JPS6245774B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital distance relay that protects a power system based on instantaneous value information of current and voltage in the power system sampled at regular time intervals.

Conventionally, digital distance relays protect power systems based on instantaneous value information of current and voltage in the power system sampled at regular time intervals, as shown in Figure 1. Instantaneous value information v(t) at time t obtained by
=Vsin(ωt+θ), i(t)Z〓 ₀ =IZ ₀ sin(ω
t+θ ₀ ), find {i(t)Z〓 ₀ −v(t)}i(t)Z〓 ₀ . However, V and I are the absolute values of voltage and current,
ωt is the angular velocity, θ is the phase difference, θ ₀ is the characteristic angle, Z〓 ₀
is the set value of the vector quantity.

Calculating this, I ² Z ² ₀ sin ² (ωt+θ ₀ )−
I ² ZZ ₀ sin(ωt+θ) sin(ωt+θ ₀ ).
However, Z=V/I.

In the above equation, if we set θ = θ ₀ = 90 degrees and further take into account the effect of the filter and remove the variable term, we get:
Since it is on the characteristic angle, using the scalar values V and I of voltage and current information, {i(t)Z〓 ₀ −v(t)}i(t)Z〓 ₀ = (IZ ₀ −V)IZ ₀ ...(1). However, Z ₀ is the absolute value of the integer value of the Bertol quantity. Based on this equation (1), the operating range is determined by the following equation. In other words, equation (1) is an appropriate scalar value ΔV
It shall operate when greater.

(IZ ₀ −V) IZ ₀ ≧ΔV (2) Furthermore, from equation (2), IZ ₀ −V≧ΔV′ (3) holds true. Here, it is assumed that ΔV'=ΔV/IZ ₀ .
Next, the absolute value of impedance up to the fault point is Z
Then, from V=IZ...(4), the operating range becomes Z≦Z ₀ −ΔV'/I...(5), and this operating range is expressed by the absolute value I of the current on the horizontal axis and the impedance Z on the vertical axis. If we take , it is expressed as shown in Figure 2. The distance relay should operate when the impedance Z is smaller than Z ₀ , but as shown in FIG. 2, in reality, an incomplete operating range occurs in a range where the current is small. However, due to quantization errors that occur when current and voltage, which are power system information, are digitized, variations occur in the operating range. This variation is expressed as follows.
The calculated value Z is Z=V/I=V ₀ ±α/I ₀ ±β ...(6) Here, V ₀ and I ₀ are the true values of voltage and current, α and β
is the quantization error of voltage and current. Minimum value of Z
Since _nio is obtained when the numerator is the minimum and the denominator is the maximum, Z _nio = V ₀ - α / I ₀ + β ... (7) The maximum value of Z Z _nax is obtained when the numerator is the maximum and the denominator is the minimum Since Z _nax =V ₀ +α/I ₀ −β (8), the range of variation is between Z _nio and Z _nax .
If these are considered in the results shown in FIG. 2, the result will be as shown in FIG. 3, and the operation within the variation range will not be determined. For this reason, in the conventional system, when the number of bits for digitizing voltage and current is determined, the limit of the characteristics is determined, and a significant improvement in characteristics cannot be expected. Therefore, it is an object of the present invention to propose a method for significantly improving characteristics without increasing the number of bits during digitization.

In the present invention, as shown in the following equation, a correction term −Z ² ₀ 2I _B |I|−Z ² ₀ I ² _B +Z ₀ |V|2
I _B +
Z ₀ I ² _B |V|/|I| is set as equation (9).

(Z ₀ I−V) Z ₀ I≧ΔV−Z ² ₀ 2I _B |I|−Z ² ₀ I ² _B +Z ₀ |V|2I _B +Z ₀ I ² _B |V|/|I| ……( 9) Here, I _B is a constant and this equation is expressed as an effective value: Z ² ₀ I ² −VZ ₀ I≧ΔV−Z ² ₀ 2Z ₀ I _B I−Z ² ₀ I ² _B +Z ₀ V・2I _B +Z ₀ I ² _B V/I...(10) The above equation can be expressed as follows.

