# Why do we use LPF?

## Why do we use LPF?

Low pass filters are used to filter noise from a circuit. ‘Noise’ is a high frequency signal. When passed through a low pass filter most of the noise is removed and a clear sound is produced.

### Which wattmeter is used in no-load test?

The 2-wattmeter method measures the input power of the system. The voltmeter measures the standard-rated supply voltage and an ammeter measures the no-load current. Since the motor is running at no-load, total power is equal to the constant iron loss, friction and winding losses of the motor.

Why OC test is performed on HV side?

In short circuit test we have to pass rated current through the short circuited side. Therefore we select High Voltage (HV) side normally for short circuiting, because it’s rated current is less and therefore it is easy to short.

Why LV side is energized in OC test of transformer?

3. Why OC test is performed on LV side? Explanation: In open circuit test all the power supplied is used to overcome iron losses and hence, by taking the reading of input power one can easily do the calculations to find shunt parameters of equivalent circuit of transformer.

## What is meant by LPF wattmeter?

A low power factor (LPF) wattmeter is an instrument used to measure power in low power factor circuits. This type of wattmeters is employed for power measurement in circuits whose power factor is less than 0.5.

### What is a Wattmeter used for?

The wattmeter is an instrument for measuring the electric active power (or the average of the rate of flow of electrical energy) in watts of any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements.

What is the purpose of OC and SC tests?

The open circuit and short circuit test are performed for determining the parameter of the transformer like their efficiency, voltage regulation, circuit constant etc. These tests are performed without the actual loading and because of this reason the very less power is required for the test.

What kind wattmeter should be used during OC test?

Answer: LPF wattmeter is used to measure power in inductive circuits. Inductive circuits have the property of lagging power factor and hence these wattmeters are used. So LPF(Low Power Factor) Wattmeter is used in OPEN CIRCUIT TEST of Transformer.

## Why copper losses are neglected in OC test?

Open Circuit Test on Transformer A voltmeter, wattmeter, and an ammeter are connected in LV side of the transformer as shown. But as said earlier, the no-load current in the transformer is quite small compared to the full load current so, we can neglect the copper loss due to the no-load current.

### Why LV side of transformer is short circuited?

In the short circuit test, usually, the low voltage side is short-circuited by a thick conductor. The reason for short-circuiting the low voltage side is as follows: The rated current on the high voltage (hv) side of a transformer is less than the low voltage (lv) side of the transformer.

Why are the LPF wattmeter designed to have a smaller controlling torque?

Small Control Torque: Low power factor wattmeters are designed to have a small control torque so that they may provide full scale deflection for power factors as low as 0.1.

Which type of wattmeter is widely used?

The electrostatic wattmeter is suitable for high voltage low power factor circuits like dielectric loss measurement in capacitors. They are used in very small power measurements. The induction type wattmeter and pivoted coil direct reading wattmeters are very commonly used for power measurement.

## Why do we use UPF watt meter in short circuit test?

In blocked rotor test or in load test the power factor will be usually higher if you calculate (around 0.7 to 0.8). So we use lpf and upf wattmeter respectively.

### Why do we need a low power factor wattmeter?

Before we study more about the low power factor meter, we need to understand why we need a low power factor wattmeter in the first place (as opposed to a standard electrodynamometer wattmeter) The answer is simple: a standard wattmeter gives inaccurate results.

Why do we not use ordinary wattmeters?

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. The value of deflecting torque is very low even though we fully excite the current and pressure coils. Errors due pressure coil inductance.

Why is an open circuit test performed on low voltage?

No-load test (or) open-circuit test in a transform is preferred on the low voltage side because the low voltage is sufficient to obtain rated flux in the core and large on-load current for convenient reading. The current drawn from this terminal is the no-load current at a low power factor corresponding to the core loss component.