Motor control systems

From Electrical Installation Guide

Different kinds of motor control solution are compared in the following tables.

Fig. N75 – Comparison of different motor control solutions
Type Is/In Ts/Tn Speed control Torque control Pros Cons
Direct on line 5-10 5-10 No No Reduced cost, high starting torque High in-rush current
Star – Delta 2-3 1-2 No No Reduced in-rush current Reduced starting torque
Auto-transformer 2-3 1-2 No No Reduced in-rush current High weight
Soft starter 3-5 1.5-2.5 No Yes Reduced in-rush current, controlled start and stop Reduced starting torque
Variable speed drive 1.5 1.5-2 Yes Yes Controlled speed, Energy saving at reduced speed Higher cost