JP2006333536A - Digital protective relay - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital protective relay which quickens the recognition of frequency and is possible of judgement even in a system including noise, for the purpose of solving the problems of a conventional digital protective relay such as that though it is equipped with a function of performing the judgement of the system frequency after being installed in a system so that it may perform changeover, according to the frequency of the two kinds of 50 Hz and 60 Hz, it is insufficient to recognize the frequency, which is requested recently, and that it is not applicable to the system including the noise of harmonic components such as an uninterruptible power source or the like. <P>SOLUTION: This digital protective relay includes a sample hold circuit which supposes system frequency and samples an AC voltage value or an AC current value in two or more sampling cycles within one cycle of the supposed input system frequency by the sample frequency higher than the supposed frequency, and an operation part which calculates the sampling data within one cycle and judges the agreement between the supposed frequency and the power system frequency by the total value. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital protection relay, and particularly to automatic detection of an input power system frequency.

  Conventionally, a digital protection relay is used to protect various devices connected to the power system. This digital protective relay has a function of switching between 50 Hz and 60 Hz depending on two types of frequencies, 50 Hz and 60 Hz, depending on the region where it is used. Conventionally, the switching setting according to the frequency has been performed by the manufacturer or the user. However, since the switching is performed manually, the input size and phase cannot be correctly determined when the setting is performed incorrectly, and malfunction or error is not detected. There was a possibility to work. In this way, in order to make it possible to share the digital protection relay even in areas with different system frequencies, the input commercial power supply frequency is assumed to be either 50 Hz or 60 Hz, and the frequency n times the commercial frequency is calculated based on this assumption. A processing unit generates a sampling control signal having a sampling period of 1/50 ns or 1/60 ns and supplies it to a sample and hold circuit to perform sampling. The A / D converter converts the data into digital data. The sampling data arbitrarily selected in 1 and the commercial AC voltage value or current value after 1/50 second or 1/60 second are confirmed from the data, and the frequency of the commercial power source is identified based on whether or not the two coincide with each other. (For example, Patent Document 1).

Japanese Patent Laying-Open No. 2002-098722 (P1, FIG. 2)

However, what is disclosed in Patent Document 1 performs sampling at a sampling period of 1/50 ns, for example, and compares the voltage and current values in sampling data after 1/50 seconds from the data, that is, after 360 ° phase, Since it recognizes commercial frequencies, its recognition speed is slow, and there is a problem that it is not always able to meet the demand for faster recognition of system frequencies that have recently been requested.
On the other hand, in recent years, uninterruptible power supplies provided in the event of a power failure of general commercial power supplies are provided in various directions. Since this uninterruptible power supply equipment is equipped with an inverter, it contains noise of harmonic components, and a clean sine wave is not guaranteed. When the technique disclosed in Patent Document 1 is applied to a system having such an uninterruptible power supply, there is a problem in that harmonic components cannot be identified, causing malfunctions and malfunctions.

  The present invention has been made in order to solve the above-described problems, and makes it possible to determine the power system frequency in a shorter time, and to make the frequency determination more accurate even in a power system including noise. It aims to provide a digital protective relay.

According to a first aspect of the present invention, there is provided a digital protection relay that assumes a frequency of an input power system, and is sampled at a frequency that is determined corresponding to the assumed frequency and higher than the assumed frequency within one cycle of the assumed frequency. Depending on the frequency
A sample hold circuit that samples an AC voltage value or an AC current value of an input power system at a plurality of sampling periods, an A / D conversion circuit that performs A / D conversion on sampling data output from the sample hold circuit, and sampling The sampling frequency and multiple sampling cycles are commanded to the sample hold circuit via the cycle control circuit, and sampling data within one cycle is extracted from the memory unit that stores the sampling data from the A / D conversion circuit and totaled And an arithmetic unit that determines that the frequency assumed when the total value is zero or almost zero is the same as the frequency of the input power system.

