Revenue Meters 1

[Sanchez01]

Need to get your input on going from multi ratio revenue meter to single ratio.
Only the CT discrepancies are listed:
The existing one:
200/400:5 DR with 1.5/2.0 RF
Thermal rating: 3000 VA

Proposed one:
200:5 SR at 4.0
Thermal rating: 4000 VA

The VT ratio (700/1200:1:1), accuracy (0.3W,X,M,Y,X,ZZ), nominal system voltage (138kV), BIL=650 kV are all same.

Would the proposed meter work? Since RF is higher, the max primary current will be same as the existing one.

Let me know if further info is needed.

 

[scottf]

You're listing a thermal rating in VA for the CTs....that should be for the VT, not the CT.

In regards to your question, if you currently have 400:5A, RF1.5 (600A continuous) and you want to replace with 200:5A, RF4.0 (800A continuous), then yes, that will work.

Also, you ask "will the meter work" and I believe you mean, "will the instrument transformers work". Note that you'll need to reprogram the meter with the new CT ratio (change the meter multiplier).

 

[Sanchez01]

Thanks Scotf

However, since it is a dual ratio meter, 200/400:5 with 1.5/2.0 RF; I think 1.5 applies to 200:5 ratio and 2 applies to 400:5 ratio. Hence, the continuous amps is 400*2=800 amps. Since the new one has 200:5 with RF 4, i.e. 200*4=800 amps that should work. Do you agree?
Ok, the thermal rating might be for VT but now that we are going down from 4000 VA to 3000 VA, I guess I have to check what kind of insulation and wirings that are used to make sure we don’t have thermal overheating issues right?

 

[scottf]

Please note, the "meter" is not dual ratio...the "CT" is dual ratio.

For a 200/400:5A 138 kV CT, the RF2.0 will apply to the 200:5A tap and the RF1.5 will apply to the full 400:5A winding.

No...the thermal burden rating is likely not an important parameter. It defines how much power the VT can output without exceeding the temp rise rating. Since you're using the VTs for metering, you don't need to worry about the thermal burden rating.

Your meter will likely draw less than 1 VA and electronic relays that may be on the circuit will draw less than 1VA each. The accuracy rating of 0.3 WXYZ,ZZ means that the VT will maintain a 0.3% accuracy class when loaded up to a ZZ burden, which is 400VA. You'll be hard pressed to ever exceed 10-20 VA burden these days with electronic devices.

Bottom line...use #12AWG and be done with it.

 

[Sanchez01]

Scottf
Appreciate the response. To me it is kind of counter intuitive that when a CT has 200/400:5 with 1.5/2.0 RF, the 1.5 factor applies to 400 NOT 200 and 2.0 applies to 200 not 400 (first to first, second to second). But since you are more exposed to this I will take your word for it.
Thanks again.

 

[scottf]

I suspect the RF is recorded backwards.

For HV CTs, the primary conductor is almost always the limiting factor for the rating factor.

For a tapped secondary, the highest RF is almost always for the tap winding and the lower RF for the full winding.