JP2874316B2 - Distance relay - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a distance relay, and more particularly, to a distance relay obtained by combining each phase voltage and current obtained from an electric power system, or directly or by synthesizing each phase current. Calculate the impedance up to the fault point in the protection section using the zero-phase current component and further the negative-phase voltage and current components obtained by combining the phase voltage and current amounts. The present invention relates to a distance relay that detects a one-phase or two-phase unbalance accident and generates an accident detection output.

(Prior Art) Conventionally, as a distance relay that actively uses this type of negative-phase current component, the amount of voltage excluding a phase voltage and the amount of current excluding a positive-phase component, that is, a zero-phase component and a negative-phase component are used. By calculating the impedance using, the fault element on the power system is identified, the distance element that determines the inside and outside of the relay operation area, and the voltage and current of the negative phase component are used to calculate the negative phase impedance. Prevents malfunction of the distance element in the power system at the time of phase loss by using the calculated direction element that supplements the distance element inside / outside of the fault point determination function and the phase difference between the magnitude of the negative-phase current and the zero-phase current. There is known a distance relay composed of the above four elements, namely, an accident phase determination element that performs an operation, and a reverse-phase overcurrent element that prevents a malfunction of the distance element due to a negative-phase component always included in a power flow on a power system.

This distance relay utilizes a phenomenon in which a reverse-phase voltage amount ₂ and a reverse-current amount ₂ appear in a reverse-phase circuit at the time of a one-phase or two-phase unbalance accident, and uses a negative-phase current component as a current amount for distance element calculation. ₂ and zero-phase current component ₀ are used. For this reason, it always contains a large amount in the tide and charging current,
And the positive-phase current component _{1 that} causes a reduction in the relay operating characteristics
Has the advantage of being less susceptible to the effects of

Here, the arithmetic expression of the distance element is, for example, the following (1),
This is realized by equation (2).

Of these, equation (1) is for detecting, for example, A-phase one-phase accident among three phases (A, B, and C phases), and equation (2) is for detecting BC-phase, two-phase accident. In each equation, is the impedance from the relay installation point to the fault point, Kg and Ks are constants determined by the power system to be protected by the relay, _A is the A-phase voltage, _BC is the BC-phase line voltage ( _BC = _B-
C ), _BC {−90} is rated frequency higher than the latest _BC.
The line voltage amounts that are retroactive to 90 ° electrical angle are shown.

When the above formulas (1) and (2) are realized by a digital protection relay, _A is a value measured directly from the power system, and _BC , ₀ is measured directly as in _A , or It is an amount obtained by combining two-phase or three-phase electric quantities measured directly from the power system, and ₀ is obtained, for example, by the following equation (3).

In _{^{I 0 n = (I A n}} + I B n + I C n) / 3 ...... (3) Equation (3), the phase current I _A, I _B, the subscript n of I _C is the data of the latest sampling time In the following, a subscript nm (m is a natural number) means data at a time preceding the present by m sampling times. Further, in the digital protection relay, the sampling time interval is usually a time corresponding to 30 electrical degrees on the basis of the rated frequency component, and hereinafter, the sampling time interval indicates the case of the above time interval.

In the above equation (3), only the amount of phase current at the same time is used.
The calculation of ₀ is performed. In this case, a calculation error of ₀ does not occur due to a system frequency fluctuation due to power fluctuation of the system.

On the other hand, the calculation of the negative sequence current component _{2, 0} and similarly with the concept of three-phase symmetrical circuit reciprocal zero-phase, the following formula capable of removing positive phase component quantity of ^{_{electricity, 2 = (A + α 2}} B + α C ) / 3 Use (4).

In the equation (4), α is a vector operator, and α = exp (j120 ゜). The reason why the equation (4) can remove the positive phase component can be understood from FIG. FIG. 4 (a)
4 shows a positive-phase electric quantity vector, and FIG. 4B shows a negative-phase electric quantity vector. When FIGS. 4 (a) and 4 (b) are applied to equation (4), FIGS. 4 (c) and 4 (d) are obtained, and the addition of the vectors does not make the negative phase component zero, but makes the positive phase component zero. You can see that.

