Please What is Different Between Kilo Watt Meter and Kilo Var Meter

kVAR is reactive power where as kW is the real power, and kVA is the apparent (total) power. See triangle below but imagine it on a real/imaginary plane where the origin is at the lower right corner.

Also, Watts are units of energy in which useful work is extracted from the power source. The unit VAR refers to reactionary energy that provides no conversion to torque or force that can be used.

You might think of it as the water required to fill a hose pipe before you can get any water out of the other end. After you completely empty the hose pipe, you will still have to refill it the next time you want water.

Maybe not the best equivalent for the concept but it is better than being told that it is imaginary power. That's what us EE's call it.

cos φ.

'...as we know they have same construction and same shape...' and even the same components, but that's where the similarity ends. On the old style induction disk meter the position of the current and potential coils are varied according to what the meter is supposed to read. On the new style digital meters the current and potential inputs are digitized and the results presented to a microprocessor which does the calculations posted above, only the desired output is displayed.

Didn't you like the answers you got on other forums?

In a wattmeter, the measured current is multiplied by the current in a theoretically pure resistive circuit connected to the measured voltage.This ignores all reactive current, which is perpendicular (90 degrees) in phase to the voltage. In reality, there is usually some inductance in the "resistive" circuit, causing a small error which may become serious at low power factors or for harmonic frequencies.

A Varmeter uses a current from a purely inductive or capacitative load connected to the measured voltage which provides a current at 90 degrees to that used in a wattmeter and cancels all active watts, while responding to reactive VA.

There is more than one way of making a wattmeter or Varmeter so the above is just an illustration of the difference for the dynamometer type. In electronic instruments there are many ways of getting a 90 degree lag or lead of the measured voltage. In the case of a regularly sampled voltage one could just take samples from 1/4 cycle ago = x samples ago rather than immediate sample to get Vars rather than watts.

Sorry 67, that's not how the induction disk meter works, there is no resistive circuit nor connection between the voltage and current coils, just the vector sum of the magnetic fluxes generated by the coils and their resultant eddy current induced in the disk. The placement of the coils relative to each other and the opposing magnet(s) determine whether the meter records Watts, VARs or VA. From Wikepedia

http://en.wikipedia.org/wiki/Electricity_meter

The electromechanical induction meter operates by counting the revolutions of an aluminium disc which is made to rotate at a speed proportional to the power. The number of revolutions is thus proportional to the energy usage. The voltage coil consumes a small and relatively constant amount of power, typically around 2 watts which is not registered on the meter. The current coil similarly consumes a small amount of power in proportion to the square of the current flowing through it, typically up to a couple of watts at full load, which is registered on the meter.

The metallic disc is acted upon by two coils. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current. The field of the voltage coil is delayed by 90 degrees using a lag coil.^[17] This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current and voltage. A permanent magnet exerts an opposing force proportional to the speed of rotation of the disc. The equilibrium between these two opposing forces results in the disc rotating at a speed proportional to the power being used. The disc drives a register mechanism which integrates the speed of the disc over time by counting revolutions, much like the odometer in a car, in order to render a measurement of the total energy used over a period of time.

Please be so kind as to wait an honorable moment, RAMConsult!

I never mentioned induction and the original post wrote "wattmeter" not "watt-hour meter".

I meant one of these [dynamometer type]............picture courtesy of Golding and Widdis' "Electrical Measurements and Measuring Instruments"

Not a bit of iron in sight. It has two coaxial fixed current coils and a rotating voltage coil. It also works on DC.

To make it read Vars (single phase), one usually arranges a 90 degree lagging current in the voltage coil, rather than the usual "in-phase with voltage current" got with a resistive ballast.

67model

My apologies! ...and thanks for pointing out the fact that I did not answer the OP's question, I had to re-read it three times to see that the word "hour" was not there, amazing how the mind works. Nice picture, I think I saw one of those in one of the ancient power stations I worked in.

THANK U VERY MUCH