JPH0452695B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a ground fault line selection relay, and more particularly to a ground fault line selection relay used for one-phase ground fault protection of multiple parallel lines.

[Technical background of the invention]

When a high-resistance grounded parallel two-circuit transmission line (hereinafter referred to as a protected transmission line) is installed on the same tower as another power transmission line (hereinafter referred to as an induced transmission line),
A zero-sequence current circulates between the two circuits of the protected power transmission line due to induction by the current in the power transmission line. A general ground fault line selection relay uses the zero-sequence difference current of the protected parallel transmission line as a calculation current to identify a ground-fault fault line, but when the above-mentioned circulating zero-sequence current is large, it Normal protection becomes impossible.

As a countermeasure to this, the circulating zero-sequence current due to induction is determined from the circulating current of the healthy phase at the time of a single-phase ground fault, and the current obtained by compensating the zero-sequence difference current of the parallel transmission line with this determined circulating zero-sequence current is used as the calculated current. As disclosed in JP-A No. 58-46832, the fault change in the detected current obtained from the fault phase difference current (or the composite current of the same phase difference current including the fault phase difference current) is Compensated ground fault line selection relays using a method (Method 2) in which the current compensated by the fault change in the compensation current obtained from the same phase difference current (or a composite current of the same phase difference current) are already available. Proposed. This makes it possible to protect against single-phase ground faults even when there is a circulating zero-sequence current.

FIG. 1 is a diagram showing a configuration example of a general digital protective relay device commonly used in the prior art and the present invention. In the figure, 1 is the bus line a,
b and c indicate each phase. 2 and 3 are parallel transmission lines, 4
and 5 is a bridge and disconnector, 6 and 7 are current transformers, 8 is an instrument transformer, 9 is an input converter, 10 is a sample and hold circuit, 11 is a multiplexer, and 12 is an A/D
It is a converter. 13 is a digital computer, which includes a CPU, memory M, input circuit I, and output circuit O.
have. The current transformers 6 and 7 obtain currents corresponding to the currents in the transmission lines 2 and 3, and by the connections shown in the diagram, the difference currents i _as , i bs and i cs of each phase of both transmission lines, i as , i _bs and i _cs , 3 × (zero-sequence difference current) = 3i _ps is obtained. or,
Voltages v _a , v b , v _c and v _p corresponding to the a, _b , c phase voltages and zero-phase voltage of the terminals of the power transmission lines 2 and 3 are obtained by the instrument transformer 8 through the bus bar. These currents and voltages are applied to the input converter 9 and converted into voltages with values suitable for the next sample-and-hold circuit 10. The input converter 9 has a built-in filter, and only the fundamental waves of each voltage and current can be obtained as output. The sample and hold circuit 10 performs a constant cycle (for example, 1/12 of one cycle of voltage or current) at the same time.
The input value is sampled and held at the cycle of This hold value is sequentially supplied to the A/D converter 12 by the multiplexer 11 and converted into a digital value. Based on this digital value, the digital computer 13 performs necessary calculations and instructs the disconnector 4 or 5 to disconnect when a predetermined condition is met.

FIG. 2 shows an example of the calculation flow performed by the digital computer 13, and shows the case where the conventional method 1 described above is used. First, when a start command is received in step _S1 , one-phase ground fault detection is performed in the next step _S2 . If a one-phase ground fault is detected in step _S2 , the process proceeds to step _S3 , where a ground fault phase selection calculation is performed. In step _S3 , a, b, and c phase ground fault detection calculations are performed in the order of _S3-1 , _S3-2 , and _S3-3 , respectively.
When a, b, or c phase ground fault is detected, respectively, judgment 3Y _a , 3Y _b , or 3Y _c is obtained, and step S ₃
If no ground fault phase is detected in , the determination 3N is obtained and the process moves on to other calculations.

When any of the judgments 3Y _a , 3Y _b , or 3Y _c is obtained in step S ₃ , it depends on which judgment among the above judgments was obtained, that is, which phase is the ground fault phase. , the calculated current in step _S4
Find i _ea , i _eb or i _ec and the polarity e _pa , e _pb or e _pc .
Once this is determined, a line selection calculation is performed in step _S5 . In step S ₅ , step S _5-1 ,
S Perform accident detection calculations for transmission lines 2 and 3 in the order of _5-2 , and if either of the above accidents is detected, each judgment will be made.
5Y ₁ or 5Y ₂ is obtained, and the disconnector 4 or 5 corresponding to the faulty power transmission line is disconnected. If no transmission line fault is detected, a determination of 5N is obtained and the process moves on to other calculations.

The above-mentioned one-phase ground fault detection calculation in step _S2 is carried out when, for example, the zero-phase voltage v _p is equal to or higher than a certain value, and the inter-phase voltages v _a − v _b , v _b − v _c , and v _c − v _a are all When the value exceeds a certain value, it is determined that a one-phase ground fault has occurred.
In the ground fault phase selection calculation in step _S3 , for example, the zero-sequence voltage v _p is changed to the inter-phase voltages v _b −v _c , v _c −v _a and v _a −v _b
a, b, respectively, within a certain phase range.
In addition, in the line selection calculation in step _S5 , for example, a fault in the power transmission line 2 is detected when the active component of the calculated current i _e with respect to the polarity e _p is greater than a positive certain value. , which detects an accident on the power transmission line 3 when the value is below a certain negative value, and all of these are well known. In addition, i _ea , i _eb , i _ec , e _pa ,
The determined values of e _pb and e _pc are indicated by i _e and i _p, respectively.