When this equation (4) is represented by sampling data in the same manner as the equation (3), the following equation (5) is obtained.

_{^{I 2 n = (I A n}} + I B n-4 + I C n-8) / 3 ...... (5) In addition, the line current amount I _AB, I _BC, when using the I _CA,
Equation (5) ′ is obtained. This equation (5) ′ is obtained by ^calculating I ₂ ^{n in} equation (5).
Since the phase is 30 ° out than the characteristic, and be referred to as I ₂ ^'n, distinguishing and I ₂ ^n.

This equation (5) 'combines (subtracts) equation (5) using phase A as a phase reference and equation A → B, B → C, C → A) obtained by exchanging the phase of equation (5). It can be said that this is the result. Before subtraction (Equation (5)), the normal phase component has already been removed.
Equation (5) 'does not include the normal phase component.

However, the equations (5) and (5) 'are different from the equation (3), and do not hold when the sampling time interval is not exactly the time corresponding to 30 electrical degrees or when the system frequency deviates from the rated value. . The error in this case appears as a phenomenon that i) the negative phase current component cannot be accurately extracted, ii) the positive phase current component cannot be completely removed, and iii) the zero phase current component cannot be completely removed. However, equation (5) 'is not affected by iii) because only the inter-line electricity is used. Therefore, a value obtained by performing a phase correction of 30 ° on I ₂ ′ ^{n of the} equation (5) ′ will be defined again as I ₂ ⁿ and will be described below.

Here, as shown in the following equation (6), the three-phase components are defined as A, B, and C phases, and the negative-phase current components are denoted as _A2 , _B2 , and _C2 . Here, the vector rotation direction of the positive-phase current component is positive.

(However, | ₂ | {0} = true value of the negative-phase current component) Here, when ω is the rated frequency and the n-th sampling is performed at t = 0, ωt = 0 at n sampling times At the sampling time of n-4, ωt = −120 ゜ At the sampling time of n−8, ωt = −240 ゜, and the equation (6) is substituted into the equation (5) ′ ( _AB ← <sub>A2
- B2, BC ← B2 - C2</sub> , CA ← C2 - A2 _{and), 2 '= | 2 |} exp (j30 °) (7), and (5)' phase difference generated theoretically by the equation (30゜)
Is corrected, the reverse-phase current component ₂ can be accurately extracted.

However, if ω deviates from the rated frequency, for example, if the frequency is 5% higher than the rated frequency, n sampling times, ωt = 0 ゜ n-4 sampling times, ωt = −126 ゜ n-8 sampling times Ωt = −252 ゜, and the result of substituting equation (6) into equation (5) ′ is When a phase correction of 30 ° is performed, ₂ = | ₂ | × 0.9963 {6.00} (8), and | I ₂ er ₂ | = | ₂ | × 0.0037 {I ₂ er ₂ = 6} (8) ′ A negative-phase component extraction error I ₂ er ₂ occurs.

On the other hand, for ii), the positive-phase current components are represented as _A1 , _B1 , and _{C1 in the same} manner as in i), and further, And substituting equation (9) into equation (5) ′,
When is the rated frequency, When ω deviates from the rated frequency, for example, when the frequency is 5% higher than the rated frequency, And a phase correction of 30 ° produces a positive phase component removal error I ₂ er ₁ of | I ₂ er ₁ | = | ₁ | × 0.0622 {I ₂ er ₁ = 114} (11) ′

The errors in the above equations (8) 'and (11)' directly lead to a decrease in the performance of the reverse phase distance relay. When a reverse-phase distance relay is mainly used for detecting a far-end accident, the transient component is almost attenuated due to the characteristic of the time domain where the current and voltage transiently change immediately after the occurrence of the accident on the power system, in other words, the steady state It is important to have the relay characteristics in a short time, and it can be said that the relay characteristics in the frequency fluctuation of the power system, which frequently changes in a long cycle, are one of the characteristics in the stationary time domain.

