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how to find apparent power and reactive power?
2011/06/05
7:58 pm
shah
Guest

how to find apparent power and reactive power?

is it different for static and rotating devices?

sorry but i want to clear my doubt.

2011/06/29
8:19 pm
Mike
Guest

S = P + jQ

P = 1.732 VI Cos(phi)     Real power

Q = 1.732 VI Sin(phi)      Reactive power

S = 1.732 VI                  Apparent power

 

Use root 3 for 3-phase i.e. 1,732

 

Static or rotary same rules apply.

2011/06/30
6:06 am
prasad saitwadkar
Guest

shah said:

how to find apparent power and reactive power?

is it different for static and rotating devices?

sorry but i want to clear my doubt.


dear Shah, if you want to make the mathematical calculation then i dont know,

if u want to measure it actually then use FLUKE POWER ANALYSERmodel

43B or 435 your job will be done in minutes.

2011/06/30
11:02 am
nael.samman
Member
Forum Posts: 19
Member Since:
2011/06/29
Offline

Hi

 

Static or rotating device : this is a mechanical difference (even for AC inductive motors which have electrical rotating magnetic flux)

But the general rule is : as long as there is inductance (or capacitor) inside the load, their is an apparent power and reactive power,

Please note that reactive power is the power responsible of creating the magnetic flux (which is 90% of cases apply on rotating machines :)

 

To know the apparent and reactive power on any machine, I'll use an inductive motor as an example,

On every motor there is a name plate, which must indicates the apperant power (  Pn in W or KW or HP ) , Voltage ( in V ), and the phase shift ( cos phy ), and nominal current ( In in A)

Those values are for the full load,

for lower loads you should measure the current I and compare it to the nominal current In and devide with the calculated ration I/In=A

P =Pn x A, Q=Qn x A

Now for Q reactive power in VAR 

Q=P x tg (Phy)

Phy can be known by any scientefic calculator,

 

Please note that the Harmonics effects are not considered here.

 

Take care

Nael Samman
2011/06/30
8:48 pm
عبده همد
Member
Forum Posts: 3
Member Since:
2011/05/27
Offline

apparent power is the balance power between real power (p)  and reactive power (Q) and has equation that P sqr and Q sqr  both under radical  and gives you aparent power (s) if it three phase times three when under the radical .

2011/07/01
11:29 am
nael.samman
Member
Forum Posts: 19
Member Since:
2011/06/29
Offline

Hi

One mistake at my post

P is the real power in Watt , S is the apperant power in VA

S=Square root (Psqr + Q sqr)

Just replace the word "REAL" instead of "apperant" in my previous post

Nael Samman
2011/07/01
4:07 pm
SHEKHAR
Guest

nael.samman said:

Hi

One mistake at my post

P is the real power in Watt , S is the apperant power in VA

S=Square root (Psqr + Q sqr)

Just replace the word "REAL" instead of "apperant" in my previous post


apparant power= voltagex current (vA or KVA)

REAL POWER= VOLTAGE X CURRENT X POWER FACTOR(COS Phi.) – WATTS /KW

 

APPARANT POWER IS VECTOR SUM OF REAL POWER(KW) AND REACTIVE POWER KVAR(KVAR).

 kva=  square root    ( (kw)square+(kvar) square )

power factor=kw/kva

IF YOU KNOW ANY TWO OF THESE (KW,KVA .KVAR OR POWER FACTOR) YOU CAN CALCULATE OTHER PARAMETERS.

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