JPH05207635A - Digital protection relay - Google Patents

Abstract

(57) [Summary] [Purpose] To obtain a protective relay that does not deteriorate the characteristics even when peculiar input data is introduced. [Structure] A voltage / current of a power system is sampled at a constant cycle, and means for converting an analog amount into digital data, a means for storing the digital data for a fixed period, and the digital data having a maximum or minimum value. And a means for interpolating the digital data in the maximum or minimum period of the digital data into sine wave data by using the past digital amount stored in the period in which the digital data is not maximum or minimum. When the digital data is maximum or minimum, the interpolated sine wave data is used to perform a calculation for detecting an accident that has occurred in the power system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects an accident that has occurred in a power system by introducing the voltage and current of the power system, and promptly removes the accident section from the main system when it is judged to be an accident. The digital protection relay of.

[0002]

2. Description of the Related Art An example of the structure of a digital protection relay according to the prior art is as follows. The voltage and current of the power system are taken in through a transformer, converted to a level suitable for digital operation by an input converter, sampled at a fixed cycle by a sample hold circuit through a harmonic elimination filter, and further A / D converter At, digital data is obtained after analog-to-digital conversion. This digital data is stored in a relay determination unit including a CPU and a memory for a certain period of time, and various relay calculations are performed by a known technique.

[0003]

In the case of a general digital protective relay having the above-mentioned configuration, the input waveform may deteriorate the performance of the protective relay and may not operate correctly.
For example, if there is a so-called relay input full scale over AC input that exceeds the input level of the A / D converter,
Despite the AC waveform on the system side, it becomes approximately a trapezoidal waveform as a relay input. The relay input full scale means the maximum amount of electricity that can be generated in the system to which the protective relay is applied, and if the full scale is set large to avoid the above full scale over input, A
The quantization error determined by the performance of the / D converter becomes large, and the accuracy of the protective relay tends to decrease. For the influence on the relay performance at the time of full scale over input, refer to P-137 to 139 of the power standard “B-401”, for example.
The characteristics will be deteriorated as described in.
Further, at the time of a cable system fault, the fault current / voltage waveform becomes a discontinuous waveform such as a needle wave or a chopping wave due to the influence of the conductance of the line, so that the relay performance is deteriorated. With the recent expansion of the system scale and the shift from overhead transmission lines to cable systems, in the near future, it will be necessary to increase the full-scale setting of the protective relays above the current level, and the voltage and current waveforms at the time of an accident Distortion is expected. In the conventional technique, no special measures are taken for the above input. The present invention has been made to remedy the above-mentioned drawbacks, and is designed to maintain and improve the performance of a protective relay without deteriorating the characteristics even when the above-mentioned unique input waveform is input to the protective relay. The purpose is to provide a digital protective relay.

[0004]

According to the present invention, a voltage / current of a power system is sampled at a constant cycle, an analog amount is converted into digital data, and a sine is approximately estimated from digital data stored for a fixed period. It has both means for deriving wave data and means for detecting that the digital data at the latest sampling time has reached the maximum or minimum value, and if the latest sampled digital data is at the maximum or minimum, the above-mentioned approximation is performed. The digital data interpolated as the estimated sine wave data was used to detect an accident that occurred in the power system. When the digital data at the latest sampling time is not obtained within the predetermined range with respect to the sine wave data, the sine wave data is used instead of the digital data at the latest sampling time to generate in the power system. Configured to detect accidents that occur.

When there is a discontinuous input that deteriorates the characteristics of the conventional protective relay, the digital data obtained by interpolating the discontinuous singular point from the normal digital data is used for the relay calculation. It is possible to prevent the performance of the protective relay from deteriorating and provide a highly reliable protective relay.

