JPH0458257B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground fault protection system for a co-located multi-line multi-terminal branch system, and more particularly to a line selection relay suitable as a countermeasure against induced circulating current between lines.

Conventional ground fault line selection relays respond to changes in the zero-sequence current of three phases at once as a measure against induced current caused by parallel installations (e.g., Japanese Patent Publication No. 56-36648).
For protection of multi-terminal systems with three or more terminals, calculations become complicated and detection performance may be insufficient.

SUMMARY OF THE INVENTION An object of the present invention is to provide a line selection relay device that reduces the influence of induced current in a combined system in a resistance-grounded multi-terminal branch system and detects ground faults with high sensitivity.

As a countermeasure against circulating current within the protection zone due to induction from the parallel system, the values of the fault current component that changed due to a single-wire ground fault in a three-phase AC system and the circulating current component due to induction are calculated by comparing the values of the fault current component that has changed due to a one-wire ground fault in a three-phase AC system and the value of the circulating current component due to induction to the so-called healthy phase other than the fault phase. This method is estimated based on the current change, and eliminates the induced current component included in the zero-sequence current by using the change ratio of the component that excludes the load current component change from the healthy phase current change as a correction coefficient. However, line selection is determined only based on the fault current component.

FIG. 1 shows an example of the system to be protected by the present invention,
The symbols and operations in the figure will be explained below.

In Figure 1, 1L, 2L, 3L, 4L, 5
L and 6L are power transmission lines to be protected, respectively, and indicate three phases of a three-phase AC power transmission line at once. HL is a high-voltage three-phase AC transmission line that runs parallel to the protected system. CB indicates a bridge or disconnection, and its subscript indicates the location. CB _HA and CB _HB indicate the A terminal and B terminal of HL, respectively, and in the following, CB ₁ , CB ₂ , CB ₃ , CB ₄ ,
CB ₅ and CB ₆ indicate each line number of the disconnector installed at each terminal by subscript. CT is a current transformer and its subscript is
Follow the same commitments as for CB.

The polarity of the CT is set so that the current flowing in the direction surrounded by the protected area A, B, and C ends is positive at 1L, 3L, and 5L (zero-sequence voltage and zero-sequence current are in the same direction), and , 4L, and 6L each have a positive input current in the direction within the protection zone.

50G _A , 50G _B , 50G _C are A, B, respectively.
This is a ground fault line selection relay device installed at the C terminal.

PT _A , PT _B , and PT _C are voltage transformers installed at A, B, and C terminals, respectively, and are 50G _A , 50G, respectively.
This is used to input the reference voltage V〓 _R for determining the direction of current input of G _B and 50G _C. For example, the zero-sequence voltage V〓 ₀ of each terminal bus voltage may be input. .

N _GR is the neutral point grounding resistance, E〓 _A , E〓 _B , E〓 _C are the back power supplies at each end, and T _rfA , T _rfB , T _rfC are the transformers.

Next, assuming that a one-line ground fault occurs at point F in Figure 1, we will connect the relays 50G _A , 50G _B ,
The operation of 50G _C will be explained. Point F is B, C
If it is close to the terminal, the zero-sequence component of the fault current
I〓Cloud 0F is Therefore, only the B terminal can be selected as a line. However, I〓 _N is the zero-sequence current flowing from the A-terminal neutral point. However, the induced current due to the parallel rack has passed through the B terminal even before the accident, and the zero-sequence circulating current at time t0 before the accident is I〓 _0nB(t0) , and at time t1 immediately after the accident, I〓 _{0nB( t1)} , the inter-line difference current at terminal _B is I〓 The zero-sequence component of B〓 _0B is at time t1, I〓 _0B(t1) = 2I〓 _0nB(t1) +I〓 _N(t1) ...( 2) becomes. I〓 _0nB(t1) is induced by the load current I _HL of the parallel system HL, and has an arbitrary phase difference from I〓 _N , so that I〓 _0nB(t1) becomes I〓 _N(t1) It may be larger than
If the component of I〓 _0nB(t1) is not excluded, there is a possibility that correct line selection may not be possible.

