![]() ![]() The moving coil is mounted on a pivoted spindle and is entirely embraced by the fixed current coils. Shunts are not used for extension of current range since they are subject to temperature errors. In the case of precision wattmeters, the two halves of the fixed coil, which are connected in series for a basic measuring range, can be connected in parallel to increase the Electrodynamometer wattmeter current range to twice its original value. The fixed coils are wound with heavy wire.This wire is stranded or laminated especially when carrying heavy currents in order to avoid eddy current losses in conductors.The fixed coils of earlier wattmeters were designed to carry a current of 100 A but modern designs usually limit the maximum current ranges of wattmeters to about 20 A.For power measurements involving large load currents, it is usually better to use a 5 A wattmeter in conjunction with a current transformer of suitable range. The reason for using fixed coils as current coils is that they can be made more massive and can be easily constructed to carry considerable current since they present no problem of leading the current in or out. The fixed coils carry the current of the circuit. ![]()
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