Hello MaVericK
Welcome to the forum.
I have several friends from L&T, seems to be a great training ground for engineers who move to NZ!
There are two issues with the under voltage, over voltage and earth fault protection. One is potential problems with the motor, and the other is potential problems with the starter.
Motor.
- Over Voltage will cause the motor to be overfluxed. This will cause a rapid increase in magnetising current, iron loss and a build up of heat in the motor.
- Over voltage will cause a reduction in the work current drawn by the motor.
- Undervoltage will reduce the flux in the motor. This will reduce the magnetising current and the maximum torque capacity of the motor.
- Under voltage will cause the work component of the current drawn by the motor to be increased.
- under voltage will increase the running slip of the motor.
Soft Starter
- Under voltage will at some point affect the operation of the electronics, typically will cause the firing of the SCRs to be less reliable.
- Overvoltage will stress power supply components i the soft starter
- Severe Overvoltage may damage the SCRs in the soft starter.
- Earth fault could damage the SCRs in the soft starter.
If you ignore the increase in iron losses due to overvoltage, then the major problem is due to excess current and the motor can be adequately protected useing the over current protection. This does leave a small potential for motor overheating due to increased iron loss if the voltage is high enough to increase the iron loss markedly with out exceeding the current rating of the motor. This would apply to motors that are running at light load and where the magnetising current rises to just under rated current. - a very rare situation. This can also happen if the supply frequency is a little low with the voltage at rated levels.
The only issue with low voltage, is that the motor may begin to stall due to lack of torque. This will once again be picked up by over current protection if it is a problem.
Earth fault protection is best achieved by the use of semiconductor fuses.
Conclusion, overvoltage and under voltage protection is not a major problem. It is probably more of an issue with contactor coils than with soft starters.
Best regards,