JPH0113293B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a protective relay device for protecting multi-circuit, multi-phase power transmission lines, and is particularly suitable for protecting power transmission lines with large ground charging currents and line-to-line charging currents. This invention relates to a method for compensating for power transmission line charging current.

[Prior art]

In recent years, there has been a trend toward multi-conductor and longer-distance power transmission lines, and such power transmission lines, even if they are overhead power transmission lines, have a large amount of floating ground capacitance and stray line-to-line capacitance. Such a large amount of capacitance causes a charging current that is too large to be ignored compared to the normal load current to flow through the power transmission line.

If an accident occurs on a power transmission line through which such a large amount of charging electricity flows, the charging current is calculated as a current flowing into the transmission line, similar to the internal fault current, so a current differential method is adopted to protect the power transmission line. In this case, unless this charging current is compensated for, there is a drawback that the detection sensitivity for internal faults decreases. Therefore, as a method of compensating the amount of charging electricity for a power transmission line through which such a large amount of charging current flows, a method has been filed that uses line voltage instead of bus voltage to compensate for charging current. This method seems to have small compensation errors and good accuracy, but
There was a problem that the number of calculations was large and the device configuration was complicated. In other words, in a multi-circuit multi-phase power transmission line, there are many types of ground-to-ground and line-to-line capacitances, so if you try to compensate for the charging current due to all capacitances, the ground voltage of all phases and It is necessary to find the line voltage between all phases. This has the disadvantage that the number of calculations increases and the device for compensating for charging current becomes complicated and large-scale, and a large number of compensation calculations slows down the operating speed of the protective relay device.

[Purpose of the invention]

An object of the present invention is to provide a transmission line charging current compensation method that eliminates the above-mentioned drawbacks, simplifies the configuration of a protective relay device that compensates for a large amount of charging current, and improves the response speed of the protective relay device. It's about doing.

[Summary of the invention]

The present invention provides a transmission line charging current compensation method for a protective relay device that protects a transmission line by detecting an abnormality in the transmission line current and opening circuit breakers at both ends of the transmission line. It is calculated using the line voltage, ground capacitance, and line capacitance, and the line-to-line charging current with other lines is the line-to-line static between the ground electrode of the own phase and the other phase in the other line. By performing approximate calculations using the capacitance, the calculation unit can be downsized, the configuration of the device can be simplified, and the response speed of the device can be improved.

Next, the principle of the present invention will be explained. Figure 1 is a schematic diagram showing a three-phase, two-circuit power transmission line with phases a, b, c and a', b', c, and Figure 2 is a schematic diagram of the transmission line shown in figure 1. FIG. 3 is a vector diagram showing phases of phase charging currents. In Fig. 2, 11 indicates the voltage to ground of the a phase V〓 _a , 12 indicates the voltage to ground of the b phase V〓 _b , 13
is the ground voltage V〓 _c of the c phase, 14 is the line voltage V〓 _ab between the ab phases, 15 is the line voltage V〓 _ac between the ac phases, 16
is the a-phase ground charging current I〓 _aa , 17 is the line-to-line charging current between the a-b phases I〓 _ab , and 18 is the line-to-line charging current between the ac phases.
I〓 _ac , 19 is the combined current of I〓 _ab and I〓 _ac , 20
teeth
It shows the a-phase charging current I〓 _a , which is a composite of I〓 _aa , I〓 _ab , and I〓 _ac . This is indicated by the reference numeral 19 in FIG.
The combined vector of line-to-line charging currents of other phases, which is a combination of I〓 _ab and I〓 _bc , has almost the same phase as the a-phase ground charging current vector indicated by reference numeral 16. The present invention focuses on this fact, and calculates the line-to-line charging current with other lines by using the sum of the ground voltage V〓 _a of the own phase and the line-to-line capacitance with other lines, C _aa ′ + C _ab ′ + C _ac ′. The aim is to simplify the configuration of the device by reducing the number of calculations, and to shorten the calculation time and improve the responsiveness of the device. The magnitude of the error when such approximate calculation is performed will be explained below.

The accurate line-to-line charging current between the a-phase and other lines is expressed by equation (1).

