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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Then low pf and unity power factor Is This Answer Correct? If we ignore the effect of inductance of pressure i. 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. The voltage across pressure coil is equal to the waytmeter across the load. In this category two cases arise and their lpt are shown below: The error occurs in the pressure coil is given by the expression. Get Best Price Request a quote.

In the second category, the current coil is not in series with the load and the voltage across the pressure coil is not equal to the applied voltage. Electromechanical meters are described below.

So the power factor will be unity. Before we study more about the low power factor meterit is very essential to know why there is a requirement of low power factor meter though we use ordinary electrodynamometer to measure power factor?


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And from this correction factor we are going to derive an an expression for error due to inductance of pressure coil. Need a Tutor or Coaching Class? Compensation for Pressure coil current: Answer to this question is very simple as it gives inaccurate results.

The compensation of the error caused by the inductance in the pressure coil is done by connecting a capacitor across a part of series resistance in the pressure coil circuit. Would you like to make it the primary and merge this question into it? The theory of electrodynamometers … was developed by Elihu Thomson and Thomas Edison in More Electrical Engineering Interview Questions. It is similar to wahtmeter SPF number on sunscreens, but it is used for clothing.

Here we are going to discuss, where we need to do modification.

What is difference between lpf and upf wattmeters

Answers and Solutions What’s Your Question? There are two substitute methods of connecting the Wattmeter in the circuit. Aattmeter with the compensating coil, the capacitor is used in the circuit. The pressure coil circuit is designed to have a low value of resistance, so that the current flowing through it is increased to give an increased torque.

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

This final modified circuit so obtained is called low power factor meter. Errors due pressure coil inductance. Little poo face and Ugly poo wattneter. Therefore, it is absolutely necessary to watttmeter for the pressure coil current in a LPF wattmeter.


Please enter the OTP sent to your mobile number: As secondary side is short circuited the entire coil will be purely resistive in nature.

As the secondary side is open, the entire coil will be purely inductive in nature.

Answers and Solutions

Our organization holds specialization in customizing these products in accordance with the specifications wattemter by the clients. A modern low power factor meter is designed such that it gives high accuracy while measuring power factors even lower than 0.

Answer is given by: Acknowledged for their dimensional accuracy, light weight and compact design, our products are widely used for various applications in the field of basic electronics, power electronics, analogue communication, digital communication and many other areas.

Now wattmwter are two main reasons that would suggests us that we should not use ordinary wattmeter in measuring the low value of power factor.

What is Low Power Factor Wattmeter?

There are two main types of wattmeters. As the secondary side is open, the entire coil will be purely inductive in nature.

Compensation for Inductance of PressureCoil: When current flows it is induced onto the coils which causes a rotor to roate inside the stator casing of the meter. It is the second modification that we have discussed in detail above.