As you know, electric motors are used to drive Air Compressor.
These electric motors are of different types as per the requirement of the customer.
As different electric motors used, the different type of starters is required to start these motors.
Particular types of starters are required for a particular type of motor.
An electrical engineering concerned are might better know about the starters.
But to understand the basic of starters, I have shared information in a simple format.
Direct On Line Starters
Normally this starter is of automatic type, simple, consisting only one main contactor.
Its starting current is 6 to 7.5 times the motor rated current.
In view of very high starting current, large capacity DOL starters are in High Voltage (HV) grade.
In the case where the direct starting method cannot be employed because of the high initial peak current, the Squirrel Cage Motor has to be started on reduced voltage i.e. Star-Delta starting method.
These are used where starting current limitations do not permit the use of DOL Starter.
In Star-delta starting, the motor is started in “Star” connection.
The connection is changed over to “Delta” when the motor has reached nearly 80% of the rated speed, and starting current dropped to lowest.
By connecting the motor in “Star” during the starting period, the impressed phase voltage is reduced58% of the voltage in “Delta” connection.
The corresponding current in “Star” is thus only one third that in “Delta”.
By starting in “Star” the current is reduced to only about 2 to 2.5 times the rated current.
The motor is started in “Star” and once it has peaked up speed, it connections is changed over to “Delta”, by means of a timer in an automatic type starter and by manual in manually operated starters.
This time varies from 6 seconds to 12 seconds or more according to the load factor.
Manual operated starters are oil immersed type, where the fixed and moving contacts are totally immersed.
Besides this information, you are suggested to read something more from below engineering books
To get the more details about the topic, I further recommended reading
- Basic Electrical Engineering
- Handbook of Electrical Motor Control Systems
- Electric Motor Maintenance and Troubleshooting
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