Various values have been proposed for the calculation current i _e and the polarity e _p in step _S4 . That is, as the polarity e _p , in addition to the voltage −v _p with the sign of the zero-sequence voltage changed, e _pa = (v _b − v _c )∠90° e _pb = (v _c − v _a )∠90° e Various values have been proposed, such as _pc = (v _a − v _b )∠90°. Also, the calculation current i _e
Both are currents obtained by compensating the detection current i _d with the compensation current i _h , and are expressed by the following equation.

i _e = i _d − i _h ...(1) The most common of these is the detection current i _d
The zero-sequence difference current i _ps is the zero-sequence difference current, and the compensation current i _h is the difference current of one phase in the healthy phase.The calculated current i _e is expressed by the following formula, and the polarity is e _pa , e _pb , and e Both _pc and zero-sequence voltage are set to −v _p .

i _ea = i _ps −K _1b i _bs …(2) i _eb = i _ps −K _1c i _cs …(3) i _ec = i _ps −K _1a i _as …(4) However, K _1a , K _1b and K _1c are constants. As disclosed in JP-A No. 58-46834, the zero-sequence difference current at the time of a fault can be calculated by compensating for the normal circulating zero-sequence current from equations (2) to (4) above. be.
That is, in a multicircuit parallel power transmission line, the relative ratio of the circulating currents of each phase and zero phase of the protected power transmission line is based on the principle that it is almost constant regardless of the operating state of the protected power transmission line.

Based on the above-mentioned principle, another example of calculating the calculation current i _e using the method shown in equation (1) has been proposed.
Representative examples of these are shown below.

i _ea = i _ps −K _1b i _bs ...(5) (same as equation (2)) i _eb = i _ps −K _1ca (i _ps + i _as ) ...(6) i _ec = i _ps −K _1b i _bs ... (7) However, K _1ca is a constant, that is, the equations (5), (6), and (7) are calculated using only the healthy phase difference current as the compensation current. Furthermore, there are also those expressed by the following formula.

i _ea = (i _cs + i _as ) − K _2b i _bs ……(8) i _eb = i _bs −K _2ca (i _cs + i _as )……(9) i _ec = (i _cs + i _as )−K _2b i _bs ...(10) (same as equation (7)) In equations (8), (9), and (10), in the arrangement of protected transmission lines, phase a is the upper phase, phase b is the middle phase, When the c phase is the lower phase, in the case of a ground fault between the upper phase (a phase) and the lower phase (c phase), the detection current i _d has the upper phase (a phase) and the lower phase (c
Using the sum of the difference currents of the middle _phase (b
phase) difference current is used. In addition, in the case of a ground fault in the middle phase (phase b), the middle phase (phase b) difference current is used as the detection current i _d , and the upper phase (phase _a ) and lower phase (c
It uses the sum of the phases). In this example, the error can be reduced even if the induction lines are located above and below, and this is because the fault current flowing in the AC circuit flows only in the fault phase.

Further, JP-A-58-46832 discloses the following content.

i _ea ＝3i _a2s −3K ₃ i _ps ……(11) i _eb ＝3i _a2s −3aK ₃ i _ps ……(12) i _ec ＝3i _a2s −3a ² K ₃ i _ps ……(13) However, i _a2s is the negative phase component of the a phase difference current a is the parameter that advances the vector by 120° K ₃ constant Equations (11) to (13) above show an example of the a phase regarding the symmetrical component of the fault phase, i _a2s = i _ps = 1 Since there is a relationship of /3i _as , i _ea = 3 (1-K ₃ ) i _ps ...(11)' i _eb = 3 (1-aK ₃ ) i _ps ...(12)' i _ec = 3 (1−a ² K ₃ ) i _ps ……(13)′, and the zero-sequence fault difference current can be obtained.

In the various examples shown by equation (1) explained above, the coefficients of the compensation current i _h are fixed (preset), but for example, as disclosed in Japanese Patent Application Laid-Open No. 106028/1982, Alternatively, there is a method of constantly calculating based on the fact that there is a certain ratio relationship between the circulating currents between lines when they are healthy.

_As an example of the above-mentioned conventional technology, method 1 using the processing shown in _{FIG .} ) − (i _h −i _hM ) ...(14). Here, i _{d and} i _dM are the post-fault and pre-fault currents of the fault phase difference current (or the composite current of the same phase difference current including the fault phase difference current), respectively, and i _h and i _hM are the same phase difference current (or the composite current of the same phase difference current including the fault phase difference current), respectively. The composite current is the current after the accident and before the accident. Note that i _d and i _h , i _dM
By using the various methods described in Method 1 for and i _hM ,
The detection current and the compensation current may be obtained before and after the accident, respectively. Then, the calculation flow is modified from Fig. 2, and when a one-phase ground fault is not detected in step _S2 , the value of equation (1) is memorized, and instead of the processing in step _S4 , the value of equation (1) after the accident is What is necessary is to perform the calculation and the value of equation (14). When formula (14) is compared with formula (1), the compensation error due to the compensation current i _h is subtracted from the compensation error due to the calculation of (i _dM −i _hM ), and the error can be further suppressed.

[Problems with background technology]

As can be seen from the above detailed description, in determining the operation of the compensated ground fault line selection relay, the phase difference current of at least one phase is input, and the detected current i _d in equation (1) is calculated from this phase difference current. It is necessary to calculate at least one of the compensation currents i and _h . The drawbacks of such prior art will be explained below.

FIGS. 3a and 3b are diagrams showing the system states of the protected power transmission lines 2 and 3 before and after the accident. Third
In figure a, power transmission lines 2 and 3 are connected to bus bars 1A and 1B and grounded by a resistor _R1 , and
It has a load L. Moreover, the power transmission lines 2 and 3 have charging capacity C ₁ . RY1 is a relay that is installed at the B end and performs ground fault line selection protection for the power transmission lines 2 and 3.It inputs a current corresponding to the difference current between the power transmission lines 2 and 3 using current transformers 6 and 7, and judges the operation. Let's do it. At least each phase difference current is used as this input current. Under this system configuration, it is assumed that load currents I _L1 and I _L2 always flow in each phase of the power transmission lines 2 and 3, respectively, and that a circulating current I _th is in the direction shown in the figure.

In FIG. 3a, the input magnitude of each phase difference current and zero-sequence difference current of RY-1 is approximately twice the respective circulating current. In this state, even if the conventional compensated ground fault selection method is employed, RY-1 can respond normally.

Figure 3b shows a state in which the 100% single-line ground fault at point F near end A caused the ground breaker CB1 to break in advance due to the compensated ground fault line selection relay (not shown) installed at end A. shows. At this time, the circulating current disappears due to the "opening" of CB1, and each phase current in the power transmission line 2 becomes as follows.