I〓 _a ′＝jωC _aa ′(V〓 _a −V〓 _a ′)＋jωC _ab ′(V〓 _a −
V〓 _b ′) +jωC _ac ′ (V〓 _a −V〓 _c ) ...(1) I〓 _a ′ expressed by the equation (1) is obtained by the conventional method, but the present invention described above Approximately calculating the charging current I〓 _a ″ with other lines of phase a using the method of
(2) becomes as follows.

I〓 _a ″=jω(C _aa ′+C _ab ′+C _ac ′)V _a ……(2) Therefore, the difference ΔI〓 _a ′ between equations (1) and (2) is the exact difference between the present invention and the conventional method. This will be a compensation error with the calculation by the method.

ΔI〓 _a ′=I〓 _a ′−I〓 _a ″= −jωC _aa ′V〓 _a ′−jωC _ab ′V〓 _b ′−jωC _ac ′V〓 _c ′
...(3) If we calculate this ΔI〓 _a ′ assuming that the voltage vector is balanced, we get equation (4).

That is, if C _ac ′=C _ab ′=C _aa ′, ΔI〓 _a ′=0.
However, in an actual power transmission line, ΔV〓 _a ′ is not 0, but C _aa ′, C _ab ′, and C _ac ′ are comparable values, and equation (4) is established by subtraction, so ΔI〓 _a will take an extremely small value.

Therefore, an example of numerical calculation will be shown below to determine the value of ΔI〓 _a ′.

｜V _a ｜ = 1000/√3 (KV), C _aa = 1.49 (μF),
C _ab = 0.74 (μF), C _ac = 0.22 (μF), C _aa ′ = 0.11
(μF), C _ab ′ = 0.23 (μF), C _ac ′ = 0.40 (μF), assuming the grid frequency to be 50Hz, enter these values into equation (1), and calculate the a-phase charging current |I〓 _a | When calculated, the value shown in equation (5) is obtained.

|I〓 _a |=704.99(A) ...(5) Also, when the above numerical example is substituted into equation (3) to calculate the compensation error |ΔI〓′ _a | according to the present invention, equation (6) is obtained.

|ΔI〓′ _a |=45.77(A) ...(6) Therefore, the compensation error |ΔI′ _a |/|I〓 _a | becomes 6.5%.

The above is a discussion under normal conditions, but next we will discuss after the accident phase is shut off in the event of an accident. Note that the following discussion will assume that phase a is in a state where no accident has occurred. This is a
This is because if a phase, that is, the own phase, causes a fault, a large amount of differential current is generated and the fault is detected, so there is no need to compensate for the charging current. The problem is compensation for the charging current of the healthy phase.

First, as a first step, we will consider the ongoing accident. If the fault occurs within the own line, the line voltage is used to determine the line charging current, so no errors occur. Considering that the accident is on another line, if the accident is a ground fault,
Since the voltage between the fault phase and the line is equal to the ground voltage of the own phase, a compensation error of charging current does not occur even if the approximate value calculation according to the present invention is performed.

FIG. 3 shows the phase of the voltage at the time of a ground fault, where 21 is the voltage vector of the own phase, and 22 is the voltage vector of the fault phase of the other line. As can be seen from this figure, 23 and 21 are almost equal, which means that even if the approximate calculation of the present invention is used, there is little error.

Next, if we consider the case where the accident is a short circuit accident, the voltage vector in this case will be as shown in FIG. 24
25b and 25c are multiphase voltage vectors before the accident, and 26 is the voltage vector of 25b and 25c at the time of the accident. 24 and 26
As you can see, the phase before the accident is 180 degrees ahead of the healthy phase, and the magnitude of the transmission voltage is 1/2. Therefore, the phase of the line voltage is equal to the ground voltage of the healthy phase, and the magnitude is 1.5 times. This means that according to the charging current compensation method using approximate calculation of the present invention, there is a 50% undercompensation for the ground voltage of the own phase. However, as in the case of a healthy phase, when viewed from the charging current of the whole healthy phase, the error due to this lack of compensation becomes so small that it can be ignored in practical terms. As an example, let us calculate the charging compensation error when a two-wire short circuit occurs between the b' and c' phases of the second line. Using the same data as in the healthy state, the above (1)
From equation (3), the a-phase charging current at the time of the accident is (7)
Since the compensation error at this time is the value shown in formula (8), the ratio of the compensation error to the charging current is 8.13%, and the compensation error is extremely small and does not pose a problem in practice. .

