JPH0158734B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a line ground fault protection relay for a power system, and more particularly to a line ground fault protection relay for a power system in which a zero-sequence circulating current is generated due to the induction of multiple interconnected lines.

When an ultra-high voltage power transmission line and an impedance grounding system transmission line are installed together, a zero-sequence circulating current is generated in the impedance grounding system transmission line, which poses a problem in terms of power line ground fault protection. Figures 1 and 2 are diagrams showing this situation, where Tr is a transformer, I1 is a power flow, and 1
is the lower system, and 2 is the upper system.

As shown in Figure 1, when power transmission lines 1 and 2 are installed together in section L, due to the imbalance in the mutual induction of the transmission lines between upper system 2 and lower system 1, during normal times, lower system 1 , a zero-phase circulating current Ic ₀ flows. The magnitude of this zero-phase circulating current Ic ₀ is proportional to the magnitude I1 of the power flow in the upper system 2 and the length of the shared section L.

A ground fault (second
If F) in the figure occurs, as shown in Figure 2,
The zero-sequence current of the power transmission line is the sum of the fault currents IF ₁ and IF ₂ and the zero-sequence circulating current Ic ₀ . Here, in general,
Earth fault fault current IF ₁ , IF ₂ of impedance grounding system
is very small, so there are cases where Ic ₀ is larger.

In this case, at the installation point P of the protective relay RY ₁ , the zero-sequence current flowing through the earth fault direction relay is applied to the protective relay RY ₁ , assuming that the fault current IF ₁ and the zero-sequence circulating current Ic ₀ are in opposite phases. The zero-sequence voltage V ₀ and zero-sequence current I _RY are as shown in FIG.

Note that the zero-sequence current _IRY is expressed by the following equation.

I〓 _RY = I〓c ₀ + I〓F ₁ Here, the ground fault direction relay is a relay that operates by determining whether the input voltage and input current are in phase or in opposite phase. Therefore, if (Ic ₀ +IF ₁ ) is in phase opposite to the zero-phase voltage V ₀ as shown in FIG. 3, the direction will be incorrectly determined.

To deal with this problem, conventional methods focused on the fact that the zero-sequence circulating current is input to the protection relay as a zero-sequence current during normal times, and used the polarity voltage that serves as a reference for the direction of the ground fault current as the reference voltage for the ground fault current. Line voltage that does not change (V _AB for A-phase relays, V BC for B-phase relays, and V _BC for C-phase relays)
V _CA ) is being used.

In other words, a sensitivity scanning ground fault direction relay, etc. that calculates the active power between each of the line voltages and outputs an operating output when the range of change in the active power exceeds a certain value. has been proposed and used.

In addition, the difference current between lines of each phase of an impedance grounding system two-line transmission line is derived, and the magnitude of the difference current between each phase line is corrected based on the ratio of the magnitude of the derived difference current, and the magnitude of the difference current between lines of each phase is corrected. A method for determining and correcting phases, and deriving the ratio of the magnitude of the difference current between each phase and the phase difference thereof, correcting the magnitude and phase difference of the difference current, and determining and correcting the ground fault phase. A method has already been proposed ((Japanese Unexamined Patent Publication No. 1983-1999)
131227).

However, all of these ground fault direction relays
Since this method focuses on the rate of change in the ground fault current, (1) the operating output duration depends on the magnitude of the ground fault current, and the system will recover even if the fault continues.

(2) Because each phase is judged, in principle, protective relay devices are required for three phases, and in addition, a ground fault phase detection relay (discrimination unit that determines the ground fault phase) is required. Therefore, the circuit becomes complicated.

(3) Since changing values are used, there is a risk of misjudgment, misjudgment, or malfunction due to sudden changes in the zero-phase circulating current that occur during normal operation of the power system.

(4) Misjudgment will occur in the event of an accident involving one line ground fault or more.

There were other inconveniences.

The present invention solves the above-mentioned disadvantages,
It is an object of the present invention to provide a shared multi-line ground fault protection relay that can obtain good characteristics by effectively taking measures against zero-phase circulating current generated in a shared multi-line power system.