Current in two healthy phases = I _L1 + I _L2 ……(15) Current in fault phase = I _L1 + I _L2 + I _F ……(16) I _F in equation (16) above is the fault current, and resistor current I It is determined by the size of _NGR and charging current I _C. In general, I _C is never larger than I _NGR , and it can be considered that there is a phase difference of 90°, so the maximum value of I _F is as follows.

I _F =√2×I _NGR ……(17) Therefore, equation (16) becomes as follows.

Fault phase current = I _L1 + I _L2 + √2 I _NGR ...(18) However, when considering the operating status of the system,
The sum of the load currents I _L1 and I _L2 is CT rating x 150
%, the size of I _NGR is several hundred A. now,
When the CT rating is 1200/5 and the I _NGR is 400A, (1
5), the values of equations (17) are as follows.

Healthy phase 2 phase current = 1.2kA x 1.5 = 1.8kA
...(19) I _OF =√2×400A≒560A ...(20) Therefore, since the maximum value of the input electricity of RY1 in Figure 3b is the difference circuit current, healthy phase difference current = 1.8kA ...(21) Fault phase difference current = I _1L + I _2L + 2I _F = 1.8kA + 2 × 560A ≒ 3.0kA ... (22) Zero-sequence difference current = 2 × I _F /3 ≈ 1.1/3kA ... (23) Therefore, RY1 must also respond correctly to the magnitude of these inputs.

On the other hand, when configuring RY1 on a digital computer,
In order to respond correctly to input, it is necessary to follow the steps in Figure 1.
It is necessary to perform analog/digital conversion in the AD converter 12 to convert the input into a size that is accurately proportional to the input. When considering converting even large inputs in this input conversion, the error becomes large for small inputs because quantization becomes slow. Therefore, when considering improving the sensitivity, it is necessary to consider the smallest possible input as the full-scale input of the AD converter 12. However, looking at the estimated values of equations (21) to (23), the magnitudes of the healthy phase difference current and faulty phase difference current are 1.5 times and 2.5 times the magnitude of the 3 x zero phase difference current, respectively, and the roughness of quantization is also similar. It will be proportional to.

Therefore, if we consider the case where the circulating zero-sequence current is negligibly small, the compensated ground fault line selection relay that needs to input each phase difference current will be able to handle the quantization error when inputting each phase difference current. Therefore, the fault detection ability is inferior to that of a general ground fault line selection relay that uses only the zero-sequence difference current as the calculation current.

This performance deterioration is due to the complete 2
This situation becomes even more serious when we consider the case where it is applied to terminal transmission lines. Figure 4 shows T with load L ₂ on transmission line 3.
This is a branched lineage, and the rest is the same as in Fig. 3b.

In Fig. 4, x% of the load current (I _L1 + I _L2 ) flowing through the transmission line 2 flows to the load L ₂ , and (1-x)%
Assume that the current flows to the load L.

At this time, the input electricity amount of RY1 is as follows: Healthy phase difference current = (I _L1 + I _L2 ) (1+x) Fault phase difference current = (I _L1 + I _L2 ) (1+x) + 2I _F
...(24) becomes. Therefore, if a compensated ground fault line selection relay is applied to a system having T-branches, each phase difference current must be considered over a fairly large range. Therefore, it is necessary to consider using the system with reduced fault detection capability, or applying it only to systems with limited load current.

[Purpose of the invention]

The present invention has been made with the aim of solving the above problems, and provides a ground fault line that can detect faults in complete two-terminal power transmission lines without degrading the performance of the compensated ground fault line selection relay. The purpose is to provide selective relays.

[Summary of the invention]

In the present invention, two terminals parallel to each other through which a circulating zero-sequence current flows
For single-phase ground fault accidents in power transmission lines, the fault is classified into two types: when there is a circulating zero-sequence current and when there is not. If it is larger than a predetermined value, it is determined that one line at the other end has been disconnected, and in this case, it is determined that the circulating zero-sequence current has disappeared, so there is no influence from the circulating zero-sequence current. In consideration, the line selection calculation is performed using the zero-sequence difference current with a small current value and the extreme value as the calculation current.On the other hand, if the healthy phase difference current or the phase current is smaller than a predetermined value, it is assumed that one line at the other end is suddenly disconnected. Because there is no
Taking into account the influence of circulating zero-sequence current, the calculated current and polarity amount are calculated from the difference between the zero-sequence difference current as the detection current and the healthy phase difference current or phase current as the compensation current. By performing line selection calculations and setting the input current as small as possible, the sensitivity of the ground fault line selection relay is improved by matching the full scale input of the A/D conversion circuit of the digital relay.

[Embodiments of the invention]

Examples will be described below with reference to the drawings. FIG. 5 is a calculation flow diagram of the ground fault line selection relay according to the present invention, and the specific configuration for realizing the present invention is the same as that in FIG. 1. Note that the same parts as in FIG. 2 are indicated by the same symbols, and detailed parts are omitted. The difference between FIG. 5 and FIG. 2 is that step _S6 and step _S7 are added.

Step _S6 is a process of determining whether the magnitude of the healthy phase difference current is greater than or equal to a certain value.
If it is less than a certain value (NO), the process moves to step _S4 , and if it is more than a certain value (YES), the process moves to step _S7 . In the process in step _S6 , the phase for which the magnitude of the difference current is determined differs depending on the fault phase.
Step S _6-1 for accidents a, b, and c.
In step _S6-2 , the magnitude of the c-phase difference current is determined, and in step _S6-3 , the magnitude of the a-phase difference current is determined. On the other hand, in step _S7 , the calculation current i _e is set to the zero-sequence difference current i _ps , and the polarity amount e _p is determined. The polarity e _p uses the zero-sequence voltage −v _p . However, by memorizing the accident phase determination in step _S6 , the same method as the conventional one can be used. Said step
After executing _S7 , the process moves to step _S5 .