前記演算した絶対値Ｃと比較して、
Ｃ≦Ｋの場合には前記仮定した周波数と同一の周波数が入力しており
Ｃ＞Ｋの場合には、前記仮定した周波数とは異なる周波数が入力している
と判定するものである。 According to a second aspect of the present invention, there is provided a digital protection relay that assumes a frequency of an input electric power system, and is sampled at a frequency higher than the assumed frequency that is determined corresponding to the assumed frequency within a plurality of cycles of the assumed frequency. Depending on the frequency
A sample hold circuit that samples an AC voltage value or an AC current value of an input power system at a plurality of sampling periods, an A / D conversion circuit that performs A / D conversion on sampling data output from the sample hold circuit, and sampling The sampling frequency and multiple sampling cycles are commanded to the sample hold circuit via the cycle control circuit, and sampling data within one cycle is extracted from the memory unit that stores the sampling data from the A / D conversion circuit and totaled And a calculation unit that calculates the absolute value C of the total value, and a predetermined value K represented by the following equation (1) is set in the calculation unit,

Compared with the calculated absolute value C,
When C ≦ K, the same frequency as the assumed frequency is input, and when C> K, it is determined that a frequency different from the assumed frequency is input.

  The digital protection relay according to the first aspect of the present invention performs sampling in a plurality of sampling periods at a sampling frequency higher than the system frequency within one cycle of the assumed system frequency, and the total value is zero or almost zero. In this case, since it is determined that the same frequency as the assumed frequency is input, it is possible to determine the system frequency within one cycle, and the time for determining the frequency of the input power system is shortened compared to the conventional case.

Ｃ≦Ｋの場合には仮定した周波数と同一の周波数が入力しており
Ｃ＞Ｋの場合には、仮定した周波数とは異なる周波数が入力している
と判定するので、ノイズを含む電力系統であっても、その系統の周波数の判定が正しく、かつ短い時間内に行えるという効果がある。 The digital protection relay according to the second aspect of the present invention samples at a sampling frequency of a frequency higher than the system frequency within one cycle of the assumed system frequency at a plurality of sampling periods, and calculates an absolute value C of the total value thereof. Compared with the predetermined value K shown in equation (1)

When C ≦ K, the same frequency as the assumed frequency is input. When C> K, it is determined that a frequency different from the assumed frequency is input. Even if it exists, there exists an effect that determination of the frequency of the system | strain can be performed correctly and within a short time.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a digital protection relay 100 according to the first embodiment. In FIG. 1, the digital protection relay 100 includes a sample hold circuit 1, an A / D conversion circuit 2, a calculation unit (CPU) 3, a memory unit 4, a sampling cycle control circuit 5, and a filter circuit 6. A power system that is a commercial power supply or an uninterruptible power supply (not shown) is input to the filter circuit 6 connected to the input terminal 7. The sample hold circuit 1 is connected to the filter circuit 6, and its output is connected to the A / D conversion circuit 2. The output of the A / D conversion circuit 2 is connected to the input terminal of the calculation unit 3, and the output of the calculation unit 3 is connected to the memory 4 and the sampling cycle control circuit 5.

Next, the operation will be described.
It is assumed that the calculation unit 3 first sets the frequency assuming that a frequency of, for example, 60 Hz is input, regardless of whether the frequency of the power system input to the digital protection relay 100 is 50 Hz or 60 Hz. The computing unit 3 corresponds to the set system frequency 60 Hz, and samples the number of samplings within one cycle of the assumed system frequency by using a sampling frequency of 720 Hz which is higher than the 60 Hz and the sampling frequency of 720 Hz. Commands to the sampling hold circuit 1 via the cycle control circuit 5. The sampling and holding circuit 1 inputs the voltage or current of the input power system based on the command of the arithmetic unit 3 with a sampling frequency of 720 Hz, and multiple times within one cycle of the assumed system frequency, for example, every 30 ° phase. Sampling 12 times.
The analog data sampled by the sampling and holding circuit 1 is sent to the A / D conversion circuit 2, digitally converted, and input to the arithmetic unit 3. The arithmetic unit 3 stores the sampling data from the A / D conversion circuit 2 in the memory unit 4 and from the memory unit 4 when the sampling of 12 times within one cycle of the system frequency by the sampling frequency of 720 Hz is completed. The sampling data is extracted and the data value is calculated to obtain the sum. When the total value, that is, the determination threshold is zero or almost zero, the determination function in the calculation unit 3 determines that the initially assumed frequency of 60 Hz is the same as the frequency of the input power system. To do.
On the other hand, when the total value does not become zero or almost zero, the determination function of the calculation unit 3 determines that a power system having a frequency different from the assumed 60 Hz frequency is input. In this case, since it is determined that the set frequency (60 Hz in this case) set in the digital protective relay 100 and the input frequency do not match, the software in the calculation unit 3 instructs the internal frequency switching function to switch the setting. Put out. Thus, the frequency of the input power system is detected and determined. If it is determined that the frequency is different from the assumed frequency, the frequency setting is automatically switched, and the frequency of the input power system and the setting of the digital protection relay 100 are set. Match the frequency.
It should be noted that the total value of the sampling values that are judgment criteria (threshold values) is “substantially zero”, which is artificially set based on the type of input power system, the surrounding environment, and various know-how.

