08-17-2017, 12:09 AM
[attachment=14905]
AIM:
To study and connect
(1) Direct Online Starter
(2) Auto transformer Starter
(3) Star Delta Starter
(4) Rotor Resistance Starter
APPARATUS REQUIRED:
SL.NO NAME OF APPARATUS QUANTITY
1. DOL Starter 1 No.
2. Auto transformer Starter 1 No.
3. Star Delta Starter 1 No.
4. Rotor Resistance Starter 1 No.
THEORY:
NECESSITY OF STARTERS:
An induction motor is similar to a secondary short circuit three phase transformer so if normal voltage is applied to the motor it takes 5 to 6 times of normal current from the mains and starting torque is also increased to around 1.5 to 2.5 times of their full load torque. This initial excessive starting current is objectionable, because it will produce large line voltage drop, which in turn will affect the operation of the other electrical equipments connected to the same mains. So the starters are used to reduce the starting current of induction motor and also to protect the motor and also used to protect the motor from overloading and low voltages.
TYPES OF STARTERS:
(1) Direct Online Starter
(2) Auto transformer Starter
(3) Star Delta Starter
(4) Rotor Resistance Starter
DIRECT ON LINE STARTER [DOL STARTER]:-
Generally when the starter winding of on induction motor are connected to the
Supply directly .a very large current of about 5-8 times full load current flow initially.
such a starting .of the induction motor is called direct on line starting. The initial stage
current decreases of the motor starts accelerating and running at normal speed.
Unlike d.c motors where such a starting can damage the windings due to a lsent 0/- back Emf at start induction motor can le started .This way through out not expandly in a short space of time called cycling .The only effect of the shorting is the sudden line voltage drop that occurs which may affect other electrically equipments on the same time line .hence direct an line