Measuring device and method for zero-sequence current of non-effectively neutral grounded system

Abstract

The invention relates to a measuring device and method for the zero-sequence current of a non-effectively neutral grounded system. In the invention, a measuring device and measuring method for a single-phase ground fault wire selection device of the non-effectively neutral grounded system is improved, and the sensibility and the accuracy for measuring the zero-sequence current are enhanced. The output of a zero-sequence current transformer is connected in series with a resistor R2 which is connected in parallel with a primary coil of a small-sized voltage transformer; the output of a secondary coil of the small-sized voltage transformer is connected in series with a resistor R3; one end of the resistor R3 is grounded, and the other end of the resistor R3 is connected with one input end of a computing circuit; the output of the computing circuit is connected with a proportional amplifier II and a proportional amplifier III; the proportional amplifier II and the proportional amplifier III are connected with a microcomputer system after being respectively connected with an A / D (Analog / Digital) conversion circuit; the microcomputer system is connected with a D / A (Digital / Analog) conversion circuit; the output of the D / A conversion circuit is connected with a proportional amplifier I; and the output of the proportional amplifier I is connected with the other input end of the computing circuit.

Description

technical field [0001] The invention relates to the field of relay protection of power systems, in particular to a zero-sequence current measuring device and method for a neutral point non-effectively grounded system. Background technique [0002] When a single-phase ground short circuit occurs in a power system where the neutral point of the power transformer is not grounded, there is no short circuit circuit and no short circuit current will be generated. The relay protection of the power system does not need to trip, and the power system is allowed to continue to run for a period of time. But single-phase grounding is also harmful to the power system. Therefore, when a single-phase ground short circuit occurs in this kind of system, the relay protection must send out an alarm signal, and the operator on duty will make corresponding treatment, and finally carry out power-off maintenance on the faulty line. In order to carry out power-off maintenance on the faulty line, th...

AI Technical Summary

Problems solved by technology

These methods require an external signal power supply, which is inconvenient to use, and the performance of the device still does not meet the requirements

[0005] When a single-phase ground fault occurs, the principle of using the fault quantity generated by the power system itself to detect is reliable. The main problem is that the measured zero-sequence current is very small, and the measurement error of the device is large, resulting in a very low correct action rate of the single-phase ground line selection device. Low

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