following are the questions asked in interviews:
1) Considering the short circuit fault, which switchgear is
preferable, SFU OR MCCB?
Which operates faster? whicg one is popular in Indian Market
and why?
2)Define SCPD. What is type2 coodination?
3)Why the contactor rating is higher for the fuseless
selection than for fuse selection? whether the ratinf of SFU
or MCCB remains the same in both the cases?
4)If the HP rating is known then can you calculate the
ratings of L.V Switchgear(SFU/MCCB, contactor, OLR) without
using the selection chart?
Answer / Neeraj P Singh
1) In a power distribution system, SFU (Switchgear Fuse Unit) provides faster fault clearing compared to MCCB (Molded Case Circuit Breaker), but MCCB is more popular due to its compact design and versatility. In the Indian market, both are used depending on the application requirements.
2) SCPD stands for Surge Capacitor Protection Device. Type 2 coordination refers to a system of protection where surge arresters are installed between current-carrying devices like transformers and service equipment to protect them from voltage surges or overvoltage conditions.
3) The contactor rating is higher for fuseless selection because it does not have a fuse, allowing the circuit to carry more current. However, the ratings of SFU or MCCB remain the same in both cases.
4) It's possible to calculate the ratings of LV switchgear (SFU/MCCB, contactor, OLR) without using the selection chart, but it requires knowledge of various factors like insulation coordination class, short-circuit ratio, and load characteristics. Consult relevant standards and manufacturer guidelines for detailed calculations.
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