Under what fault current condition does the circuit breaker (CB) for over-current protection of a thyristor activate__________?
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Answer: A. of long period
Explanation
Circuit breakers possess inherent mechanical delay times, making them suitable for long-duration over-current faults. Thyristors have extremely low thermal mass and can be destroyed by rapid over-current surges. Long-duration faults generate excessive heat accumulation that circuit breakers are designed to interrupt. Thyristor protection schemes combine fast semiconductor fuses with slower mechanical circuit breakers. Over-current conditions can cause severe junction overheating and permanent semiconductor failure. Fuses act within milliseconds to clear short-circuit faults before thermal damage occurs.
Industrial power converters require coordinated protection schemes to safeguard expensive semiconductor stacks. Engineers carefully match protective device clearing times with thyristor surge current ratings. Reliable fault protection prevents costly downtime and equipment replacement in power systems. Short duration faults are cleared by semiconductor fuses rather than slower mechanical circuit breakers. Both a and b is incorrect because circuit breakers cannot act fast enough for short faults. Neither a nor b ignores the established coordination between breakers and long faults.
- Subject
- Engineering
- Category
- Electrical Engineering
- Topic
- —
- Difficulty
- medium
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