Metering

[Blondie]

Hello

I am looking for advice on the metering system RA we have on site and the reason why we are out by 6/7%. of total PM8000 vs ION 7650

We have a ION 7650 on our MV main income and 13 transformers with PM 8000 on the LV side.

Over 24hr ION 7650 = 42153kWh & the total 13 PM 8000 = 39461kWh = 2692kWh Difference. 

I know we will have small loses in the transformers and maybe the system but I don't think it would be this  much.

Each transformer has its own PF and this is good and well maintained, to be honest most of them would not be called in. I am told that all the meters were all set up correctly at the time on installation 8/9 years ago.

The few questions I have is, Do The PM8000 record the PF load in total energy used/ is this down to loses in the whole system/ is it down to metering issues.

Any Help would be much  appreciated.

Thanks 

[Mehran_Mehrnia]

Hi @Blondie 

Yes, by default, PF is recorded every 15 minutes under 'Historic Average' Data Recorder.

Regarding 6.7% Energy reading difference between main income and 13 transformers outgoing feeders, if all parameters such as CT/PT ratio, etc, in all meters have been set accordingly, I am wondering if 13 times of phase shift caused by transformers(on average 0.5% per each transformer) could cause such difference that can be checked by PF measured by ION7650 and PM8000 meters.

Best Regards,

-Mehran

L3 Expert Advanced metering

[Charles_Murison]

Hello @Blondie ,

There are many elements to include in a topic like this. First that comes to mind is tolerances of elements used. There is not just the PTs and CT, there is also the meter as well. CTs are typically the single largest tolerance however the construction of the CT can make a difference, as can the placement of the conductor though the CT. Is conductor centered in the CT, is the CTs spaced far enough apart to not provide interference etc.?

Another factor to consider is are all meters synced to the same time source. If one meter is way ahead of other meters in time the logging intervals will not be the same.

Another element that could come into play is settings on the meters. Could one or more meters have incorrect settings that can account for the differences. One item you could investigate, assuming meters are all time synced, is calculating the energy per interval for the main meter and all sub meters. If you plot the difference between total and summation of sub meters, then plot the interval of each sub meter to this difference oy might see trends where if one meter goes up, the difference also goes up, or if a meter goes down the difference goes down. If one or 2 meters have a strong correlation to the difference those would be meters I would want to check first.

Do you have 15 minute Energy from the main meter and the sub meters?

Regards,

Charles