JPS6218917A - Distance relay - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a distance relay, and particularly to a distance relay using a distance measurement method based on differential equations.

[Technical background of the invention]

In recent power grid failure phenomena, waveform distortion of voltage and current increases,
In addition, distortion components tend to be of lower order. In conventional distance relays that focus on steady state impedance,
It is expected that application will become difficult due to problems such as an increase in distance measurement errors due to distortion components and a delay in operating speed due to the filter used to sufficiently remove the distortion. As an example of this type of device, the one shown in Japanese Patent Application No. 144988/1988 has been proposed.

As a distance measurement method for a distance relay using a microcomputer, the transmission line voltage υ, current i, and resistance R1 are
A method using a differential equation that holds true between the inductance L has been proposed, but since equation (1) holds true even in a transient state during a system failure, it is important to improve the characteristics of distance relays with respect to waveform distortion. is possible.

The principle of the distance measurement method based on differential equations is to obtain the L value and R value from equation (1), but it is necessary to solve simultaneous equations in order to obtain the two unknowns. That is, at different times t and t, m
n υ□, im holds the relationship between the voltage and current values at time trn, but if the L and R values are constant within the time under consideration, equation (2) can be solved as simultaneous equations, and (3 )
The L and R values are determined as shown in the formula.

As is well known, when a system failure occurs, the L and R values become values that correspond to the system impedance up to the failure point, so it is possible to determine whether the failure point is internal or external based on the result of equation (3).

Here, the differential value j of the current can be determined by hardware, but it can also be calculated from the current value by software. - As an example, an approximate equation for obtaining the current differential value is shown in equation (4).

Gradient ΣKk (i to 'm- to -1) ・・・・・・
(4) However, N p Kk (k −0 − N) is a constant, and at least KoNO, 40 According to equation (4), the approximation error becomes zero at p at least at two frequencies, and Since the error in frequency can also be reduced, it becomes possible to calculate the L and R values using approximate expressions over a wide frequency range.

Note that in equation (4), the differential value J is obtained as the sum of the current differential values at times tm and tm-1, which differ by one sampling time, so the equations for calculating the L and R values are modified as follows.

That is, if we set the formula (2) here, the L value and the R value can be obtained from the following formula (7).

FIG. 3 is a hardware configuration diagram of the distance relay. Third
In the figure, 1 is the power transmission line to be protected, 2 is the transformer, and 3
1 is a current transformer, 4 and 5 are input converters, 6 is an analog/digital conversion circuit (conversion circuit), and 7 is an arithmetic processing section. In this case, the system voltage is introduced via the transformer 2, converted to an appropriate voltage level by the input converter 4, and then passed through a pre-filter to obtain the output υ. Similarly, the system current is transferred to current transformer 3.
The data are sampled simultaneously at intervals, sequentially converted into digital quantities, and processed by an arithmetic processing unit 7 consisting of a microcomputer.
is input.

FIG. 4 is a functional block diagram showing the processing contents in the arithmetic processing section 7. As shown in FIG. In FIG. 4, reference numeral 8 denotes a current differential calculating means which calculates the current differential amount J from the input current data, as shown in equation (4) above, for example. Reference numeral 9 denotes a current calculation means, and reference numeral 10 denotes a voltage calculation means, each of which performs the calculation shown in equation (6) to obtain a current tI and a voltage amount V. 11 is a denominator value calculation means for the L and R value calculation formula shown in formula (7), and the denominator value U□-ImJ
n-InJm is obtained.

12 is a numerator value calculation means in the L value calculation formula of equation (7) to obtain the numerator value tn1−■rnvn−Invm, and 13 is a common value calculation means in the R value calculation formula to obtain the numerator value. Obtain rm-vmJn-vnJm. Reference numeral 14 denotes an L value calculation means that calculates the L value by dividing the denominator value U and the numerator value t of the L value. Reference numeral 15 denotes an R value calculation means, which similarly calculates the R value by dividing the denominator value U and the numerator value r of the R value. These calculated L and R values are introduced into the relay operation determining section 16 to perform operation determination according to the characteristics of the distance relay, and output the results.

[Problems with background technology]

The above method is based on differential equations that hold true even in transient conditions during system failures.

In principle, it does not depend on the frequency of the current or voltage, but if an approximation formula is used to calculate the current differential value, it will be affected by the accuracy of the approximation. However, if the approximation formula shown in equation 4) is used, in the frequency range where the approximation holds, [, L value,
Since the R value can also be calculated with high accuracy, the frequency characteristics of the distance relay can be significantly improved.

