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Descriptions: A Dual starterconnects the motor terminals directly to the power supply. Hence, the motor is subjected to the full voltage of the power supply. Consequently, high starting current flows through the motor. This type of starting is suitable for small motors below5 hp (3.75 kW).
Reduced-voltage starters are employed with motors above5 hp. Although Dual motor startersare available for motors less than150kW on400 V and for motors less than1 MW on6.6 kV.
Supply reliability and reserve power generation dictates the use of reduced voltage or not to reduce the starting current of an induction motor the voltage across the motor need to be reduced. This can be done by1. Autotransformer starter,2. Star-delta starteror3. Resistor starter. Now-a-days VVVF drive used extensively for speed control serves this purpose also.
An induction motor draws large current at start. The current drawn by motor is more because the rotor has more inductive reactance and the reactance gets reduced as motor accelerates and become minimum when motor attains its synchronous speed.
The voltage is reduced to limit the starting current of an induction motor.The star delta starter is one of the starting method for squirrel cage induction motor. In star the voltage gets reduced to % of the line voltage and correspondinlgly the starting current gets reduced.
Read More:Star Delta starter for Squirrel Cage Induction Motor
• Starting current is reduced 3-4 times of the direct current due to which voltage drops and hence it causes less losses. • Star delta starter circuit comes in circuit first during starting of motor, which reduces voltage 3 times, that is why current also reduces up to 3 times.