JPH04364315A - Digital protective relay - Google Patents

Abstract

PURPOSE:To prevent erroneous operation by checking the validity of AC data after bit extension or checking the allowable range of data thereby detecting the variation of data through a simple method. CONSTITUTION:Check is made for each sample whether the extended four significant bits(#15-#12) in 16 bits of an AC data 3 always have same values as bit #11. If they have different values, a decision is made that the variation of data caused an error.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital protection relay for protecting an electric power system, and more particularly to a monitoring method therein.

0002

[Prior Art] Digital protective relays using microcomputers have been widely used for the purpose of detecting the occurrence of accidents in power systems. The instantaneous values of alternating current electrical quantities (voltage, current) are sampled at regular intervals (for example, at intervals of 30 degrees of alternating current electrical angle), and A/D (analog/digital) conversion is performed to generate digital data (hereinafter referred to as alternating current data). It is introduced into a digital arithmetic processing unit (hereinafter referred to as MPU), performs predetermined protection arithmetic processing, and outputs the results.

[0003] Generally, a 12-bit A/D conversion is used, while a 16-bit one is used for the MPU. In this way, while AC data is 12 bits, MPU is 16 bits, so M
When importing into the PU, the upper 4 bits are added (extended) to the 12-bit AC data to make it into 16-bit data, and then the data is imported. FIG. 3 shows the state of this 4-bit expansion. Figure 3 shows an example of 16-bit AC data after expansion, where bits #0 to #11 are 12-bit AC data before expansion, and bits #12 to #15 are the upper 4 expanded data.
It's a bit. Among them, bit #11 is a sign bit of 12-bit AC data, and when it is "0", it means positive data, and when it is "1", it means negative data. Here, since the original AC data is 12 bits, the possible values of the AC data are within the range of +(211-1) to -(211), that is, +2047 to -2048.

To expand this 12-bit data to 16 bits, as shown in the figure, the same value as bit #11, ie, the sign bit, is added to the upper 4 bits. For example, +2047 data has the original 12 bits as X'7FF' in hexadecimal, but to expand this to 16 bits, add the same value "0" as bit #11 to bits #15 to #1.
2, resulting in data X'07FF'. Similarly, for the data of -2047, the same value "1" as bit #11 of X'800' is added to bits #15 to #12, resulting in data X'F800'. The AC data changes instantaneously within this range of +2047 to -2048.

[0005] This upper 4-bit extension is generally performed by hardware, as will be described later. However, in such extended 16-bit AC data, if the upper 4 bits of the data change due to some factor, such as external noise or a hardware failure in the 4-bit extension part, the above-mentioned original range of data may change. This results in a significant deviation from +2047 to -2048. For example, originally X'0
7FF' data (+2047), but when bit #14 changes from "0" to "1", it becomes X'4
This is an extremely large value of 7FF' (+18431). If this value is taken into the MPU and a protection calculation is performed, an erroneous output will occur as a protection relay.

For example, in the case of an overcurrent relay, the amplitude value is calculated from AC data to determine whether or not it exceeds a predetermined detection level. However, if the data change described above occurs, the amplitude value may exceed the detection level. Exceeding this will result in erroneous output. This trend is the same no matter which bit among the 16 bits changes, but the higher the bit, the greater the effect. Therefore, it is very important to monitor the above-mentioned upper 4 bits.

[0007]

[Problem to be Solved by the Invention] As mentioned above, it is important to monitor whether AC data is correct or not, but with conventional digital protective relays, there was no effective means for monitoring this. . One possible method is to perform a parity check, which is a well-known method, but this method cannot detect a change in an even number of bits in the data, and is therefore not sufficient. As described above, the reality is that there has been no effective monitoring method in the past, and people have relied on inadequate methods such as parity checks. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a digital protective relay that can detect changes in AC data using a simple method and prevent malfunctions.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for converting AC data 3 extended by the upper 4 bit extension unit 4 shown in FIG. Data changes are monitored by checking whether #11 and bits #15 to #12 have the same value. [Operation] Among the 16 bits of AC data 3, check that bit #11 and bits #15 to #12 are always the same value at each sampling, and if they are different data, it is error data due to data change. It is determined that this is the case, and measures such as locking the output of the protective relay are taken to prevent malfunction.

[0009]

Embodiments Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of a protective relay according to the present invention. In the figure, 1 is an input converter that converts the voltage V and current I introduced from the power system into appropriate levels, and 2 is an input converter that samples the output of the input converter at regular intervals and converts it into digital data. Bit A/D converter, 3
is the AC data (digital data) output from the A/D converter 2, 4 is the upper 4 bit extension part that adds the upper 4 bits to the 12-bit AC data to make it 16-bit data, and 5 is the 16-bit AC data. A digital arithmetic processing unit (MPU) that takes in AC data 3 in the form of bits and performs predetermined protection calculations, is composed of a microcomputer, and produces an operational output when operating conditions are met.