｜I〓 _a ｜=702.85(A) ……(7) ｜ΔI′ _a ｜=57.13(A) ……(8) Next, consider what happens after the fault phase is shut off as the second stage.
In the event of an accident, the circuit breakers at both ends of the transmission line are opened by the protective relay device, resulting in a difference between the bus voltage of the fault phase and the transmission line voltage. Therefore, the compensation error value obtained by the above-described approximate calculation according to the present invention differs depending on whether the ground voltage of each phase is measured at the bus bar or on the transmission line side of the circuit breaker. First, consider the case where the ground voltage of each phase is measured on the power transmission line side. If the faulty phase is within the own line, no problem will occur because the line voltage will be measured correctly. If the fault phase is in another circuit, the ground charging current I _ab flows from the own phase to the ground via the cutoff phase, as shown in FIG. Therefore, in the compensation method of the present invention, although the phase of the charging current is accurate, an error occurs in its absolute value, that is, its magnitude. a in Figure 5
The line-to-line charging current from the phase to the b′ phase is shown by equation (9),
The amount of compensation based on the approximate calculation of the present invention is expressed by equation (10).

I _ab ′＝jωC _ab ′C _b ′ _b ′／C _ab ′＋C _b ′ _b ′V〓 _a ……
(9) I″ _ab ′=iωC _ab ′V〓 _a ...(10) By subtracting (10) from the above (9), the compensation error shown in equation (11) can be obtained.

｜ΔI _ab ′｜＝｜ωC ² _ab ′／C _ab ′＋C _b ′ _b ′V〓 _a ｜…
...(11) If we insert the previous value into equation (11) and perform a numerical calculation, we get |I _ab ′| = 7.44A. This value is extremely small, about 1/100 compared to the entire a-phase charging current, and the error can be practically ignored. The state described above is a state in which the circuit breakers at both ends of the power transmission line have been opened but have not yet been opened.

Next, if the circuit breakers at both ends of the transmission line are opened and the phase whose transmission current is cut off is grounded by a grounding switch, the potential of the faulty phase becomes zero, so the compensation method using the approximate calculation of the present invention is applied. No errors occur.

Next, consider the case where the ground voltage of each phase is taken from the bus bar side. In this case, the line voltage between the fault phase and its own phase cannot be determined accurately, regardless of the location of the fault phase. Therefore, the discussion of equations (9), (10), and (11) above holds true whether the fault phase is within the own line or another line, and the error is the same as (11) above.
As mentioned in the equation, it is so small that it can be ignored in practice.

As described above, the feature of the present invention is that the charging current compensation method is divided into the charging current within the own line and the charging current between other lines, and the compensation method for the charging current within the own line is as accurate as before using the line voltage. In contrast, when calculating the line-to-line charging current with other lines, the calculation unit calculates the line-to-line charging current by approximating the line-to-ground voltage instead of the line-to-line voltage without measuring the line-to-line voltage. This simplifies the device, shortens calculation time, and improves the response of the protective relay device.As mentioned above, the error associated with the approximate calculation is within a range that does not pose a practical problem. It is becoming.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 6 to 8. FIG. 6 is a block diagram showing an outline of an embodiment of a protective relay device to which the power transmission line charging current compensation method of the present invention is applied. Both ends of the power transmission line 31 are connected to the substation busbar 3 via circuit breakers 32 and 33, respectively.
4,35. The voltage of the power transmission line 31 is detected by transformers 36 and 37 and input to arithmetic units 38 and 39, respectively. The arithmetic device 3
In 8 and 39, the compensation charging current of the own phase and each phase is calculated from the power transmission voltage, but especially the compensation charging current of each phase is calculated from the transmission voltage.
Calculate by performing approximate calculation according to equation (2). Transmission currents are detected by transformers 40 and 41 attached to the busbar side, and these transmission currents are input to subtracters 42 and 43. In these subtracters 42 and 43, the transformer 4
From the power transmission current detected by 0 and 41, the arithmetic unit 3
The true transmission current 44, 45 after subtracting the compensation charging current calculated in 8, 39 is the true transmission current 44, 45 of the circuit breaker switching device 46, 47.
The circuit breaker switching devices 46 and 47 issue interrupt commands 48 and 49 to the respective circuit breakers 32 and 33 based on the input current. Note that the true power transmission current 44, which is the output of the subtracter 42, is the output of the transmitter 5.
0 to the receiver 51 at the other end, and is input to the circuit breaker switching device 47 at the other end. Also, subtractor 4
The true power transmission current 45, which is the output of the circuit breaker 3, is transmitted by the transmitter 52 to the receiver 53 at the other end and input to the circuit breaker switching device 46.

