Motor Starting

[electricalexpert65]

What is teh maximum permissible voltage drop at the three phase squirrel cage induction motor terminals during (a) Normal Running with full rated load and ( during acceleration? Can you also trace your answers to some National and/or International Standards?

[marke]

Hello electricalexpert65

 

The major consideration is usually the voltage during run as any continuous voltage drop is power loss.

Commonly in Australia and New Zealand, the standards call for a maximum of 5% but many target 2% voltage drop during run.

 

The major concern with voltage drop during start is the effect on other equipment.

Most equipment designed to operate on a 50Hz supply can tolerate a minimum voltage of Vnom - 15%.

If we allow for a 3% drop in the line voltage (bottom end of allowable supply voltage, then you would want to restrict the voltage drop during start to 12%.

 

Note most motors starters are of areduced voltage type so voltage drop during start does not hame a negative impact on the motor unless you require full DOL torque at start.

 

Best regards,

Mark.