Phase shift compensation for metering (Satec PM174)

[Buckeye46]

Hello,

We had a 69/13.2 delta wye bank fail a few months back and were able to find a new one sitting around somewhere. The issue I am running into is metering. The transformer doesn't have 3 low side CT's nor does it have 3 phase pots on the high side. The design has us using the high side CT's, and a broken delta pot setup on the low side. How could I input this into a satec and still get accurate power factor and etc?? I can easily compensate for the 13.2 to 69 voltage by multiplying by the turns ratio of the transformer but how do I compensate for the 30 degree phase shift??? Is this even possible using a Satec PM174 and no additional equipment?

Thanks.

 

[DTR2011]

From your voltages, I'm assuming North America. I briefly checked the Satec manual and it appears you could find a wiring convention and meter configuration setting to accommodate most of what you want. For the remainder, I suggest you utilize auxiliary instrument transformers for phase shift correction. It was one the de facto ways to deal with similar issues for transformer protection. Delta>Wye & Wye > Delta. If considering this option for voltage, consider the voltage ratings carefully. For clarity, you describe "broken delta pot setup" - could you mean Open Delta with 2 transformers or do you indeed mean broken delta? Does your PWR Transformer have an LTC?

What is the meter use? Local Indication,SCADA, energy?

 

[Buckeye46]

Whoops sorry i meant open delta so yes 2 transformers. The meter is used for local and SCADA. When i looked thru the satec manual it seems the wiring configurations don't really specify using voltages and currents from opposite sides of a delta wye transformer. They allow for the use of the open delta PT's and other configurations. I even contacted satec directly their engineers didn't seem to think it was possible but to be honest they didn't seem entirely convinced it wasn't. I have already tried stressing to my management and they are going down the path of just not caring sadly and using the amps and volts only. I doubt I will get them to add a phase shifter, or additional CT's or PT's. The transformer does have a beckwith LTC.

 

[DTR2011]

The LTC is likely to throw a monkey wrench into the equation. Can you utilize a secondary main breaker CT?

 

[waross]

Is this revenue metering or protection metering?
Link

LinkApplication-specific features include:
Continuous data recording of up to 13 specified quantities
10 onboard communication protocols
2 RS-232 ports, an RS-485 port, fiber optic port, and an optional Ethernet port
A second method of Line Drop Compensation especially for distribution substations
Inverse time curve option
kWhr and kVArhr metering
Exclusive ΔVAR paralleling method

It may be productive to investigate the possibility of using the features of the Beckwith or having the features retrofitted if they are not presently available.


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

 

[waross]

A query to management explaining that without the installation of either more CTs or more PTs the Beckwith controller must be removed and the transformer locked on one tap. Which voltage setting should the taps be set on?
On second thought, probably not.

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

 

[stevenal]

The Beckwith controllers I'm familiar with take a single current and a single voltage input for one element metering. Power is calculated by multiplying by three. For accurate low side metering, you need 3 element metering. I have found slipover CTs to be a handy way to make up for lack of internal bushing CTs.

 

[jwatty]

The PT connection is going to phase shift 30 degrees to match the transformer phase shift (hopefully). At most you're going to get a decent operational watt reading + amp reading from the meter. You're going to be blind to the VARS lost in the transformer itself, so you're not going to get a reliable power factor measurement. I don't believe the PM174 is capable of handling the math necessary to try to correct that.

I agree with Stevenal, get some slip over CTs.