The low power factor meter is used for measuring the power of the highly inductive circuit. It is also used in the resistive circuit which has a power factor range from 0. The ordinary Wattmeter used for measuring the low power factor gives the inaccurate result. This happens because of two reasons. Some additional features are added on the ordinary Wattmeter so that the meter can measure the power of the low power factor circuit.
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As the secondary side is open, the entire coil will be purely inductive in nature. So the power will be lagging due to inductive property of the circuit. In short circuit test the secondary winding of transformer is short circuited.
As secondary side is short circuited the entire coil will be purely resistive in nature. So the power factor will be unity. Lpf is used in power measuring in high inductive circuit and upf is used in power measuring in resistance circuit which power factor ranges 0. Low Power Factor wattmeters are specially designed to measure power at low power factor. Ordinary wattmeters i. UPF are not accurate in measuring power at low power factor beacuse of - low deflecting torque.
So some modifications are done in LPF wattmeters- low value of pressure coil resistance to increase the torque. In lpf meter pf compensation is done and is accurate at the specified low pf. Then low pf and unity power factor. Post New Answer. Is This Answer Correct? Then low pf and unity power factor Is This Answer Correct?
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UPF and LPF Wattmeters
Electrodynamometer wattmeter and Low Power Factor LPF wattmeters are mostly similar in construction and operation, except for the following modifications are carried out in the electrodynamometer wattmeter to convert it into a LPF wattmeter:. As the name suggests the low power factor meter are the instruments that measures lower values of power factor accurately. There is a requirement of low power factor meter because, the usage of ordinary electrodynamometer wattmeter to measure power factor of a low pf load gives inaccurate results. Now there are two main reasons that would suggests us that we should not use ordinary wattmeter in measuring the low value of power factor.
Difference between Electrodynamometer Wattmeter and Low Power Factor Wattmeter
Low Power Factor Wattmeter