As a countermeasure for this, in the present invention, since I〓 _0nB(t0) can be determined based on the zero-sequence current before the fault, current information on phases other than the faulty phase (hereinafter referred to as healthy phases) is also used for I〓 _0nB(t1). and exclude it from equation (2).
This assumes that the I〓 _0nB component changes at the same rate in the same line for each phase a, b, and c, and in the event of an a-phase fault, the circulating current component of the b-phase or c-phase will change.
When the values of I〓 _nb and I〓 _nc change, find the respective change ratios and calculate the zero-sequence circulating current according to that value.
Remove the I _0nB component.

For example, if we look at the inter-line difference current I〓 _b during normal phase b, it consists of the load current component I〓 _Lb and the circulating current I〓 _nb , and is expressed as I〓 _b = I〓 _Lb + I〓 _nb ... (3) . Here, assuming that I〓 _Lb is only the positive-sequence component, and let the positive-sequence component of the three-phase line difference current be I〓 _1s , I〓 _nb = I〓 _b −a ² I〓 _1s ... ...(4). However, a ² is a vector operator and is a complex number of a ² =-1/2-j√3/2.

Find out how I〓 _nb changes between the times t0 and t1 from the current data at t0 and the current data at t1 in equation (4), and calculate the change ratio K〓 _b(01) as K〓 _b(01) =I〓 _nb(t1) /I _nb(t0) =I〓 _b(t1) −a ² I〓 _1s(t1) /I _b(t0) −a ² I _1s(t0) ……(5
) far. By knowing K〓 _b(t0) , the value of the zero-sequence current circulating portion I〓 _0nB shown in equation (2) can be calculated as I〓 _0nB(t1) =K〓 _b(01) ×I〓 _{0nB(t0 )} ...(6) Then, I〓 _0B(t1) =2{I〓 _0nB(t1) +I〓 _N(t1) /2−K〓
_b(01) ×I〓 _0nB(t0) }=2I〓 _N(t1) ...(7) is found.

Comparison of I〓 _0nB(t0) and I〓 _0nB(t1) can be made using the difference between integer cycles of the commercial frequency. For example, if the time used to determine the operation of a 50G _B relay is within 3 cycles, the difference between 4, Alternatively, you can memorize the value from 5 cycles ago and use this as a reference to multiply the value by K〓 _b(01) and subtract it. The same holds true for equation (5) for finding K〓 _b(01) .

As a result, if I〓 _0nB(t0) at the B terminal becomes t1
If there is no change at _all even if
The value of 2I〓 _N(t1) in equation (7) can be obtained.

As a current input of 50G _B , get I〓 _0B(t1) = 2I〓 _N(t1) ,
As shown in Figure 2, the reference voltage is the zero-sequence voltage of the B terminal.
V〓 Compare the phase difference with _0B and select the fault line. In FIG. 2, _I〓P is the level judgment value of _I〓0B . It is better to make the phase characteristic angle θ as narrow as necessary to prevent unnecessary operation of 50G _B.

Based on the above, it is determined that there is an accident at the B terminal 3L, and a shear breaker command is given to the shear breaker CB ₃ to disconnect the shear. The current distribution after the CB ₃ of 3L is disconnected is as shown in the example of FIG. 3, and the value in this state is defined as time t2. Even at t2, the components of the fault current passing through the A terminal are approximately equal at 1L and 2L, therefore,
Line selection is possible only with the C terminal. However, C
Also at the terminal, by cutting the 3L B terminal,
There is a change in the fault current with respect to time t1, and it is assumed that there is a change in the zero-sequence circulating current and a current change due to the shunting of the load current for the B terminal.If only the fault current distribution is not accurately derived, it is necessary to select the line at the C terminal. is not done correctly.

Therefore, for the C terminal as well as for the B terminal, the fault current component at t2 is derived based on the current signal at t0 before the fault.

