Current Measurement

KVA.

Can please brief that how to conclude it as a KVA current. Please don't say P=1.732*V*I*0.8

Because it just IS.

(However, if you have power correction capacitors, you can measure separately the KVA, KVAR, and KW currents, and then compute actual PF.)

"AC power flow has the three components: real power (also known as active power) (P), measured in watts (W); apparent power (S), measured in volt-amperes (VA); and reactive power (Q), measured in reactive volt-amperes (var).^[15]

The power factor is defined as:

.

In the case of a perfectly sinusoidal waveform, P, Q and S can be expressed as vectors that form a vector triangle such that:

If is the phase angle between the current and voltage, then the power factor is equal to the cosine of the angle, , and:

Since the units are consistent, the power factor is by definition a dimensionless number between -1 and 1. When power factor is equal to 0, the energy flow is entirely reactive, and stored energy in the load returns to the source on each cycle. When the power factor is 1, all the energy supplied by the source is consumed by the load. Power factors are usually stated as "leading" or "lagging" to show the sign of the phase angle. Capacitive loads are leading (current leads voltage), and inductive loads are lagging (current lags voltage).

http://en.wikipedia.org/wiki/Power_factor#Definition_and_calculation

I spy homework!!

Simple.... amps are measured with an amp meter.... volts with a voltmeter.. the rest you calculate!

as had been already said ammeters record only ampere readings.if your ammeter is connected before the power factor correcting capacitors than it is the power factorised reading.than to know the power factor you may have to hook up another pf measuring instrument.So now it depends where your ammeter is connected, but anyhow the actual current consumed by the motor is unpower factorised.

Depends on the type of ammeter you are taking/viewing the readings with/on.

If you are using an analog ammeter that is reading directly off the CT circuits or a "hand held" clamped arround the conductor, the readings will be actual current values in Amperes only and the power factor is not visible nor factored into the display.

The KVA calculation formula would be P=1.732*V*I wherein you would substitute the reading(s) taken for the I character in the formula.

This method does not in any way yield the Power Factor of the circuit nor take it into consideration.

Using current readings taken on a oven and applying your second formula that assumes a PF of .8 (P=1.732*V*I*.8PF) would yield a much more accurate result if you are certain the power factor is reasonably close to .8. (Since this would/should be an almost pure resitive load I am pretty sure the PF would be much higher than .8 and most likely >.9.)

Using current readings taken on a motor is quite a different situation as the power factor is directly affected by: mechanical load or abscence of mechanical load on the motor, circuit voltage level, circuit frequency, type of motor (squirrel cage induction, wound rotor, synchronous, VFD, etc.), and if there are motor capacitors present and functioning. Therefore the general practice of assuming a .8PF for a motor may not yield accurate numbers.

All the above being said;

If you are obtaining the current readings from a digital device such as a Motor Protection Relay the power factor may already be taken into account.

In order to determine if the readings are power factor corrected, you must read and understand the meter function and display parameters.

The motor is an inductive load, which means it will comprise both active power, kW (for motor rotation) and reactive power, kVAr (to create magnetic field ). The current read therefore will comprise the power factor which is usually labelled on the motor name plate. eg 0.8, 0.85 etc.. That is, I = P/V x pf (for single phase) and I = P/1.732 x V x pf.

For the oven, it is a resistive load, hence it requires only true power and no reactive power. Therefore the power factor will almost be unity. Hence, I = P/V (for single phase) and, I = P/1.732 x V (for three phase)

It is always KVA current except when you running unity power factor ( power factor=1)then KW=KVA