RSPower - to capture max. demand

ckchew666 · Apr 29, 2011

Hi guy,

We have a site using 3 units of Power Meter M6. All of them are link to the workstation thru Ethernet, we can monitor the voltage, amp, etc.. using RSPower & RSLinx software

Does anyone knows how to capture the maximum demand? Client wants to tally the utility provider billing with the reading in the power meter.

One of the power meter is located at the incoming, another 2 power meter located at the MCC panel (highest consumption motor).

Thank you.

Tom Jenkins · Apr 29, 2011

You won't get an exact match with the power company no matter what, but you can get close.

The max demand is actually an average of the highest kW use over a 15 minute window. Some utilities use a sliding window - they adjust the starting and stopping of the 15 minute window to maximize the demand charge. Others use fixed 15 minute windows, with the second 15 minute time period starting as soon as the first ends. The power company won't tell you when the windo starts and stops.

So, you can use a kW meter and integrate the kW readings over 15 minutes, and get close. Or you can get a pulse outout from the power company meter, one pulse = x kWh, and total them over 15 minutes.

Having said that, the odds of the power company screwing up the client demand charge is very slight. I see that you are in hte US, and that is very tighlty regulated in all states. Mistakes happen, but this is a low probability problem.

ckchew666 · Apr 29, 2011

Tom Jenkins said:
You won't get an exact match with the power company no matter what, but you can get close.

The max demand is actually an average of the highest kW use over a 15 minute window. Some utilities use a sliding window - they adjust the starting and stopping of the 15 minute window to maximize the demand charge. Others use fixed 15 minute windows, with the second 15 minute time period starting as soon as the first ends. The power company won't tell you when the windo starts and stops.

So, you can use a kW meter and integrate the kW readings over 15 minutes, and get close. Or you can get a pulse outout from the power company meter, one pulse = x kWh, and total them over 15 minutes.

Having said that, the odds of the power company screwing up the client demand charge is very slight. I see that you are in hte US, and that is very tighlty regulated in all states. Mistakes happen, but this is a low probability problem.

Tom,

Thanks and appreciate your replies.

Our project is in Malaysia. The utility provider interval time is fixed 30 minutes.

I'm using ALL the difference of KW used in 30 minutes to calculate the max KW used. The max KW used in 30 minutes is the Max Demand?

Example:

Date & Time______KWh forward__Difference KW
2/5/2011 23:30___2950.999_______1.114
2/5/2011 23:00___2949.885_______0.766
2/5/2011 22:30___2949.119_______2.234
2/5/2011 22:00___2946.885_______0.884
2/5/2011 21:30___2946.001

From the above log, the Max Demand for this motor is 2.234KW. Am I right?

The log file can be download from here (cvs format):
http://www.megaupload.com/?d=HC36SZK3

Thanks.

RSPower - to capture max. demand

ckchew666

Member

Tom Jenkins

Lifetime Supporting Member

ckchew666

Member

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