Next, a series of responses will be explained below. First, when a start command is received in step _S1 , the process moves to step _S2 to determine whether or not there is a one-phase ground fault. If a one-phase ground fault is detected here, the process moves to step _S3 to calculate the ground fault phase, and each determination 3Y _a , 3Y _b , 3Y _c and 3N corresponding to each phase is obtained.
When each of the above judgments is obtained (except in the case of 3N), the process moves to step _S6 , and a judgment is made as to whether the healthy phase difference current is large or small. That is, step _S6 is a process for determining whether or not one end is broken, and when the healthy phase difference current is equal to or higher than a certain value, it is determined that one end is broken. Therefore, after an accident occurs, the same judgment as before is performed until it is determined that one end is ruptured (from step 1 to step 3), and after it is determined that one end is sintered, the zero-sequence difference current is reduced in step _S7 . Judgment is made based on the operating principle based on i _ps and the polarity e _p . That is, since the circulating zero-sequence current disappears after one end is disconnected, malfunction will not occur even if the zero-sequence difference current is used as the calculation current. In addition,
If the healthy phase difference current is below a certain value in step _S6 , the process moves to step _S4 to obtain the calculated current and polarity, and further, in step _S5 , a faulty line is determined. Then, after the processing in step S ₇ , the process continues in step S ₅ .
The process of moving to is the same as above.

Here, the determination level of the healthy phase difference current in step _S6 can be determined as follows.

In other words, when a single-phase ground fault occurs, the difference current between the healthy phases before one end becomes disconnected is equal to the current value 2I _th due to the circulating current I _th (as shown in Figure 3a). Assuming that the load currents are balanced for wires 2 and 3). Generally speaking, the magnitude of this difference current 2I _th is about 5% of the load current (in the calculation example) when the induced power transmission line is healthy.
(approximately 100A as a load current of 2000A),
If an accident occurs in an induced power transmission line, the current will be approximately 10% of the fault current (in the calculation example, approximately 500A as a single-phase ground fault current of 7000A).

The maximum value of the differential current of a healthy phase before one end is interrupted is 2I _th , and when it flows more than 2I _th , it can be considered that at least one end is interrupted. Therefore, the determination level of the difference current in step _S6 can be determined from the maximum circulating current (500 A in the above calculation) assumed under various operating conditions of the induction power transmission line. This value is sufficiently small compared to the calculated value of the zero-sequence difference current shown in equation (23).

Therefore, according to the arithmetic processing method shown in FIG. 5, the maximum input value of each phase difference current can be reduced. This makes it possible to reduce the error in analog/digital conversion, thereby reducing the calculation error in the calculation current of the compensated ground fault line selection relay and improving the fault detection ability.

In addition, in determining the magnitude of the difference current in step _S6 , the b, c, and a phases are used for ground fault detection of the a, b, and c phases, respectively, but the present invention is not limited to this. , c for b-phase ground fault
It is clear that any of the two healthy phases may be used for the phase difference current, such as using the a phase for a c-phase ground fault. Furthermore, the sum of the absolute values of the two healthy phases, the average value of the respective absolute values of the two healthy phases, etc. may be used.

Also, when applying the above method to a two-terminal power transmission line with a T-branch, the judgment value in step _S6 is determined by considering the unbalanced portion (I _L1 - I _L2 ) of each load current I _L1 and I _L2 . do it.

FIG. 6 is a calculation flow diagram of another embodiment according to the present invention.

In the present embodiment, after determining the ground fault phase, confirmation of disconnection of one line at the other end is performed by calculating the positive phase component of each healthy phase difference current. That is, between the ground fault phase discrimination process in step 3 and the calculation process for the calculated current and polarity amount in step 4, the process for calculating the positive phase component of the healthy phase difference current is inserted as step 8, and the rest is as described above. This is the same as the case in FIG.

The calculation of the positive phase component in step 8 is performed as follows.

i _a1s = 1/3 (i _as + ai _bs + a ² i _cs ) ...(25) Here, i _a1s is the positive phase component of the i _as standard.

Then, in steps S _8-1 , S _8-2 , and S _8-3, the magnitude relationship between the positive phase component i _a1s and a predetermined value is determined. If the result of this judgment is less than a predetermined value (one end of the other end is not disconnected), the process moves to step _S4 , where the zero-sequence difference current that compensates for the normal circulating zero-sequence current and the polarity amount are determined. If the value exceeds a predetermined value (one end of the other end is disconnected), the process moves to step _S7 and the zero-sequence difference current and polarity are determined in the same manner as shown in FIG.

Here, an example of the circulating current flowing through each phase of the parallel line is as follows, and this has already been proposed.

The induction power transmission line is in normal operation and each load is
At 1000A, 2i _ath = 94.4∠25° (A) 2i _bth = 42.8∠27° (A) 2i _cth = 25.6∠27° (A) ……(26) The electromotive transmission line is in no-load operation, When a 1-phase ground fault occurs and the fault current is 7000A, 2i _ath = 474∠142° (A) 2i _ath = 474∠142° (A) 2i _bth = 232∠143° (A)2i _cth = 150∠144 ° (A)……(2
7) However, i _ath , i _bth , and i _cth are circulating currents of a, b, and c phases, respectively.

As is clear from the above equations (26) and (27), the circulating currents flowing in each phase flow in almost the same phase regardless of the operating status of the induced power transmission line, and only the magnitude differs to some extent. On the other hand, each phase difference current is the load current I _L1 of power transmission lines 2 and 3
If I L2 and I _L2 are almost balanced, there is no influence of load current. Therefore, under the conditions described above, the value of equation (25) is determined as follows.

｜i _a1s ｜=｜1/3 (2i _ath +2ai _bth +2a ² i _cth )｜ =｜1/3 (474+2×232∠120°+2×150∠240°)｜ =97 (A)……(28) Calculation of the positive phase component will be the value of equation (28) regardless of which phase is used as the reference.

As can be seen from the calculation example of equation (28) above, steps S _8-1 , S _8-2 , and S ₈ The judgment level for _-3 is that the maximum value of circulating current is 474A.
Even in the case of , it can be reduced to 97A.

In the calculation example of equation (28) above, we have explained the case where the load currents I _L1 and I _L2 are balanced, but below we will explain the case where the load is unbalanced, such as a two-terminal transmission line with a T-branch. .