(Problems to be Solved by the Invention) When a reverse-phase distance relay is used for detecting a far-end accident, its operation range is usually the same as that for detecting a near-end accident and a far-end accident as shown in FIG. Set a wider range than the distance relay that calculates the positive phase impedance of the shape.
In FIG. 3, the operation range is indicated by hatching. For this reason, the characteristics of the distance relay described in the related art due to frequency fluctuations and the like are subject to fluctuations in a wider operating range than other relays, and the performance of the relay is greatly reduced. This is because there is a main problem that errors such as the equations (8) 'and (11)' occur in the negative-phase current component extraction equations by the equations (5) and (5) '.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to obtain good characteristics by eliminating as much as possible negative phase component extraction errors and positive phase component removal errors due to frequency fluctuations in a power system. It is an object of the present invention to provide a distance relay as described above.

(Means for Solving the Problems) In order to achieve the above object, a first invention calculates an impedance using a voltage amount, a zero-phase current component, and a negative-phase current component of a three-phase power system, and calculates an impedance based on the calculated impedance. A distance relay having a distance element that generates an accident detection output by specifying a one-phase or two-phase unbalanced fault point in the protection section and performing an inside / outside determination of the relay operation area based on the
Negative-phase current component I ₂ ⁿ And in the second invention, I ₂ ⁿ = (I _AB ⁿ + I _BC ⁿ⁻² ) + (I _BC ⁿ⁻² + I _CA ⁿ⁻⁴ ) (13) In the third invention, And in the fourth invention, Further, according to the fifth aspect of the present invention, I ₂ ⁿ = (I _AB ⁿ + I _BC ⁿ⁻⁴ −I _CA ⁿ⁻² ) + (I _BC ⁿ⁻² + I _CA ⁿ⁻⁶ −I _AB ⁿ⁻⁴⁾ ) Calculated by (16). Where I _AB , I _BC , I _CA is A,
The three-phase current expressed as the B- and C-phase line-to-line electric quantities, the subscript n is the value at the latest sampling time, and the subscript nm (m = 1
To 6) indicate values before m sampling times.

(Operation) The arithmetic expression for extracting the negative-sequence current component is as described in the above (5),
There are several types other than the expression (5) ', for example, the following expression (17) can be given.

However, equation (17) also has a negative phase component extraction error and a normal phase component removal error due to system frequency fluctuations inherent to each equation, as in equation (5) '. Accordingly, in the present invention, a combination that cancels each of the above errors and realizes a good frequency variation characteristic by combining a plurality of negative phase component extraction arithmetic expressions having different negative phase component extraction error and positive phase component removal error characteristics. An arithmetic method was adopted.

For example, the equations (18) and (19) are defined as follows by changing the equation (5) '.

_{^{I 2 'n = I AB n}} + I BC n-4 -I CA n-2 ...... (18) I 2' n = I BC n-2 + I CA n-6 -I AB n-4 ...... (19) In each of these equations, the error of negative phase component extraction and normal phase component removal at the rated frequency is zero. Furthermore, for example, the error of equation (18) at a frequency 5% higher than the rating is When a phase correction of 30 ° is performed, ₂ = | ₂ | × 0.9909 {3.00}, and | I ₂ er ₂ | = | I ₂ | × 0.00091 {I ₂ er ₂ = 3} When a phase correction of 30 ° is performed, ₂ = | ₁ | × 0.0297∠57.00 ゜, and | I ₂ er ₁ | = | I ₁ | × 0.0297 {I ₂ er ₁ = 57}. Similarly, for equation (19), | I ₂ er ₂ | = | I ₂ | × 0.0091 {I ₂ er ₂ = −54} | I ₂ er ₁ | = | I ₁ | × 0.0297 ∠I ₂ er ₁ = In this case, both equations (18) and (19) have the same magnitude of the negative phase component extraction error and the normal phase component removal error.
Moreover, the phase characteristic relating to the positive phase component removal error I ₂ er ₁ is
The difference between the errors in equations (18) and (19) is 57 ° + 126 ° = 183 °, which is almost the opposite polarity.

