DEVICE FOR PROTECTIVE DISCONNECTIONS IN A C ELECTRIC POWER SYSTEM WITH SOLIDLY GROUNDED NEUTRAL Russian patent published in 1994 - IPC

FIELD: electrical engineering. SUBSTANCE: current of leakage through water of pool to ground within the limits from 0.5 to 1.0 mA is formed intentionally in compliance with algorithm of proposed device from phase wire of power system via current limiting resistor 9 or 10 and electrode on body of pump. This leakage current isolated with leakage current pickup 1 is fed to two-threshold comparison elements 3 and 4 which disconnect electric pump from power system if leakage current is less than 0.5 mA or greater than 1.0 mA. This is explained as follows. Decrease of leakage current to values markedly less than 0.5 mA (practically by factors 10¹...10²) corresponds to breakage of electric connection of electrode through water to ground which refers to coming of this electrode out of water. This disconnection ensures enhanced reliability of electric pump. If value of leakage current lies within 0.5-1.0 mA then protective device switches on, if it is in healthy condition, and feeds power supply to electric pump. If protective device fails then it will not switch on preventing operation of electric pump with faulty protection. This is provided by self-test of protective device. Disconnection of power supply to electric pump with leakage current exceeding 1.0 mA secures electric safety of pump as increase of leakage current over 1.0 mA indicates that either a man touched current-carrying parts or insulation of electric pump deteriorated. EFFECT: increased safety of operation. 1 tbl, 1 dwg