JPH0757066B2 - Distance relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a distance relay using a distance measurement method based on a differential equation.

(Prior Art) As a distance measuring method based on a differential equation, there is, for example, JP-A-60-39312. This distance measuring method is a differential equation established between voltage v, current i, resistance R and inductance L of the transmission line. Is used to calculate the resistance R and the inductance L to obtain the distance. In order to obtain two unknowns, the equation (1) established at different times t _m and t _n is solved to obtain the L value, Calculate the R value.

However, .., v _m , i _m and v _n , i _n are voltage values and current values at times t _m and t _n . Further, it is assumed that the L value and the R value are constant within the time taken into consideration.

Here, an example of an approximate expression for obtaining the current differential value j _m from the current value i _m is shown in the following expression.

However, N, K _k (k = _{0 to} N) is a constant and at least k ₀ ≠ O, k
Let ₁ ≠ 0. In equation (3), the approximation error is zero at least at two frequencies, and the error is small even at intermediate frequencies, and approximation can be performed over a wide frequency range.
In order to apply the equation, the equation (2) is set as the sum of the equations (1) which differ by one sampling time as shown in the following equation.

here, In other words, the L value, R
The value is calculated by the following formula.

As shown in the block diagram of FIG. 3, the distance relay using the distance measuring method described above introduces voltage and current from the transmission line 1 through the transformer 2 and the current transformer 3, and the transformer 2 side. The input conversion circuit 4 converts the voltage signal to an appropriate voltage level and outputs the voltage signal v through the filter. The input conversion circuit 5 on the side of the current transformer 3 converts the current signal to an appropriate voltage level and passes the filter to the current signal i. Is output. The A / D conversion circuit 6 simultaneously samples the voltage signal v and the current signal i from the input conversion circuits 4 and 5 at regular intervals, sequentially performs digital conversion, and outputs them to the arithmetic processing unit 7. The arithmetic processing unit 7 comprises, for example, a microcomputer having a functional block diagram as shown in FIG. The differential calculating means 8 calculates the equation (3) from the data of the current signal i from the A / D converter 6 to produce the differential electric quantities j _m , J _n , and the current calculating means 9 and the voltage calculating means 10 The current amount I is calculated by calculating the equation (5) from the data of the current signal i and the voltage signal v.
_mm , I _n and voltage amounts V _m , V _n are produced. These differential electric quantity _{J m, J n,} the amount of current _{I m, I n} and the voltage amount _{V m,} with _{V n,} (6) formula denominator value _{u m = I m J n -I} n J m,
Molecular value _{l m = I m V n -I} n V m and _r m ₌ V m _{J n}
-V _n J _{m is produced} by the denominator value calculating means 11, the numerator value calculating means 12 and 13, and the L value calculating means 14 divides the denominator value u _m and the numerator value l _m to calculate the L value, and R The value calculation means 15 divides the denominator value u _m and the numerator value r _m to calculate the R value.
Relay operation determination unit 16 for inputting the calculated L value and R value
If the system fault is within the protection range compared to the settled characteristic, the operation signal is output.

(Problems to be solved by the invention) In the above distance relay, since it is based on the differential equation that holds even in the transient state at the time of a system fault, the theoretical point does not depend on the frequency of current or voltage, but When the approximation formula is used to calculate the differential value, the approximation accuracy is affected. Therefore, by using equation (3), L can be accurately measured over a wide frequency range.
Value and R value can be calculated, and a distance relay with good frequency characteristics can be realized.

However, in recent system fault phenomena, voltage and current waveform distortions tend to increase, and distortion components tend to become low-order. In conventional filters, due to problems such as delays in relay operation speed, low-order distortion components Could not be removed.

Here, in the distance relay described above, consider a waveform in which the current contains a high frequency component of the following equation.

i = I ₀ sin ωt + ρ I ₀ sin (Mωt + θ) (7)) where ρ is the high frequency content rate, M is the high frequency order, and θ is the harmonic content phase. For simplification, the current differential value j is expressed by the following equation when the theoretical value obtained by differentiating the equation (8) is used.

