Answer / maniveer

LOW POWER FACTOR(LPF) & HIGH POWER FACTOR(UPF)

 In open circuit test the secondary winding of transformer is kept open.As the secondary side is open, the entire coil will be purely inductive in nature.So the power will be lagging due to inductive property of the circuit. So LPF(Low Power Factor) Wattmeter is used in OPEN CIRCUIT TEST of Transformer.
          
            In short circuit test the secondary winding of transformer is short circuited. As secondary side is short circuited the entire coil will be purely resistive in nature.So the power factor will be unity. So UPF(Unit Power Factor) Wattmeter is used in SHORT CIRCUIT TEST of Transformer.

Answer / venkata krishna

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 ranges from
0.5 to unity.

Answer / potnur hemarao

Lpf is used in power measuring in high inductive circuit and upf is used in power measuring in resistance circuit which power factor ranges 0.5 to unity

Answer / nitish kennedy

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

Ordinary wattmeters (i.e. UPF) are not accurate in measuring power at low power factor beacuse of -

low deflecting torque.
error due to inductance of of pressure coil is large at low power factor.
So some modifications are done in LPF wattmeters-

low value of pressure coil resistance to increase the torque.
pressure coil current is compensated using compensating coil.
capacitor is connected in pressure coil to reduce the error due to pressure coil inductance.
control torque is made very small.

Answer / k.prakashchandra

LPF -low pf UPF- unity pf.In lpf meter pf compensation is
done and is accurate at the specified low pf.

Answer / suresh

HERE LPF USED TO measure the low current & UPF is used to measure the high current. Then low pf and unity power factor

Answer / subha

can i get the expansion of lpf and upf

Why power factor is arising in electrical circuit, is it possible to eliminate from the circuit, why

2 Answers  

what is the definition of a power transformer ?

4 Answers  

How much allowable difference current between on three phases Dear sir, We have a 1870 KW HT motor, 11 Kv supply,FLA-120A,2870 rpm,2-pole squirrel cage induction Motor.And stator is connected in star connection with Liquid resistance stater to limit the starting current.It has coupled with Centrifugal air compressor.My question is it is loading 73% of FLA taking R-phase 86.7 A, Y-phase-85.4A,B-phase- 78.3A.why the B phase current is that much of difference.Is it allowable, or any one tell me how much allowable current.If any method to calculate.

1 Answers  

what is the function of mccb?

6 Answers  

if the number of poles generated in stator and rotor side of an induction motor are different then what will happen and why?

0 Answers  

Why electrical engineer use Cu Strip for transformer neutral why not GI Strip? What if we use GI instead of Cu does it affects the transformer performance.

7 Answers  

AL=0B9H,bl=75H, ADD AL,BL AL=____________? CF________? OF___________?

0 Answers  

What is the voltage b/w nutral and earth

11 Answers   Mind Space,

power factor is max for which welding a.arc b.resistance c.gas

2 Answers   Bhel, HCL,

which motor is used in mixies

10 Answers  

why we increase the small speed of turbine when alternator just synchronized to grid in steam power plant

2 Answers   PSEB,

why we are using starter

5 Answers