Different types of Starter for Motor
Different types of Starter for Motor
1)DC
-TWO point starter
A two-point starter is used for starting dc motor which has the problem of over-speeding due to loss of load from its shaft.
-Three point starter
A three-point starter is used for starting a dc shunt or compound motor. The coil of the hold-on electromagnet is connected is series with the shunt-field coil.
- Four point starter
The 4 point starter like in the case of a 3 point starter also acts as a protective device that helps in safeguarding the armature of the shunt or compound excited DC motor against the high starting current produced in the absence of back emf at starting. The 4 point starter has a lot of constructional and functional similarity to a three point starter, but this special device has an additional point and a coil in its construction. This naturally brings about some difference in its functionality, though the basic operational characteristic remains the same. The basic difference in circuit of 4 point starter as compared to 3 point starter is that the holding coil is removed from the shunt field current and is connected directly across the line with current limiting resistance in series.
2)AC
- Direct on line (DOL) starter
The simplest form of motor starter for the induction motor is the Direct On Line starter. The Direct On Line Motor Starter (DOL) consist a MCCB or Circuit Breaker, Contactor and an overload relay for protection. Electromagnetic contactor which can be opened by the thermal overload relay under fault conditions.
- Star-Delta starter
Most induction motors are started directly on line, but when very large motors are started that way, they cause a disturbance of voltage on the supply lines due to large starting current surges. To limit the starting current surge, large induction motors are started at reduced voltage and then have full supply voltage reconnected when they run up to near rotated speed.
- Auto transformer starter
An auto-transformer starter makes it possible to start squirrel-cage induction motors with reduced starting current, as the voltage across the motor is reduced during starting.In contrast to the star-delta connection, only three motor leads and terminals are required.
- Semi-Automatic Star Delta Starter
In semi-automatic starter Timer is not required for changing star to delta contactor. In this change-over take place as we unhold start button.
- Automatic Star Delta Starter
In automatic starter Timer is required for changing star to delta contactor. In this change-over take place after getting signal from timer. This type of starter use for higher ratting motor. Because it take more time to reach normal ratting of motor current.