FIG. 7 is a block diagram showing a part of the protective relay device shown in FIG. 6 in more detail. A first line power transmission line 31a and a second line power transmission line 31b are connected to each phase of the bus bar 34 via circuit breakers 32a and 32b, respectively. A transformer 36a is attached to each phase of the power transmission line 31a of the first line, and a transformer 36b is similarly attached to each phase of the power transmission line 31b of the second line. The detected voltages of these transformers 36a and 36b are input to arithmetic units 38a and 38b, respectively.
In these arithmetic units 38a and 38b, charging currents are calculated for the own phase using the conventional method and for each phase using the approximate calculation according to the present invention, and these are output to subtracters 42a and 42b. On the other hand, current transformers 40a and 40b are attached to each phase on the bus side of the first line and second line, respectively, and the transmission currents detected by these current transformers 40a and 40b are input to adders 42a and 42b. The true transmission currents 44a, 44b from which the charging current has been subtracted by these subtracters 42a, 42b are input to a circuit breaker switching device (not shown in FIG. 7).

Next, the relational expressions for performing calculations in the calculation devices 38a and 38b will be explained. That is, the arithmetic unit 38
In a and 38b, the charging current is calculated based on equation (12) shown below.

However, in equation (12), I〓′ _a ~ I〓′ _a ′ represents the charging current of each phase, V〓 _a ~ V〓 _a ′ represents the transmission line voltage of each phase, and the admittance Y _1j {i∈( a, b, c, c', b', a')} are determined by equation (13) shown below.

For example, by expanding equation (12) for I〓 _a of phase a, we get (13)
If we transform it based on the equation, we get equation (14).

I〓′ _a ＝Y〓 _aa V〓 _a +Y〓 _ab V〓 _b +Y〓 _ac V〓 _c ＝jωC _aa V〓 _a ＋jωC _ab (V〓 _a −V〓 _b )＋jωC _ac (V〓 _a
−V〓 _c ) ＋jωC _ac ′V〓 _a ＋jω _ab ′V〓 _a ＋jωC _ac ′V〓 _a ……(1
4) The above equation (14) corresponds to the equation (2) described in the principle of the invention, and I〓′ _a is the arithmetic unit 38a, 38b.
This is the output of Therefore, I〓 _a is the transformer 40a, 40
If the transmission current is obtained from b, then the attenuator 42
In a and 42b, the calculation shown by equation (15) is performed.

I〓'' _a = I〓 _a −I〓′ _a ... (15) I〓 _a '' obtained by this equation (15) is the true a-phase transmission current obtained by removing the charging current from the transmission line current. The circuit breaker switching device 46 shown in FIG. 6 determines whether to trip the circuit breaker 32a or 32b based on this _I〓''a and the current information at the opposite end.

According to this embodiment, the calculation circuits 38a and 38b perform approximate calculation of the line-to-line charging current with other lines using equation (13) without measuring the line-to-line voltage. This reduces the amount of information used, simplifies the configuration of the arithmetic circuits 38a and 38b, and improves the reliability of the arithmetic device.
Further, by reducing the number of calculation circuits through approximate calculation, when calculations are performed using digital circuits, there is an effect of shortening the calculation time and improving the responsiveness of the protective relay device. This reduction in calculation time is approximately 1/2 compared to the conventional method of calculating accurate charging current.

