JP3681142B2 - Differential protection relay - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a protective relay device, and more particularly to a differential protective relay device that protects a system by mutually transmitting system electricity through transmission means at both ends of a power transmission line.
[0002]
[Prior art]
FIG. 5 is a system configuration diagram of a conventional PCM differential protection relay device to which a digital transmission method is applied. In FIG. 5, A and B are electric stations, and circuit breakers 12 </ b> A and 12 </ b> B are connected to both ends of the protection section transmission line 11. The end currents are taken in by the current transformers 13A and 13B at both electric stations and introduced into the differential protection relays 1A and 1B.
[0003]
The current taken in the differential protection relays 1A and 1B is converted into a predetermined amount of electricity by the input converters 14A and 14B, and the amount of electricity of unnecessary frequency components is removed via the filters 15A and 15B. Holds by hold circuits (S / H) 16A and 16B until the next sampling.
[0004]
The held quantity of electricity is converted into digital data by analog / digital converters (A / D) 17A and 17B and then sent to determination units (PU) 19A and 19B. The A / D outputs of both ends A and B are transmitted to the counterpart terminals via signal transmission devices (CC) 18A and 18B, respectively, and sent to the decision units (PU) 19A and 19B of the respective terminals.
[0005]
The bit lengths of the digital data transmitted to the counterpart terminal, the digital data of the counterpart terminal transmitted to the terminal, and the digital data of the analog / digital conversion circuit output are the same. Determination unit (PU) 19A, the 19B, determines the presence or absence of fault current flowing into the protected section transmission lines using A substation current data I _A and B substation current data I _B.
[0006]
The judgment result is output as a trip command to the circuit breakers 12A and 12B. This determination is performed by the equation (1) as an example using the current data I _A and I _B. This characteristic takes Σ | I | = | I _A | + | I _B | on the horizontal axis and | I _d | = | I _A + I _B | on the vertical axis, and shows the phase difference between the two end data I _A and I _B. For example, when it is kept constant at 180 degrees, the ratio characteristic as shown in FIG. 6 is obtained.
[Expression 1]
| I _A + I _B | ≧ K 1 (| I _A | + | I _B |) + K 0 · Minimum Sensitivity ……………… (1)
(K0 and K1 are constants)
[0007]
As shown in FIG. 7, the input converters 14A and 14B have a switching circuit 71 for switching the conversion ratio, and the minimum sensitivity of the differential protection relay is set to “0.5A, 1.0A, 1.5A by the switching circuit. , 2.0A ".
[0008]
For example, if the minimum sensitivity as viewed from the transmission line is 800A, and the conversion ratio of the current transformer at A is 8000/5, the minimum sensitivity of the differential protection relay at A is 0.5A (800A × 5 / 8000), and the conversion ratio of the current transformer at B electric station is 4000/5, the minimum sensitivity of the differential protection relay at B electric station is 1.0 A (800 A × 5/4000).
[0009]
[Problems to be solved by the invention]
As described above, in the method in which the minimum sensitivity is switched by the switching circuit, differential protection may not be possible depending on the conversion ratio of the current transformer. For example, as shown in FIG. 8, assuming that the minimum sensitivity as viewed from the transmission line is 800 A, the minimum sensitivity of the differential protection relay at the A station is 0 when the conversion ratio of the current transformer at the A station is 8000/5. .5A (800A × 5/8000) may be selected.
[0010]
However, when the conversion ratio of the current transformer at B electric station is 6000/5, it is desirable to select 0.667A (800A × 5/6000) as the minimum sensitivity of the differential protection relay at B electric station. There is no minimum sensitivity of 0.667A. Therefore, it was necessary to add an auxiliary transformer 81B having a conversion ratio of 3/4 to the outside of the differential protection relay at the B electric station.
[0011]
If an auxiliary transformer is not provided outside in this way, differential protection cannot be performed because a differential current flows when there is no accident. In addition, instead of providing an auxiliary transformer externally, in the case of the method of 3/4 times by software, setting of the magnification is required in addition to selecting the minimum sensitivity of the differential protection relay, and the setting operation is complicated. .
[0012]
The present invention has been made to solve the above-mentioned problems, and by setting the minimum sensitivity of the differential protection relay with a continuous set value, differential protection can be achieved without adding an auxiliary transformer outside the relay. It aims to provide a possible differential protection relay device.
[0013]
[Means for Solving the Problems]
A differential protection relay device according to claim 1 of the present invention is a sampling circuit that detects sampling data by converting each terminal current value of a power system into a predetermined electrical level by an input conversion unit and sampling with a predetermined period. An analog / digital conversion circuit for converting the sampling data into digital data, a transmission means for transmitting the digital data to a counterpart terminal, a setting means for inputting the minimum sensitivity of the differential protection relay, and the digital data In the differential protection relay device comprising an arithmetic circuit for performing a predetermined differential protection operation using digital data of the counterpart terminal obtained at the counterpart terminal and transmitted to the local end via the transmission line, the counterpart terminal The bit length of the digital data transmitted to the terminal and the bit of the digital data of the counterpart terminal transmitted to the terminal A length X, the when the bit length of the analog / digital converter and Y (X <Y), the digital data to a constant obtained from the analog / digital conversion circuit ^{[1 / (2 (YX)} ) × K / difference Multiplier means for multiplying the minimum sensitivity of the dynamic protection relay (K is a constant)].