That is, when the load is unbalanced, unbalance occurs in each phase difference current i _as , i _bs , and i _cs .
When calculating the positive phase component using equation (25), the magnitude of the unbalanced component is derived. Therefore, when considering the calculation example using equation (28) above, the value obtained by adding the unbalanced load of each phase to the value of equation (28) is
This is the judgment level at each step S _8-1 , S _8-2 , and S _8-3 . However, even in this case, it is clear that the determination of whether or not the other end is disconnected shown in step _S8 can be correctly determined even in a transmission line with a small load current.

FIG. 7 is another configuration diagram of a digital protective relay device to which the present invention is applied.

In general, digital computers are capable of determining the operation of multiple elements, and there are cases where a ground fault line selection relay and a back-up protection relay are housed in one computer. In this case, it is necessary to input the current for each line for back-up protection, and the difference current is calculated internally. FIG. 7 shows an example of application in such a case.

Therefore, in FIG. 7, the currents corresponding to each phase current and zero-sequence current of each power transmission line 2 and 3, i _a1 , i _b1 ,
Each of i _c1 , i _a2 , i _b2 , i _c2 , i _p1 , and i _p2 is input to the input converter 9
The configuration is the same as that shown in FIG. 1 except for the configuration input in . Therefore, if a method is used that calculates the difference between each phase current and zero-sequence current taken in for each line prior to operation judgment by the digital computer 13, each calculation flowchart explained using the configuration of FIG. 1 can be used as is. Applicable.

FIG. 8 shows an embodiment of the calculation flow according to the present invention. In FIG. 8, step _S9 is a process of calculating and storing the difference current between each phase current and the zero-sequence current prior to calculation of the compensated ground fault line selection relay. Step _S10 performs processing to determine the magnitude of the current value of the healthy phase of each line, and when the same phase currents of both lines are both below a predetermined value, the process moves to step _S4 , and when either one is above a predetermined value. When , execution moves to step _S7 . In step _S10 , when an a-phase ground fault is determined, processing step _S101-1 is executed to determine the magnitude of the b-phase current i _b1 in the power transmission line 2. Here, when i _b1 is smaller than the predetermined value, the next step is
Execute S _102-1 . In this step _S102-1 , the magnitude of the b-phase current i _b2 in the power transmission line 3 is determined. This size determination level is the same as step _S101-1 . If it is smaller than each of the predetermined values, then step _S4 is executed. Also, step
If it is determined in step S _101-1 and step S _102-1 that the value is larger than the predetermined value, the process moves to step S ₇ . Similarly, steps S _101-2 , S _102-2 , S _101-3 ,
In _S102-3 , the sizes of i _c1 , i _c2 , i _a1 , and i _a2 are determined, respectively. The size determination levels in step _S10 above can be made equal and can be determined as follows.

That is, when a one-phase ground fault occurs, the maximum value of the current in each healthy phase of each line until one end is disconnected can be expressed as follows.

i _p = i _L + i _th ... (29) where i _L is the load current and i _th is the circulating current.

Here, it can be considered that the load current i _L is balanced for each phase. On the other hand, the circulating current of each phase is (2
6), as shown in equation (27), it varies somewhat depending on the situation of the induced power transmission line, so the expected maximum circulating current can be selected by calculating the i _th value of equation (29).

On the other hand, after one end is disconnected, the current value of the healthy phase on the healthy line side is as follows.

i _p ′=2i _L ……(30) Therefore, for a transmission line where the load current i _L is larger than the circulating current i _th , both of the two healthy phases are below the value determined by equation (29). It is possible to determine whether or not there is an end or not. Therefore, the magnitude of each phase input can be determined by considering equation (29).

FIG. 9 shows another embodiment of the calculation flow according to the present invention.

This example is intended to explain a case where the assumed circulating current is larger than the load current. 9th
In the figure, step _S11 calculates the positive phase component of each line phase current i _a1 and i _a2 reference. The other configurations are the same as in the case of FIG. 8. Step _S111-1 calculates the positive phase component i _a11 for the a phase of one line, and when the value is less than a predetermined value, the process moves to the next step _S112-1 . In step _S112-1 , the positive phase component i _a21 of the second line a phase i _a2 is calculated, and when the value is less than a predetermined value, the process moves to the next step _S4 . In step _S111-1 and step _S112-1 , if the value is greater than the predetermined value, the process moves to step _S7 . In step S _111-2 , step S _112-2 , step S _111-3 , and step S _112-3 , the determination process of positive phase components i _a11 and i _a21 regarding i _a1 and i _a2 is performed in the same manner as described above. This step
To calculate the positive phase component in _S11 , phase current may be used instead of the difference current in equation (25). Note that since the differential current was used in equation (25), only the circulating current component was slightly calculated as shown in equation (28), but in the calculation of the positive phase component in step _S11 , the load The current is also included, so i _q = i _L + Δi _th ...(31). Since Δi _th is calculated from the circulating current included in the phase current, it corresponds to 1/2 of the value shown in equation (28). Therefore, when compared with equation (29), the influence of the circulating current on the magnitude of the positive phase portion of the phase current is small. Therefore, it can be said that if the calculation flow shown in FIG. 9 is used, it is possible to determine with sufficient accuracy whether or not the other end is disconnected even for a power transmission line where the circulating current is larger than the load current.

FIG. 10 is a calculation flow diagram of another embodiment according to the present invention.

In this embodiment, the amount of change in the difference between the detected current and the compensation current before and after the accident is used as the calculated current. That is, the difference from FIG. 5 is that in the one-phase ground fault detection process in step _S2 , when a one-phase ground fault is not detected, steps _S12 and _S13 are executed;
and step _S4 has replaced step _S14 . Only this changed part will be explained below.

In step _S12 , when a one-phase ground fault detection determination is not made in step _S2 , it is subsequently determined whether or not there is a short circuit accident. However, if a short circuit accident is detected in step _S12 , the process moves to short circuit processing (not shown). Further, if no short circuit fault is detected in step _S12 , the process moves to the next step _S13 . Here, in step _S13 , values of various quantities described later are stored.
After performing this memorization, the process returns to the start of step _S1 . Step _S14 uses the voltage, current, and the amount of memory in step _S13 described above to calculate the calculation amount in each step _S14-1 , _S14-2 , and _S14-3 depending on which phase is the ground fault. Find e _ea , e _eb or e _ec .

