Method for preventing electric leakage false alarm, electric fire monitoring detector and monitoring system

Abstract

The invention discloses a method for preventing electric leakage false alarm, which sequentially carries out current magnitude judgment, current frequency judgment and waveform form judgment on induced current detected by a current transformer, wherein the waveform form judgment comprises the following steps: calculating the waveform area by adopting a sine wave calculation method to obtain a waveform effective value A; calculating the waveform area by adopting an integration method to obtain a waveform effective value B; calculating the difference percentage according to |waveform effective value B-waveform effective value A| / waveform effective value B; and comparing the difference percentage with a set alarm threshold, if the difference percentage is smaller than the set alarm threshold,an alarm being raised normally, and if the difference percentage is larger than the set alarm threshold, an alarm not being raised. The invention also discloses a residual current type electric firemonitoring detector adopting the algorithm and an electric fire monitoring system comprising the same. The method for preventing electric leakage false alarm utilizes the algorithm to remove harmonicinterference in the residual current, is suitable for scenes with harmonic interference in all low-voltage power distribution places, is simple and convenient in judgment rule, and greatly reduces theelectric leakage false alarm rate.

Description

technical field [0001] The invention relates to the field of leakage protection of low-voltage distribution networks, in particular to a method for preventing false leakage alarms, an electrical fire monitoring detector and a monitoring system. Background technique [0002] The residual current electrical fire monitoring detector is mainly used to monitor the residual current in the low-voltage distribution network. It is used in conjunction with the current transformer and installed on the wires of the low-voltage distribution network. Under normal circumstances, the vector sum of the three-phase and neutral currents is 0, and the induction value on the current transformer is 0; when there is leakage current, the vector sum of the three-phase and neutral currents is not 0, and the current transformer The corresponding current is sensed above, and the residual current type electrical fire monitoring detector collects the current value of the current transformer, and then dir...

AI Technical Summary

Problems solved by technology

[0003] The above alarm methods are prone to false alarms. For low-voltage power distribution places, loads such as inverters and switching power supplies are generally connected to the circuit. Loads such as inverters and switching power supplies will generate high-order harmonics, and high-order harmonics will generate The leakage current is a harmless current

For example, take the frequency conversion drive system in low-voltage power distribution places as an example, because there is a frequency converter on the circuit, the high-speed pulse of the frequency converter generates high-order harmonics, and the high-order harmonics flow through the induction coil on the motor, and the winding coil of the motor and There is a distributed capacitance between the shells. Due to the high frequency, the capacitive reactance of the capacitor will decrease, and the leakage current generated by the distributed capacitance will increase, sometimes reaching hundreds of mA, but this current is a harmless leakage current.

However, the alarm threshold of conventional residual current electrical fire monitoring detectors is much lower than this value. Therefore, this kind of capacitive leakage generated by high-order harmonics can easily cause false alarms in residual current electrical fire monitoring detectors, which will cause Seriously affect the work of the system

[0004] This shows that above-mentioned existing electric leakage alarm method obviously still has inconvenience and defect, and urgently needs to be further improved

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