[0005]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a block diagram showing an embodiment of the present invention. In Fig. 1, the voltage and current of the power system are taken in through the transformer,
It is converted to a level suitable for digital calculation by the input converter 1, sampled at a constant cycle by the sample and hold circuit 2, and further digital data is obtained by the A / D converter 3. This digital data is stored in the relay determination unit 4 including the CPU and the memory for a certain period. Further, in the present invention, in the software processing of the relay determination unit, it is configured to determine whether or not the latest sampling data fetched by the relay determination unit is full scale over. An example of this determination method is shown in FIG.

In the process of S1 in the figure, it is judged whether or not the input amount is the maximum of the positive wave. When the maximum input is made when the A / D converter is 12 bits, the digital data Dm is 7FF (HEX) in binary representation. In the case of, it is determined that the full scale is over. On the other hand, if the result of the determination is small, it is determined that the digital data does not exceed the full scale, and is used in the data interpolation process described later. Further, in the processing of S2 in the figure, it is judged whether or not the input amount exceeds the maximum of the negative wave. The judgment method is the binary expression 800 (HE
If it is larger than X), it is determined to be full scale over. If it is determined to be the opposite, it is used as the normal data for the data interpolation processing. For the data determined to be full scale over by the above method, the relay determination is performed by substituting the digital data approximated to the sine wave data by the data interpolation processing according to the following method.

A method of approximating a sine waveform by data interpolation processing will be described below with reference to FIG. In general, a polynomial approximated from data at regular intervals can be obtained by Newton's interpolation formula. Newton's interpolation formula is expressed by the following formula. Here, t ₁ , t ₂ , ..., T _n are times at fixed time intervals Δt, D ₁ is data at time t ₁ , and ΔD ₁ is times t ₁ and t _2.
, The data difference (difference value), Δ ² D ₁ , ..., Δ ^n-1 D ₁ indicates a higher-order difference value. From 0 ° to 60 ° in Figure 3 15
A value of 75 ° is calculated by Newton's interpolation formula from digital data sampled at intervals (for the sake of simplicity, considered as decimal values). Each sampling time t
_{Using 1 to} t ₅ , t = t ₁ + Δt · n ₁ (n ₁ = 5) t = t ₂ + Δt · (n ₁ −1) t = t ₃ + Δt · (n ₁ −2) t = t ₄ Since + Δt · (n ₁ −3) t = t ₅ + Δt · (n ₁ −4), the equation (1) can be expressed as the equation (2).

[0008] Substituting the difference values shown in Table 1 into equation (2), the time t
The value of ₆ (75 °) is calculated as D ′ = 0 + 5 × 0.2588 + 10 × (−0.0176) + 5 × (−0.0166) = 0.966. This is an error of 0.01% with respect to the true value and is not a problem in practical use. It is obvious that the error becomes smaller as the order of the approximate polynomial becomes larger, and the shorter the data interval is, the more accurate the interpolation can be performed even if the period of full scale over is long. desirable. Table 1

FIG. 4 is a flow chart showing the above interpolation processing. In the subscripts in the figure, m is the latest calculation data, m-
n indicates that the latest calculation data is data calculated before n sampling. The process of S3 in FIG.
Is a process of calculating each difference value, and S4 is a process of obtaining the current data by interpolation. FIG. 5 is FIG.
And a flow chart including the process of FIG. By the above means, the digital data at the time of full scale over can be approximately interpolated into the sine wave data, and the relay operation can be correctly performed. In this embodiment, a configuration is provided that has both means for determining whether or not the digital data introduced into the relay is full scale over, and means for calculating data interpolated from digital data that is not full scale over. Therefore, even if an input exceeds the full scale, the conventional performance can be maintained without degrading the conventional characteristics.

In the first embodiment, the data is interpolated using the digital data which is not judged to be full scale over. However, the data used for the interpolating process is peculiar to the sine waveform (for example, In the case of a chopping wave, etc.), the interpolated data may contain a large error and may lead to deterioration of the relay characteristics. In the second embodiment, the reliability of the data used for the interpolation is always taken into consideration by adding a means for always checking the coincidence with the digital data approximate-interpolated to the sine wave even for the data which is not judged to be full scale over. Configured to check.

