Rating of Circuit Breaker: Short Circuit Breaking & Making Current
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What is the Meaning of the Rating of Circuit Breaker?
FAQ Related to Rating of Circuit Breaker
FAQ Related to Rating of Circuit Breaker
SF6 circuit breakers have higher short circuit withstand capability compared to vacuum circuit breakers. This is because SF6 has much higher dielectric strength than air or any other insulating medium.
What is the relationship between a short circuit breaking current and making current ratings of a circuit breaker?
The rated short circuit making current of a circuit breaker is usually 1.5 to 2.5 times higher than its rated short circuit-breaking current. This is because the peak value of the current during closing is higher than the RMS value during opening.
Can a 630A-rated MCCB be used where the distribution board rating is 400A?
No, using an MCCB with a higher ampere rating than the distribution board is not allowed as it may not coordinate properly with upstream protection or overload the distribution wiring. The MCCB rating should always be lower than or equal to the distribution board's current rating.
What should be the short time current rating of a 400A MCCB
As per standards, the short time current rating of MCCB should be a minimum of 3 times its nominal current rating. Therefore, for a 400A MCCB, the short time current rating needed is a minimum of 1200A.
Why do utilities prefer numerical relays over electromechanical relays?
Numerical relays have advantages like the flexibility of setting, self-diagnosis, communication capability, continuous monitoring, and fault recording. They offer more dependable, versatile, and secure protection compared to electro-mechanical relays.