A transformer connected to a 135 V(rms) ac line is to supply 13,000 V (rms) for

Question

A transformer connected to a 135 V(rms) ac line is to supply 13,000 V (rms) for a neon sign. To reduce shock hazard,a fuse is to be inserted in the primary circuit; the fuse is toblow when the rms current in the secondary circuit exceeds9.00 mA. What power must be supplied to the transfromer when the rmssecondary current is 9.00 mA?
What current rating should the fuse in the primary circuithave?
This is one of my homework problems and I don't know howto set it up. Any help would be greatly appreciated. A transformer connected to a 135 V(rms) ac line is to supply 13,000 V (rms) for a neon sign. To reduce shock hazard,a fuse is to be inserted in the primary circuit; the fuse is toblow when the rms current in the secondary circuit exceeds9.00 mA. What power must be supplied to the transfromer when the rmssecondary current is 9.00 mA?
What current rating should the fuse in the primary circuithave?
This is one of my homework problems and I don't know howto set it up. Any help would be greatly appreciated.

Explanation / Answer

Please remember to rate! -- The transformer is a step up transformer from 135v to 13000v,thus the current is stepped down, so the current in the primarywill be higher, and if this is considered an ideal transformer thenpower in primary = primary in secondary. -- Power = V*I Power in secondary is (since voltage and current are alreadygiven): P(s) = 13000*0.009 P(s) = 117 watts -- And the current in the primary will be (since power inprimary = power in secondary): P(p) = V*I 117 = 135*I I = 117 /135 I = 0.867 amps or 867 mA -> primary fuse should be ratedfor at least this value if fuse is to blow when secondary >9mA -- Hope this helps.

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