Sub-registration 16S Meter without Neutral?

[bg_1735]

Hi,

Recently, we found that a customer with a GE 3 Stator Watt Hour Meter model VM64S was missing the neutral connection to the meter.

Looking at the meter face you wouldn't be able to tell that there was a problem, but when we installed a new electronic meter it didn't turn on.
After inspecting the socket, we found that the neutral was connected at the socket end but not at the distribution board end.

Now, we wonder how the GE 3 Stator Watt Hour Meter model VM64S was working without the neutral and, if there was sub-registration, how to calculate it?

Regards.

 

[waross]

In the original meter all three potential coils are wye'd together internally. The physical potential coils will work with a floating wye point. Bad practice but it works.
Not surprisingly, the electronic sampling does not work with a floating neutral.

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

 

[bg_1735]

Thanks for the response.

Do you think that the absence of the neutral was causing energy sub-registration?
Or, does meter register accurately even without the neutral?

Regards.

 

[waross]

Do you think that the absence of the neutral was causing energy sub-registration?

I don't know for sure but consider:
Wye connected transformers even with a connected neutral may have distortion issues when unloaded due to non-linearity related to hysteresis. These issues disappear for all practical purposes when a load is placed on the transformer bank.
However, The resistance of the potential coils in a meter is fairly high to minimize phase shift. The potential coil acts as its own load.
I can't say for sure if the accuracy will be 100% but I suspect that the accuracy will be quite good with a floating neutral.
I can foresee accuracy issues if the line to line voltages are not well balanced.
I have used some non-traditional metering schemes, but I have never encountered a floating neutral on meter potential coils.
I have not seen any utility approved metering schemes that allow a floating neutral on the potential coils.
The definitive answer would be determined by a shop test of a correctly connected electronic meter in series with an electro-mechanical meter with a floating neutral.

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

 

[bg_1735]

Thanks for your answer.

We'll try to do some testing.

Regards.

 

[waross]

I'll be interested to hear your results. Thanks in advance.

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