As you know,electric motors are used to drive Air Compressor.These electric motors are of different types as per the requirement of customer.As different
electric motors used,different type of starters are required to start these motors.Particular type of starters are required for particular type of motor.
Here I will disclose the working of DOL and Star-Delta type Starter.
01)Direct On Line Starter:-
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 case where the direct starting method can not 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.
02)Star-Delta Starter:-
These starters 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 being 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 reduced
58% 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 are changed over to “Delta”,by means of a timer in a automatic type
starter and by manual in manual operated starters.This time varies from 6 second 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.
