1. ELECTRICAL DEPARTMENT ELEMENT OF ELECTRIC DESIGN
Prepared by: Urvashi Gadhavi( ) Devangi Dhandhukiya( )

2. starter

3. NEED OF STARTER
If a rated stator voltage is applied to the motor at the time of starting, then the motor will draw heavy starting current.
This will lead to excess i2R losses in the winding which will overheat the motor.
Secondly due to a heavy current drawn from the AC supply voltage will reduce.
The heavy starting current may damage the motor windings.
In order to avoid these problems, we can use some kind of a starter to start the induction motor safely.

4. TYPES OF STARTER Auto transformer starting Star-delta starter
Direct on line (DOL) starter

5. AUTO-TRANSFORMER STARTER
An autotransformer is used to apply a low voltage to the stator winding at the time of starting. When the motor speed reaches the desired level, autotransformer is disconnected and motor is connected directly across the supply.
The stator of the motor is connected through a 6-way double throw switch.
While starting, the switch is thrown to ‘Start’ side so that a reduced voltage is applied to stator. This keeps the starting current safe limits.
Once motor take up the speed, the switch is throw to ‘Run’ side so that full supply voltage is applied to stator.
A specific advantage of this starter is that reduction in voltage during starting, can be done to any desired level by selecting proper tapping of the autotransformer.

7. 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.

8. Star-Delta Connection in motor

9. Star delta power circuit

10. Motor Starting Characteristics of Star-Delta Starter:
Available starting current: 33% Full Load Current.
Peak starting current: 1.3 to 2.6 Full Load Current.
Peak starting torque: 33% Full Load Torque.

11. Advantages of Star-Delta starter:
The operation of the star-delta method is simple and rugged
It is relatively cheap compared to other reduced voltage methods.
Good Torque/Current Performance.
It draws 2 times starting current of the full load ampere of the motor connected

12. Disadvantages of Star-Delta starter:
Low Starting Torque, only 33% starting torque
Break In Supply – Possible Transients
Six Terminal Motor Required (Delta Connected).
It requires 2 set of cables from starter to motor.
The delta of motor is formed in starter and not on motor terminals.
Applications with a load torque higher than 50 % of the motor rated torque will not be able to start using the start-delta starter.

13. Wiring Diagram of DOL Starter:

14. Motor Starting Characteristics on DOL Starter:
Available starting current:    100%.
Peak starting current:           6 to 8 Full Load Current.
Peak starting torque:            100%

15. Advantages of DOL Starter:
Most Economical and Cheapest Starter
Simple to establish, operate and maintain
Simple Control Circuitry
Easy to understand and trouble‐shoot.
It provides 100% torque at the time of starting.
Only one set of cable is required from starter to motor.
Motor is connected in delta at motor terminals.

16. Disadvantages of DOL Starter:
It does not reduce the starting current of the motor.
High Starting Current: Very High Starting Current (Typically 6 to 8 times the FLC of the motor).
Mechanically Harsh: Thermal Stress on the motor, thereby reducing its life.
Voltage Dip: There is a big voltage dip in the electrical installation
High starting Torque: Unnecessary high starting torque, even when not required by the load.

17. Suitability DOL is Suitable for:
Small water pumps, compressors, fans and conveyor belts.
Motor rating up to 5.5KW
DOL is not suitable for:
The peak starting current would result in a serious voltage drop on the supply system
Motor rating above 5.5KW

18. Application Cane Carrier Drive, Feeder Table Drive,
Milling Plant Drive,
Raw juice Pumps,
Sulphited Juice Pumps,
Molasses Pumps,
Injection Pumps,
Cooling Tower Pumps and
Centrifugals for a Sugar Curing and Chemical Dosing pump.

19. Difference between DOL/Star delta /Autotransformer
Sr.
DOL Starter
Star delta starter
Auto transformer starter 1
Used up to 5 HP
Used 5 HP to 20HP
Used above 20 HP 2
Does not decrease the starting current
Decreases the starting current by 1/3 times
Decreases the starting current as required 3
It is cheap
It is costly
It is more costly 4
It connects directly the motor with supply for starting as well as for running
It connects the motor first in star at the time of starting in delta for running
It connects the motor according to the taping taken out from the auto transformer

20. THANK YOU