FIG. 2 is a flowchart of the processing contents calculated by the MPU of FIG. 1, and particularly shows the contents of monitoring processing of AC data. Step S21 reads instantaneous value data (AC data) of each sampling of voltage V and current I of the power system, and step S22 reads bit #11 and bits #15 to #15 of the AC data as described above.
#11 is compared and checked, and in step S23, if the values are not the same, "AC data defect" is stored in step S24, and if all values are the same, "AC data defect" is reset in step S25. . In step S26, a predetermined protection calculation is performed using the voltage V and current I, and in step S27 it is determined whether the AC data is defective, and if it is defective, step S28 is performed.
The output is locked in step S29 to prevent erroneous output, and if there is no defect, a correct operation output is generated in step S29. This process is repeated at regular sampling intervals.

The operation of the protective relay configured as described above will be explained in more detail. 16 for each sampling
Bit AC data 3 (V, I) is read into the MPU in step S21, but the upper 4 bits #15 to #12
is always the same value as bit #11 by the upper 4 bit extension unit 4. The state of the data values is as explained in FIG. 3. Next, steps S22 and S23
Check whether these 5 bits #11 and #15 to #12 have the same value, that is, all “1” or all “1”.
A comparison check is made to see if the value is 0. If all the values are the same, the read AC data is determined to be a correct value, and the memory of "AC data defect" is reset in step S25. However, if the values are different even by 1 bit, the AC data is is the predetermined range mentioned above +2047
~-2048 is determined to have deviated from the range, and the process proceeds to step S24.
, and memorizes the fact that "AC data is defective".

[0012] In step S26, a predetermined protection calculation process is performed, and if there is no ``AC data failure'', operation output processing is performed based on the calculation results in steps S27 to S29, but if ``AC data failure'' has occurred. If so, the process moves from step S27 to step S28, and the operation output is locked to prevent erroneous output. As explained above, in this embodiment, changes and errors in AC data can be reliably detected by using a simple method in which software compares and checks the bit values of AC data taken into the protective relay. , malfunctions can be prevented.

[0013] In the explanation so far, the method of locking the output of a protective relay has been explained as an example of a method to take when a defective AC data is detected. A method of controlling in the direction may also be used. For example, in the case of an overcurrent relay, when the aforementioned data failure is detected, processing is performed to forcibly set the sampling AC data to zero. As a result, even if the AC data changes to an extremely large value, the calculation result of the amplitude value will be small, and control will be performed in the non-operating direction, making it possible to prevent erroneous output.

Furthermore, in the case of an overvoltage relay, it is conceivable to control the voltage to a rated voltage value, for example, and it goes without saying that various methods may be adopted without departing from the spirit of the present invention. In addition, in the explanation of FIG. 2, for simplicity of explanation,
When a defect in AC data is detected, the operation output is locked only for that sampling, but this is not limited to this, and is applicable to operation judgment algorithms where the influence of defective AC data continues for a long sampling period. Needless to say, the output lock may be continued during that time. Further, in the explanation of FIG. 2, an example is given in which the operation output is locked when a defect in AC data is detected, but in addition to locking, an alarm may be output to the outside as an alarm. Alternatively, depending on the purpose, only an alarm may be used without locking the operational output.

In the explanation so far, bit #11 and bits #15 to # are used as a method for detecting defects in AC data.
The explanation was given using an example of checking each bit to see if the 12 values are the same, but there is another method to check whether the data after expanding to 16 bits is within the range that can be taken as 12 bit data before expansion. Even if you check whether it is true or not, you will get exactly the same effect. For example, the range that 12-bit data can take is +2047 to -2048 as described in FIG.
Therefore, it may be checked that +2047≧16-bit AC data≧−2048. In addition, in the explanation in the main text, an example was described in which 12 bits of AC data were expanded to 16 bits, but it goes without saying that the present invention is applicable without being limited to these bit numbers in view of the spirit of the present invention. stomach.

[0016]

[Effects of the Invention] As explained above, according to the present invention, the validity of AC data after bit expansion is checked by bit checking or by checking the possible range of data, so that digital protection is simple and reliable. It becomes possible to monitor the relay, and a more reliable digital protection relay can be provided.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart showing the processing contents of the present invention.

FIG. 3 is a diagram explaining the concept of bit extension of AC data.

[Explanation of symbols]

1 Input conversion section 2 A/D conversion section 3. Exchange data 4 Upper 4 bit extension part 5 Digital calculation processing section

Claims (1)

[Claims] Claim 1: After introducing the electrical quantity of the power system and sampling it at regular intervals, perform n1-bit analog/digital conversion, add n2 bits to the n1-bit digital data, and generate n1 + n2-bit data. 1. A digital protective relay configured to perform a protection calculation, wherein the digital protective relay is configured to monitor whether the most significant bit of the n1 bit and the value of the n2 bit are all equal.