Here, at the distance relay described above, the current i is as follows (8
) shows the response when a waveform containing harmonics is applied.

i-den I. dB ωt + II I . 9 stones (N・ω is 10) ...... (8) However, ρ: harmonic content rate N: harmonic order θ: harmonic content phase For simplicity, the current differential value j is (8) Use the theoretical value obtained by differentiating the equation.

j−ωl0−cosωt+NωρI 0CQI(N ・
ωt+θ) −−−−・−(9) At this time, the above (6)
From the formula and formula (7), the denominator value U is given by the following formula.

um ” ImJm-1-'m-IJm+4ρωl2c
ca calendar GoC (N+1) dn Soshishiki Tsugu (No 2 2
2 -1)(ωt-ωT)〇)-(N-1)dn■1bi■
((N+1) (ω is one ωT) 10)] ・
... αQ However, in equations 6) and (7),
n5wm-1°T is the sampling period α1 As is clear from the equation, if the denominator value U is the voltage ff and i is a single frequency input, that is, ρ=O, then uwm 4ωI2・■2””・m(dT becomes ,ωT
If π, then it becomes a constant positive value. However, when the current i contains a harmonic component, the denominator value U changes and may become O in U depending on the harmonic order and content rate. Theoretically, even if the denominator value is U out of O, the L and R values can be calculated correctly using equation (7), but in reality, errors in the input circuit and quantization errors due to conversion to digital quantities occur. etc., the calculation errors of the L value and R value may increase significantly when the denominator value is U or O. This phenomenon is based on the differential equation, regardless of the method used to derive the current differential value, and (3)
This is an essential problem in distance relays using the basic formula as follows.
This causes a decrease in ranging performance.

[Purpose of the invention]

The present invention was made to solve the above problems, and an object of the present invention is to provide a distance relay with improved distance measurement performance.

[Summary of the invention]

In the present invention, the system voltage tv, current amount i, current differential tj
, inductance L, and resistance R.
−R, ; + Lj for distance measurement, m
Each of the electrical quantities υ and υ in n, the current quantity im, i:n
, m n current differential k jmr jn to electricity 't 'm'n
'njm' 1v-iυ, jυ-jυ are obtained, and each of the electricity 171n rl171 m
This method attempts to measure the distance by determining the L value and the R value based on a plurality of addition and subtraction values at different times.

[Embodiments of the invention]

Examples will be described below with reference to the drawings. FIG. 1 is a functional block diagram of an embodiment of a distance relay according to the present invention.

Note that since the hardware is the same as that in FIG. 3, explanation of the configuration diagram will be omitted.

In FIG. 1, 17 is a means for adding and subtracting the denominator value U of the L value and R value calculation formula of formula (7), 18 is a means for adding and subtracting the numerator value t of the L value calculation formula of formula (7), and 19 is R This is means for adding and subtracting the numerator value r of the value calculation formula. Note that the addition/subtraction means means means for performing addition, or means for performing addition or subtraction depending on the positive or negative sign. In this embodiment, the addition/subtraction means each calculate α and the expression, and the addition value L
Obtaining J, L, and R 0 20 calculates the L value by division using the above-mentioned U and L in the L value calculation means. 21 is an R value calculation means which similarly calculates the addition value U.
, R value is calculated from R. The calculation formula for each is as follows.

Other lectures are the same as in Figure 4.

According to this embodiment, it is possible to improve the distance measuring performance of the distance relay as described below. To simplify the explanation, L
Paying attention to the value calculation formula, set the true value of the L value as "Ideal,"
The calculation error eLm of equation (7) at time tm is defined by the following equation.

”m = ”Ideal +”m ”'”'
a3 This calculation error corresponds to the calculation error of the L value calculation means 14 in FIG. 4, and when both sides of the α1 equation are multiplied by the denominator value um, the following equation holds true.

um”rr+=um”LIdeal+et, m””tm
``'''' (Substituting the relationship in equation 14a → into the equation for calculating the addition value of the equation for α, Lm″″Σ(um−k ′ (Lideal +eLm
)) k=0. Therefore, from equation (6), the L value can be determined by the following equation.

The second term of the α9 formula described above indicates the calculation error IEL of the L value. - As an example, the error EL when formula 01 is closed by N-3 is shown.

...... α force Here, the error eL at each time may increase significantly when the denominator value is UζO as described above, but if the absolute value of the denominator value is lul
>O, it can be considered as e♂■ in practical terms. In the α-th equation, for example, consider the case where the denominator value becomes false ζO at time t and the corresponding error eLm becomes large.
From the 1η formula, the coefficient of error eLm is um / (um +
um-+ + um-2+ unl-5).

However, uo<(u□+um-, 10um-2+um
-3), the influence of the error eLm is significantly alleviated as a whole, and the other error terms eLm-11eLr
As for l-2' eLm-5, as described above, if the denominator value is large, eLζ0 is obtained, so the calculation error ξ of equation 01 is reduced overall. For comparison, the error EAv when simply averaging the L value calculation results over 47' - evening using the relationship of the α1 formula as above is found.
EAv= (6Lm+6Lm-, +eLm-, +eLm
-3)/4 ・Qe.