J = ωI ₀ cosωt + MwρI ₀ cos (Mωt + θ) (8) At this time, if n = m−1 and the sampling period is T, the denominator value u _m is Becomes From the equation (9), the denominator value u _m is such that if the current i is a single frequency input, that is, ρ = 0, Therefore, if ωT <π, it becomes a positive constant value. However, when a higher harmonic component is contained, u _m ≈0 may occur depending on the higher harmonic content ratio ρ and the higher harmonic order M. In this case, even if the denominator value u _m ≈0 theoretically,
Values and R values are obtained, but in practice, the error in the input conversion circuits 4, 5 and the quantization error in the A / D conversion circuit 6 due to the digital conversion may make the L and R value calculation errors noticeable. . In this case, there is a concern that the relay operation may be erroneously determined due to a calculation error and the distance relay may be erroneously operated.

Therefore, the present invention provides a distance relay that prevents malfunction due to a reduction in distance measurement performance due to a calculation error when an input containing low-order high-frequency components that cannot be removed by a filter has a denominator value u _m ≈0. With the goal.

[Structure of Invention]

(Means for Solving Problems) The present invention will be described with reference to the functional block diagrams of FIGS. 1 and 2.

Electric signals obtained from the voltage and current of the power system are sampled at equal intervals, and voltage values v _m , t _n at different times t _m , t _n
v _n, the current value _{i m, i n} the differential current amount _{J m, J n,} the amount of current _{I m, I n} and the voltage value _{V m,} differential operation means for calculating a _{V n}
8, current calculating means 9 and voltage calculating means 10, and the differential current amounts J _m , J _n , current amounts I _m , I _n and voltage values V _m , V _n calculated by these calculating means 8, 9, 10 respectively. electric quantity u _m, the denominator value calculating means 11 for calculating a l _m and r _m, the molecular value calculating means 12 and 13, these denominator value u _m, molecules value l
Type the denominator value u _m of the denominator value calculating means 11 at time t _m at a distance relay comprising a relay operation judging unit 16 operating condition perform distance measurement from _m and r _m to output a and the operation signal is established, the comparison value K A comparator that generates an output signal that invalidates the determination result of the relay operation determination unit 16 when it is less than
It is a distance relay with 18,20.

(Operation) The comparators 18 and 20 input the denominator value u _m calculated by the denominator value computing means 11 at the time t _m , and compare that the denominator value u _m is close to zero with the comparison value K. When the denominator value u _m is smaller than the comparison value K, the relay operation determination unit at time t _m is detected.
The relay operation determination unit outputs the output signal that invalidates the 16 determination results
Output to 16.

(Embodiment) An embodiment of the present invention will be described with reference to FIGS. 1 and 3. In FIG. 3, the transmission line 1 of the distance relay of this embodiment
The configuration for introducing more voltage and current is the same as that of the conventional distance relay, but the arithmetic processing unit 17 comprises a microcomputer as shown in the functional block diagram of FIG. First
In the drawings, like operating means and Figure 4, the determination unit Yes been provided with the same reference numerals, feature points of the arithmetic processing unit 17 of this embodiment, the denominator at time t _m, which is calculated in the denominator value calculating means 11 Value u
Comparing _m with a constant comparison value K ₁ , the denominator value u _mm is compared value K ₁
It is to provide a comparator 18 for generating an output signal to disable the determination result of the relay operation judging unit 16 at time t _m when smaller. Here, to disable it without performing the determination result of the relay operation judging unit 16 at time t _m, is to hold the previous determination result, the error comparison value K ₁ constants determined by the relay sensitivity of distance relay It is a predetermined value set in the range.

Therefore, a current containing low-order high-frequency components that cannot be removed by the filter is input, and the denominator value u _m <comparison value K _{1 and} L
When there is a possibility that the error between the R value and the R value is significantly increased, the comparator 18 invalidates the determination result of the relay operation determination unit, so that the malfunction of the distance relay due to the calculation error can be prevented.

