A.C. & D.C. Drives

Three-phase thyristor starters for a.c.low-voltage motors


Intended for contactless smooth on and off switching of three – phase induction motors (for pumps, fans, conveyers, compressors, etc.).

Used in

– machine building industry;       
– metallurgy;       
– petroleum- and gas producing and the like.  

Design modifications of starters and their potentialities:

Uncontrolled starter (thyristor commutator) affords:

  • contactless ON– and OFF – switching under normal conditions;
  • emergency OFF – switching of load circuit in case of incomplete phase – number mode of operation, at short circuit currents and overloads in excess of preset values.

Controlled starter enables to ensure:

  • smooth acceleration of a motor with starting current limited to preset value, or according to preset time – current diagram;
  • smooth stopping of a motor with preset time of transient mode of operation;
  • dynamic braking mode of operation (if a special device is available).

Soft start series starters are intended for operation with a shunt contactor. When starting is completed, the contactor by – passes the thyristors. Starter provides for arc – free OFF – switching of the shunt contactor.

Main specifications

Parameter name Value
Rated voltage of power circuit, V 220; 380; 660
Frequency of supply voltage, Hz 50; 60
Motor power rating, kW  10 ÷ 1000

Duration of permissible starter overloads at continuous operation         

1.25  Irated;         
2.5    Irated;         
4.0    Irated

2 hrs         

90 sec         

20 sec 
Time of starting (stopping), sec 0,5 ÷ 120

Protection facilities

  • against short circuit Imax;
  • against current overload Iovld;
  • against incomplete phase number operation;
  • against overheating;
  • against rupture of insulation.


Starting of low – speed motor, with the shunt capacitors switched – OFF by the special contactor.

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