Static and Dynamic Motor Starting

I think you are talking about the study of the electrical system for motor starting in ETAP (or any such software). Here are the answers:

1. When do we use Static and Dynamic motor starting?

If you know the Motor torque characteristics, Load torque characteristics and the inertia information of the motors, bearings and loads, you can do the Dynamic motor starting study. Otherwise, do the Static motor starting study - it simply needs the starting time and the locked rotor current of the motor.

2. What is the difference between the two?

(1) The Dynamic motor starting develops the motor starting current characteristics based on the motor starting torque, load torque and the inertia, while the starting current remains flat at locked rotor current during the starting time for Static acceleration. (See the previous posting http://cr4.globalspec.com/thread/42981 , comment # 2 for detail how the starting time is calculated for Dynamic acceleration).

(2) Dynamic starting acceleration requires additional data than the Static acceleration.

(3) The Dynamic acceleration calculates the acceleration time and current from the input data, while the Static acceleration assumes you know the starting time and current.

(4) For Dynamic acceleration, the starting current is not 100% flat during the starting time, but in Static acceleration it is flat.

(5) Static acceleration is simple, Dynamic acceleration is rather complicated.

3. Can we evaluate the system using Static only not dynamic?

Yes. Make sure you have the correct information for motor locked rotor current and the stating time for the load.

Go the ETAP tutorial site (http://www.etap.com/training/tutorials-training-videos.htm) and see the tutorial #12 (Dynamic Acceleration) and #13 (Static acceleration).

- MS