ABB DOL Starter for Induction motor

DOL starters are manufactured by many companies. Function and working remains the same but having the different design & configuration. In this post, We are going to discuss DOL starters made by ABB.

ABB dol starters are compact in design. It contains an assembly of contactor and an overload relay. The whole arrangement is connected in a series pattern.

Push buttons for Start & Stop functions are assembled on the front cover of the Starter.

Input 3 phase supply is connected at the top of contactor & motor terminals are connected down below the thermal overload relay. Total assembly is shown in an image below.

Like any other DOL Starter, There is also two wirings :

1. Power Wiring
2. Control Wiring

1. Power wiring

Blue phase is directly looped with adjacent auxiliary NO contact which is used to hold the circuit. After the NO contact, Control phase is passing through the NC contact of thermal overload relay. At last, second terminal of the coil is been connected.

Actually in this starter, There is no NO contact for start. But a Push button on the cover of starter directly presses the contactor’s plunger which results Auxiliary NO contact get closed & contactor get hold.

The contactor’s hold get break in two conditions:

1. When stop button of starter cover is been pressed which directly presses the reset button of thermal overload relay.
2. When NC contact of thermal overload relay get trips.

“Thermal overload relay is a type of safety element. Which contains 3 bimetallic thermal strips for all the 3 phases. Line current flows through these strips. Whenever current exceeds the limit either due to overload or short circuit, A bending movement get produced in these strips. These strips further triggers the NO–NC contacts.”

Thermal overload relay contains NO, NC contacts, ampere range setting & reset button.

Relay reset button is having both the options ‘Auto and Manual’.

• In Auto mode, Relay got reset automatically after some time when thermal got cooled down.
• In Manual mode, We need to reset the relay by self, For this we just need to press the stop button.

 

Advantages of abb dol starter

• Compact and fully covered design.
• Easy and simple connections.
• Contactor is repairable & replaceable.
• Less components & easy assembly.

Disadvantages of Abb dol starter

• Start button actually presses the contactor directly. In trip conditions, Motor is not completely isolated from power supply. Power still can be connected to the motor by keeping the start button pressed. This is not only dangerous for the motor but for the entire series line from MCB to contactor to thermal overload relay.

 

Where is ABB DOL Starter Used?

• Pumps

• Compressors

• Small motors (up to 5–7.5 HP typically)

• Industrial machines

When NOT to Use DOL Starter

• Not suitable for large motors

• High starting current (6–8 times rated)

Summary

• In DOL Starter, Power supply to motor terminals get connected directly without any change in terminal connections, frequency & voltage.
• DOL starter is an arrangement of two components; Contactor & overload relay. Motor terminals & power supply is being connected across this arrangement.
• Power supply get connected to the motor When contactor’s coil get energized.
• DOL starters are manufactured by many companies but working & function remains the same. ABB DOL Starters are simple & compact in size.

CLICK- For DOL starter type MK-1 by L&T !