Calculating KWh from KW

Marc_U · Aug 3, 2010

We have a few sites that have Redlion G3 HMIs which are monitoring Hydro-electric generation sites.

The HMIs have access to the generator kW reading (via modbus), but we would like to also able to calculate how many kWh (kW hours) have been generated.

Any suggestions?

rdrast · Aug 3, 2010

Uhhh... Totalize the readings up over some time interval?

For example, take a reading every minute, divide it by 60, and add it to an accumulator. The accumulated value represents kWh.

BobB · Aug 3, 2010

If the kW is varying considerably during the period of one minute the reading will be inaccurate. Better to do it every second on varying load.
Lot easier to buy a kWh pulser from Crompton Instruments to be honest.

Andybr · Aug 4, 2010

I would go further than Bob and suggest that even 1 second updates will not be accurate unless the load is stable and linear. If you are already using Modbus then I would look at a multifunction energy meter like the Schneider PM710 which will give all of the information you are likely to need and does not cost too much.

BobB · Aug 4, 2010

Strangely enough my favourite power monitors come from Cromnpton Instrumenst in the UK Andy.
Love em - real easy on Modbus RTU - very accurate too.
Also use the blind ones for 4-20ma outputs - up to 4 per unit.

Marc_U · Aug 18, 2010

Thanks for the suggestions.

Precision is not too critical, as it is intended more as an indication.

Like a few of you have said, for the critical precision kWh (where loss of revenue is involved), then if possible I would use a Modbus link to a calibrated instrument.

Thanks again.

Calculating KWh from KW

Marc_U

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Andybr

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