Direct-on-line (DOL) starting of induction motors is normally restricted to motors of_____________ size?
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Answer: A. low horsepower motors
Explanation
Connecting large motors directly to the power line draws massive initial starting current surges. High starting currents can cause severe voltage drops across the local electrical distribution grid. Restricting direct-on-line starting to small motors protects sensitive electrical equipment from voltage sags. Direct-on-line starting applies full rated supply voltage instantly to the stationary motor windings. Starting current in induction motors can reach up to seven times normal operating levels. Specialized motor starters reduce initial voltage to keep starting current within safe grid limits.
Residential workshops use direct-on-line starting safely because small motors draw minimal current. Large industrial factories utilize star-delta starters or variable frequency drives for big motors. Utility companies enforce strict regulations regarding maximum allowable motor starting current spikes. Variable speed motors require advanced electronic drives regardless of their physical horsepower size. High horsepower motors require reduced voltage starters to prevent catastrophic utility grid voltage drops. High speed motors are not automatically restricted from direct-on-line starting based solely on speed.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
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