The feature of the present invention is to focus on the fact that the zero-sequence current given from the grid is a zero-sequence circulating current in normal times when there is no ground fault, and by storing this for a scheduled period, the delayed zero-sequence current is A calculation is performed to calculate a value equivalent to the effective amount (as the operating force) using Then, the effective component of the normal zero-sequence current, that is, the zero-sequence circulating current, against the zero-sequence voltage generated by the ground fault can be found, and when determining the direction of the ground fault fault, by subtracting that value from the operating force, The point is to implement countermeasures against zero-phase circulating current in the shared system.

FIG. 4 is a block diagram showing one embodiment of the present invention implemented in a digital device. In the figure, 3 is the power transmission line to be protected, and although it is not shown in the figure, as in Figures 1 and 2,
It is co-extended with other power transmission lines, and a zero-sequence circulating current Ic ₀ is generated as shown in the figure.

20 is a current transformer, which transforms the current of the power transmission line 3,
The protective relay device converts it into an easy-to-handle current value. 1
A is a busbar to which the power transmission line 3 is connected via a disconnector 5, and a parallel counterpart line is connected to one side. 4 is a voltage transformer, which, like the current transformer 20, converts the grid voltage into a voltage that can be easily handled by the protective relay device.

15 and 6 respectively sample the zero-sequence current signal S1 inputted by the current transformer 20 and the zero-sequence voltage signal S2 converted by the voltage transformer 4 at fixed time intervals Δt, and convert them into digital values. An analog-to-digital converter (A/D converter) for conversion.

Reference numeral 7 denotes a storage unit that stores the zero-sequence current current value signal S3 converted into a digital value by the A/D converter 15 for a certain period of time. 8 is a zero-phase voltage signal S4 stored in the storage section 7 and a zero-phase voltage signal S5 converted into a digital value by the A/D conversion section 6.
This is a calculation unit that calculates a value corresponding to the effective portion of the zero-sequence current.

The value corresponding to the effective component can be calculated using the formula (1), for example, V _p (t) I _p (t-n) _cps θ _p = PIc ₀ ... (1) However, V _p (t)... The current value I _p (t-n)...the value θ _p of the zero-sequence current before the storage period... can be carried out by calculations such as the phase angle between the zero-sequence voltage and the zero-sequence current.

Reference numeral 10 denotes an accident detection section that detects the occurrence of a ground fault accident based on the zero-phase voltage signal S5, and detects an accident using calculations such as equation (2).

｜V _p ｜≧V _S ...(2) However, V _S ... Setting value for accident detection In other words, when the value of zero-sequence voltage is larger than V _S ,
Detects occurrence of ground fault.

Reference numeral 9 denotes a storage unit for holding the value of the output signal S6 of the calculation unit 8 at the time when a ground fault accident is detected by the accident detection unit 10, and stores the value at the accident detection point during accident detection. .

Reference numeral 11 denotes a ground fault direction detection unit, which performs a predetermined calculation using the current value signal S5 of the zero-sequence voltage and the current value signal S3 of the zero-sequence current, and determines whether or not the direction is the protection direction.

Here, the operating force is obtained by calculation such as equation (3) V _p (t _o ) I _p (t _o ) _cps θ ₁ =P _pp (3). In addition, to determine whether or not the direction is in the protection direction, the signal S8 held at the time of accident detection is used to perform the calculation as shown in equation (4) P _pp −PIc ₀ ≧P _S ……(4), When the condition of equation (4) is satisfied, the operation output signal S9 is output.

Reference numeral 12 denotes a logic judgment unit, which performs a predetermined logical judgment (which itself is publicly known), and when it is determined that it should be cut off, outputs a shearing command S10, and sets the shearing cutter. An open command is output to 5. In the embodiment shown in FIG. 4, the logic determining section 12 may be an AND circuit having input signals S7 and S9.

FIG. 5 is a program for implementing the operations shown in the block diagram of FIG. 4 on a digital device such as a computer.

First, when the device is started in step D1,
At step D2, the zero-sequence voltage input from the grid
V _p and zero-sequence current I _p are sampled at regular intervals and converted into digital values. Next step D3
Then, use V _p to perform the calculation as in equation (2) above,
Detects ground faults.

In step D4, the result of step D3 is determined. Here, if there is no system accident, proceed to step D.
5, I _p converted into a digital value in step D2 is stored for a certain period of time.

