Four Quadrant Power meter and Readings

[FreddyNurk]

I'd recently been called in to look at the metering setup (indicative only, not for tariff purposes) for a processing plant. They'd had a number of 4 quadrant power meters fitted to various feeders, including the incomer for the site, and a couple of the larger feeds to the site.

Anyway, the process people (who aren't aware of the details of kVA versus kVAr etc) have come back and stated that they had some readings of kWh from the feeders. As the meter is 4 quadrant capable, it gives forward, reverse and net readings. They stated that the incoming feeder had 550kWh forward, 399kWh reverse, and 949kWh net. As I understand it, given the definition of kW, and subsequently kWh, the only way that they could get a reverse reading is if they were actually generating back to the grid.

As they don't have a generator onsite, this is a difficult process to achieve.

I would expect to see a possibility of forward and reverse kVArh, depending on how much the power factor fluctuates, and also assuming that it isn't just a lagging load all of the time. But I can't understand a reason for kWh being this way, unless theres either a mistaken reading, or the meters aren't correctly set up. I don't have access to the configuration data, or as constructed drawings to confirm that the meters are set up correctly or not.

I'd appreciate your comments on this one.

 

[apowerengr]

If the PT's and the associated CT's are not connected to the same "phase" then you'd have positive and negative power flow on a per phase basis with the sum being either positive or negative.

If the downstream system is not always radial and some tie is closed this could also cause a reversal of power flow.

If the meter is programmed for the wrong meter form but the PT's and CT's are matched on a per phase basis I would predict incorrect magnitudes but not incorrect direction.

I'd bet the phases are not matched

 

[waross]

I have had to trouble shoot some metering problems recently.
In my experience, when an electro mechanical meter fails, it either runs slow or stops.
When a digital electronic meter fails, anything is possible.
That said,
1> Possible meter failure.
2> To borrow a phrase from one of the other posters on this forum;
"There are about 27 wrong ways to connect a meter and only one right way."
Possibly wrong connections.
3> Possibly a connection cable going bad and CT circuits crossing.

I have seen more than one digital electronic meter go strange.
One was reporting impossible errors. That is it was showing no errors, a few minutes later it showed an excess neutral current error. Then it added a phase reversal error. Then another error. These are all indicative of wiring errors, but the error notifications were changing on the fly with no wiring changes being done.
I only get out to this site once or twice a year and fortunately I had jury rigged a hidden check meter. We were able to reconstruct billing data from the check meter.
But as a result of this adventure, we will be upgrading our check meters at this and another industrial site. This was a revenue meter and I was working for the utility. The electronic digital meter that failed was about 6 months old.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[slavag]

Hi.
In additional to previous posts.
Seems as wrong connection, but please pay attention on the
forward 550kWh
reverse 399kWh and net is 949kWh.
Something wrong in the setting of meter. net is differnce between export/import, actually you pay for the net (ok in your case it's for metering porpuse only).
Best Regards.
Slava

 

[waross]

Hi slava. I hadn't noticed that detailbut I am not surprised.
The newest digital electronic meters for residential use show that as a default setting. The basic North American residential meter is a form 2S, direct connected, plug in meter. If these meters are installed upside down the connections are reversed and the meter runs backwards. A common default setting on the new digital electronic meters is to measure both forward and reverse energy, but to display the sum. customers may no longer steal energy by installing their meters upside down for several days each month. (Yes, I know that the meters are supposed to be sealed etc. but the thieves are resourceful.)
The point is that it is not surprising for an electronic meter to sum forward and reverse energy.
There still remains the fact that there should be no reverse energy.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[FreddyNurk]

Thanks for all the comments. I do feel confident now that the meters are not configured correctly. What is interesting, is that as I stated earlier, there are multiple meters fitted to the board, and all of them seem to be reading reverse figures. I'd basically referred this one back to the supplier at the client's request, so I'm not sure if I'll get to confirm that they're not correctly configured.

An interesting exercise indeed however, and thanks for all the responses.