Motor control systems
From Electrical Installation Guide
Different kinds of motor control solution are compared in the following tables.
| Is / In | Ts / Tn | Speed control | Torque control | |
| Direct on line | 5-10 | 5-10 | No | No |
| Star – Delta | 2-3 | 1-2 | No | No |
| Auto-transformer | 2-3 | 1-2 | No | No |
| Soft starter | 3-5 | 1.5-2.5 | No | Yes |
| Variable speed drive | 1.5 | 1.5-2 | Yes | Yes |
| pros | cons | |
| Direct on line |
Reduced cost High starting torque when necessary |
High in-rush current |
| Star – Delta | Reduced in-rush current | Reduced starting torque, switching voltage & currents |
| Auto-transformer | Reduced in-rush current | Weight |
| Soft starter |
Reduced in-rush current controlled start and stop | Reduced starting torque |
| Variable speed drive |
Controlled speed Energy saving at reduced speed | Higher cost |
Fig. N63a: Comparison of different motor control solution