Next, another embodiment will be described with reference to FIG. In FIG. 2, the same calculation means and determination unit as those in FIG. 4 are designated by the same reference numerals, and the characteristic point of the arithmetic processing unit 19 of this embodiment is that the denominator value u _m of the first embodiment is a constant. Instead of the comparator 18 for comparing with the comparison value K ₁ , a comparator 20 for comparing with the comparison value K ₂ from the data of the denominator value is provided, and the comparator 20 is the adder 2
1, a coefficient unit 22 and a comparator 23. The adder 21 adds a predetermined number of additions T to the denominator value u calculated by the denominator value calculation means 11, and obtains an addition value U _m at time t _m. And the coefficient unit 22 calculates the addition value u calculated by the adder 21.
_A comparison value K ₂ = δ · U _m is calculated by multiplying _m by a coefficient δ. still,
The coefficient δ is a value determined from the number of additions T and the allowable calculation error, and usually takes a value of 1 or less. Where the comparator 23
Is the denominator value u _m at time t _m calculated by the denominator value calculation means 11.
Is compared with the comparison value K ₂ calculated by the coefficient unit 22, and the denominator value u _m
There generating an output signal for invalidating the determination result of the relay operation judging unit 16 at time t _m when the comparison value K ₂ is smaller than.

Therefore, in addition to the effect of the first embodiment, by calculating the comparison value K ₂ from the data of the denominator value, the denominator value u _{m is} relatively increased.
It is possible to reduce the invalidity of the extra determination result when becomes smaller.

Also, in the second embodiment, the denominator value u _m in the comparator 23
The absolute value; the added value U _m as follows, it is clear that the same effect as the absolute value of the denominator value u _m can be obtained.

[Effects of the Invention] As described above, according to the present invention, the relational expression v = Lj established among the voltage v, the current i, the current differential amount j, the inductance L and the resistance R.
In distance relay using the distance determination method which puts + Ri, L value, the denominator value u _m senses in comparison with comparison values near not a be had zero time t _m at time t _m of the middle R value calculated Since the comparator that generates the output signal that invalidates the relay operation determination result is provided, it is possible to provide the distance relay that prevents the malfunction due to the deterioration of the distance measurement performance due to the calculation error at the time of input containing the harmonic component.

[Brief description of drawings]

1 and 2 are functional block diagrams of the arithmetic processing unit of the distance relay of the present invention, FIG. 3 is a block configuration diagram of the distance relay, and FIG. 4 is a functional block diagram of the arithmetic processing unit of the conventional distance relay. Is. 1 ... Transmission line, 2 ... Transformer, 3 ... Current transformer, 4,5 ... Input converter, 6 ... A / D conversion circuit, 7, 17, 19 ... Arithmetic processing unit, 8 ... Differential computation Means, 9 ... Current computing means, 10 ... Voltage computing means, 11 ... Denominator value computing means 12, 13 ... Numerator value computing means, 14 ... L value computing means, 15 ... R value computing means, 16 ... Relay operation judgment unit 18,20,23 …… Comparator, 21 …… Adder 22 …… Coefficient unit

Claims (3)

[Claims] 1. A sampled at regular intervals an electrical signal obtained from the voltage and current of the power system, different times t _m, the voltage value v _m at t _n, v _n, the current value i _m, differential current from i _n Quantity J _m , J
_n , current amounts I _m , I _n and voltage amounts V _m , V _n , differential calculating means, current calculating means and voltage calculating means, and differential current amounts J _m , J _n , current amounts calculated by these calculating means and I _m, I _n and the voltage amount V _m, electric respectively from V _n quantity u _m, the denominator value calculating means for calculating a l _m and r _m, the first numerator value calculating means and the second molecule calculating means, these denominator value u _m, the distance relay comprising a operating condition perform distance measurement from molecules value l _m and r _m is established the relay operation judging unit which outputs an operation signal, the denominator value of the denominator value calculating means at the time t _m distance relay which enter a u _m, characterized in that a comparator for generating an output signal for invalidating the determination result of the relay operation judging portion is smaller than the comparison value. 2. The distance relay according to claim 1, wherein the comparison value of the comparator is a predetermined constant value. 3. The distance relay according to claim 1, wherein the comparison value of the comparator is a value calculated from denominator value data.