2. PURPOSE OF STARTER
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• 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.
3. DOL STARTER BASIC POWER CIRCUIT
MAIN PARTS:- Circuit Breaker , Contactor , O/L Relay .
USES :- it To prevent damage to the windings due to the
high starting current flow .
STARTING CHARACTERSTICS
it does not decrease starting current .
Available starting current: 100%.
Peak starting current: 6 to 8 Full Load Current.
Peak starting torque: 100%
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4. DOL STARTER RELAY SETTING
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1. Over Load Relay Setting
2. Relay Min (70% of FLC Phase)
3. Relay Max (120% of FLC Phase)
4. Relay Setting (85% of FLC Line)
Contactor (for DOL starter)
1. Type of Contactor
2. Making / Breaking Capacity of Contactor:
3. Main Contactor (100% of FLC Line):
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BASIC DOL STARTER
7. ADVANTAGES OF DOL STARTER
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1. Most Economical and Cheapest Starter .
2. Simple to establish, operate and maintain .
3. Simple Control Circuitry .
4. Easy to understand and trouble‐shoot.
5. It provides 100% torque at the time of starting.
6. Only one set of cable is required from starter to motor.
7. Motor is connected in delta at motor terminals.
8. DISADVANTAGES OF DOL STARTER
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1. Starting current:- It does not reduce the starting current of the motor.
2. High Starting Current:- Very High Starting Current (Typically 6 to 8 times the FLC of the motor).
3. Mechanically Harsh:- Thermal Stress on the motor, thereby reducing its life.
4. Voltage Dip:- There is a big voltage dip in the electrical installation because of high in-rush current
affecting other customers connected to the same lines and therefore not suitable for higher size
squirrel cage motors
5. High starting Torque:- Unnecessary high starting torque, even when not required by the load, thereby
increased mechanical stress on the mechanical systems such as rotor shaft, bearings, gearbox,
coupling, chain drive, connected equipment's, etc. leading to premature failure and plant downtimes.
9. PURPOSE OF STAR DELTA STARTER
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1. At the time of starting the motor, rotor is at standstill and the slip ( between stator's magnetic field and
rotor) is large which causes the large inrush of armature current (which is 6–7 times the rated value).
This large current can damage the stator windings and burn the motor.
2. To avoid this situation, we use star delta starter. At the time of start, motor connections (stator
connections) are made in star mode so impressed voltage is reduced by 1/√3 (Phase voltage = Line
voltage/√3) which reduces the starting current.
3. Once the rotor is at 80–90% speed, centrifugal switch operates changing the connections from star to
delta mode (full line voltage is impressed).
10. ADVANTAGES OF STAR DELTA STARTER
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1. Good Torque/Current Performance. It draws 2 times starting current of the full load ampere of the motor
connected .
2. if we start the motor with DOL(direct on line) or simple starter the motor requires more current to start
, which is 6-8 times the full load current. because the higher
torque is require to start the motor . and then motor after start gets full speed and star
contactor is disconnect and motor runs in delta
connections. because torque is less and lower current is
required.
3. The operation of the star-delta method is simple and rugged
4. It is relatively cheap compared to other reduced voltage methods.
11. DISADVANTAGES OF STAR DELTA STARTER
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1. Low Starting Torque, only 33% starting torque Break In Supply – Possible Transients Six Terminal Motor
Required (Delta Connected).
2. It requires 2 set of cables from starter to motor.
3. The delta of motor is formed in starter and not on motor terminals.
4. Applications with a load torque higher than 50 % of the motor rated torque will not be able to start using
the start-delta starter.
5. 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 .
12. BASIC STAR DELTA STARTER
CONTROL CIRCUIT
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13. BASIC STAR DELTA STARTER POWER
CIRCUIT
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14. BASIC STAR DELTA STARTER
CONTROL CIRCUIT
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