The instrument that measures the low value of power factor accurately is known as the Low Power Factor Wattmeter (LPFW). The low power factor meter is used. So LPF(Low Power Factor) Wattmeter is used in OPEN CIRCUIT TEST of Transformer. In short circuit test the secondary winding of transformer. LPF wattmeter is used for measuring power in highly inductive circuits & UPF wattmeter is used for measure power in resistance circuit in which the power factor.

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The field induces in the compensating coil is because of the current I p. Would you like to make it lpv primary and merge this question into it?

JAYAM Portable Wattmeter – LPF – UPF, Usage: Industrial, Laboratory | ID:

View Contact Call Seller Now. If, by ‘upf’, you mean ‘unity power factor’, then all wattmeters measure the in-phase component of the load current, so the term wtatmeter quiet unnecessary.

Inductive circuits have the property of lagging power factor and hence these wattmeters are used.

Furthermore, owing to the state-of-the-art infrastructure, we are able to meet with the exceeding demands of our clients. For reducing the error, the compensation coil is used in the circuit. Thus the error occurs in the pressure coil is neutralized. Power Factor Meter in Chennai. In open circuit test the secondary winding of transformer is kept open. Watt,eter is also used in the resistive circuit which has a power factor range from 0. What is difference between lpf and dattmeter wattmeters?

Resistive circuits have unity power factor hence UPF wattmeters are used to measure power in these circuits.

Low Power Factor Wattmeter

Answer to this question is very simple as it gives inaccurate results. A short-circuit te … st is used to determine the true power loss in the transformer, which is exactly what a wattmeter measures. The compensating coil is connected in series with the pressure coil circuit and is made nearly identical to the current coil.


The compensating coil is so connected that it opposes the field of the current coil. In this power shown by the second watt meter is equal to the power loss in the load plus the power loss in the pressure coil. In case of no load only magnetizing current is flowing which is somewhere around 75 degree out of phase and so the power factor is very low.

Some additional features are added on the ordinary Wattmeter so that the meter can measure the power of the low power factor circuit. What does upf stands in upf wattmeter?

Then low pf and unity power factor. UPF are not accurate in measuring power at low power factor beacuse of – low deflecting torque. So the power factor will be unity. Get in Touch with us Jayam Electronics.

The rotation of the rotor causes the display dials to count up at certain values per rotation. In short circuit test the secondary winding of transformer is short circuited.

What is Low Power Factor Wattmeter? – Definition & Explanation – Circuit Globe

The voltage across pressure coil is equal to the voltage waftmeter the load. In the second category, the current coil is not in series with the load and the wattjeter across the pressure coil is not equal to the applied voltage.

Hence, the error due to pressure coil current flowing in current coil is neutralized. Hence it that case it lag by an angle Where, R is electrical resistance in series with pressure coil, r p is pressure coil resistance, sattmeter we also conclude that the current in the current coil is also lagging by some angle with wattmteer current in pressure coil.


Errors due pressure coil inductance. 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. In low power circuit, the value of current is high, and that of the power is low.

Why is LPF wattmeter used for no load test? Why a LPF Wattmeter is needed? The capacitor is placed in parallel with the pressure coil resistance.

F meter in parallel.

Compensation for Inductance of PressureCoil: Low Power Factor wattmeters are specially designed to measure power at low power factor. 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: A modern low power factor meter is designed such that it gives high accuracy while measuring power factors even lower than 0.

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JAYAM Portable wattmeter – LPF – UPF, Usage: Industrial, Laboratory

These are discussed one by one below:. In this category two cases diagrams arises and these are shown below: The compensating coil compensates the error in the circuit which induces because of low power factor.

The value of deflecting torque is very low even though we fully excite the current and pressure coils. Industrial, Laboratory Get Latest Price. And the current coil is connected in series with the supply voltage. Little poo face and Ugly poo face. There is a requirement of low power factor meter wattmeher, the usage of ordinary electrodynamometer wattmeter to measure power factor of a low pf load gives inaccurate results.

Difference between electrostatic and electrodynamic wattmeters?