Switching of Analog Voltage Inputs 1

[Mbrooke]

For switching analog potential inputs via auxiliary relays, would option A or option B go into practice? Why or why not so?

When a 421 or 311C looses voltage inputs for a few milliseconds, how long does it take for the relay to recover with and without LOP enabled?

If I was to place re-closing and sync check away from the relay in question and use VAZ, VBZ, VCZ (terminals 19-24) for my second voltage input could I configure the relay to "select" analog values based on MOD (open/close) aux contact inputs? And do this seamlessly (without dropping 21p/g protection) when switching between busbars? Could I use freeform logic to configure the relay such for the loss of a normally selected voltage input the relay would automatically select the other provided an input told it the bus coupler and its associated disconnects are closed?

I wish SEL would make a relay with more voltage inputs along with the required logic required with such schemes. My only gripe, other than that I love SEL.

https://files.engineering.com/getfi...4f7b-42a7-a726-a1b7ffcaebf7&file=IMG_1519.jpg

 

[waross]

Take your voltage signal from the input of the CB.
That will be more dependable than switching inputs.
Ride through?
Use the limit switches to inhibit a trip if neither D1 nor D2 are closed.

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

 

[thermionic1]

Its pretty easy to switch SEL 400 series voltage inputs.

https://selinc.com/api/download/117109/?lang=en

is an example of metering. I believe its a 4-8 cycle delay between switching (different parts of the manual say different times).

Some older distribution stations in my area utilize a similar Aux relay scheme to transfer voltages (xfmr side) on a M-T-M for SCADA metering.

IIRC the internal LOP delay is 15 cycles.

 

[Mbrooke]

@Waross: 3 CCVTs on the outgoing line? You're to practical! I was hoping to avoid SOTF, but, that might be a much better alternative.

Will the 421/311C automatically know which bus to draw its sync/reclose voltage from?


@Thermonic1: Thanks! I just looked, LOP can indeed be used to switch over to the another set of 3 phase voltage inputs. I'll just have to take one extra copper input run through the aux of the bus coupler breaker and its discos into account.

Is 15 cycles to initiate LOP or 15 cycles to come out of LOP?

 

[bacon4life]

In the 321 the LOPD is a settable timer, not sure about the two relays you are using. We routinely have LOP incorrectly operate for remote faults.

Be aware the pickup and dropout times for contactors can be quite different. Depending the on the contactor, there could be some amount of contact bounce as well.

 

[Mbrooke]

We routinely have LOP incorrectly exert for remote faults.

Can you give me more info/detail? I've been looking for exactly this anecdote for some time but haven't been able to find any. It would mean a lot to me if you could share what you know about these events.

 

[bacon4life]

See

https://www.eng-tips.com/viewthread.cfm?qid=459352

regarding LOP misoperations.

 

[Mbrooke]

I know. I was wondering if you've had more invents since or learned more regarding them. Its alright if you haven't or can't share more detail. No push.

I also want to add: You are not the first utility to encounter LOP asserting for remote faults. I can't give away which POCOs or who told me but it is indeed happening in the real world.

 

[bacon4life]

In our EMS (SCADA headend) we added a timer to all LOP status points so they have to be in the alarm state for at least 30 seconds before the EMS sends an alarm to dispatchers. I assume the relay LOPs continue to occur, but I stopped paying attention to this issue once the LOPs stopped showing up as nuisance EMS alarms.

 

[Mbrooke]

Appreciate your input. It seems like this is indeed an issue but hush-hush for some reason. I've had EEs tell me it can't happen unless a real LOP event actually took place like a blown fuse but at the same time I had an EE come to me saying that during hurricanes line faults were triggering LOP and LOP alarms.

When I think of relaying settings I don't think of blue sky days or even terms of N-1-1 but something like two dozen transmission lines out of service.

 

[davidbeach]

As long as the LOP condition doesn't latch in the momentary assertion during faults isn't much of an issue.

What can be more interesting is doing something similar to detect CT issues - negative sequence current without a corresponding negative sequence voltage. If there's the possibility of currents taking different routes, they will. It can take small differences in impedances, even differences due to non-transposition, to make loops or parallel paths behave oddly.

We had one instance several years back that a temporary system configuration resulted in one substation being the balance point on a loop, two lines and power into the station on both lines. But one of the lines supplied most of the phase A and phase C current while the other line supplied most of the phase B current. The CT fail logic didn't like that. Over time, the CT fail logic has found far more problems on the system on the primary side of the CT than on the secondary side.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

Ok, so I have this:

(Numbers are off, I am well aware that)

Step distance and directional over-current from the transmission line, sync and reclose from the busbar.

My question is, could I eliminate the aux relays and wire directly into the SEL relay? Do I need logic or will the relay "select" automatically?

With the bus coupler open I could have very different phase angles, even different frequencies during restoration procedures.

https://files.engineering.com/getfi...75e-4a81-b98b-240127fc6371&file=VT_Inputs.jpg

 

[davidbeach]

Take both single phase voltages into the relay. One becomes VS1 and the other becomes VS2. Then use logic to determine if it should synch-check using VS1 or VS2. That's based on getting the 3-phase voltage from the line.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

Thanks David

 

[Mbrooke]

Oh- so I don't have to ask again in the future- can I do VS1, VS2 and VS3 should I ever run into a triple busbar scheme or am I limited to just VS1 and VS2?

 

[davidbeach]

The relay only has VS1 and VS2, but you can roll your own VS3 in free form logic. Not sure how easy a full synch-check would be to write, but magnitude based supervision would be easy enough.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

Awesome! I'll give it a try. That might be good enough based on what we are doing.

Happy Thanksgiving btw. May yours have lots of Turkey!