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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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, here we also conclude that the current in the watfmeter coil is also lagging by some angle with the current in pressure coil. LPF wattmeter is used to measure power in inductive circuits.

Difference between electrostatic and electrodynamic wattmeters? LPF wattmeters are designed to have a small control torque so that they give full scale deflections. Answer is given by: Calibration of LPF wattmeter by phantom loading? This current produces the deflecting torque on the wattmrter coil. Number of Employees 11 to 25 Wattmetet. Thus, the resultant field is due to current I only.

The supply voltage is equal to the voltage across the pressure coil. Legal Status of Firm Partnership firm.

If we ignore the effect of inductance of pressure i. Here we are going to discuss, where we need to do modification. These are discussed one by one below:. In this category two cases arise watmeter their diagrams are shown below: Why a LPF Wattmeter is needed?


Learn how your comment data is processed. So the power will be lagging due to inductive property of the circuit.

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

The control torque of the low power factor Wattmeter is kept small so that the full-scale deflection is obtained even for the small value of the power wattmetee. Electromechanical meters are described below.

View Contact Call Seller Now. The compensating coil and the pressure coil are in series with each other.

In this category two cases diagrams arises and these are shown below: If we consider the inductance of pressure coil we don’t have voltage across pressure in phase with the applied voltage. Answer to this question is very simple as it gives inaccurate results. What is difference between lpf and upf wattmeters? In this power shown by the second watt meter is equal to the power loss in the load plus the power wttmeter in the pressure coil. More Electrical Engineering Interview Questions.

The voltage across pressure coil is equal to the voltage across the load.

The pressure coil is placed such that the field produced by the compensating coil is opposed by the field produced by pressure coil as shown in the above circuit diagram. 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. Now let us derive an expression for the correction factor for pressure coil inductance. Compensation for Pressure coil current: Thus in this case we have power shown by the first wattmeter is equal to the power loss in the load plus power loss in the current coil.


In figure b the pressure coil is not connected in parallel with the load. In the first category both the ends of the pressure coil is connected to supply side i. The output power obtains from the circuit is equal to the sum of the load power loss and the power loss of the pressure coil. Why is LPF wattmeter used for no load test?

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Auto Ranging Digital LPF Watt Meter, Mumbai, India

Thus in this case we have power shown by the first wattmeter is equal to the power loss in the load plus power loss in the current coil. Notify me when new comments are added. The error caused by pressure coil inductance is.

In either case, the sum of the wattmeter readi … ngs will give you the total power of the load.

Low Power Factor Wattmeter

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. The supply voltage is equal to the voltage across the pressure coil. As secondary side is short circuited the entire coil will be purely resistive in nature.

This final modified circuit so obtained is called low power factor meter.

Get 5 credit points for each correct answer. Compensation for Inductance of PressureCoil: What is Low Power Factor Wattmeter?

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