MOTOR STARTERS

MOTOR STARTER

When we apply power to an electric motor to cause it to start running we use a motor starter to safely do so, safety can be to defend a motor from the effects of overloading which can end up damaging the motor and cause fire, we also need the starter to securely disengage a motor from the supply to stop it. In a motor starter there is a ‘power circuit’ and the ‘control circuit’, the control circuits activates the power circuit to execute operations on the motor.

The simplest type of motor starter for the induction motor is the Direct On Line starter. The

Direct On Line starter is basically made up of a contactor and an overload protection relay. However we will learn more about DOL in the later topic. We are going to start with the jogging circuit.

JOGGING CIRCUIT

The jogging or inching means the frequent closing of a circuit to start or run a motor in order to achieve small movements of with it.

Below there is a simple jogging circuit:

NOTE THAT WE ASSUME THAT YOU ALREADY KNOW OPERATIONS OF MOTOR CONTROL COMPONENTS IF NOT THEN WAIT FOR OUR SECTION ON MOTOR COMPONENTS DESCRIPTION

 

COMPONENTS

F1-Thermal Overload Relay,

KM1-Contactor

3phase Induction Motor

S2-Start push button (NO)

CB1-3phase circuit breaker

CB2-Single phase circuit breaker

OPERATION

S1 is the JOG button, when S1 is pressed the circuit is completed and the coil of the motor starter KM1 is energized and the contacts of KM1 at the power circuit close to let the power pass to the motor thus the motor will start running. When the JOG button is released it immediately breaks the circuit to KM1 coil then the coil will de-energize, KM1 contacts at the power circuit will also become open thus cutting power from passing to the then the motor will stop running.

Basically jogging circuit is all about preventing the “self holding contact”(check DOL).In coming articles we will do two more advanced jogging circuits, the next topic is the DOL starter.