In other words, the zero-sequence component of the inter-line difference current at terminal C, I〓 _0c , at each time is I〓 _0C(t0) = 2I〓 _0nC(t0) ……(8) I〓 _0C(t1) = 2I〓 _{0nC( t1)} +I〓 _0F5L(t1) +I〓 _0F6L(t1) ≒2I〓 _0nC(t1) ……(9) I〓 _0C(t2) =2I〓 _0nC(t2) +I〓 _0F5L(t2) +I〓 _{0F6L(t2 )} ≒2I〓 _0nC(t2) +I〓 _N(t2) ……(10). Here, considering that I〓 _0nC(t0) , I〓 _0nC(t1) , I〓 _0nC(t2) vary depending on the configuration of the parallel system, at the B terminal
In the same way as finding K〓 _b(t0), the change ratio can also be found from the healthy phase at the C terminal, and from t0 to t1,
If the change ratio at t2 is K〓 _b(01) and K〓 _b(02) , then I〓 _0C(t2) = 2 {I〓 _0nC(t2) +I〓 _N(t2) /2 −K〓 _{b( 02)} ×I〓 _0n(t0) } =I〓 _N(t2) ……(11) is obtained. The fault current component I〓 _N(t2) is obtained from equation (11) and is 50
The direction is judged by _GC and an accident on the 5L side can be detected. Therefore, 50G _C can cut 5L of CB ₅ . At time t3 after the shingle failure, only 1L of the fault current component passes through the A terminal, so line selection is possible; Therefore, as in the case of B and C terminals, the zero-phase component change ratio K〓 _b(03) is calculated and corrected from the healthy phase current signal, and the zero-phase component line difference current at the A terminal is calculated. I〓 _0A(t3) =2 {I〓 _0nA(t3) +I〓 _N(t3) /2 K〓 _b(03) ×I〓 _nA(t0) ｝ I〓 _N(t3) /2 ......(12) get. According to the signal of equation (12), A terminal 50G _A is 1
It was determined that the accident was on the L side, and CB ₁ was cut off.

With the above, the desired accident removal is achieved at t1, t2,
It can be treated by t3 and 3 steps.

FIG. 5 shows a block diagram of hardware for implementing the invention. The figure assumes a digital relay.

The input signal I〓 is the line difference current, V〓 ₀ is the zero-phase voltage signal, and 51 is a digital conversion circuit that converts an analog quantity into a digital quantity. This is a circuit that digitizes commercial frequencies using measures such as using a low-pass filter to prevent this from occurring.

52 is a positive-sequence detection filter that derives the positive-sequence component of the input current I〓. 53 is a circulating current detection circuit that obtains a signal I≓ _n from which the positive phase component of the healthy phase is removed. The selection of healthy phases is performed by a faulty phase selection relay shown at 54.
As a failure phase selection relay, a phase voltage shortage relay may be used to select when only one phase is operated.

Based on the output of 54, signals corresponding to the healthy phases 52 and 53 are selected, the circulating current _I〓n of the healthy phase is detected, and this is stored in the memory circuit 55. The contents of the memory store the value of I〓 _n(t0) mentioned in the present invention, and output 53.
The ratio with I〓 _n(t1) is taken, and K〓 _b(01) = I〓 _n(t1) /I _n(t0) ... (13) is calculated using 56 comparison circuits. The output of 56 changes as the circulating current reaches t1 from t0, and the change ratio is K〓 _b(01) .

57 is a zero-phase current detection filter, and the input signal
Obtain the zero phase component of I〓 I〓 ₀ .

58 is a memory circuit, which stores data before the accident detection in 54.
This is a circuit that stores I〓 _{0 (t0)} when I〓 ₀ is taken as time t0. 59 is a multiplier that outputs 58's output I〓 _0(t0) to 56
Multiply the output K〓 _b(01) and output K〓 _b(01) ×I〓 _0(t0) .

60 is a subtracter, which is a circuit for subtracting the output of 59 from the output of 57 to extract a fault current component. The output of 60 is I〓 _R0 = I〓 _0(t1) −K〓 _b(01) I〓 _0(t0) ...(14) and at the time tn of recognition after the accident, I〓 _R0 = I〓 This is a circuit that can output _0(to) −K〓 _b(0o) ×I〓 _0(t0) ...(15).

61 is a phase determination circuit, which is a part that determines whether or not the operating range shown in FIG. 2 is entered.

