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what is the difference between LPF and UPF wattmeter and
where it is used.
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Answer Posted / nitish kennedy
Low Power Factor wattmeters are specially designed to measure power at low power factor .
Ordinary wattmeters (i.e. UPF) are not accurate in measuring power at low power factor beacuse of -
low deflecting torque.
error due to inductance of of pressure coil is large at low power factor.
So some modifications are done in LPF wattmeters-
low value of pressure coil resistance to increase the torque.
pressure coil current is compensated using compensating coil.
capacitor is connected in pressure coil to reduce the error due to pressure coil inductance.
control torque is made very small.
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