Discussion in 'General Electronics Chat' started by madhura, Sep 25, 2009.
please can anyone tell me which power is taken for billing
Do you mean on your house? The standard meter is for real (active) power in watts, the meter records Watt-hours. If the power factor on your house is too low, the power company can (and will) install a a VAR (Volt Amps Reactive) meter as well and also charge you for reactive power measured in VARs.
Yes, the more proper term is true power and is defined mathematically as follows:
True Power = the instantaneous product of: Eline * Iline. It's actually calibrated in RMS for an analog meter, there are two windings for the meter movement that are perpendicular so as to perform the instantaneous multiplication of the line voltage times the line current. This, in turn, spins a wheel which is geared to several smaller wheels to record the product of power and time, which is recorded in Kilowatt-Hours.
In the newer electronic power meters that the electric companies use, the True RMS power is computed as follows:
PTRMS=Square Root( (1/T)*Integral from 0 to T of [(Eline * Iline)^2])
Then, it's multiplied by elapsed time to get watt-hours or Kilowatt-hours.
In a 3-phase system, it's only slightly more complicated, but the same idea is used and the TrueRMS Power of each Phase is metered separately and added together to get the total 3-phase power, then multiplied by elapsed time to get KWH used. In the older analog meters with the geared wheels, the meter reader takes the reading at the end of the month and subtracts the reading from the end of the previous month to get the total KWH for each month for billing. The newer electronic meters can send the data to the meter reader by bluetooth or some similar short-range communication means so that the meter reader doesn't have to leave his/her truck to read the meters and more important, doesn't have to enter the premises of the places they are reading the meter of. In other electronic meter systems, the data can be directly sent to the main electric utility office without the need for any meter reader employees.
I don't know if you have heard and felt the noise of transformer that has
That by itself is not correct. True power is Eline X Iline X Power factor. The reason the windings are 90 degrees apart is to include the phasor product in the multiplication.