Therefore, the following equation (16) obtained by synthesizing the equations (18) and (19) is defined (reprinted).

Error of _{^{I 2 n = (I AB n}} + I BC n-4 -I CA n-2) + (I BC n-2 + I CA n-6 -I AB n-4) ...... (16) At this time, ₂ ′ = | ₂ | × 1.0138 {4.5} | I ₂ er ₂ | = | I ₂ | × 0.0138 {I ₂ er ₂ = −25.5} for the negative phase component input On the other hand, ₂ ′ = | ₁ | × 0.0009 {175.5} | I ₂ er ₁ | = | I ₁ | × 0.0009 {I ₂ er ₁ = 145.5}, and the positive-phase component removal error I ₂ er ₁ is small. You can see that.

In general, the positive-phase component is larger than the negative-phase component in the power system, and when heavy power flows, the positive-phase component can be several tens times larger than the negative-phase component. It is desirable that the elimination error I ₂ er ₁ be small as a negative-phase component extraction arithmetic expression. Therefore, Expression (16), which is a combination of Expressions (18) and (19), is more appropriate as an inverse phase component extraction operation expression than the case where Expressions (18) and (19) are used alone.

In general, the three-phase order is delayed in the lag direction (A-phase → B-phase, B-phase →
The inverse-phase component extraction operation formula composed of values that are replaced by C-phase, C-phase → A-phase) and that are two sampling times back (electrical angle is delayed by 60 °) is I ₂ er _{1 in the} expression (17). The phase is almost opposite to that of the case. Therefore, by combining this operation expression and Expression (17), it is possible to realize a negative-phase component extraction operation expression excellent in I ₂ er ₁ error characteristics.

Therefore, in the present invention, the above formulas (12) to (16) are derived by using the above-described combination method based on the formula (17), and the inverse phase component ₂ is calculated using any of these formulas. It is what it was.

Here, the features of each invention using the equations (12) to (16) are as follows.

Equation (12) shows that when the system frequency fluctuation is within the rated frequency ± 5%, the positive phase component removal error is 0.079% at maximum and the negative phase component extraction error is 3.786% at maximum, and equations (12) to (16) Inside, the sampling data of the minimum time width (n to n-3)
Therefore, relay characteristics with a short operation time can be expected.

Equation (13) shows that within the same system frequency fluctuation range, the positive phase component removal error is 0.091% at maximum and the negative phase component extraction error is
3.067%, which can be realized with the minimum number of sampling data (3 points) and the coefficient of 1 or 2 in the equations (12) to (16). And high-speed processing can be expected.

In the equation (14), the positive phase component removal error is 0.047% at the maximum and the negative phase component extraction error is 4.544% at the maximum in the same system frequency fluctuation range, and the best one among the equations (12) to (16) is obtained. A positive phase component removal error characteristic is obtained.

In the equation (15), the positive phase component removal error is 0.119% at the maximum and the negative phase component extraction error is 1.622% at the maximum in the same system frequency fluctuation width, and the positive phase component is compared with the equations (12) to (14). The difference between the component removal error and the negative-phase component extraction error is small.

In the equation (16), the positive phase component removal error is 0.093% at the maximum and the negative phase component extraction error is 1.636% at the maximum in the same system frequency fluctuation width, and has the same error tendency as the equation (15). However, equation (16) requires data one sampling time older than equation (15), and all coefficients are 1.

As described above, the negative phase component is calculated by using any one of the equations (12) to (16), and the negative phase component is calculated as the distance element of the equations (1) and (2) and the negative phase component of the conventional combination relay element. By applying this, it is possible to realize a distance relay that is hardly affected by frequency fluctuations of the power system.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration of a relay arithmetic processing unit of a distance relay using a negative-phase current component, and corresponds to a portion indicated by reference numeral 38 in FIG. 2 showing the entire configuration of the distance relay.

