Electricity Meters

[scotman]

Can anyone tell me for certain whether electro-mechanical electricity meters recording is based on the actual power(kW) or do they record the VA product?

thanks

[ChuckFickens]

I'm not sure I get what you are asking?

they measure the volts and amps, but as watts=volts*amps they are also measuring watts which is then averaged over a period of time to give the KWh used.

[scotman]

Chuck

Thanks for the reply. I have found the answer elsewhere in the meantime.
Also, VxA = W only if the load Power Factor is 1. That was the basis of my question and it seems that meters take account of PF in their operation and so measure W hence energy used.

[beso]

They measure real power. The actual energy not the simple product of volts and amps (or apparant power) measure in VA. Power factor is the real power divided by the apparant power.

Only when the current is in phase with the voltage does the power factor equal the VA.

The phasing of the current in many types of loads such as electric motors lags behind the voltage because of the energy stored in the magnetic fields of the motor. They use more than the expected current for the energy extracted.

Large consumers are often charged on the basis of current drawn rather than the actual energy. This is because the electrical machinery is limited by the current which governs the losses in the winding of the generator.

Large consumers often correct their power factor to reduce the current.