2) It advances by degrees, becoming i'' in Figure 1 a.

i'' is a constant determined by the settling impedance multiplied by K.
-1'', and this is expressed in the vector diagram shown in Figure 1b. If the voltage V1 and current 1 are now in the relationship as shown in Figure 1b, then subtract v from K-1'' and express this by the vector diagram shown in Figure 1b. -1″-v), and the angle between (K●i″-v) and v is 0″, and θ
It can be seen that if ''=90 degrees, the voltage v lies on a circle (indicated by a dotted line) whose diameter is K-1'' shown in FIG. 1b.

It can also be seen that the voltage v is inside a circle whose diameter is K-1'' (if θ'' is 90 degrees). That is, (K-1″-
Angle θ″-90 between the vector of voltage v) and the vector of voltage v
If it can be determined that 0≦θ″≦900, the relationship between current and voltage, that is, the relationship between impedance indicated by current and voltage, can be expressed as a circular characteristic with K as the diameter on the RX diagram shown in Figure 1-c. It can be defined as a Mo characteristic.
FIG. 2 is a waveform diagram for explaining the method for determining the angle 0'' formed by K.1''-V (5V). As Ki''-v=IO, v is I.

If it is assumed that there is a delay of θ″, then equation (6) holds true.

That is, the product of the digital quantity of the difference vector of K-1''-v and the digital quantity of voltage is I at sampling points 1, 2, and 3, respectively, shown in FIG.

Find lXVl and in 2 I. 2×V2 is I in 3.

Calculate each of 3X■3 and get the first product value 1.

The second product value 1 from 1×V1.

By multiplying and subtracting 2×V2 by a constant Y determined by the sampling interval ψ and adding the third product value 1 (0×V3) to the result, the result becomes the sampling interval ψ as shown in equation (6). and I.

It is expressed as the product of the constant R determined by the effective value of 5V and 1.
) By determining whether the result of the equation is positive or negative, it is determined that θ'' has an absolute value of 90 degrees or less when it is positive, and that θ'' has an absolute value of 90 degrees or more when it is negative.

Therefore, if the voltage V shown in Figure 1b is within a circle with a diameter of K-1'', the result of equation (6) is positive; otherwise, it is negative, and the R-X coordinate shown in Figure 1c is The Moh characteristic can be realized as shown above. Next, the establishment of equation (6) will be further explained.

The amount of alternating current J shown in Figure 2 now. , v are respectively A and b in order to generalize, and sampling point 2 is n1, sampling point 1 is n-1, and sampling point 3 is n+1, and each instantaneous value at arbitrary sampling points N, n-1, n+1. Set as below. However, A and B are effective values, θ is the delay angle of b with respect to a (θ'' shown in Figure 2), and ψ is the sampling angle. If equation (7) x equation (8) is Sn, then ~1~
'No (9) formula X (10) formula is set to Sn-1, (11
) Formula
4), Equation (15) will be organized by focusing on so COS (2ωt-θ).

From equation (13), by substituting equation (17) into equation (16), it becomes 1. If K'' is replaced with Y and KAB is replaced with R, equation (6), that is, (IOl x V1) - Y (IO2 x V2) +(1
03×V3)=RcOsθ″ is established.

FIG. 3 is a block diagram showing an embodiment of the present invention. Third
The example shown in the figure shows an example of subtracting the current 11 from one sampling ago, that is, the current current 12 shown in equation (3), where 1 is the power transmission line, 2 is the current transformer, and 3 indicates a voltage transformer. The current 11 voltage VL obtained in each transformer is converted into digital quantities by 4 and 5 analog-to-digital converters. The current, which has become a digital quantity, is subtracted by the digital quantity before the saw constant, that is, one sampling ago in this example, from the current digital quantity by a difference calculation circuit 6 to obtain a current 1'' which is more advanced than the current 1, and is then converted to i by a multiplier 7. '' is multiplied by a constant (K) determined by the settling impedance. Multiplication circuit 7 by subtraction circuit 8
Subtract the digital quantity of voltage from the result obtained, and get the product,
The arithmetic circuit 9 that performs difference and sum calculations performs the product, difference, and sum of equation (6), and the positive/negative discrimination circuit 10 determines the results of the product, difference, and sum, and when it is positive. It outputs an output and gives a command to trip the circuit breaker, etc. As described above, the present invention samples instantaneous values of voltage and current and converts them into digital quantities.
Create a current that advances the converted current by a certain angle, multiply it by an integer, subtract the digital amount of voltage from this digital amount, and calculate the digital amount of only 3 samplings based on equation (6) when performing calculation processing. Since a distance relay with Moh characteristics can be obtained by calculation, the calculation can be performed extremely stably in a short time, and this calculation requires only three multiplications and one addition/subtraction each. The good news is that calculations are simple.

In addition, the technical effects based on equation (6) are great, such as the need to memorize only the two sampling values before the current sampling as data for calculation, which reduces the number of electronic inputs. . As described above, in the present invention, after digitally converting the current and voltage, i'', which is more advanced than the current, is determined in 2 to 3 samplings, and after i'' is determined, the distance to the fault point on the power transmission line or the like is determined in 3 samplings.

Generally, if the sampling interval ψ is about 15 degrees, it is 5ms.
It is possible to realize a distance relay system that is capable of extremely high-speed operation and can locate the fault point within a short period of time.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram, a vector diagram, and an RX diagram for explaining the principle of the present invention.

Claims (1)

[Claims] 1. An analog-to-digital converter that samples the analog quantities of current and voltage obtained from the current transformer and voltage transformer installed on the power transmission line at a constant synchronized period ψ/ω and converts them into digital quantities, and the current Difference calculation means for subtracting the current digital amount of current from the current digital amount n sampling periods (n is a positive integer) output from an analog-to-digital converter for converting the amount, and the output of this difference calculation means. introducing a multiplication means for multiplying the value by a constant determined by a setting impedance, and a digital quantity of the voltage converted by an analog-to-digital converter for converting the output value of the multiplication means and the voltage quantity, respectively; A subtraction means for subtracting the digital quantity of voltage from the multiplied value, and a digital quantity of the vector of difference obtained by this subtraction means and the digital quantity of the voltage are respectively introduced to calculate the product value for each sampling. The constant 2cos2ψ is calculated from the first product value of the sampling point to the second product value of the sampling point.
a calculation means for subtracting the multiplied value of , and adding the product value of the third sampling point to this value; and a positive/negative determining means for determining whether the output value of the calculation means is positive or negative depending on whether it is inside or outside the setting impedance. A distance relay method characterized by the following.