First, the overall configuration of this relay will be briefly described with reference to FIG. 2. In FIG. 2, three relays obtained from a power system using measuring devices such as a PT (instrument transformer) and a CT (current transformer) are shown. The amount of phase voltage and the amount of three-phase current are determined by the input transformer 32 in the distance relay 30,
The data is filtered through an analog filter 34 and an A / D converter 36 and is converted into digital data. Then, the digital data of the three-phase voltage amount and the three-phase current amount is
It is input to the relay operation processing unit 38 having the configuration shown in FIG.

In the relay operation processing unit 38 shown in FIG. 1, reference numeral 1A denotes a negative-phase voltage component extraction unit. The extraction unit 1A performs an operation corresponding to any of the above equations (12) to (16) for each line voltage. no line, and calculates an inverse-phase voltage component V _2, and its output is added to the direction element 4. Reference numeral 1B denotes a negative-phase current component extracting means. The extracting means 1B performs any one of the expressions (12) to (16) using the three-phase current amount as a line-to-line electric amount, calculating the component I _2. The output of the extracting means 1B is applied to a distance element 3, a direction element 4, an accident phase determination element 5, and a negative-phase overcurrent element 6.

Here, the direction element 4 has a function of calculating the negative-sequence impedance using the negative-sequence voltage component and the negative-phase current component, and supplementing the fault element inside / outside determination function of the distance element 3. Has a function of preventing a malfunction of the distance element 3 at the time of phase loss in the power system by using the magnitude of the negative-phase current component and the phase difference with the zero-phase current component. Has a function of preventing a malfunction of the distance element 3 due to a negative-phase component always included in the power flow on the power system, but is not directly related to the present invention, and thus the detailed description is omitted.

Further, reference numeral 2 denotes a zero-phase current component calculating means, which performs the operation of the above equation (3) based on the three-phase current amount to obtain a zero-phase current component I _0.
Is calculated and output to the distance element 3 and the accident phase determination element 5. The zero-phase current component calculation means 2 can be omitted when the zero-phase current component is directly input from the power system.

In the distance element 3, the three-phase voltage amounts, the zero-phase current component I ₀ from the zero-phase current component calculation means 2, negative sequence current component extracting means 1B
Based on the negative sequence current component I ₂ from the expression (1) or (2) it performs the calculation of the expression, of the relay operating range by calculating the impedance from the relay installation point to the fault point in the relay protection segment Perform external judgment. The output of the distance element 3 is applied to the AND means 7 together with the outputs of the other direction element 4, the fault phase determination element 5, and the negative-phase overcurrent element 6, and the operation of the distance relay is determined as a whole. A relay output is generated. The relay output is sent to the operation output processing unit 40 shown in FIG. 2, from which the final output of the relay 30, such as a circuit breaker trip command, is obtained.

(Effects of the Invention) As described above, according to the present invention, the negative-sequence current component is calculated using a predetermined arithmetic expression, so that the negative-phase component extraction error and the positive-phase component removal error due to the frequency fluctuation of the power system are reduced. The characteristics of a distance relay that positively uses a negative-phase current component, such as a negative-phase distance relay installed for detecting a far-end accident, can be improved.

In the equations (12) to (16), the phase sequence of the three-phase power system is A → B, B → C, C → A, or A → C, B → A, C → B
In principle, the same effect as that of the above-described embodiment can be obtained, and substantially the same effect can be obtained. In any case, the above-described case is within the technical scope of the present invention.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of one embodiment of the present invention, FIG. 2 is an overall block diagram of the same, FIG. 3 is an explanatory diagram of an operation range of a distance relay, and FIG. FIG. 1A ... Negative-phase current component extraction means 1B ... Normal-phase current component extraction means 2 ... Zero-phase current component calculation means 3 ... Distance element 4 ... Direction element 5 ... Failure phase determination element 6 ... Reverse Phase overcurrent element, 7 ... AND means 30 ... distance relay, 32 ... input transformer 34 ... analog filter, 36 ... A / D converter 38 ... relay operation processing section, 40 ... operation output Processing unit

