3 PHASE INDUCTION MOTOR STARTER

• Prepared by:-• Boghani Kaushal(130760109002)• Patel Kishan(130760109013)• More Aditya(130760109017)• Submitted to:-• Prof Keyur Denpiya• Assistant Professor• Electrical Department

STARTER

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.

TYPES OF STARTER

• Stator resistance starter • Auto transformer starting • Star-delta starter• Rotor resistance starter• Variable frequency starting• Direct on line (DOL) starter

STATOR RESISTANCE STARTER

• A starter resistance is connected in each line in series with each phase winding of the stator.

• Initially all the starter resistance are kept in “Start” position so that they offer their maximum resistance .

• The switch is turned ON to connect the three phase AC supply to the stator winding.

• Due to starter resistance in series, each phase winding will receive a reduced voltage. Due to reduction in the value of V1

, the starting current is limited to a safe value.

• As the motor accelerates, the starter resistance is reduced by moving the variable contact of the resistance towards the “Run” position.

• In the “Run” position, the starter resistance is shorted out and full stator voltage is applied across the stator winding.

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.

ROTOR RESISTANCE STARTER.

• This starter is used with a wound rotor induction motor. It uses an external resistance/phase in the rotor circuit so that rotor will develop a high value of torque.

• High torque is produced at low speeds, when the external resistance is at its higher value.

• At start, supply power is connected to stator through a three pole contactor and, at a same time, an external rotor resistance is added.

• The high resistance limits staring current and allows the motor to start safely against high load.

• Resistors are normally of the wire-wound type, connected through brushes and slip rings to each rotor phase. They are tapped with points brought out to fixed contactors.

• As the motor starts, the external rotor resistance is gradually cut out of circuit ; the handle or starter is turned and moves the three contacts simultaneously from one fixed contact to the next.

• The three moving contacts are interconnected to form a start point for the resistors.

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.

STAR-DELTA CONNECTION IN MOTOR

STAR DELTA POWER CIRCUIT

STAR DELTA CONTROL CIRCUIT

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.

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

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.

• Low Starting Torque: reduction of the line voltage by a factor of 1/√3 (57.7%) to the motor and the current is reduced to 1/3 of the current at full voltage, but the starting torque is also reduced 1/3 to 1/5 of the DOL starting torque .

WIRING DIAGRAM OF DOL STARTER:

 MOTOR STARTING CHARACTERISTICS ON DOL

STARTER:

• Available starting current:    100%.• Peak starting current:           6 to 8 Full Load Current.• Peak starting torque:            100%

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.

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.

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

VARIABLE FREQUENCY DRIVE (VFD)

• A variable-frequency drive (VFD), also termed adjustable-frequency drive, variable speed drive, AC drive, micro drive or inverter drive is a type of adjustable-speed drive used in electro-mechanical drive systems.

• It controls AC motor speed and torque by varying motor input frequency and voltage.

PRINCIPLE OF VFD

• Variable frequency Drive, principle of the same is by regulating the frequency, we can regulate the speed of drive

• Example - n=120f/p• Where, • n - speed• f - frequency• p – nos. of poles

VFD FLOW DIAGRAM

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.

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

THANK YOU