Per NEC Table 450.3(A), the primary fuse rating is not more than 300% of primary rated current (for 600V and over) and the secondary fuse rating is not more than 125% of secondary rated current (for 600V and less). However, do the device coordination for the proper selection of the fuse or get it suggested by the transformer manufacturer.
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Depends on make and type of fuse as well as transformer. Get time characteristics of the proposed fuse, transformer damage curve and starting inrush current.
Basically the protecive fuse should not fuse on starting inrush current (consider about 12FLC for 6 cycles if no data avaialble from transformer manufacturer) and overload (consider 125% if possible over load or overloading cpacity of transformer not avaialble) and shall trip within transformer damage time (if details not available, consider to trip before 2s for for fault current = FLC/%age impedance)
thanks. but for a 11KV and above systems upto 33 KV how do u select the fuses. for example for a 630 KVA transfomer in 11 KV system what is the fuse rating to be used in the DO fuse.
Did you learn anything in electrical engineering school? You asked a question that you could easily have researched yourself, and then don't accept the very good answers from msamad and ahameedp? They told you all you need to figure it out!
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HT Fuse Rating Selection
Re: HT Fuse Rating Selection
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