JPS6022772Y2 - Digital protective relay device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a digital protection relay device that performs analog-to-digital conversion of voltage, original information, etc. from a power system, and protects the power system using digital quantities.

In the past, analog protection relay devices were commonly used to protect and control power systems using analog amounts of current and voltage, but in recent years, due to increases in transmission voltage and capacity, as well as longer distances, information on multiple power points has become increasingly important. Digital processing of current and voltage is effective in the comprehensive protection control used, and there is a trend toward the realization of digital protection relay devices using small computers.

Various digital protective relay devices have also been proposed.

However, there have not been many proposals for digital protective relay devices that actively have anti-timeout characteristics.

This is the reason for the major difference between the analog type and the digital type.The reason is that the analog type (electromagnetic type) can easily have inverse time characteristics by increasing the contact spacing to some extent, whereas the digital type has a protection calculation. This is because the algorithm has to be changed.

Inverse timing characteristics are necessary to ensure that when there is a fault in the power system, the operating time is delayed when the fault is at a point far from the fault and the effect of the fault is small, and the system is shut down to the minimum extent necessary. It is.

The object of the present invention is to provide such inverse timing characteristics in a digital protective relay with a relatively simple device.

Figure 1 shows a basic block diagram of a digital protective relay device. 1 inputs digital data obtained from the power system and calculates a value proportional to the effective value or average value (hereinafter referred to as calculated value). ), an effective value calculation device for calculating 2
is a comparison device that determines whether the calculated value from the effective value calculation device 1 is larger than a constant value.

As a simple example, assuming an overcurrent relay, the following equation holds.

■≧Anti ・・・・・・・・・(1)
Here ■: current effective value, KO: set value, that is, current effective value I is set value K.

When this happens, the comparator 2 performs an operation such as outputting a cutoff signal to the breaker as a protection output.

FIG. 1 can be compared to an overcurrent relay shown by equation (1).

However, equation (1) does not have a time element and does not have an inverse time characteristic.

The inverse time characteristic is expressed by the following equation.

It≧Ko・・・・・・・・・
(2) where I: current effective value, t: operating time, KO=set value inverse time limit characteristics are shown in FIG.

In Figure 2, the horizontal axis is the effective current value I, and the vertical axis is the operating time t.
represents.

For analog types, especially electromagnetic types, this inverse time characteristic is quite naturally related, but it is not so easy for digital types.

As a method to obtain inverse time characteristic in digital type (2)
From the equation, if the current at the time of the accident is constant, equation (2) becomes equation (3) after the time of the accident.

f”tIdt≧Ko ・・・・・・
(3) That is, by calculating the effective value, performing integration, and outputting a cutoff signal when the value exceeds the set value, an inverse time limit characteristic can be obtained.

Figure 3 shows an example of a digital protective relay device for obtaining inverse time characteristics from equation (3). Digital data obtained by sampling the amount of alternating current in the power system is input, and the protective The output is a command to shut off the breaker, etc.

In the same figure, 3 is the effective value (or average value) of the digital data input obtained by sampling the AC amount from the power system.
8, the output (effective value) of the effective value calculating device 3 is a constant I;

This is a comparator device which outputs a pulse to the clock counting device 5 when the output of the effective value calculation device 3 is smaller than a constant and outputs the effective value to the adding device 6.

Next, the operation of the device shown in FIG. 3 will be explained using an overcurrent relay as an example.

When there are no accidents in the power system, large currents do not flow, so
The effective value of the input current is small.

Therefore, since the output of the effective value calculation device 3 is small,
In the comparator 8, each sample is outputted to the counting device 5, but not to the adding device 6.

Therefore, the output of the adder 6 becomes 0, and the comparator 7 does not send out a protection output.

Next, when an accident occurs in the power system, a large current flows such that the effective value of the current exceeds at least the set value of the comparator 8.

Therefore, the comparing device 8 does not output an output to the counting device 5, but inputs the output of the effective value calculating device 3 to the adding device 6.

At this time, the diagram in FIG. 3 is equivalent to a configuration consisting of only the effective value calculation device 3, addition device 6, and comparison device 7, and its operation is (3
) becomes the expression itself.

That is, since the output of the adder 6 exceeds the constant Is, the comparator 7 outputs a protection output (such as a breaker signal).

After that, if the accident disappears, the adding device 6 is reset every n samples (n is the set value of the counting device 5) by the output of the counting device 5, the output of the adding device 6 no longer exceeds Is, and the protection output becomes Return.

That is, the comparator 7 no longer sends out a protection output.

That is, the digital effective value calculation device shown in FIG. 3 has an inverse time limit characteristic.

Note that the effective value calculation method in the effective value calculation device 3 shown in FIG. 3 has conventionally been a method of adding the absolute value of input sicycles (n is a natural number), and a method in which the phase differs by 90 degrees depending on the electrical angle of the input. Methods such as squaring the data and adding it, or adding sums and subtractions to three consecutive samples have been considered, but other methods include obtaining the absolute value of the instantaneous value of the sampled alternating current amount and adjusting the fundamental frequency. There is a method of comparing the absolute values of cycles (n is a natural number) and extracting the maximum value.

