JPH0320965B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protective relay device for a power system.

Conventionally, there has been a device of this type as shown in the figure. In the figure, 1 is a current transformer that detects the current of the power transmission line 1a of the grid, 2 is a transformer that converts the output level of current transformer 1, 8 is a filter that extracts the fundamental wave component from the output of transformer 2, 4 is a converter ADC that converts the output of filter 8 into a digital signal, 5 is an ADC
4 is the central processing unit connected to CPU, 6 is CPU5
A memory 6 is connected to the CPU 5 and stores a program used for the arithmetic processing, and an output section 6 is connected to the CPU 5 and outputs a signal indicating an accident to the outside. The transformer 3 to the output section 7 constitute a protective relay device 8 .

Next, the operation will be explained. The current of the power transmission line 1a passes through a current transformer 1, a transformer 2, and a filter 3.
After being input to the ADC 4 and converted into a digital signal, the data is sequentially written into the memory 6 as data by the CPU 5. The CPU 5 uses the data of the power transmission line 1a according to a program stored in the memory 6 to determine whether or not there is an accident on the power transmission line 1a, and if there is an accident, outputs a signal from the output section 7. .

Generally, the current flowing through the power transmission line 1a (neighboring value)
has a relationship with the one before 90° as shown in the following equation.

(Isinωt) ² + {Isin (ωt−90°)} ² = I ² sin ² ωt + (−Icosωt) ² = I ² sin ² ωt + I ² cos ² ωt = I ^2As is clear from the above equation, at 90° Has a phase difference,
The above two instantaneous values not including the DC component are each 2
The multiplied and added value is equal to the square value I ² of the peak value I.

Therefore, the CPU 5 uses data having such a relationship and executes the calculation as shown in the above formula to obtain the peak value 1.
is determined and compared with a predetermined value, and if it is greater than or equal to the predetermined value, it is determined that an accident has occurred.

Conventional protective relay devices are configured as described above, so if the input data contains DC components due to offsets in the ADC, temperature characteristics, noise, etc., the error in fault judgment becomes large. It also has the disadvantage that a complicated circuit is required to remove such a direct current component.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by removing the DC component from the input data and then performing the accident determination process, reliability can be improved. The purpose of the present invention is to provide a protective relay device that is capable of highly accurate accident determination.

Hereinafter, one embodiment of the present invention will be described with reference again to the drawings used in the description of the conventional device. It should be noted that the explanation of each block in the figure will be omitted since it will be repetitive.

By the way, for convenience of calculations described later, let the current data be Isin (ωt + 45°) and find the difference A between the instantaneous values of data Isin (ωt - 45°) that differs from this data by 90° in electrical angle. It will look like this:

A=Isin(ωt+45°) −{Isin(ωt-45°)} =Isinωtcos45°+Isin45°cosωt −｛Isinωtcos45°−Isin45°cosωt｝ =2Isin45°cosωt =√2Icosωt =√2I sin(ωt＋90゜) Therefore , the difference A is √2 times the peak value I, and the phase is 45° ahead of the current instantaneous value.

Note that the above calculation uses the current data as
(ωt + 45°), but even if two arbitrary sampling data with a phase difference of 90° are used, the peak value is √2 and the phase difference is 45° advanced compared to the current data as the reference. data can be obtained. Also,
Since each instantaneous value has a phase difference of 90 degrees, the same DC component, 4th harmonic component, and 8th harmonic component are superimposed, so by taking their difference as in the above formula, , DC component, 4th harmonic component, 8th component
The harmonic components are removed, and an instantaneous value of the alternating current component with a magnitude of √2 and a phase lead of 45 degrees is obtained. Note that the 4th harmonic and the 8th harmonic are generated due to the system configuration, and are caused by the transformer 2, filter 4, and
Input via ADC4. Furthermore, by using data with a 90° phase difference, the second harmonic component increases; however, this type of protective relay used for protecting transformers, etc. When the wave component is extracted and its content exceeds a certain value, it is determined that the transformer is turned on without load, and the unnecessary operation of the transformer protection relay is prevented. Therefore, the second harmonic component is removed. should not be done. To obtain an absolute value from such an instantaneous value in order to determine whether or not there is an accident on the transmission line 1a, the instantaneous value with a difference of 90 degrees in electrical angle is calculated as before using the same calculation as above. , these values may be squared and added.

The program required for such calculations is stored in memory 6.
The data of transmission line 1a is also stored in
The data is sequentially written from the ADC 4 to the memory 6.
The CPU 5 periodically executes the above-mentioned calculation according to the program and data in the memory 6, calculates the peak value I, and then determines whether an accident has occurred in the conventional manner. In the above embodiments, the case where a system current is introduced has been described, but the same effect can be obtained even when other quantities of electricity such as voltage are derived.

As described above, according to this invention, in electrical angle
Since system faults are judged based on the difference between instantaneous data with 90° phase difference, errors in the DC component, 4th harmonic component, and 8th harmonic component included in the input data can be calculated. Since the accident is determined after removing the information, the accuracy of the determination can be improved.

[Brief explanation of the drawing]

The figure is a block diagram of a protective relay device. 1... Current transformer, 2... Transformer, 3... Filter, 4... Converter, 5... Central processing unit, 6
...Memory, 7...Output section, 8...Protective relay device.

Claims (1)

[Claims] 1. A converter that converts the amount of alternating current electricity into a digital amount, a memory means that sequentially stores the data converted by this converter, and two data that differ by 90 degrees in electrical angle from the data stored in this memory means. What is claimed is: 1. A protective relay device comprising: a central processing unit that calculates the difference between the numbers and performs calculation processing to protect the system based on the difference; and an output unit that outputs the calculation result of the central processing unit.