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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Please enter the OTP sent to your mobile number: The ordinary Wattmeter used for measuring the low power factor gives the inaccurate result.

How is UPF Wattmeter different from LPF Wattmeter? – Find 1 Answer & Solution | LearnPick Resources

HPF is high p … ass LTI filter which passes the high frequencies and reduce the amplitude of the frequencies lower than filter’s cutoff frequency. Blondel’s Theorem states that you can have one less wattmeter than there are conductors supplying a balanced or unbalanced load. In the first category both the ends of the pressure coil is connected to supply side i. The total power measured by the pressure coil is equal to the sum of the power loss in the load and the power loss in the current coil.

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

These are discussed one by one below:. If, by ‘upf’, you mean ‘unity power factor’, then all wattmeters measure the in-phase component of the load current, so the term is quiet unnecessary. UPF are not accurate in measuring power at low power factor beacuse of – low deflecting torque. Little poo face and Ugly poo face.


A modern low power factor meter is designed such that it gives high accuracy while measuring power factors even lower than 0. As secondary side is short circuited the entire coil will be purely resistive in nature.

This is all wattmmeter by the supplier of the meters or utility using magnets within the meter. The pressure coil current I p flows through it. LPF wattmeters are designed to have a small control torque so that they give full scale deflections.

Some additional features are added on the ordinary Wattmeter so that the meter can measure the power of the low power factor circuit. The modified circuit is shown below: The pressure coil is placed such that the field produced by the compensating llf is opposed by the field produced by pressure coil as shown in the above circuit diagram.

As the secondary side is open, the entire coil will be purely inductive lfp nature. The figure below wattmmeter these two methods.

What is Low Power Factor Wattmeter?

In lpf meter pf compensation is done wattmdter is accurate at the specified low pf. What is ac wattmeter? Merge this question into. 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 wwttmeter.

Difference between electrostatic and electrodynamic wattmeters? 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. Answer is given by: What does upf stands in upf wattmeter? The best one gets 25 in all. Contact this tutor View Details. The rotation of the rotor causes the display dials to count up at certain values wattmeted rotation. So the power factor will be unity.

Inventor of the wattmeter?

Auto Ranging Digital LPF Watt Meter

Until then the only meter available was a zink plate meter very unreliable and inaccurate and a light meter which basically detected wattmeher the lights were on and turned on a clock if they were. Notify me when new comments are added. Furthermore, owing to the state-of-the-art infrastructure, we are able to meet with the exceeding demands of our clients. Why is LPF wattmeter used for no load test?


Subscribe to our mailing list and get wattmetee stuff and updates to your email inbox. These are discussed one by one below: 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?

LPF is a low pass LTI filter which passes the low frequency signals and reduce the amplitude of the signals with frequencies higher than the cutoff frequency. So the power will be lagging due to inductive property of the circuit. Along with the compensating coil, the capacitor is used in the circuit. Wattmter final modified circuit so obtained is called low power factor meter.

Wattmetwr 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.

How does a wattmeter work? However by doing some modification wattketer adding some new features we can use modified electrodynamic wattmeter or low power factor to measure the low power factor accurately.

Low Power Factor wattmeters are specially designed to measure power at low power factor. 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.