FIG. 6 shows a flowchart when the contents shown in FIG. 5 are processed by a computer or the like.

The block A1 in the figure shows a function of sampling input signal voltage and current and converting them into digital data.
A2 is a block that identifies a fault phase and a healthy phase from an input voltage signal; for example, a phase whose phase voltage has decreased below a normal state is considered a fault phase, and a phase whose voltage has increased is considered a healthy phase. The present invention is intended to protect against one-wire ground faults, and A3 is a one-wire ground fault determination section, which performs the processes following A4 only when only one phase is in fault.

If a phase one line ground fault is detected in A2 and A3, in A4, the difference current between lines I〓positive phase component of input signal I〓 ₁ ,
Also performs calculation to obtain zero phase I〓 ₀ .

A5 stores the value I〓 _0(t0) at time t0 before the accident.

In A6, the circulating current component of the healthy phase (e.g. phase b) I〓 _nb
In the block that calculates the line current I〓 _b , subtract the b-phase equivalent of the positive sequence current I〓 ₁ calculated in A4, a ² I〓 ₁ , and calculate b
Obtain the phase circulating current I〓 _nb .

A7 stores _I〓nb(0o) at time t0.

A8 is a block that calculates the change ratio K〓 _b(0o) of I〓 _nb , and the change ratio of the value at any time tn to time t0 K〓 _b0o = I〓 _nb(to) /I _nb(t0) Find it by.

In A9, the change in the zero-sequence current I〓 ₀ calculated in A4 is calculated from the data at time t0 in t0: I〓 _R0 = I〓 _0(to) −K〓 _b(0o) ×I〓 _{0 (t0)} ...(16) is calculated.

A10 compares the phase of V〓 ₀ and I〓 _R0 , and the second
Determine whether or not it is in the operating range shown in the figure, and output the output to 5
This is the judgment output of the 0G relay.

With the above invention, it is possible to select a ground fault line with high sensitivity by removing the influence of induced current in the parallel system.

It is also applicable to protection of multi-terminal systems with three or more terminals.

In addition, in the present invention, the change ratio of the zero-sequence circulating current K〓 _b is treated as the healthy phase when the a-phase fault occurs, but the c
The values of the phases or the b-phase and c-phase may be used, and in some cases, the change ratios of the b-phase and c-phase may be averaged and used.

Also, K〓 _b(0o) is a coefficient that converts the vector quantity, but in a system where the phase change of the induced current can be ignored,
It may also be obtained as K〓 _{b( 0o)} = |I〓 _nb(to) | / |I _nb(t0) | ...(17) with K〓 b(0o) as a scalar quantity.

Equation (17) has the advantage that the calculation process is easy because it is an absolute value calculation.

Further, in the inter-line difference current for each phase, the amount of change after removing the load current (positive phase portion) of the fault phase instead of the zero-sequence current may be detected, and a 50G current signal for determination may be used.

[Brief explanation of the drawing]

FIG. 1 shows a conceptual diagram of the overall configuration for explaining an embodiment of the present invention. FIG. 2 shows an example of phase characteristics of a line selection relay. Figure 3 shows the current distribution before and after the break. FIG. 4 shows the current distribution during the second-stage shunt break. FIG. 5 shows an example of a circuit configuration for implementing the present invention.
FIG. 6 shows an arithmetic processing flow diagram of the present invention. 51... Digital conversion circuit, 52... Positive phase detection filter, 53... Circulating current detection circuit, 54... Fault phase selection relay, 55... Memory circuit, 56... Comparison circuit, 57... Zero phase current detection filter, 58... Memory circuit , 59... Multiplier, 60... Subtractor, 61... Phase determination circuit.

Claims (1)

[Claims] 1. In a ground fault line selection relay that uses zero-sequence current and zero-sequence voltage to detect single-line ground faults in parallel two-line systems, the first current signal is obtained by removing the positive phase component from the line difference current of healthy phases. The signal obtained by subtracting the product of the ratio of the current value and the value before T time and the zero-sequence current before T time from the current zero-sequence current is the zero-sequence current, and this zero-sequence current and zero-sequence voltage are A ground fault line selection relay characterized by detecting a ground fault.