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Judgment basis for disconnection of current loop

time:2020/12/10   source:华天电力  reading:648 time

The basis for discriminating the disconnection of the protection current circuit of the microcomputer relay protection tester includes: according to the differential current discrimination, when the differential current exceeds a certain value and the bus voltage is normal, it is considered that the TA is disconnected, the alarm signal is delayed, and the bus differential protection is blocked. If the one-phase or two-phase current of any circuit is zero, and the other two or one phases have load current, it is considered that the TA is disconnected, the alarm signal is delayed, and the bus differential protection is blocked. To judge, when low voltage, negative sequence voltage or zero sequence voltage appears on the bus, an alarm signal will be sent after a delay.

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The microcomputer relay protection tester has protection functions such as incoming line protection, presentation protection, section protection, distribution transformer protection, motor protection, capacitor protection, main transformer backup protection, generator backup protection, PT monitoring protection, etc., and the microcomputer relay protection test The input signal of the meter is the analog quantity of the power system, and the accounting machine can only calculate and judge the digital quantity. Therefore, the analog input from the power system through the voltage transformer and/or current transformer must first pass the pre-processing relay protection In most cases, the fundamental analog quantity in the input signal is used. In order to ensure the correct calculation and judgment of the accounting machine, and to realize the principle of relay protection based on the sinusoidal power of a certain frequency, the A/D must be changed. The digital quantity is filtered once again. Because the digital filter has high precision, reliability and sensitive adjustment, the equipment can be simplified through time division multiplexing, so digital filters are widely used in microcomputer protection.

The microcomputer relay protection tester is composed of highly integrated, bus-free chip single-chip microcomputer, high-precision current and voltage transformer, high insulation strength export center relay, high-reliability switching power supply module and other components. The microcomputer protection measurement and control equipment is used for measuring, Control, protection, and communication are an integrated economical protection. The digital filter itself can be understood as an accounting program or algorithm. It converts the digital time series representing the input signal into the digital time series representing the output signal, so that the signal follows The reservation method is changed. In the microcomputer relay protection, the corresponding digital filter should be planned and selected according to the characteristics of the power system signal and the protection principle. The primary performance indicators of the mathematical filter are frequency domain characteristics, time delay and accounting volume.

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