The above-described operation is shown as a flowchart in FIG.
In ST1, the engineer who manages the digital protective relay 100 sets the setting frequency of the calculation unit 3 assuming 60 Hz, for example, regardless of the system frequency, and further assumes that the sampling frequency is 720 Hz, for example. The number of samples in one cycle of the system frequency is set to 12, and a threshold value is set for the determination function in the calculation unit 3.
In ST2, the sampling hold circuit 1 performs 12 samplings at a sampling frequency of 720 Hz.
In ST3, the sampling results are summed and determined. If the total value is zero or nearly zero, the frequency of the input power system is determined to be 60 Hz, and normal processing is performed in ST6 without changing the setting. In ST3, in the case of NO, the frequency switching function in the calculation unit 3 is switched to 50 Hz in ST4, and in ST5, the same sampling as described above is performed at the sampling frequency 600 Hz corresponding to 50 Hz. After confirming that the frequency is 50 Hz, normal processing is performed in ST6.

Next, an example of sampling according to the first embodiment will be shown.
FIG. 3 shows sampling values at system frequencies of 50 Hz and 60 Hz, assuming that the power system frequency is 50 Hz, the sampling frequency corresponding to 50 Hz is 600 Hz, and the number of samplings is 12 (sampling every 30 degrees of phase).
In addition, the vertical axis | shaft of a figure shows a voltage or an electric current. As can be seen from the figure, the total sampling value is 0 at 50 Hz and 0.5878 at 60 Hz, and this system frequency is determined to be 50 Hz.
FIG. 4 similarly assumes that the system frequency is 60 Hz, and the sampling frequency corresponding to 60 Hz is 720 Hz. The total sampling value is 1.5607 at 50 Hz and 0 at 60 Hz, and this system frequency is determined to be 60 Hz. The
FIG. 3 shows an example in which the total value of 50 Hz is shown in FIG. 4, and the total value of 60 Hz is 0 in FIG. 4, but this is a pure sine wave without noise, and a general commercial power supply system includes some noise. It is. Therefore, it is affected by noise, and the total value is not zero but almost zero depending on the degree of the influence. This “nearly zero” is determined as a threshold value for frequency determination in consideration of the surrounding situation and experience and know-how. As described above, in the first embodiment, since sampling is performed 12 times in one cycle, there is an effect that the frequency determination speed is increased.

Embodiment 2. FIG.
The example shown in FIGS. 3 and 4 of the first embodiment described above is purely a sine wave. And the criterion for the case where some noise is included in a general commercial power supply system is shown. However, in recent years, an uninterruptible power supply provided in the event of a power failure of a general commercial power supply has been provided in various fields, and since this power supply is usually output via an inverter, it contains a lot of noise of harmonic components. The digital protection relay connected to such a power system is difficult to determine depending on the magnitude, type, number of occurrences, and the like of sampling within one cycle of the assumed system frequency according to the sampling frequency according to the first embodiment. Therefore, it is conceivable that the accuracy of determination is lowered. In the second embodiment, the sampling frequency is 2 cycles (720 °, 24 times) as shown in FIGS. 5 and 6, and the sampling frequency is 3 cycles (1080 °, 36 times) as shown in FIGS. Then, as shown in the figure, in the case of different frequencies, the total sampling value becomes large and the determination becomes easier. In addition to that, a predetermined value K is set in the calculation unit 3, and the predetermined value K and the absolute value C of the sampling total are compared to determine the system frequency to be input, thereby further improving the determination accuracy. Is. The operation for determining the frequency follows that shown in FIG. 5 to 8 show a pure sine wave.

