JP2677732B2 - Digital protection relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital protective relay device, and more particularly to a digital protective relay device capable of converting a system electricity quantity used for protection processing into highly accurate digital data and performing a protective relay operation. Regarding the device.

[0002]

2. Description of the Related Art The technique of applying a microcomputer to a protection device for a power system is well known. today,
Along with the expansion of the power system scale, the increase in the protection equipment of the system has become a problem. As one solution to this problem, it is possible to protect a large number of protection targets and to make the device compact. There are digital protective relays available.
One of the major characteristics of these digital type protection devices is that the system electricity quantity, which is an analog quantity, is converted into digital data and processed, and the protection relay operation and processing are performed using the converted digital data. . Therefore, it can be said that the function of converting digital data is a very important function for the digital protective relay device. The conventional technique will be described below by taking a digital relay as an example.

FIG. 5 shows the basic structure of a conventional arithmetic type digital protective relay device. The digital protection relay device shown in the figure comprises an input conversion section 1, a filter 2, a sample hold circuit 3, a multiplexer 4, an analog / digital converter 5, and a digital arithmetic processing section 6 for handling digital data. Composed of. The digital arithmetic processing section 6 is composed of a RAM 61, a CPU 62, and a ROM 63. The input converter 1 is an input converter that converts a current or voltage signal from the power system (an analog input signal related to the state of the power system) into an appropriate voltage signal on the digital protection relay side, and the filter 2 is each input converter. It is a circuit for extracting the fundamental frequency component of the power system from the output of No. 1 and mainly for removing the harmonic component. The sample-hold circuit 3 is a sample-hold (S / H) circuit that holds the analog output data from each filter 2 at the sampling time at the value at that time, and is analog-digital converted (hereinafter referred to as A / D conversion). It is intended to prevent the value from changing during the time.

The multiplexer 4 is a switching circuit which sequentially connects a plurality of sample and hold circuits 3 and the A / D converter 5 and sequentially outputs the analog output data held at the same time to the A / D converter 5. With this multiplexer 4, a single A / D converter 5 can be used to obtain a plurality of inputs of the same time data. Further, the digital signal converted by the A / D converter 5 is temporarily stored in the random access memory (RAM) 61 in the order of sampling, and then output to the CPU (arithmetic unit) 62, in accordance with the program stored in the ROM 63. The protection calculation process is executed by the CPU 62.

[0005]

As described above, the function of converting an analog quantity into a digital quantity is important in the digital type protective relay device. In FIG. 5, this is the input converter 1, the filter 2, the sampling hold. An analog circuit composed of a circuit 3, a multiplexer 4, and an A / D converter 5.
It is realized by a digital conversion unit. What is most required of this analog-to-digital converter is to faithfully convert analog data into digital data. That is, it is to obtain highly accurate error-free digital data. However, it is a well-known fact that the accuracy is actually limited due to the quantization error, the analog fixed error, and the analog proportional error that occur in the analog-to-digital converter (for example, the Electric Cooperative Research No. 41). Vol. 4, "Digital Relay", page 51). Among these, A /
The quantization error generated in the D converter 5 is peculiar to the digital type device, and has a great influence on the relay characteristic error especially in the small current region. In order to solve this, the input full scale may be reduced and the resolution (quantization step) per digit may be reduced. However, the input full scale is determined by the system voltage and the maximum fault current, and if the input full scale is made too small, accurate accident detection becomes impossible. In order to keep the input full scale to the required size and to suppress the error in the small current range, A / D
A method of increasing the number of quantization bits of the converter 5 can be considered.
Hereinafter, this will be described quantitatively.

In a digital relay, a 12-bit A /
A D converter is used, and the quantization error in this case is expressed by the following equation. Therefore, the size of the quantization error occurs without depending on the size of the input. When the size of the input is large, its influence is small, but when the size of the input is small, its influence is relatively large. . For example, if the input size is 1 full scale
At / 200, the effect of quantization error is Becomes

As is apparent from the equations (1) and (2), in order to reduce the influence of the quantization error, the number of bits of the A / D converter may be increased. For example, 14-bit A / D converter If is adopted, the influence of the quantization error becomes 1/4, which is 1.25%. If the number of bits is further increased, the quantization error can be theoretically completely ignored. However, as described above, since there is a fixed component error in the analog part and a proportional component error,
Even if the number of bits of the A / D converter is increased, if it exceeds a certain level, the error in the analog section becomes dominant and the overall error does not decrease. As mentioned above, there is a limit to the error reduction in the actual analog-digital conversion method,
It can be said that it is difficult to improve the accuracy of protection relay characteristics. The present invention has been made in order to solve the above-mentioned problems, and it is possible to reduce the influence of a quantization error without reducing the input full scale and to enable a highly accurate relay operation in a digital protective relay. The purpose is to provide a device.

[0008]

To achieve the above object, the structure of the present invention will be described with reference to the block diagram shown in FIG.
The present invention uses plural electric quantity input circuits 10, 11, ..., 1n having different full scales for inputting the same system electric quantity A and digital data from the plural electric quantity input circuits.
Electricity input circuit 10, 11, ..., 1n for protection relay calculation
Protection relay computing means 20, 21, ..., 2n corresponding to
And an output selecting means 30 for selecting an output from the protection relay computing means and setting it as a protection operation output.

[Operation] The system electricity quantity A is input to a plurality of electricity quantity input circuits 10, 11,
..., 1n, and protection relay computing means 21, 2 using digital data obtained through these electric quantity input circuits
2, ..., 2n perform the protection relay calculation, and the output selection means 30 selects the result of the protection relay calculation according to the magnitude of the system electricity amount A, and makes it the protection operation output.