Steps _S13 and _S14 will be explained below.

In step _S13 , the following calculation is performed and its value is stored.

i _psM ×v _beM , i _psM ×v _caM , i _psM ×v _abM , K _4b i _bsM ×v _bcM , K _4ea (i _csM + i _asM ) × v _caM , K _4b i _bsM ×v _abM ……(31) However, i _psM , i _bsM , i _csM , and i _asM are zero phase, b phase, and i asM, respectively.
The stored values of the difference currents i _ps , i _bs , i _cs and i _as of the c-phase and a-phase, v _bcM , v _caM , v _abM are the values of the bc-phase, ca-phase and ca-phase, respectively.
The values at the time of storage of the inter-phase voltages v _b -v _c , v _c -v _a and v _a -v _b of the ab phase, K _4b and K _4ca are constants. Further, the above equation is all cross products, and the relationship is shown below with the symbol x.

A×B=|AB|sim(θ _A −θ _B ) ...(32) However, A and B are vector quantities, |AB| is A,
The absolute values of the product of B, θ _A and θ _B , are the angles of the vector quantities A and B, respectively.

Note that it takes some time after the occurrence of the accident for the ground fault and short circuit fault to be detected in step _S2 or _S12 . Therefore, the calculation in step _S13 is performed using the values at the time of the accident from the time the accident occurs until the accident is detected. However, it is not desirable for this value to be used as a memorized value, so if a change is observed in the memorized value when updating the memorized value, the old value is retained for a short period of time, and an accident is detected within a certain period of time. The stored value will be updated when the value is not stored.

FIG. 11 is a flow diagram of the calculation performed in step _S13 . First, if no short circuit fault is detected in step _S12 of FIG.
In S _13-1 , the value of equation (31) described above is calculated. Next, in step _S13-2 , the calculated value in step _S13-1 and the stored value in step _S13-4 are compared to determine whether there is a significant difference. If there is no difference, return to step _S1 . If there is a difference, the process moves to step _S13-3 , and it is detected that the difference has continued for a certain period of time since it occurred. If the predetermined time has not been reached, the process returns to step _S1 , and this process is repeated until it is determined that the predetermined time has continued.
If it is determined that it will continue for a certain period of time, step S _13-4
The process moves to step _S13-1 and stores the calculated value. Note that the above-mentioned fixed time is a slightly longer time than the short circuit and ground fault detection time in step _S12 and step _S2 . As a result, even if there is a slight delay in detecting a short circuit or ground fault, the value before the fault is stored. In step _S14 of FIG.
In S _14-1 , S _14-2 , or S _14-3 , the values of the calculation amounts e _ea , e _eb , and e _ec each expressed by the following equations are calculated.

e _ea = e _da −e _ha e _eb = e _db −e _hb e _ec = e _dc −e _hc ...(33) However, e _da , e _db and e _dc are the detected amounts, e _ha , e _hb and
e _hc is the amount of compensation, both of which are expressed by the following equations.

e _da = i _ps ×v _bc −i _psM ×v _bcM e _db = i _ps ×v _cb −i _psM ×v _caM e _dc = i _ps ×v _ab −i _psM ×v _abM ……(34) e _ha = K _4b i _bs ×v _bc −K _4b i _bsM ×v _bcM e _ha =K _4b i _bs ×v _bc −K _4b i _bsM ×v _bcM e _hb =K _4ca (i _cs +i _as )×v _ca −K _4ca (i _csM + i _asM )×v _c
aM e _hc = K _4b i _bs ×v _ab −K _4b i _bsM ×v _abM ……(35) However, v _bc , v _ca and v _ab are interphase voltages v _b −v _c , v _c −
v _a and v _a −v _b .

The detection amount according to equation (34) above is the fault detection of the cross product of the zero-sequence difference current i _ps and the voltage in quadrature to the fault phase (hereinafter simply referred to as quadrature voltage) v _bc , v _ca or v _ab . This is the amount of change in the value after the accident detection with respect to the previously stored stored value (hereinafter simply referred to as the amount of change in the accident). In addition, the compensation amount in equation (35) is the difference current i _bs of one phase in the healthy phase or the composite value i _cs of the difference current of two healthy phases.
This is the accidental change in the cross product of +i _as and the orthogonal voltage.

As explained above, in the compensated ground fault line selection relay that responds to the change in the difference between the detection current i _d and the compensation current i _h before and after the fault, the amount of electricity in a healthy state is memorized before the detection of a 1-phase ground fault, Step after detecting 1-phase ground fault
Determine the magnitude of the difference current of the healthy phase based on the results for each ground fault phase in _S3 . If the magnitude of the difference current of this healthy phase is smaller than the predetermined value, step _S14 returns (3
3) Calculate the formula to select a compensated ground fault line, but if it is larger than a predetermined value, select a normal ground fault line that responds to the magnitude of the zero-sequence difference current, regardless of the value stored in step _S13 . It is something to do.

Note that the amount of calculations in steps _S13 and _S14 is (3
1), (34), and (35), and the calculation amount shown in equation (13) can be used.

FIG. 12 is another calculation flow diagram according to the present invention, and the configuration of the digital protective relay is based on FIG. 1.

In this embodiment, step _S6 of the calculation flow in FIG. 5 is replaced with step _S15 ,
Since the other parts are the same as those in FIG. 5, only the changed parts will be explained.

In step _S15 , after the ground fault phase is detected in step _S3 , it is determined whether the maximum value of each phase current is less than or equal to a predetermined value, and if the maximum value is less than or equal to the predetermined value, step S15 is executed.
The process moves to step _S4 , and when the value is equal to or greater than a predetermined value, the process moves to step _S7 . In step _S15 , first, step _S15-1 is performed.
The determination result of the ground fault phase in _S3 is stored. In step _S15-2 , the magnitude of each phase difference current i _as , i _bs and i _cs is calculated, and the maximum value thereof is determined. Next, in step _S15-3 , the maximum value calculated in step _S15-2 is compared with a predetermined value, and when it is larger than the predetermined value, the process moves to step _S7 . On the other hand, if the value is smaller than the predetermined value, the process moves to step _S15-4 .
In step S _15-4 , the contents stored in step S _15-1 are read out to determine the ground fault phase, and in step S ₄
It is possible to perform calculation processing according to the ground fault phase in the ground fault phase.

