Why we use starter in induction motor

What Does an Electrical Motor Starter Do? Why Regular Switches Are Unsafe for Large Motors

I will not go in for ‘Start Delta’ or Electronic soft starters, etc.

In this answer, I will try to explain why a motor starter is used and not a simple regular switch.

Suppose you used a simple switch for the water pump in your home to pump water from the ground storage to the overhead storage. While it was ON, the electricity failed, and you forgot to switch it OFF. What will happen?

1. Ground storage water will finish.
2. The overhead water tank will overflow, wasting precious water.
3. The motor will run dry and get damaged.
4. Electricity wasted.

Motor starter prevents unintentional starting:

Why all the above consequences? Because the motor started unintentionally. In the industrial setup, no load is allowed to start unintentionally. It is also very important from a safety point of view. Imagine you are doing maintenance inside the machine, and it starts suddenly, unintentionally.

Hence, we use a DOL starter for the motor load.

It magnetically latches the output to the ON state. If electricity fails, the load becomes OFF. So the load (motor) is always started intentionally only.

This arrangement also gives some more advantages by integrating an overload relay, a dry run relay, an over-temperature relay and any other safety interlocks that can shut off the motor automatically to protect it.

FAQ Set:

Q1: What is an electrical motor starter?

A motor starter is a device that starts, stops, and protects electric motors by controlling the voltage and current supplied to the motor.

Q2: Why can’t I use a regular switch for a large motor?

Large motors draw high inrush current when starting, much higher than the running current. A regular switch cannot handle this surge, leading to:

• Switch damage or welding

• Excessive arcing

• Fire hazards or motor damage

Q3: What are the main functions of a motor starter?

• Safe motor starting: Gradually supplies voltage/current

• Overload protection: Prevents the motor from overheating

• Short-circuit protection: Prevents damage due to fault currents

• Control operation: Allows remote start/stop

Q4: What types of motor starters are available?

• Direct On-Line (DOL) Starter: Simple, full-voltage starting

• Star-Delta Starter: Reduces starting current for large motors

• Soft Starter: Gradually ramps up voltage to reduce mechanical stress

• Automatic Motor Starter (AMR): Includes advanced protection and monitoring

Q5: How does a starter protect the motor?

• The overload relay cuts off the current if the motor draws too much

• The contactor disconnects the supply under fault conditions

• Reduces mechanical stress on shaft, gears, and belts during startup

Q6: What happens if a motor is started with a regular switch?

• High inrush current can burn out winding insulation

• Switch contacts can weld or arc

• Motor and connected machinery can suffer mechanical damage

Q7: Are motor starters necessary for all motors?

They are essential for medium and large motors (generally >1 HP), while small fractional horsepower motors may use simple switches safely.

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