[0009]

An embodiment will be described below with reference to the drawings. FIG.
FIG. 1 is a block diagram of an embodiment of a digital protective relay device according to the present invention. 2, the same parts as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted. The features of the present invention are:
The point is that a plurality of electric quantity input circuits are provided for the same electric quantity A, specifically, the input converter 1-1 and the filter.
2-1, an input circuit 10 composed of S / H3-1 and an input circuit 11 composed of an input converter 1-2, a filter 2-2 and S / H3-2 are provided. Is. The analog data obtained by both input circuits is the A / D converter 5
Are converted into digital data respectively to obtain digital data d1 and d2. Based on the digital data d1 and d2, protection relay calculations 21 and 22 are performed, respectively. Where 2
1 and 22 are the same protection relay calculation. Also, the input circuit 10
And the input full scale of the input circuit 11 are made different so that the input circuit 10 has a large full scale with respect to the input circuit 11. The level detection circuit 31 introduces the digital data d2 obtained by the input circuit 11 to detect the magnitude of the instantaneous value of the introduction amount, and when this exceeds a predetermined value, locks the output of the protection relay operation unit 22. If it does not exceed, by locking the output of the protection relay calculation 21, either 21 or 22 is selected as the protection operation output of the device. Here, the predetermined value is a level determination value for detecting that an input exceeding the input full scale of the input circuit 11 is applied.

As shown in FIG. 3, when a large amount of system electricity is input when a system fault occurs, the digital data d2 has a waveform with the dotted line portion in the figure cut off. This is because the characteristics of the input circuit 22 are as shown in FIG. Note that FIG. 4 shows that the input circuit 21 has a characteristic that it does not saturate even with a larger input, that is, has a larger input full scale. By comparing the conventional configuration, it is possible to reduce the influence of the quantization error and to perform highly accurate relay calculation without reducing the input full scale of the entire device by adopting the above configuration. To do. In the conventional configuration, one system electricity amount A
On the other hand, since there is only one input circuit, it is assumed that there is an input circuit having the same characteristics as the input circuit 11. in this case,
Although there is no problem in operation for a relatively small system electricity input, if there is an input exceeding the input full scale, the digital waveform used for the relay calculation becomes a saturated waveform as described above. Therefore, relay calculation with an accurate input becomes impossible, and as a result, a correct protection operation output cannot be obtained. For example, there should be an operation output, but the output should be restored, or conversely, the output should have been restored, but it should be activated, which is extremely useful as a protection relay for protecting the power system. It becomes unreliable.

On the other hand, in the configuration according to the present invention, the input circuit 11
When a large input exceeding the input full scale of is input, the output of protection relay calculation 22 is locked to prevent erroneous output, and at the same time, the calculation is performed via input circuit 10 having a larger input full scale. The output of the means 21 will be adopted as the operation output. Therefore, as compared with the conventional configuration, there is no fear of erroneous output even with a larger input. Here, as one method in which the protection operation output is not erroneous even when a large input is input in the conventional configuration, it is conceivable to make an input circuit of a sufficiently large input full scale in advance. As one example, the input circuit 10 in FIG.
It is a characteristic like. By doing so, even if there is a large input exceeding the full scale of the input circuit 11, the obtained digital data will not be saturated and correct protection relay calculation can be performed. However, in this way, as explained from Eqs. (1) and (2) above, the effect of the quantization error becomes conspicuous in the small input region, and it is not possible to realize highly accurate relay operation. become. On the other hand, according to the configuration of the present invention, for a small input, the operation output is obtained by the protection relay calculation 22 based on the digital data obtained from the input circuit having a small input full scale, so that a highly accurate relay calculation is realized. You can do it. According to the above embodiment, it is possible to select an input circuit suitable for the input and a corresponding protection relay calculation means according to the input, and it is possible to obtain a protection relay device having a wide input full scale and high accuracy as a whole. . In the embodiment described above, two input circuits are provided for the same system electricity quantity, but the same is true if three or more are provided. The more input circuits provided, the larger the input full scale and the higher accuracy. It will be possible to calculate glue relay.

[0012]

As described above, according to the present invention, a plurality of input circuits having different input full scales and protection relay calculation means corresponding to the same are provided for the same system electric quantity to correspond to the input value. By selecting the most suitable protection relay calculation means, the entire device can realize a large input full-scale and high-precision protection calculation, and a digital protection relay device with high accuracy and reliability. Can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of a digital relay according to the present invention.

FIG. 2 is a configuration diagram of an embodiment of a digital relay.

FIG. 3 is an example of level detection when converting a system electricity quantity into digital data.

FIG. 4 shows an example of characteristics of an input circuit.

FIG. 5 is a basic configuration diagram of a digital protective relay device.

[Explanation of symbols]

 1-1, 1-2 Input converter 2-1, 2-2 Filter 3-1, 3-2 Sample-and-hold circuit 4 Multiplexer 5 Analog-digital converter 6 Digital arithmetic processing unit 10-1n Electric quantity input circuit 20- 2n Protection relay calculation means 30 Output selection means

Claims (1)

(57) [Claims] 1. In a digital protective relay device for inputting the electric quantity of a power system and converting it into digital data to protect the power system, a plurality of different full-scale electric quantities for inputting the same system electric quantity. an input circuit, a plurality of protective relay computation means corresponding to said plurality of electrical quantities input circuit for performing a protection relay operation by using a plurality of digital data obtained through a plurality of electrical quantities input circuit, said
Input the amount of electricity from the electricity amount input circuit and instantly
Protection relay that responds when the magnitude of the value exceeds a specified value
Lock the output of the arithmetic circuit and
Electric quantity input circuit with upper full scale for road
And a output selecting means for deriving an output of a protection relay arithmetic circuit corresponding to the digital protective relay device.