Table of Contents
What is LPF in 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 the purpose of the open-circuit test in a transformer?
The open-circuit test, or no-load test, is one of the methods used in electrical engineering to determine the no-load impedance in the excitation branch of a transformer. The no load is represented by the open circuit, which is represented on the right side of the figure as the “hole” or incomplete part of the circuit.
Why in an open-circuit test the HV side is open and in short circuit test the LV side is shorted?
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 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.
Why is open-circuit test done 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. Core loss is calculated by multiplying the applied voltage and no-load current.
Why in an open-circuit test the HV side is open?
In open circuit test HV is left open on no load and the rated voltage is applied to the low voltage side to get the constant losses. Rated voltage on LV side is lesser than the HV side. For convenience and better readings, OC test is always preferred to be conducted on LV side and leaving HV side open.
Why is open-circuit test generally on low voltage side?
What are the errors in LPF Electrodynamometer wattmeter and what is the remedy?
Errors in Electrodynamometer Wattmeter Pressure Coil Inductance – The pressure coil of the Electrodynamometer has some inductance. Because of the inductance, the current of the pressure coils lags behind the voltage. Thus, the power factor of the wattmeter becomes lagging, and the meter reads high reading.