Note that the predetermined value to be compared in step _S15-3 is set so that it can be determined whether or not the magnitude of the input exceeds the full scale of A/D conversion. That is, the full scale of A/D conversion is
In order to properly respond to the other end and before disconnection, the circulating current value is naturally set to be higher than the expected circulating current value. Therefore, in this embodiment, even if the other end is disconnected or disconnected, as long as the input of each phase difference current is within the full scale of A/D conversion, ground fault line selection using the "compensation type" is continued. However, only when there is a risk of exceeding the full scale of A/D conversion, the switch is made to the normal ground fault line selection. According to the present embodiment described above, the full scale of the input can be minimized, so that the sensitivity of the ground fault line selection relay can be improved.

The method of step _S15 in this example is the 12th
The present invention is not limited to the one shown in the figure, but can also be applied to the configuration shown in FIG. 7, which uses currents in each phase. In this case, each phase current of both lines i _a1 , i _a2 , i _b1 , i _b2 , i _c1 ,
The calculation flow may be such that the process of detecting the maximum value among i _c2 and determining that the magnitude thereof is smaller than a predetermined value is performed instead of step _S10 in FIG.

Furthermore, by replacing step _S15 in this embodiment with step _S6 in FIG. 10, (13)
It is clear that the formula can be applied to a compensated ground fault line selection relay based on the principle of

FIG. 13 is another calculation flow diagram according to the present invention, and the configuration of the digital protective relay is as shown in FIG. 7.

In this embodiment, step _S10 of the calculation flow in FIG. 8 is replaced with step _S16 , and since the rest is the same as in FIG. 8, only the changed part will be explained.

In step _S16 , after the ground fault phase is detected in step _S3 , it is determined whether the difference in the magnitude of the same phase current of the two lines is larger than a predetermined value, and even one phase is larger than the predetermined value. If both values are _smaller than the predetermined value, the process moves to step S ₇ .
This is the process that moves on to execution. In step _S16 , first, in step _S16-1 , the ground fault phase determination result in step _S3 is stored.
In step _S16-2 , the a-phase current i _a1 of transmission lines 2 and 3 is
i Calculate the size of _a2 . Next, in step _S16-3 , it is determined whether the difference in magnitude between the a-phase currents i _a1 and i _a2 is larger than a predetermined value, and when it is larger than the predetermined value, the process moves to step _S7 , and When the value is smaller than the predetermined value, the process moves to step _S16-4 . Also, b,
The same is true for the c-phase current, and its magnitude is calculated in steps S _16-4 and S _16-6 , respectively, and it is determined that it is a predetermined value in steps S _16-5 and S _16-7 . If it is determined in step _S16-7 that the value is smaller than the predetermined value, the process moves to the next step _S4 .

Normally, the load is balanced and the negative phase and zero phase components of the load current are negligible, but as the load current increases and the negative phase component increases, the following problems occur.

That is, as shown in (10) to (12), the principle of a compensated ground fault line selection relay that uses negative sequence current for calculation is as follows.
The purpose is to eliminate the circulating current from the calculation current on the premise that the negative phase component can be ignored with respect to the load current. Therefore, if the load current contains an anti-phase component, that amount becomes a calculation error and causes performance deterioration. In other words, even after an accident occurs, when all terminals are closed, calculations are performed using the difference current, so there is no effect of the negative phase component, but after the other end is disconnected or disconnected, the negative phase component due to the difference circuit There is no cancellation, and each phase difference current includes a negative phase component and becomes a relay input.

However, under system conditions where the load current is large and its negative phase component becomes a problem, I _th ≪ I _L1 , I _L2 , so at all times in Figure 3a, for each phase current, |
i _a1 ｜≒｜i _a2 ｜, ｜i _b1 ｜≒｜i _b2 ｜ and ｜i _c1 ｜≒｜i _c2
| holds true, and after one end of Fig. 3 b, |i _a1
|=|i _b1 |=|i _c1 |=I _L1 +I _L2 . However, the accident phase is I _L1 + I _L2 + I _F. Therefore, considering the difference in the magnitude of each phase current of both lines, it is always "0".
It is equal to (I _L1 + I _L2 ) after one end is cut off.
Therefore, the determination levels in steps S _16-3 , S _16-5 , and S _16-7 can be set to values almost close to "0" compared to the load current, and detection can be performed with high sensitivity.

Therefore, by using this embodiment, even in systems where the load current is large and its negative phase component is a problem, it is possible to improve the performance of the compensated ground fault line selection relay that uses the negative phase component current for calculation.

It goes without saying that the determination process in step _S16 can be applied to a compensated line selection relay based on the principle of equation (13).

〔Effect of the invention〕

As explained above, according to the present invention, when detecting a one-phase ground fault accident in a two-terminal parallel two-circuit transmission line through which a circulating zero-sequence current flows, it is possible to detect whether one line at the other end is disconnected or not. The effect of the circulating zero-sequence current is determined by using a compensation type ground fault line selection relay before one line is disconnected, and a fault that is not affected by the circulating zero-sequence current is detected. Since the configuration is configured so that fault detection is performed using a conventional ground fault line selection relay that responds only to Performance can be improved.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a general digital protective relay device commonly used in the prior art and the present invention, Fig. 2 is a conventional example diagram of the calculation flow performed by a digital computer, and Fig. 3 a and b are two-line circuit diagrams. Figure 4 is a diagram showing the state of a one-phase ground fault occurring in a two-circuit transmission line with a T-branch, and Figure 5 is a diagram showing the system status before and after an accident on a protected power transmission line consisting of a T-branch. Calculation flow diagram of ground fault line selection relay by
FIG. 6 is a calculation flow diagram of another embodiment, FIG. 7 is another configuration diagram of a digital protective relay device to which the present invention is applied, FIG. 8 is a calculation flow diagram of another embodiment, and FIG. 10 is a calculation flow diagram of yet another embodiment. FIG. 11 is a detailed calculation flow diagram of step _S13 in FIG. 10. FIG. 12 is a calculation flow diagram of still another embodiment. , FIG. 13 is a calculation flow diagram of still another embodiment. 1... Bus bar, 2, 3... Parallel power transmission line, 4, 5...
...Shield disconnector, 6,7... Current transformer, 8... Instrument transformer, 9... Input converter, 10... Sample hold circuit, 11... Multiplexer, 12...
A/D converter, 13...Digital computer, 1
A, 1B...Each end bus bar, I _L1 , I _L2 ...Load current,
I _th ... Circulating zero-sequence current, I _F ... Fault current.