FIG. 8 is a block diagram showing another embodiment of a protective relay device that implements the power transmission line charging current compensation method of the present invention. The power transmission line 31a of the first circuit has a circuit breaker 32
The power transmission line 31b of the second circuit is connected to the bus bar 34 via a circuit breaker 32b. Current transformers 40a and 40b are installed between the bus bar 34 and the circuit breakers 32a and 32b to detect the transmission current of each phase of the power transmission lines 31a and 31b,
The transmission currents detected by these current transformers 40a, 40b are input to subtracters 42a, 42b. Bus line 3
A transformer 36 is attached to each phase of 4, and the bus voltage detected by these transformers 36 is sent to the arithmetic unit 3.
8a and 38b. Arithmetic device 38
The compensation charging current calculated in a and 38b is subtracted by subtractor 4.
2a, 42b, and these subtracters 42a,
42b outputs true power transmission currents 44a and 44b. The arithmetic units 38a and 38b in this embodiment perform approximate calculations based on equation (16).

The above equation (16) corresponds to the equation (12) in the previous embodiment, but the difference is that the second term on the right side all uses the bus voltages V〓 _a , V〓 _b , V〓 _c It is in. This is because the number of current transformers 40 is reduced from six in the previous embodiment to three, as shown in FIG. Note that the other symbols in equation (16) are the same as in equation (12).

According to this embodiment, three current transformers 40 are used, which reduces the number of current transformers by half compared to the previous embodiment, which has the effect of simplifying the configuration of the protective relay device. Since the configuration of the calculation devices 38a and 38b is also simpler and the number of calculations is reduced, there is an effect that the responsiveness of the protective relay device is higher than that of the previous embodiment. However, although the compensation error increases compared to the previous embodiment, since the previous embodiment is originally an approximate calculation, the present embodiment can be fully used as long as the error is within an allowable range.

〔Effect of the invention〕

As described above, according to the power transmission line charging current compensation method of the present invention, the line-to-line charging current with other lines can be calculated by adjusting the line-to-ground voltage of the own phase and the line-to-line capacitance between the other phases in the other circuits. Since the calculation is performed using , it is possible to simplify the configuration of the power transmission line protection relay device and improve its responsiveness.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the capacitance distribution seen from the a-phase in a three-phase two-circuit transmission line, Figure 2 is a charging current vector diagram of the a-phase, and Figure 3 is the phase voltage of each phase at the time of a one-line ground fault. Vector diagram, Figure 4 is a phase voltage vector diagram of each phase at the time of a two-wire short circuit accident, and Figure 5 is the phase voltage vector diagram for each phase when the b' phase is cut off.
FIG. 6 is an explanatory diagram showing the capacitance relationship between phases ab', FIG. FIG. 6 is a partial detailed configuration diagram of the protective relay device shown in FIG. 6, and FIG. be. 31...Power transmission line, 32, 33...Breaker, 3
4, 35... Bus bar, 36, 37... Transformer, 3
8, 39... Arithmetic device, 40, 41... Transformer,
42, 43... Subtractor, 46, 47... Circuit breaker switching device.

Claims (1)

[Claims] 1. A circuit breaker inserted at both ends of the busbar side of a multi-circuit multi-phase power transmission line, an arithmetic device that calculates charging current for the own line and other lines based on the multi-phase power transmission line voltage of the multi-line, and the multi-circuit and a circuit breaker switching device that opens and closes the circuit breaker based on the transmission line current obtained by subtracting the charging current calculated by the calculation circuit from the current of the multiphase transmission line, the calculation device In this example, the charging current for the own line is calculated using the ground voltage, line voltage, ground capacitance, and line capacitance of the own line, and the line charging current for other lines is calculated using the ground voltage of the own line, and the line-to-line capacitance. A method of compensating for a power transmission line charging current, characterized in that calculation is performed using line capacitance between lines and other phases within the line.