で示され、この所定値Ｋが演算部３に設定される。
（５）ユーザにて、実際の電力系統において、前記と同様の入力系統周波数と異なる高い周波数のサンプル周波数における複数回のサンプリング周期でサンプリングし、演算部で演算した合計値の絶対値をＣとする。
（６）Ｃ≦Ｋの場合、演算部は入力系統周波数と同一周波数と判定する。
Ｃ＞Ｋの場合、演算部は入力系統周波数と異なる周波数と判定する。 Hereinafter, how to obtain the predetermined value K will be described.
In this second embodiment, the maximum value of the noise of the input power system is the content rate of the distorted wave that guarantees the operation of the protective relay defined in standards such as JEC.
(1) The absolute value of the total value of the values sampled at a plurality of sampling periods within one cycle or a plurality of cycles of the input system frequency at a high sampling frequency different from the input system frequency without noise is α1 To do.
(2) Let α2 be the absolute value of the total value of the values sampled under the same conditions as in the case of no noise shown in (1) in the presence of noise.
(3) Let β2 be the absolute value of the sum of the values sampled at a plurality of sampling periods within one cycle or a plurality of cycles at the same sampling frequency as the input system frequency in the presence of noise.
That is,
Absolute value of the total value of the sampling period due to a high frequency different from the input system frequency .... No noise α1
Absolute value of the total value of the sampling period due to a high frequency different from the input system frequency.
Also,
Absolute value of the total value of the sampling cycle at the same frequency as the input system ......... No noise 0
Absolute value of the total value of the sampling period at the same frequency as the input system ......... There is noise β2 β2> 0
And α1, α2, and β2 are values determined by the manufacturer.
(4) The predetermined value K is

This predetermined value K is set in the calculation unit 3.
(5) In the actual power system, the user samples at a plurality of sampling periods at a high sampling frequency different from the input system frequency similar to the above, and the absolute value of the total value calculated by the calculation unit is C To do.
(6) When C ≦ K, the calculation unit determines that the frequency is the same as the input system frequency.
When C> K, the calculation unit determines that the frequency is different from the input system frequency.

In this way, the predetermined value K, which is a threshold value, is set in the calculation unit 3, and the power system frequency is assumed in an actual system, and C sampled and calculated under the condition shown in the above (5) is calculated. Since the comparison determination is performed, the determination accuracy is improved.
The value of K is appropriately changed according to the surrounding environment where the digital protection relay 100 is installed.

Embodiment 3 FIG.
In the third embodiment, a display unit is provided in the digital protection relay 100, and when the calculation unit 3 determines that the frequency is different from the power system frequency, the display unit is turned on or displayed as a sound. When the display unit is provided in this way, when it is determined that the setting is clearly wrong, the setting is automatically changed by a command from the arithmetic unit 3, but the power system frequency is noisy and is difficult to identify. When it is necessary to change the predetermined value K shown in the second embodiment, the management engineer can be notified easily.

In the first embodiment described above, as shown in FIGS. 3 and 4, twelve sample times are indicated by sampling frequencies of 600 Hz and 720 Hz. However, the number of samples is not limited to twelve, and any number of samples may be obtained. It may be the number of times.
Further, in the first embodiment, sampling is assumed within one cycle of the assumed input system frequency. However, as shown in FIGS. 5 to 8 of the second embodiment, any number of times within two cycles or three cycles may be used. May be the number of samples.
Furthermore, in the second embodiment described above, the sample counts of 24 times and 36 times in 2 cycles and 3 cycles are shown as shown in FIGS. 5 to 8. In addition, the number of samples in one cycle is not limited to 12, and any number of samples in one cycle may be used.

  Embodiments 1 to 3 of the present invention can be applied to a digital protection relay installed in a power system.

