JP5924014B2 - Protective relay - Google Patents

Description

The present invention is installed in various places from power companies and railway companies' power stations to substations and receiving terminals, detects abnormalities such as accidents and breakdowns in power transmission and substations, and immediately disconnects the power system where the accident occurred. The present invention relates to a protective relay that outputs a TRIP signal and ensures a stable supply of electric power, and more particularly, to a protective relay related to a short-circuit overcurrent element input.

Protective relays delivered to electric power companies, etc. must detect the above-mentioned abnormalities and issue a TRIP signal normally when an accident or failure occurs. For this purpose, the operation test of the protective relay for various input signals, which simulates the actual input signal, is performed by using a protective relay test device or the like before the delivery to the field.

As a concrete current input waveform, a generally considered waveform is a normal operation input (FIG. 3a). Waveform at full scale over (Fig. 3b). A short-time input waveform (FIG. 3c) pulse, noise, or the like can be considered. In the case of FIGS. 3a and 3b, normal operation (TRIP signal output) is performed as an overcurrent, and in the case of the waveform as in FIG. 3c, unnecessary operation (TRIP signal output) is not performed as single-time noise. Is desired.

よって、１０Ａを３ｍｓ間、入力した場合、演算上では、８．５３Ａと認識するので、整定値以上となり、ＴＲＩＰ信号出力となる。 As an example, a calculation example when the test is performed under the following conditions is shown. Current single input element settling: 1 A, input current: 10 A, input time: 3 ms, sampling frequency: 5 times. FIG. 4 shows the maximum input value at 15 ° sampling, and the effective value is √2sinθ when the sampling phase is around 90 ° and sampling (3 ms) is performed.
[Formula 1]

Therefore, when 10 A is input for 3 ms, it is recognized as 8.53 A in the calculation, so that it becomes equal to or higher than the set value and becomes a TRIP signal output.

For example, Japanese Patent Laid-Open No. Hei 6-292322 is disclosed as a method for distinguishing between an excitation inrush current and an overcurrent when an excitation inrush current is included. This prior art document includes a component ratio calculation unit that calculates a component ratio of input current and a sine wave likelihood calculation unit that calculates the sine wave likelihood of the input current, and inputs the values calculated by the two calculation units. As an overcurrent protection relay, a fuzzy inference unit is provided to determine whether the current is a magnetizing inrush current. However, this apparatus has a problem that processing is complicated.

JP-A-6-292322

When an excessively short time input is applied to a single current input element, an unnecessary operation may occur depending on the input timing. An object of the present invention is to provide a protective relay that performs a TRIP operation when an actual current is exceeded or a full scale is exceeded without performing an unnecessary operation with an excessively short time input of a single current input element in a simple manner. That is.

In order to solve the above problems, the present invention transforms, filters, samples and holds currents and voltages to be protected, and then sequentially converts analog quantities into digital quantities in an A / D converter and stores them in a memory. In the digital protection relay that CPU stores and calculates using the data in the memory, the sum of the instantaneous value current is calculated for each relay calculation cycle, and the sum is compared with a predetermined threshold, Is determined to be TRIP when a predetermined number of times (n times) continues.

  According to the present invention, when an excessive single time input signal as described above is input, it is determined that the input is instantaneous noise or the like, and software processing that does not output the TRIP signal is incorporated. Unnecessary operation can be prevented.

Hardware block diagram of the present invention Flow chart of the present invention Waveform pattern considered as current input: a. Normal operation input, b. When full scale over, c. Input for a short time Cutout point that is the maximum input at 15 ° sampling

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of the protective relay of the present invention. The input current detected by CT 1 is converted by the transformer 4, and the S / H circuit 5 samples and sequentially captures data. The captured data is converted into a digital value by the A / D conversion 6. A predetermined calculation is performed by the memory 8 and the CPU 9 of the determination unit 7 using this digital value. Thereafter, the determination result is output to the auxiliary RY10.

In the present invention, a new process is added to the determination unit 7. The new process will be described with reference to the flowchart of FIG. The settling value which is the TRIP condition of the relay is input in advance. If the input current is sampled and is equal to or higher than the set value, the sampling value is skipped by one during the determination period, and a total of four instantaneous values are totaled to determine whether it is smaller than the threshold value (S2). . If it is smaller than the threshold value, the possibility of instantaneous noise is high, and the determination number k is cleared (S3). If it is larger than the threshold, the number of determinations is incremented (S4). If the number of determinations is equal to the set number of determinations, element operation is performed (S5). If the set number of determinations has not been reached, sampling continues and normal determination continues.

  In this example, the TRIP settling value was implemented with a current positive phase minimum operating value of 0.5 A. The number of samplings was 24 times per cycle (every 15 degrees), and one determination, that is, a relay calculation cycle was performed at 5.56 ms. The full scale of the A / D converter sets 14 bits = 16384 counts to 163.84A (that is, 1 bit is 10 mA). 0.5A is about 0.3%. The safety factor is 90%, and 0.3% × 90% = 0.27% is set as a threshold value. The full scale is 16384 × 0.27% = 44 counts. However, since the positive half wave is used for the calculation, the count is 22 counts. This numerical value is one of the optimum values in the present embodiment, and in practice, it is necessary to adjust according to the situation at the site.

  Sampling is performed 8 times (every 15 °) within one determination (5.56 ms). However, in this embodiment, 4 times (0, 2, 2) of the 8 samplings due to the calculation speed of the CPU. Using the 4th and 6th sampling data, a determination process is performed to determine whether or not 22 counts × 4 times = 88 counts or less. If the sum of the sampling data of the instantaneous values is less than 88, the determination count data is cleared. If the sum of sampling data is 88 or more, the number of determinations is incremented, sampling is continued, and the same processing is repeated.

  In this embodiment, the number of setting determinations is set to 4 (one period of the fundamental wave + 1 determination). Therefore, when the sum of the sampling data is 88 or more, it is continuously set to 4 times (the number of setting determinations). If it becomes, the element operation is performed. By performing such processing, when a single input waveform as shown in FIG. 2 is input, unnecessary operations are not performed. The number of setting determinations is not limited to four, but it is necessary to set a value larger than one period of the fundamental wave and smaller than the relay operation time. Therefore, 4 to 5 times is a preferable value.

  The present invention can be applied to, for example, a contact output circuit for preventing erroneous output such as a protective relay and a monitoring control device.

1 CT
2 Transmission line 3 Protective relay 4 Transformer 5 Sample hold circuit 6 A / D converter 7 Judgment unit 8 Memory 9 CPU
10 Auxiliary RY

Claims (1)

Takes voltage and current from the power system as sensor detection signals,
An arithmetic processing unit for determining the operation of the contact output;
In the protective relay that outputs a trip signal when the condition of operating by the arithmetic processing unit is satisfied,
When the arithmetic processing unit determines that the operation and protection relay and outputs a contact signal when the sum of the instantaneous values in one decision cycle exceeds continuously the threshold setting determination number of times or more.

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