In addition, as the effective value calculation method, obtain the absolute value of the instantaneous value of the sampled alternating current amount, compare the absolute values for n cycles of the fundamental frequency (n is a natural number), and calculate the second from the maximum value among them. There is a method of extracting a large value, and in this case malfunctions due to instantaneous noise mixed in the analog section, digital transmission section, etc. are reduced.

Therefore, the effective value calculation device 3 can be configured as a device that calculates a numerical value proportional to the effective value or average value of the alternating current amount using each of the above-mentioned methods as necessary.

As the effective value calculation device 3, for example, the absolute value of the instantaneous value of the sampled alternating current amount is obtained, the absolute value of one cycle of the fundamental frequency (n is a natural number) is compared, and the FIG. 4 shows the configuration of an apparatus for calculating a numerical value proportional to the effective value or average value of the alternating current amount by the method of extracting the maximum value.

In FIG. 4, digital data (input data) of the instantaneous value of an alternating current sampled one after another at a predetermined period, for example, is inputted to the absolute value conversion block 11, and the absolute value of the instantaneous value data is obtained. It will be done.

Further, 12, .about.12m are shift registers, respectively, and these shift registers 12, .about.12. n is a circuit that holds the absolute value of m fixed past instantaneous values.

13 is a circuit that detects the maximum value of the past data 1111 to 11m1 and the current data held in the shift registers 12□ to 12□.

Here, 1m is data before m sampling, and io is current data.

Generally, the number m of shift registers depends on the sampling angle,
Only one cycle of the fundamental frequency is required.

In addition, as the effective value calculation device 3, the absolute value of the instantaneous value of the sampled alternating current amount, for example, the current as described above, is obtained, and n cycles of the fundamental frequency (n
Figure 5 shows the configuration of an apparatus for calculating a numerical value proportional to the effective value or average value of the alternating current amount by comparing the absolute values of the values (where is a natural number) and extracting the second largest value from the maximum value. Shown below.

The difference between FIG. 5 and FIG. 4 is that the maximum value detection circuit 13 is replaced by a circuit 14 that detects the second largest value from the maximum among the absolute values of the instantaneous value data for n cycles. .

Here, detecting the second largest value from the maximum means that if the maximum value among the data input to the circuit 14 is two or more data, the maximum value is detected; If there are more than 1, the second value is detected.

Further, in general, the number m of shift registers is required depending on the sampling angle, and n cycles are required.

This circuit of FIG. 5 obtains the absolute value of instantaneous value data for n cycles, removes the maximum value, and returns the maximum value of the remaining absolute values,
That is, this is a circuit that calculates the second largest value from the maximum among the absolute values of instantaneous value data for n cycles as an amount proportional to the effective value.

Although only the overcurrent continuation device was mentioned in the above embodiment, the present invention is not limited thereto and can of course be applied to other relays.

Furthermore, in carrying out the present invention, it is also possible to implement the present invention using a computer such as a microcomputer, which has recently made remarkable progress.

As described above, according to the present invention, it is possible to realize a digital protective relay device with inverse timing characteristics with a relatively simple device, and because it is digitally processed, it is resistant to noise, has good accuracy, and is easy to design. Its effects are extremely significant, such as the ease of changing settings and changing characteristics.

It is clear that by applying the present invention, arbitrary characteristics such as inverse time limit characteristics and constant time limit characteristics can be easily obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a digital effective value calculation device, FIG. 2 is a diagram showing inverse time characteristics, FIG. 3 is a block diagram showing an embodiment of the digital effective value calculation device according to the present invention, and FIG. The figure and FIG. 5 are the effective value calculation device 3 of FIG.
It is a block diagram showing each example of. 3... Effective value calculation device, 5... Counting device, 6... Adding device, 7... Comparison device, 8... Comparison Device.

Claims (3)

[Scope of utility model registration request] (1) In a digital protective relay device that protects the power system using digital data obtained by sampling alternating current information such as voltage and current in the power system and converting it from analog to digital, the effective value of the sampled alternating current amount is used. or an effective value calculation device that calculates a numerical value proportional to the average value, an addition device that adds only output numerical values larger than a predetermined value among the output numerical values of the effective value calculation device, and an output numerical value of the effective value calculation device. a comparison device that determines whether each sample is larger than a predetermined value, supplies the output numerical value of the effective value calculation device to the addition device when it is larger than the predetermined value, and sends out a pulse when it is less than or equal to the predetermined value; , a counting device that counts the pulses sent out from the comparator, and sends a heliset signal to the adding device when the pulses are equal to or higher than a predetermined value to zero the added value of the adding device; and an output of the adding device. What is claimed is: 1. A digital protective relay device comprising a comparison device that compares an added value with a predetermined value and sends out a protective output when the added value is greater than the predetermined value, and has an inverse time limit characteristic. (2) Use the effective value calculation device to obtain the absolute value of the instantaneous value of the sampled alternating current amount, compare the absolute values for n cycles (n is a natural number) of the fundamental frequency, and extract the maximum value among them. A digital protective relay device according to claim 1, which is constituted by a device comprising: (3) Use the effective value calculation device to obtain the absolute value of the instantaneous value of the sampled alternating current amount, compare the absolute values for n cycles of the fundamental frequency (n is a natural number), and find the second largest value from the maximum. A digital protective relay device according to claim 1, which is constituted by a device for extracting.