Next, the process proceeds to step D6, where calculations such as the above-mentioned equation (1) are performed using I _p from a certain period of time ago, which was stored in step D5, and the current value V _p , which was converted in step D2. Return to

If there are no system failures, the above steps are repeated at regular intervals.

On the other hand, if the occurrence of an accident is detected in step D4, the process advances to step D7, and the calculation result of step D6 that was calculated before the accident detection (i.e.,
The effective part of I _p calculated from I _p and V _p is retained and memorized.

Step D8 is a step for carrying out the main calculation of the protection operation, and uses the current value of I _p and the current value of V _p to carry out calculations such as the above-mentioned equation (3) to determine the operating force. Next, in step D9, step D
Using the operating force obtained in step D7 and the value stored in step D7, calculations such as equation (4) are performed.

In step D10, the ground fault direction is determined based on the calculation result in step D9. Here,
If the direction of the ground fault fault is the protection direction and it is determined that the operation is possible, the process proceeds to step D11, where a logical judgment is made for tripping the breaker.

The content of the logical judgment itself is publicly known; for example, whether the usage conditions of the device are met;
For example, whether or not a short circuit accident has been detected.

In the next step D12, in response to the result of the logical judgment, it is determined whether or not a shear cutoff command should be output to the shear cutter. If the conditions are satisfied, the process proceeds to step D13, where a tripping command to the shroud breaker is output, and the shunt breaker is opened. This completes the protection operation.

If it is determined in step D10 that there is no operation, and if it is determined in step D12 that the condition is not satisfied, the process returns to step D2 without outputting the tripping command. As a result, the program route described above is repeated.

FIG. 6 is a time chart showing the operation explained in FIGS. 4 and 5, and shows how a ground fault occurs at time t ₀ and a zero-phase voltage V _p is generated.

Here, I _p is the zero-sequence current. It goes without saying that the current before time t ₀ is a zero-sequence current in a normal state when there is no ground fault current, and represents a zero-sequence circulating current.

PIc ₀ indicates the calculation result of equation (1) calculated in the calculation unit 8 of FIG. 4 or step D6 of FIG. That is, the storage section 7 in FIG.
This is a value calculated from the zero-sequence circulating current with a time interval T _M from the time point t ₀ of the accident occurrence stored in step D5 in the figure, and V _p caused by the ground fault.

However, in Figure 6, the value calculated using the following equation (1A) is set as PIc ₀ .

PIc ₀ = _to 〓 ^t=to V _p (t)·I _p (t− _TM ) (1A) Moreover, the example in this figure shows the case of a negative value. The PIc ₀ is maintained at a constant value at the accident detection time _to .

Note that T _pp in the figure is the accident detection time (time from time t ₀ to t _o ), which is generally called the operation time. Further, T _M is the storage period of the zero-sequence current. If the value of T _M is selected to be an integral multiple of the period of the system frequency, it is possible to easily judge the calculation result.

Here, the operating time T _pp and the zero-sequence current storage period T _M are selected so that the relationship of equation (5) holds true: T _M > T _pp ...(5) By doing so, I _p becomes It is clear that the normal zero-sequence current that does not include the fault current can be used as the zero-sequence circulating current.

P _pp is the calculated value for ground fault direction determination, and is
This is the calculation result shown by equation (3). In Figure 6,
The calculation of P _pp starts at the time t _o when the accident occurrence is detected.
Furthermore, since the illustrated example shows a case in the protection direction, it shows a gradual increase in the positive direction with time.

(P _pp −PIc ₀ ) indicates the calculated value of equation (4).
This value is the value at time _to , that is, the value at the accident detection point (−
PIc ₀₁ ), it gradually increases in the positive direction, and −PIc ₀₁
An operating output is generated at a time point t _o+A when P S is increased by more than P _S .

FIG. 7 is a diagram showing the characteristics of the earth fault direction relay device according to the embodiment described above. This diagram is
A characteristic diagram for a method that determines the direction of a ground fault fault by determining operation when the in-phase component of I _p with respect to V _p , that is, the effective component, exceeds a set value, that is, when V _p is set to a constant value. It is a phase characteristic diagram.

