Frequency converter for group soft start of synchronous motors with voltage 6 kV and power 2200 kW is designed for alternate frequency-controlled start of electric drives of heavy-loaded mechanisms with large moments of inertia and constant static torque. It consists of controlled rectifier with input current limiting reactors, smoothing choke and bridge inverter with natural commutation of thyristors.
The circuit is realised on single-operating thyristors. All system components are located in hermetically sealed single-sided service cabinets with forced ventilation of thyristor sections.
At frequency-controlled start-up, linear and smooth increase of motor speed with current limitation at the level of no more than 1.2 Inom is achieved. After the rated speed is reached, a special phase controller synchronises the mains and motor voltages and switches on the bypass contactor.
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