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Topic Title: Electric meter readings KWH and KVAr
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Created On: 03 October 2013 07:14 PM
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 03 October 2013 07:14 PM
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Joined: 02 June 2008

I recently installed two electric meters with current transformers, one on a farm house and one on a dairy to settle a dispute among a family run business regarding electric bills. The idea being that there are three areas needing metering and these two subtracted from the overall usage would give the third. The reason for not metering the third is that it is spread over several circuits.

My question relates to the KWH and KVAr readings. The dairy shows significantly higher KVAr than KWH and the farm house higher on the KWH, presumably due to the different loads types being utilised. The meter supplier suggested adding the the two readings together to obtain the actual usage for each metered area. However this does not relate to the overall bill and effectively means that they are using more than the overall electric bill.
How can I derive the actual usage from the readings? it appears that taking the higher reading for KWH or KVAr for each supply is nearer the mark, when compared to the overall electric bill.
thanks in advance.
 03 October 2013 07:26 PM
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Firstly, if the KVAr is seen to be higher than the KWH you have got serious problems with your power factor (its more than 45° when it should be as close to 0° as possible)

You can work out power using phytagoras' triangle

Apparent Power, VA (s)
Reactive Power, VAR (q)
True Power, W (p)

s^2 = q^2 + p^2

p^2 = s^2 - q^2

q^2 = s^2 - p^2


Edited: 03 October 2013 at 07:39 PM by Zuiko
 03 October 2013 07:35 PM
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Don't add the readings.

use the kWh readings, as you say one from each meter and then the difference to find the third.

Providing there are no reactive unit charges or power factor charges on the bill you can ignore the kVArh meters.

If there are reactive charges sounds like these all belong with the dairy.

As Zuiko has said you really need to think about power factor correction there if the load is of any size. If its just a few kW though its probably not worth bothering.

Hope this helps
 03 October 2013 08:57 PM
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Press the button on the meter and record all 7 readings

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