Starter in DC Shunt Motor
Starter in DC Shunt Motor
Blog Article
A starter in a DC shunt motor is an essential control device designed to limit the high starting current that occurs when the motor is energized. Unlike series motors, DC shunt motors have a field winding connected in parallel (shunt) with the armature, and their starting current can be significantly higher—often 5 to 10 times the rated current—due to the low armature resistance. The starter reduces this current by inserting external resistance in the armature circuit during the starting phase, gradually cutting it out as the motor gains speed.
Working Principle:
- Resistance Insertion: At start-up, the starter places variable resistors in series with the armature to limit current flow. As the motor accelerates, the back electromotive force (EMF) increases, reducing the need for external resistance.
- Gradual Resistance Removal: Contactors or manual switches in the starter progressively short out the resistors, allowing the motor to reach full speed with minimal current surge.
- Overload and No-Voltage Protection: Most DC shunt motor starters include protective elements:
- Overload relays to trip the circuit during excessive current.
- No-voltage release coils to disconnect the motor if power fails, preventing sudden re-engagement when power is restored.
Types of Starters for DC Shunt Motors:
- Three-Point Starter: Suitable for shunt and compound motors, featuring a handle with notches that correspond to resistance steps and a spring-loaded return mechanism to prevent "runaway" if power is lost.
- Four-Point Starter: Similar to a three-point starter but separates the field circuit from the no-voltage release, allowing independent field current adjustment without affecting the protective mechanism.
Importance in DC Shunt Motors:
Without a starter, the high starting current in a DC shunt motor could:
- Damage armature windings or commutator segments.
- Cause voltage dips in the supply system.
- Lead to excessive sparking at the commutator, reducing motor lifespan.
For detailed starter configurations, installation guides, or to explore starter solutions for DC shunt motors, visit starter motor for specialized electrical components and resources.
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