Z ² ₀ (I ² + 2II _B + I ² _B ) - Z ₀ V/I (I ² + 2 I _B I + I ² _B B) ≧ ΔV ...... (11) Z ² ₀ (I + I _B ) ² - Z ₀ V/I ( I+I _B ) ² ≧ΔV… (12) {Z ₀ (I+I _B )−V/I(I+I _B )}Z ₀ (I+I _B )≧ΔV …(13) Expressing this as, and finding the operating range, we get { Z ₀ (I+I _B )−V/I(I+I _B )}≧ΔV″…(14
) Here, ΔV″=ΔV/Z ₀ (I+I _B ).Furthermore, if we set Z ₀ −V/I≧ΔV″/Z ₀ (I+I _B ) ……(15) V/I=Z, Z≦Z ₀ −ΔV''/Z ₀ (I+I _B )...(16) In other words, the operating range at this time is expressed as shown in Figure 4, and the characteristics in Figure 2 are subtracted by I _B. This is a characteristic shifted to the left.The actual characteristic only exists in the range I>0, and the performance is greatly improved compared to the conventional characteristic shown in Fig. 2.In actual processing, Equation (13) is set as (Z ₀ I-V)Z ₀ I≧I ² /(I+I _B ) ² ΔV (17), and compared to the conventional method, I ² and (I+I _B ) ² are calculated. In addition, only the process of calculating I ² /(I+I _B ) ² is added, and the increase in processing time is slight.The explanation so far has been based on the example of the characteristic angle, but the characteristic angle In other cases, formula (2) can be expressed as {IZ ₀ −Vcos (θ−θ ₀ )}IZ ₀ ≧ΔV (18) By using the same idea as in the case of characteristic angles, formula (17) can be obtained. can be expressed as {IZ ₀ −Vcos(θ−θ ₀ )}Z ₀ I≧I ² /(I+I _B ) ² ΔV (19).

As described above, it can be handled in the same way regardless of the characteristic angle and impedance angle.

FIG. 5 shows a schematic block diagram. Block 11
The current instantaneous value information i(t) is multiplied by Z ₀ in block 12, the voltage instantaneous value information v(t) is subtracted from the output of block 11, and the block 13 is multiplied by Z0.
In block 14, the output of block 13 is multiplied by a certain number, and
Find (IZ ₀ - V) IZ ₀ . Block 15 calculates the square of instantaneous current value information i(t), and block 16
Then, the output of block 15 is integrated by a certain number. In block 17, a constant number of instantaneous current value information i(t) is added, in block 17, the output of block 23 and a constant number I _B are added, in block 18, the output of block 17 is squared, and in block 19, The output of block 18 is integrated by a constant number. Block 2
At 0, the output of block 16 is divided by the output of block 19. In block 21, the output of block 20 is multiplied by .DELTA.V, and in block 22, the output of block 21 is subtracted from the output of block 14, and if the result is positive, it is activated, and if it is negative, it is inactivated.

By adding this processing, the number of bits for digitizing power systems and the characteristics of distance relays, which were determined in principle, can be improved without installing any external equipment in the conventional method, and the economic effect is extremely large. .

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of a distance relay, Fig. 2 is an explanatory diagram of the principle operation of the conventional system, Fig. 3 is an explanatory diagram of the variation width during digitization, and Fig. 4 is an explanatory diagram of the characteristics of the present application. Figure 5 shows a schematic block diagram. 11...Multiplication section, 12...Subtraction section, 13...Product operation section, 14...Filter, 15...Square operation section, 16...Filter, 17...Addition section, 18...
. . . square calculation section, 19 . . . filter, 20 . . . division section, 21 . . . multiplication section, 22 .

Claims (1)

[Claims] 1 In a method for protecting the power system using power system information sampled at fixed time intervals, the first method involves storing a certain number of current sampling values and multiplying the stored sampling values by a certain number.
means for subtracting the sampling value of the voltage from the output of the first means, and third means for multiplying the output of the first means by the second means, and for keeping the output of the third means constant. a fourth means for adding a number, a fifth means for squaring the sampled value of the current, a sixth means for adding the output of the fifth means by a fixed number, and a fixed number for adding the sampled value of the current. a seventh means; an eighth means for squaring the output of the seventh means; a ninth means for adding the output of the eighth means by a fixed number; a tenth means for dividing by the output of the means; an eleventh means for multiplying the output of the tenth means by a constant number; and a twelfth means for subtracting the output of the eleventh means from the output of the fourth means; This digital distance relay is characterized in that it is determined to be operating if the output of the 12 means is positive, and non-operating if it is negative.