How does the starting current of motor differ with different starters?

Answer 1

Starting Current (also sometimes referred to as Inrush Current or Locked Rotor Current) is dependent on a couple of things. There is the inertia of the load, the inertia of the drive motor, the inductance and resistance of the motor winding, and the time allowed for acceleration. The PERCENTAGE current (relating starting to normal operating current) varies with the applied voltage.

Basically, the current will be higher for larger loads (i.e. higher inertias), shorter acceleration times, and lower inductance/resistance windings.

Starting a motor "across the line" (i.e. no reduction in voltage supplied and/or zero assumed voltage dip due to starting) is the toughest condition. This is because the power system has to be "stiff" enough to handle the sudden load swing without appreciably changing the line voltage. Not very many places can do this, particularly with large industrial loads of several thousand horsepower.

Adding a "starter" to the circuit basically changes the circuit inductance and resistance, effectively limiting the amount of current drawn from the system and thereby also limiting the voltage swing seen on the incoming line. It really doesn't matter whether the starter is a series of resistors that can be manually or remotely dropped out of the circuit, or if the device is a collection of power electronics that effectively does the same thing by opening and closing a series of gates to regulate the incoming signal.

Each starter has its own characteristics - investigating each will give enough information to make an intelligent choice. Remember though - there has to be sufficient current to create a strong enough magnetic field to actually rotate the combined inertia of load and motor; this means that some starters will increase the time it takes a motor-and-load to get up to full operating speed.

Answer 2

Traditional Electromechanical Motor Starters.
Traditional Electromechanical Starters.
A.C. Induction motors are traditionally started and stopped by applying and removing the A.C. supply. In some cases, a full voltage start is acceptable, but in many situations, the start current must be reduced, and so a reduced voltage starter is employed.