Therefore, when the error eLm becomes large at time tIn, the coefficient of eLm in the α barrel type is 1/4, but it is clear from the above explanation that the coefficient of eLm in the 04 type becomes 1/4 or less, It can be seen that the L value calculation error is improved and distance measurement performance can be improved.

Although the L value calculation formula has been described above, the same applies to the R value calculation formula. Further, in equation (6), it is also possible to determine the operation of the relay by finding the ratio between the U value and the L value or the U value and the R value without performing division to calculate the L value or the R value.

FIG. 2 is a functional block diagram for explaining another embodiment of the distance relay according to the present invention. Note that the same parts as in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

22 is a means for adding and subtracting the denominator value U of the L value and R value calculation formula shown in equation (7), which adds when the denominator value U is positive and subtracts when it is negative to obtain the absolute value U shown below.

Um-Σl um-, l ...... (5
) Further, 23 is an addition/subtraction means for the numerator value t of the L value calculation formula shown in equation (7), and 24 is an addition/subtraction means for the R value calculation formula, each of which performs the following calculations.

When tm-k is added, when um-1<o, trn-
The same operation is performed even if k is subtracted, but as is clear from the relationship α → expression, this is because the denominator value U is added like α expression, so there is no need to preserve the sign of the L value or R value. It is processing. Therefore, according to the α4 formula, (g) formula, and (7) formula, the calculation error of the L value is given below.

Here, the Q]) formula of this embodiment and α1 of the embodiment explained earlier
Comparing the calculation errors in the equations, for example, the coefficients of the error eLm at time trfl have the following relationship.

Therefore, according to this embodiment, the error coefficient is further reduced, its influence can be alleviated, and distance measurement performance can be improved. It goes without saying that the same applies to the R value.

In each of the above embodiments, the reference numerals 17° and 18. shown in FIG.
Although the addition/subtraction means 22, 23, and 24 shown in FIG. 19 and FIG. It is clear that the time interval of can be any value.

〔Effect of the invention〕

As explained above, according to the present invention, there is provided a distance relay that measures distance using the relational expression υ-Ri+Lj that holds between the system voltage meter, current ti, current differential amount j, inductance L, and resistance R. At different times tm and tn
The voltage amount at -9vn.

Current amount im, current differential amount jm, j. From this, the quantity of electricity 'mjn 'njm' Fuku υ. -invm and rare υn jnvm are obtained, and the distance is measured by determining the L value and R value based on the multiple addition and subtraction values of each electric quantity at different times, so the distance measurement performance is improved. We can provide relays.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram explaining one embodiment of a distance relay according to the present invention, FIG. 2 is a functional block diagram of another embodiment according to the present invention, and FIG. 3 is a hardware configuration diagram of a general distance relay. , FIG. 4 is a functional block diagram of a conventional distance relay. DESCRIPTION OF SYMBOLS 1... Power transmission line 2... Transformer 3... Current transformer 4, 5... Input converter 6... Conversion circuit 7... Arithmetic processing unit 8... Differential calculation means 9
... Current calculation means 10 ... Voltage calculation means 11 ...
- Denominator value calculation means 12.13...Numerator value calculation means 14.20...L value calculation means 15.21...R value calculation means 16...Relay operation determination section 17.18, 19, 22 , 23.24... addition/subtraction means

Claims (3)

[Claims] (1) Input the voltage signal and current signal of the power system, obtain the voltage amount v, the current amount i, and the current differential amount j, and establish between each of the above electrical amounts and the inductance L and resistance R of the power system. Using the relational expression v=Ri+Lj, the voltage amounts v_m, v_n, and the current amount i_ at different times t_m and t_n
m, i_n, electric quantity i_ from current differential quantity j_m, j_n
The first means of obtaining mj_n−i_nj_m, i_mv_
Second means for obtaining n-i_nv_m and j_mv_n-
In a distance relay that includes third means for obtaining j_nv_m and performs distance measurement based on the amount of electricity from each of these means, at least one of time t_m and t_n is a plurality of third means for obtaining j_nv_m at different times. a fourth means for obtaining an addition/subtraction value of the outputs of the first means; a fifth means for obtaining an addition/subtraction value of the plurality of outputs from the second means at the same time as the plurality of outputs from the first means; a sixth means for obtaining an addition/subtraction value of a plurality of outputs from the means, and a seventh means for obtaining a ratio between the output from the fourth means and the output from the fifth means; and eighth means for determining the ratio of the output from the means and the output from the sixth means. (2) The distance relay according to claim 1, wherein the fourth means, the fifth means, and the sixth means each obtain an added value of a plurality of outputs. (3) The fourth means adds the output when the output from the first means is positive and subtracts it when it is negative to obtain the sum of the absolute values of the plurality of outputs, and the fifth means and the sixth means Claim 1, characterized in that the means adds when the output from the first means is positive and subtracts when it is negative to obtain the respective calculated values.
Distance relay as described in section.