direct online starter wiring|ELECTRECA|PART 2

Construction of DOL Starter :
DOL Starter basically comprises only two buttons, one of which is ‘green’ and the other is ‘red’.‘The green button is used for starting, and the red button is used for stopping the motor. The Direct On-Line Starter actually consists of a contactor, an MCCB or circuit breaker, and an overload relay for protection whenever a fault condition occurs. The above mentioned two buttons ‘stop’ and ‘start’, or also called ‘Red’ and ‘Green’ buttons, are used to control the contacts. For starting the motor, we press the Green Button and the contact is closed and therefore full line voltage start appearing across the motor. A contactor can either consist of 3 poles or 4 poles, depending on the design. In our case, the contactor used is of the 4-pole type. There are three “Normally Open” contacts where the motor is connected to the supply lines, and the fourth contact is called as “hold on contact”, which is an additional contact and this one energises the contactor coil after the start or green button is released. The additional coil gets de-energised if there is a fault occurs, and then the starter disconnects the motor from the supply mains.

APPLICATION.

DOL starting is sometimes used to start small water pumps, compressors, fans and conveyor belts where high inrush currents do not cause any harm

If the high current of the motor does not cause an excessive voltage drop in the supply circuit, a direct online starter can be used.

MERITS OF DOL

1 From starter to motor, only one set of cables is required.
2 Very cheap
3 The control circuit is simple

DEMERITS OF DOL

1 DOL starter is only suitable for motors of rating less than 10kw.
2 DOL starter has a high starting current

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