The high-voltage frequency converters (type: PCHSD-V-G) for soft start of synchronous motors are made as the converters, intended for multiple soft start of synchronous motors with a voltage of 6, 10 kV and a power of 0,63…12,5 MW, that provide a staggered frequency-controlled start of electric drives of heavy-duty machines with high moments of inertia and a constant static moment: drum mills, crushers, conveyors, tube furnaces, sinter exhausters, large-sized smoke suckers, fans and others.
The frequency converter circuit of the following configuration is used: a controlled rectifier — a motor-controlled current inverter. It consists of a controlled rectifier with the input current-limiting reactors, a smoothing inductor and a bridge inverter with natural thyristor commutation. During a frequency-controlled start a linear and smooth motor speed increase is achieved, accompanied by current limitation to the level of not more than 1,2 times the rated value. When the rated speed value is reached, a special phase adjuster synchronizes voltages of the mains and the motor and activates a bypass contactor.