[0015]
In the differential protection relay device according to claim 1 of the present invention, the bit length of the digital data of the counterpart terminal transmitted to the terminal is X, and the bit length of the analog / digital conversion circuit is Y (X <Y). Then, the digital data obtained from the analog / digital conversion circuit is multiplied by a constant [1 / (2 ^{( YX )} ) × K / minimum sensitivity of differential protection relay].
[0016]
As a result, by fixing the number of digits of the minimum sensitivity at any minimum current value, not only can the quantization error at the minimum sensitivity be kept constant, but also the matching with the counterpart terminal can be taken. Can be used as dynamic protection data.
[0017]
A differential protection relay device according to a second aspect of the present invention includes the filter processing means for extracting a predetermined frequency component in the first aspect.
[0018]
According to a third aspect of the present invention, there is provided a differential protection relay device according to the first aspect, further comprising means for making the minimum sensitivity of the differential protection relay a continuous value of a predetermined step width.
[0019]
A differential protection relay device according to a fourth aspect of the present invention is the differential protection relay device according to the first aspect, wherein the sampling circuit and the analog / digital conversion circuit and the input conversion unit, the sampling circuit, and the analog / digital conversion circuit of another relay are shared. Equipped with.
[0020]
The differential protection relay device according to claim 5 of the present invention is the differential protection relay device according to claim 1, wherein when the differential protection relay is used as the main protection relay, the backup protection input conversion unit is used as the input conversion unit of the main protection relay. And shared means.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a configuration diagram of an embodiment of a PCM differential protection relay device according to the present invention. In this embodiment, the bit length of the digital data transmitted to the counterpart terminal and the bit length of the digital data of the counterpart terminal transmitted to the terminal are set to X and the bit length of the analog / digital conversion circuit, compared to the conventional configuration. When Y is set, X <Y, and multiplication means is added. In FIG. 1, the same parts as those of FIG.
[0022]
As shown in FIG. 2, the input converters 14A and 14B are configured not to have a switching circuit for switching the conversion ratio. 10A and 10B are constant multiplication means, which are newly added in the present embodiment. As an example, here, when the bit length X is 12 bits and the bit length Y is 16 bits, constant [1 / (2 ^(16-12) ) × K / minimum sensitivity of the differential protection relay (K is a constant) ] Is transmitted to the counterpart terminal, and the determination unit (PU) 19A, 19B performs, for example, differential protection calculation based on the determination formula (1).
[0023]
Next, the meaning of multiplying by a constant will be described. Since one of the 16 bits is assigned to a positive or negative sign, the magnitude of the electric quantity can be represented by a digital quantity of 0 to 32768 (2 ¹⁵ ) digits. Since the input converters 14A and 14B do not have a switching circuit, the input full scale is constant.
[0024]
For example, when the input full scale is 102.4A, when the minimum sensitivity is 0.5A and K = 2, the constant of the constant multiplying unit is [1 / (2 ^{( 16-12 )} ) × K / differential protection relay. Minimum sensitivity (K is a constant)] = 1/16 × 2 / 0.5 = 0.25. Therefore, the number of digits of the minimum sensitivity current 0.5 A is 32768 digits × 0.5 A / 102.4 A × 0.25 = 40 digits.
[0025]
When the minimum sensitivity is 1.0 A and K = 2, the constant multiplication means constant is [1 / (2 ^{( 16-12 )} ) × K / minimum sensitivity of the differential protection relay (K is a constant)] = 1/16 × 2 / 1.0 = 0.125. Therefore, the number of digits of the minimum sensitivity current of 1.0 A is 32768 digits × 1.0 A / 102.4 A × 0.125 = 40 digits.
[0026]
When the minimum sensitivity is 0.667A and K = 2, the constant multiplication means constant is [1 / (2 ^{( 16-12 )} ) × K / minimum sensitivity of the differential protection relay (K is a constant)] = 1/16 × 2 / 0.667 = 0.187. Therefore, the number of digits of the minimum sensitivity current 0.667A is 32768 digits × 0.667A / 102.4A × 0.187 = 40 digits.
[0027]
As described above, the number of digits with the minimum sensitivity is fixed at any minimum current value. By fixing the number of digits of the minimum sensitivity, not only can the quantization error at the minimum sensitivity be kept constant, but also the current with the other end can be matched, so that it can be used directly as differential protection data.
[0028]
Since the conventional minimum sensitivity corresponds to the number of turns of the input converter, for example, discrete values such as “0.5 A, 1.0 A, 1.5 A, 2.0 A” are used. Is set by the setting means, for example, a continuous value having a predetermined step width such as “0.500A, 0.501A, 0.502A,..., 2.000A” can be obtained.