Claims (5)

(57) [Claims] An impedance is calculated using a voltage amount, a zero-phase current component, and a negative-phase current component of a three-phase power system, and a one-phase or two-phase unbalance fault point in a protection section is identified based on the impedance. In a distance relay having a distance element that generates an accident detection output by performing an inside / outside determination of the relay operation area, the negative-phase current component I ₂ ⁿ is (I _AB , I _BC , and I _CA are three-phase currents expressed as A, B, and C phase line amounts, the subscript n is the value at the latest sampling time, and the subscripts n-1 to n-3 are power system A distance between 1 and 3 sampling time before sampling at a sampling frequency that is 12 times the fundamental frequency. 2. An impedance is calculated using a voltage amount, a zero-phase current component, and a negative-phase current component of a three-phase power system, and a one-phase or two-phase unbalance fault point in a protection section is identified based on the impedance. In a distance relay having a distance element that generates an accident detection output by performing the inside / outside judgment of the relay operation area, the negative-sequence current component I ₂ ⁿ is calculated as follows: I ₂ ⁿ = (I _AB ⁿ + I _BC ^n-2 ) + (I _BC ⁿ⁻² + I _CA ⁿ⁻⁴ ) (I _AB , I _BC , I _CA are three-phase currents expressed as A, B, C phase line quantities, and the subscript n is the latest sampling time The values and subscripts n-2 and n-4 indicate the values two sampling times before and four sampling times before sampling at a sampling frequency 12 times the fundamental frequency of the power system, respectively. Distance relay. 3. An impedance is calculated using a voltage amount, a zero-phase current component, and a negative-phase current component of a three-phase power system, and a one-phase or two-phase unbalance fault point in a protection section is specified based on the impedance. In a distance relay having a distance element that generates an accident detection output by performing an inside / outside determination of the relay operation area, the negative-phase current component I ₂ ⁿ is (I _AB , I _BC , and I _CA are three-phase currents expressed as A-, B-, and C-phase line-to-line electrical quantities, subscript n is the value at the latest sampling time, and subscripts n-1 to n-4 are power system A distance between 1 and 4 sampling times before sampling at a sampling frequency that is 12 times the fundamental frequency.) 4. An impedance is calculated by using a voltage amount, a zero-phase current component, and a negative-phase current component of a three-phase power system, and a one-phase or two-phase unbalance fault point in a protection section is identified based on the impedance. In a distance relay having a distance element that generates an accident detection output by performing an inside / outside determination of the relay operation area, the negative-phase current component I ₂ ⁿ is (I _AB , I _BC , and I _CA are three-phase currents expressed as A, B, and C phase line quantities, the subscript n is the value at the latest sampling time, and the subscripts n-2, n-3, and n-5 The distance relay is calculated based on two sampling times, three sampling times, and five sampling times before sampling at a sampling frequency that is 12 times the fundamental frequency of the power system. 5. An impedance is calculated using a voltage amount, a zero-phase current component, and a negative-phase current component of a three-phase power system, and a one-phase or two-phase unbalance fault point in a protection section is specified based on the impedance. In a distance relay having a distance element that generates an accident detection output by performing the inside / outside judgment of the relay operation area, the negative-sequence current component I ₂ ⁿ is calculated as follows: I ₂ ⁿ = (I _AB ⁿ + I _BC ^n-4 −I _CA ⁿ⁻² ) + (I _BC ⁿ⁻² + I _CA ⁿ⁻⁶ −I _AB ⁿ⁻⁴ ) (I _AB , I _BC , and I _CA are expressed as the inter-line electric quantities of the A, B, and C phases. Three-phase current, suffix n is the value at the latest sampling time, suffixes n-2, n-4, n-6 are two sampling times before and four samplings when sampling at a sampling frequency 12 times the fundamental frequency of the power system The values before and 6 sampling times before, respectively) are calculated.