Capacitor Bank

1) What happens if power factor is leading?

If you are a utility consumer and maintain the power factor leading, it will have the same effect as you maintain it lagging. In this case, you are spending your money (such as for using capacitor bank) and helping the utility for no benefit (unless you maintain it close to unity and get power fator penalty waived).

If your power is supplied from generator and you maintain the overall power factor leading, the generator will be unstable. Synchronous generator is able to supply power to the loads of lagging power factor only.

2) What is hot start and cold start in case of HT (6.6kv, 3MW motors)?

Hot and Cold condition of the motor refer to state of the temperature of the motor as a whole (especially the stator and rotor winding) when the motor is started.

Cold condition: When the temperature of the motor stator and rotor winding is at ambient temperature, the motor is considered 'cold condition'. If a motor remains stopped for relatively long period of time (generally half an hour - depends on motor size), it is considered cold condition and the start of a motor at this condition is called cold start.

Hot Condition: When the temperature of the motor stator and rotor winding is above the ambient temperature, the motor is considered 'hot condition'. If a motor is already hot from either an initial start or a period of recent full-load operation, it is considered hot condition and the start of a motor at this condition is called hot start. The hot start of the motor further raises its temperature to a higher level due to the subsequent restart and cause the motor damage. The motor protection relay generally prevents motor damage by limiting the number of start per hour and/or from further hot starting of the motor.

See this link for more detail: http://findarticles.com/p/articles/mi_qa3726/is_200806/ai_n27900075/ (click Next to move forward)

Note: the answer is copied from my earlier post: http://cr4.globalspec.com/comment/546312

3) Why current drawn by capacitor bank is not added to the system load?

Capacitor current (leading) contributes to reactive load (power), not to the real load (power).

- MS