Metering a 3WD with a form 9S meter and 3 CTs

[greenspark1]

Hello,
I have an involved situation where several form 9S meters may have been (incorrectly) wired to a 3WD service using a 4WY configuration. It is straightforward to resolve fixing the voltage issue but the current (CTs) are a bit more tricky. The meters are all instrument rated, and for a 4WY used 3 CTs, one for each phase ABC.

To fix it into a 3WD, we typically we use 2 CTs, phases AC. But physically removing a CT is a major pain and requires a full outage. Rewiring is just a local outage since we have a test switch and a shorting terminal block. I am trying to work out what would happen if the meter remains wired with all 3 CTs. I don't see how it would cause a problem, or cause an incorrect reading. I also thought there is actually a standard way to meter a 3WD with 3CTs, but haven't been able to find it through googling. Any metering folks out there have some input?

Unfortunately this project is not local so I can't just try it and see what happens.

 

[GoldDigger]

Electrical theory tells us that if we choose the reference points correctly either a wye or a delta meter looking at the same source and a delta load should give the same result.
One way to do what you want would be to treat the CTs as being in the three hot wires only with no current in the missing neutral. But to do that you must create a "neutral" point using a control sized wye-wye transformer or using a (zig-zag wound?) wye primary as an autotransformer.
If your delta is corner grounded, and you use an autotransformer, this will raise the synthesized neutral to be above ground, so be careful how you handle it.
Now all of this is purely theory and may fall apart based on the actual construction of your meter.

 

[greenspark1]

Yea this is a strange situation where the transformers being metered are actually constructed as 4WY but the neutral is disconnected at the X0 of the xfmr and unused.