It is a block diagram which shows the structure of the digital protection relay of Embodiment 1-3 of this invention. It is a figure which shows the operation | movement flowchart of Embodiment 1, 2 of this invention. It is a figure which shows the example of the sampling of Embodiment 1 of this invention. It is a figure which shows the example of the sampling of Embodiment 1 of this invention. It is a figure which shows the example of the sampling of Embodiment 2 of this invention. It is a figure which shows the example of the sampling of Embodiment 2 of this invention. It is a figure which shows the example of the sampling of Embodiment 2 of this invention. It is a figure which shows the example of the sampling of Embodiment 2 of this invention.

Explanation of symbols

1 sample hold circuit, 2 A / D conversion circuit, 3 arithmetic unit (CPU),
4 memory section, 5 sampling period control circuit, 100 digital protection relay.

Claims (5)

A digital protection relay, which assumes the frequency of the input power system, and within one cycle of the assumed frequency, with a sampling frequency determined corresponding to the assumed frequency and higher than the assumed frequency,
A sample and hold circuit that samples the AC voltage value or AC current value of the input power system at a plurality of sampling periods; an A / D conversion circuit that performs A / D conversion on sampling data output from the sample and hold circuit; The sampling and holding circuit is instructed to the sampling and holding circuit via a sampling period control circuit and the sampling data from the A / D conversion circuit is stored in the memory unit that stores the sampling data from the A / D conversion circuit. A sampling unit is extracted and summed, and an arithmetic unit that determines that the assumed frequency is the same as the frequency of the input power system when the sum is zero or almost zero is provided. Digital protective relay. A digital protection relay, which assumes the frequency of the input power system, and within a plurality of cycles of the assumed frequency, a sampling frequency which is determined corresponding to the assumed frequency and is higher than the assumed frequency,
A sample and hold circuit that samples the AC voltage value or AC current value of the input power system at a plurality of sampling periods; an A / D conversion circuit that performs A / D conversion on sampling data output from the sample and hold circuit; The sampling and holding circuit is instructed to the sampling and holding circuit via a sampling period control circuit, and from the memory unit that stores sampling data from the A / D conversion circuit, A sampling unit is extracted and summed, and an arithmetic unit that determines that the assumed frequency is the same as the frequency of the input power system when the sum is zero or almost zero is provided. Digital protective relay. A digital protection relay, which assumes the frequency of the input power system, and within one cycle of the assumed frequency, with a sampling frequency determined corresponding to the assumed frequency and higher than the assumed frequency,
A sample and hold circuit that samples the AC voltage value or AC current value of the input power system at a plurality of sampling periods; an A / D conversion circuit that performs A / D conversion on sampling data output from the sample and hold circuit; The sampling hold circuit is instructed to the sampling and holding circuit through the sampling frequency and the plurality of sampling periods, and the sampling unit within the one cycle from the memory unit that stores the sampling data from the A / D conversion circuit. A calculation unit that extracts and sums the data and calculates an absolute value C of the total value, and the calculation unit is set with a predetermined value K represented by the following equation (1),

Compared with the calculated absolute value C,
When C ≦ K, the same frequency as the assumed frequency is input. When C> K, the calculation unit determines that a frequency different from the assumed frequency is input. Features digital protective relay. A digital protection relay, which assumes the frequency of the input power system, and within a plurality of cycles of the assumed frequency, a sampling frequency which is determined corresponding to the assumed frequency and is higher than the assumed frequency,
A sample and hold circuit that samples the AC voltage value or AC current value of the input power system at a plurality of sampling periods; an A / D conversion circuit that performs A / D conversion on sampling data output from the sample and hold circuit; The sampling hold circuit is instructed to the sampling and holding circuit through the sampling frequency and the plurality of sampling periods, and the sampling unit in the plurality of cycles is stored from a memory unit that stores sampling data from the A / D conversion circuit. A calculation unit that extracts and sums the data and calculates an absolute value C of the total value, and the calculation unit is set with a predetermined value K represented by the following equation (1),

Compared with the calculated absolute value C,
When C ≦ K, the same frequency as the assumed frequency is input. When C> K, the calculation unit determines that a frequency different from the assumed frequency is input. Features digital protective relay. 5. The display unit according to claim 3, wherein a display unit is provided, and when it is determined that the different frequency is input, display is performed on the display unit. 6. Digital protective relay.

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