What do you think of these phase angle readings? 1

[westex]

Part of our relay maintenance procedure we have to prove that the current and voltage inputs to the relay are correct. When we triggered the event (screen shot provided) on the SEL-311C (substation A) we saw that the phase angles didn’t quite make sense (IB was almost in phase with VA). When talking to the boss he said something is wrong. We than compared the SEL phase angle readings to the bus diff relay and all the readings were the same. Doing that just proved that if the line relay readings (SEL-311C) are wrong so is the bus diff readings. We also went to the other end of the line (substation B) to check those readings expecting those to be 180° different than (substation A) and they were. So we can’t find anything wrong but boss still says asks how can our angles look that bad. I know power factor and vars could throw the readings off. If these reading are correct (and I believe they are) what good is “proving” the inputs to the relay in this case? Also how would you explain these readings? If anyone has AcSELerator Analytic Assistant and wants to look more at the event I can provide that.

 

[PHovnanian]

How are the PTs and CTs connected? (Delta, Wye, etc.)

Are there any relay settings that would compensate for wiring/phasing differences? How are they set?

 

[Skogsgurra]

Is this a 40 kV system?
If it is, then your VTs are connected in delta and that adds 30 degrees to the phase angle. Or does the system correct for that?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[westex]

How are the PTs and CTs connected? (Delta, Wye, etc.)

Are there any relay settings that would compensate for wiring/phasing differences? How are they set?

PTs and CTs are Wye.

As far as the settings not sure what you mean by that, please explain

 

[DTR2011]

There are certain SEL relays that can accommodate for delta connections.

Could you list the model numbers of the relays involved?

 

[westex]

Could you list the model numbers of the relays involved?

The SEL-311C I only number I have is the FID=SEL-311C-R110-V0-Z005004-D-20060320

The readings on all the other equipment are the raw readings in the relay test switches.

Yes this is a 40Kv L-N 69Kv L-L

 

[davidbeach]

How big is the capacitor bank?

 

[Skogsgurra]

OK, the VTs are wye connected, then. So, if everything is correct, I can't see any other explanation than there isn't one - or that you are heavily overcompensated. Extremely. Was this reading taken when station was very lightly loaded?

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[westex]

How big is the capacitor bank?

I know they just installed a new fuseless one at substation B. Think it's 15.6M mvar. You think thats why?

 

[davidbeach]

The "load" on the line is mostly a capacitor bank.

 

[waross]

Nice call David. Do you think that the capacitor bank may be running at about 2 MVAR?

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

 

[PHovnanian]

Next question: Which protection functions of the SEL-311C are enabled or disabled?

Its possible that you do have a real connection problem. But you've never seen it because you aren't using functions that use an I/V relationship (Distance, Directional Overcurrent, etc.). My money is still on some delta/wye setting or display discrepancy.

 

[westex]

"Which protection functions of the SEL-311C are enabled or disabled?"

This relay (SEL-311C at substaion A) is used for DTF (distance to fault) on a electromechanical relay plane only.

"My money is still on some delta/wye setting or display discrepancy."

If this is the case how can I explain the why other end of the line at substaion B being the same as substation A only 180° out?

 

[PHovnanian]

I think I'm going to change my answer to 'capacitor bank' as well. The magnitudes suggest a very light load (assuming these are primary numbers).

How are your substations (A and B) configured w.r.t. the bank location, open breakers, etc?

 

[westex]

How are your substations (A and B) configured w.r.t. the bank location, open breakers, etc?

Cap bank is at substation B and now that I've talked with our control center they have had this bank in for the last week or so if that answers your questions about breaker status. There is an auto 138Kv to 69Kv at substation B. The 69Kv bus at B only has one other line on it that feeds a radially feed sub.

 

[vandal06]

I'm with David on this one. That looks like loading due to the capacitor bank, resulting in your IA leading VA by close to 90 degrees. This is further corroborated by your relays at substations A and B agreeing when their instrument polarities are compensated for.

 

[PHovnanian]

You have either very light loads at the remote station. Or something is open such that the line between stations A and B is only feeding the caps and the other loads are being fed from another source.

 

[davidbeach]

So, I can't help but wonder why the heck you'd use a 311C as just a fault locator and continue to use electromechanical relays for tripping? I'd be rid of the EM relays at any opportunity.

 

[7anoter4]

If the measured currents and voltage sequence are checked and found to be as measured then this is not fundamental wave measured as angle more than 90 degrees it is impossible. So check how THD% is and filter the fundamental. First of all shut down the capacitance bank and check another time.

 

[davidbeach]

Given that the data is from an SEL-311C, the values are only fundamental. There aren't many Watts involved, just a lot of VArs. At low power flows it is entirely possible that one phase can have Watts in the opposite direction of the other phases. Also, between CT errors, VT errors, and relay errors there can be differences in how the phases are measured. I'd also suspect that the image is from the first sample in the event report; I always go into the event a cycle or a bit more before I start using the phase angles.