Claims (1)

[Scope of Claims] 1. In a ground fault line selection relay that protects a 1-phase ground fault in a 2-terminal parallel 2-line power transmission line through which a circulating zero-sequence current flows, means for detecting a 1-phase ground fault in each line; , means for selecting the ground fault phase of the ground fault accident, means for deriving a healthy phase current or positive phase current and comparing it with a predetermined value and detecting a break in one line at the other end according to the magnitude thereof; a first ground fault line selection means that calculates a phase difference current and a polarity amount and calculates a ground fault line when one line at the other end is interrupted; The second method calculates the ground fault line when one line at the other end is not disconnected.
1. A ground fault line selection relay characterized in that said first and second fault line selection means are respectively provided with compensated ground fault line selection means, and are switched in response to a disconnection state of one line at the other end. 2. A patent characterized in that one line at the other end is determined to be disconnected based on the magnitude of the line current value of at least one of the two healthy phases or the magnitude of the difference current being larger than a predetermined value. A ground fault line selection relay according to claim 1. 3. The ground fault line selection relay according to claim 1, wherein the fault determination of one line at the other end is performed based on whether the positive-sequence portion of the differential current is larger than a predetermined value. 4. In a ground fault line selection relay that protects a 1-phase ground fault accident on a 2-terminal parallel 2-line transmission line through which circulating zero-sequence current flows, means for deriving and storing the difference current between each phase current and zero-sequence current of each line; Means for detecting a one-phase ground fault fault in each line; means for selecting the ground fault phase of the ground fault fault; and means for deriving the magnitude of the current value of the same healthy phase of each line and individually setting it to a predetermined value. A means for detecting a break in one line at the other end according to the magnitude thereof compared to A second compensation type ground fault line that calculates a ground fault line selection means and a zero sequence difference current that compensates for the constant circulating zero sequence current and a polarity amount and calculates a ground fault line when one line at the other end is not disconnected. 1. A ground fault line selection relay, characterized in that said first and second fault line selection means are respectively provided with selection means, and are switched between said first and second fault line selection means in response to a disconnected state of one line at the other end. 5. The ground fault line selection relay according to claim 4, wherein the fault determination of one line at the other end is performed based on whether the positive phase component of the same phase reference for each line is larger than a predetermined value. 6. In a ground fault line selection relay for protecting a 1-phase ground fault in a 2-terminal parallel 2-circuit transmission line through which a circulating zero-sequence current flows, a means for detecting a 1-phase ground fault in each line, and a means for detecting a 1-phase ground fault in each line; A means for detecting the presence or absence of a short-circuit accident when it is not an accident, and a means for storing each difference current and polarity of each phase current and zero-sequence current, respectively, and when a change is recognized in the memorized value, and when the value is constant. a storage means for updating a stored value when no fault is detected within the time; a means for detecting the ground fault phase of the ground fault fault; and a means for deriving a healthy phase difference current and comparing it with a predetermined value, A means for detecting a line breakage at one end, and a first means for calculating a ground fault line when a line breakage at the other end is detected by calculating the zero-sequence difference current and the polarity amount.
The ground fault line selection means calculates the zero sequence difference current and polarity amount that compensated for the constant circulating zero sequence current, and uses the stored contents of the storage means to select the ground fault line when one line at the other end is not disconnected. and a second compensating ground fault line selection means for calculating the ground fault, and the first and second ground fault line selection means are switched depending on the failure state of one line at the other end. Line selection relay. 7 In a ground fault line selection relay that protects a 1-phase ground fault in a 2-terminal parallel 2-circuit transmission line through which circulating zero-sequence current flows, a means for detecting a 1-phase ground fault in each line, and a means for detecting a 1-phase ground fault in each line, A means for selecting a phase-to-ground phase,
means for storing the ground fault phase; means for calculating the magnitude of the same phase difference current for each line and determining the maximum value; a first ground fault line selection means for calculating a zero-sequence difference current and a polarity amount to determine a ground fault line when one line at the other end is interrupted; and a constantly circulating zero-sequence current. and a second compensated ground fault line selection means for calculating a ground fault line when one line at the other end is disconnected by calculating the zero-sequence difference current and the polarity amount compensated for. A ground fault line selection relay, characterized in that the first and second fault line selection means are switched in accordance with a ground fault state. 8. In a ground fault line selection relay that protects a 1-phase ground fault accident on a 2-terminal parallel 2-line transmission line through which circulating zero-sequence current flows, means for calculating and storing the difference current between each phase current and zero-sequence current of each line; means for detecting a one-phase ground fault fault in each line; means for selecting the ground fault phase of the ground fault fault; means for storing the ground fault phase; calculated and compared with a predetermined value, and the difference as the comparison result is at least 1
Means for determining that one line at the other end is disconnected when it is larger than the phase, and a first ground fault line selection for calculating a ground fault line when one line at the other end is disconnected by calculating the zero-sequence difference current and polarity amount. and a second compensated ground fault line selection means that calculates the zero-sequence difference current that compensates for the constant circulating zero-sequence current and the polarity amount, and calculates the ground fault line when one line at the other end is not immediately disconnected. 1. A ground fault line selection relay, characterized in that said first and second fault line selection means are respectively provided and switch the respective first and second fault line selection means in response to a disconnection state of one line at the other end.