The basic characteristics when there is no zero-sequence circulating current are as follows: V _p (t _o )・I _p (t _o ) _cps θ ₁ >I _S The basic characteristics are V p (t o )・I _{p (t o )} cps θ 1 >I The upper hatched area is the operating area.

Furthermore, when there is a zero-phase circulating current, it can be easily estimated that the upper diagonal line of the straight line offset by the zero-phase circulating current becomes the operating region, as explained with reference to FIGS. 4 to 6.

In other words, the origin 0 of the basic characteristics becomes 0', and P~Q
The axes are axes P' to Q'. The operating range is parallel to the P' to Q' axes and is indicated by the upper oblique line of the straight line separated by _IS .

In Fig. 7, assuming that IF ₁ , Ic ₀ , and I _RY are the fault current, zero-sequence circulating current, and input zero-sequence current of the relay device explained in Figs. 2 and 3, the basics of A. According to the characteristic, it is inoperative, but by implementing the present invention, the operating region becomes the characteristic (b), so it can operate.

As is clear from the detailed description above,
According to the embodiment of the present invention, the influence of zero-sequence circulating current is eliminated, and effective ground fault protection can be achieved.

In addition, in the above-mentioned embodiment, the method of calculating the ground fault direction was explained as a method of calculating the active power using the zero-sequence current and the zero-sequence voltage, but it is also possible to use a method based on other principles such as the impedance calculation method. However, it goes without saying that the same effect can be obtained by correcting the operating force with a current corresponding to the zero-sequence circulating current obtained by storing the normal zero-sequence current for a certain period of time according to the calculation formula.

In addition, in the above embodiment, it was explained that the zero-sequence voltage does not change after the occurrence of an accident, but in consideration of the fact that the nature of the accident changes, the value of the zero-sequence voltage is continuously measured, and the value is adjusted accordingly. Then, the value PIc ₀ of equation (1) held at the ground fault detection point is expressed as the following equation (6): PIc ₀ (n+i)=|V _p (n+i)|/|V _p |・PIc ₀ ...
...It is also possible to improve accuracy by correcting according to (6).

As explained above, according to the present invention, it is possible to almost eliminate the influence of zero-sequence circulating current in shared multi-circuits, and to obtain a ground fault protection relay that can detect ground faults with high accuracy. The effect is huge.

[Brief explanation of drawings]

Figure 1 is a schematic diagram to explain the generation of zero-sequence circulating current in a shared multi-circuit line, Figure 2 is a diagram showing the current distribution when a ground fault occurs in the line in Figure 1, and Figure 3 is a diagram showing the current distribution when a ground fault occurs in the line in Figure 1. 4 is a block diagram showing an embodiment of the present invention, FIG. 5 is a program flowchart when the present invention is implemented in a digital device, and FIG. 6 explains the operation of the present invention. FIG. 7 is a characteristic diagram of a relay according to an embodiment of the present invention. 1A... Bus bar, 3... Power transmission line to be protected, 5...
Line breaker, 6, 15...A/D converter, 7...Zero-sequence current storage section, 8...Zero-sequence current effective component calculation section, 9
. . . Storage section, 10 . . . Accident detection section, 11 . . . Earth fault direction detection section, 12 .

Claims (1)

[Scope of Claims] 1. In a relay system for protecting against ground faults in a shared multi-line power transmission system in which a large number of power transmission lines are co-installed on the same tower, a first system that stores zero-sequence current input as system information means, a second means for calculating a value corresponding to the operating force using the zero-sequence voltage and the zero-sequence current before the scheduled time stored by the first means; a ground fault is detected by the zero-sequence voltage or the zero-sequence current; a third means for holding the value calculated by the second means when the
A fourth means for determining the direction of a ground fault fault by comparing the value held by the means with the effective value obtained from the current values of zero-sequence voltage and zero-sequence current. Multi-line ground fault protection relay. 2 The fourth means subtracts the value held by the third means from the effective value obtained by the current values of the zero-sequence voltage and zero-sequence current, and the obtained difference is the expected value. 2. The shared multi-line ground fault protection relay according to claim 1, wherein the shared multi-line ground fault protection relay is characterized in that the direction is determined to be a ground fault direction when the direction is exceeded.