A flow chart of the second embodiment is shown in FIG. Figure 6
In the above, S5 has the same configuration as in the first embodiment,
S6 is a process for inspecting the consistency between the digital data approximately interpolated to the sine wave from the reliable data obtained up to the previous time and the digital data introduced into the relay. In this processing, D ′ of | D′−D _m | ≧ ε is
Digital data approximately interpolated to a sine wave from the reliable data obtained up to the previous time, D _m indicates the digital data which has been A / D changed, and if the difference between the two is within the range indicated by ε. Since it is peculiar to the approximately interpolated sine wave data, it is excluded from the data of the subsequent interpolation processing. It should be noted that instead of the excluded data, digital data that is approximately interpolated into sine wave data is used to ensure reliable data for the subsequent relay calculations.
According to the second embodiment, the reliability of the data used for the approximate interpolation can be ensured, and the data can be interpolated even for the peculiar data having a discontinuous portion such as a cutting wave. The performance can be maintained and the performance can be maintained and improved without deteriorating the characteristics.

In the second embodiment, there is a possibility that it may be judged as an accident if there is a peculiar input such as an inrush waveform that is not an accident. Therefore, in the third embodiment, the purpose is to prevent this. It has the following configuration. In the case of an inrush waveform, it can be considered that some harmonics are contained in addition to the fundamental wave, so it is obvious that extracting only the fundamental wave is different from the interpolated sine wave data described above. is there. Therefore, in the third embodiment, the means for extracting the fundamental wave component from the digital data by the Fourier transform is used to judge the coincidence between the extracted data and the interpolated sine wave data. It is configured to perform a relay operation with the data of the fundamental wave component obtained by the conversion. Generally, the fundamental wave component of the function waveform of D (θ) = a ₀ + a ₁ cos θ + a ₂ cos 2θ + ... + b ₁ cos θ + b ₂ cos 2θ + Here, it is assumed that the sampling is performed at time intervals obtained by dividing one cycle into P equal parts. FIG. 3 is a flow chart showing the processing of the third embodiment. S7 in the figure is the processing for extracting the fundamental wave component by Fourier transform, and D _i is the sampling data at the time point i. In addition, according to the third embodiment, even in the case of an input waveform containing a harmonic, the fundamental wave component is extracted, which is effective for the relay calculation.

[0013]

As described above, according to the present invention, even if a peculiar input is introduced into the relay, the interpolation is performed by the data judged to be normal. Performance can be maintained and improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing the present invention.

FIG. 2 is a process for determining whether or not sampling data is full scale over.

FIG. 3 is a specific example of a data approximation method using Newton's interpolation formula.

FIG. 4 is a flowchart showing an interpolation process.

FIG. 5 is a data interpolation process according to the present invention.

FIG. 6 is a flowchart showing a second embodiment.

FIG. 7 is a flowchart showing a third embodiment.

[Explanation of symbols]

 1 Input Converter 2 Sample and Hold Circuit 3 A / D Converter 4 Relay Judgment Section S1 Maximum Value Detection Processing S2 Minimum Value Detection Processing S3 Difference Value Detection Processing S4 Interpolation Processing S5 Fifth Processing S6 Reliability Check Processing S7 Fundamental Wave Component Extraction process

Claims (1)

[Claims] 1. A means for converting an analog quantity into digital data after sampling a voltage / current of a power system at a constant cycle, a means for storing the digital data for a predetermined period, and a maximum or minimum value of the digital data. And a means for detecting that the digital data has a maximum or minimum period, and the digital data is interpolated into sine wave data by using the past digital amount stored in a period when the digital data is not the maximum or minimum. The digital protection relay is characterized in that when the digital data is maximum or minimum, the interpolated sine wave data is used to perform an operation for detecting an accident that has occurred in the power system. ..