Soft motor start is gentle on power supply and mechanical components

21.05.2001

Siemens Automation & Drives (A&D) is offering a new soft starter solution for the medium-voltage range: the Simostart MV permits gentle startup and coasting of three-phase asynchronous motors.

The motor terminal voltage will be reduced when starting a system, and then raises it continuously. This avoides mechanical shocks at the pump components as well as pressure surges in piping systems.

Soft motor start is gentle on power supply and mechanical components

Siemens Automation & Drives (A&D) is offering a new soft starter solution for the medium-voltage range: the Simostart MV permits gentle startup and coasting of three-phase asynchronous motors. This increases the service life of the power transmission elements - for example V-belts or gear units - and the driven production machines. Maintenance requirements and operating costs are reduced. The soft starter also has a positive effect on the supply voltage since this is no longer subject to current peaks. The motor can be incorporated into host process control systems by means of the Simostart MV communications interface, for example Profibus or Modbus. Simostart MV itself is maintenance-free.

It is often impossible to connect three-phase asynchronous motors directly to the power supply because of their starting current. Without starting aids, current peaks occur when starting which significantly strain the power and drive systems. Depending on the type of motor, the starting current may be up to six times the rated motor current. This has an influence on other consumers, and weak power supplies may fail. The Simostart MV soft starter reduces the motor terminal voltage when starting a system, and then raises it continuously. Current peaks and mechanical shocks are completely eliminated in this manner. Further positive effects: V-belts do not slip, conveyor belts do not tear, gear unit teeth are treated gently, and pump drives no longer generate pressure surges in piping systems.

Simostart MV can be adapted to specific power supply conditions and production machines: the startup and coasting times are freely-selectable, and users can select special settings in an input menu, for example to protect the motor from overloads or to overcome the breakaway torque.

The soft starter is equipped with a bypass including controller and line contactor. The motor protection software recognizes malfunctions such as an undervoltage or overvoltage. Phase losses, faulty power supply connections and motor faults are also signalled. Following the detection of a fault, the system immediately triggers the necessary countermeasures. Parameters for the soft starter are entered on a menu-based display, and default settings shorten the commissioning time.

Together with the Siemens high-voltage motors H-compact and H-compact plus, the soft starter comprises a matched drive package. As a result of its versatile parameter settings, the Simostart MV can also be used with all models from other vendors without problem and without having to carry out special adaptation of the motors.

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