[0029]
For example, if the minimum sensitivity as viewed from the transmission line is 800A, and the conversion ratio of the current transformer at A is 8000/5, the minimum sensitivity of the differential protection relay at A is 0.500A (800A × 5 / 8000), and when the conversion ratio of the current transformer at B Electric Station is 6000/5, the minimum sensitivity of the differential protection relay at B Electric Station is 0.667A (800A x 5/6000) Differential protection is possible.
[0030]
According to the present embodiment, there is no need to add an auxiliary transformer outside the relay. Further, instead of providing an auxiliary transformer externally, it is not necessary to set the magnification in addition to selecting the minimum sensitivity of the differential protection relay as in the method of matching by software.
[0031]
FIG. 3 is a block diagram showing another embodiment of the PCM differential protection relay device of the present invention. In FIG. 3, the same parts as those in FIG. The characteristic part of the present embodiment is that the constant of the multiplication means 10A is set to [1 / (2 ^{( YX )} ) × K (K is a constant)], and the others are the same as in FIG. In the present embodiment, the same effect as described above can be obtained.
[0032]
FIG. 4 is a block diagram showing another embodiment of the PCM differential protection relay device according to the present invention. In FIG. 4, the same parts as those in FIG. The characteristic part of this embodiment is that a digital filter (DF) (41A) is added to FIG.
[0033]
According to the present embodiment, by adding the digital filter means (DF), the DC component included in the input current can be removed to reduce the quantization error after A / D conversion. Harmonics included in the current can be removed.
[0034]
Furthermore, the present invention eliminates the input converter switching circuit, so that the input conversion unit, sampling circuit and analog / digital conversion circuit of the PCM differential protection relay and the input conversion unit, sampling circuit and analog / digital of other relays are provided. The conversion circuit can be shared, and the hardware can be reduced, thereby simplifying the hardware and improving the reliability.
[0035]
【The invention's effect】
As described above, according to the present invention, not only can differential protection be possible even when the conversion ratios of the current transformers at both terminals are different, but also the common use with the input current transformer of another relay can be achieved. This can greatly reduce the hardware.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an embodiment of a PCM differential protection relay device of the present invention.
FIG. 2 is a configuration diagram showing an embodiment of an input converter to which the present invention is applied.
FIG. 3 is a configuration diagram showing another embodiment of the PCM differential protection relay device of the present invention.
FIG. 4 is a configuration diagram showing another embodiment of the PCM differential protection relay device of the present invention.
FIG. 5 is a configuration example of a conventional PCM differential protection relay device.
FIG. 6 is a ratio characteristic diagram of a PCM differential protection relay device.
FIG. 7 is an example diagram of an input converter of a conventional PCM differential protection relay device.
FIG. 8 is an installation example of an external auxiliary transformer of a conventional PCM differential protection relay device.
[Explanation of symbols]
1A, 1B differential protection relay
10A, 10B Constant multiplication means
11 Protection section transmission line
12A, 12B circuit breaker
13A, 13B current transformer
14A and 14B input converter (CT)
15A, 15B filter (FIL)
16A, 16B Sampling and holding circuit (S / H)
17A, 17B Analog / digital converter (A / D)
18A and 18B signal transmission equipment (CC)
19A, 19B judgment part (PU)
41A, 41B Digital filter (DF)
81B Auxiliary transformer

Claims (5)

A sampling circuit for detecting sampling data by converting each terminal current value of the power system to a predetermined electrical level by an input conversion unit and sampling with a predetermined period, and an analog / digital conversion circuit for converting the sampling data to digital data Transmission means for transmitting the digital data to the counterpart terminal, settling means for inputting the minimum sensitivity of the differential protection relay, and the digital data obtained at the counterpart terminal and transmitted to the local terminal via the transmission line. In a differential protection relay device comprising an arithmetic circuit for performing a predetermined differential protection operation using the digital data of the counterpart terminal, the bit length of the digital data to be transmitted to the counterpart terminal and the self-terminal are transmitted. X is the bit length of the digital data of the other terminal, and the analog / digital conversion circuit The bit length Y When (X <Y), the constant [1 / the digital data obtained from the analog / digital converter (2 ^(YX)) minimum sensitivity × K / differential protection relay (K is a constant) ] A differential protection relay device characterized by comprising multiplication means for multiplying 2. The differential protection relay device according to claim 1, further comprising a digital filter processing means subsequent to the analog / digital conversion circuit . 2. The differential protection relay device according to claim 1, further comprising means for setting the minimum sensitivity of the differential protection relay to a continuous value having a predetermined step width . 2. The differential protection relay device according to claim 1, wherein the input conversion unit, sampling circuit and analog / digital conversion circuit of the differential protection relay are shared with the input conversion unit, sampling circuit and analog / digital conversion circuit of the relay of another element. A differential protection relay device characterized by that. The differential protection relay device according to claim 1, wherein when the differential protection relay is used as a main protection relay, a backup protection input conversion unit is shared by the input conversion unit of the main protection relay. Differential protection relay device.

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