Step Distance Transformer

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mbrooke said:
Need some schooling on this one. :dunce: I mean I know what DTT is and how to apply it, just not in the specific scheme.
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Just saw this one. Once you have a fault like you described DTT to the transformer breaker it isolate it. If your wanting to isolate for CCVT fault.
 
Hv&Lv said:
Just saw this one. Once you have a fault like you described DTT to the transformer breaker it isolate it. If your wanting to isolate for CCVT fault.
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Just need to figure how to switch DTT inputs and outputs. Remember, any bay has access to either busbar.
 
I finally found that paper..
I don’t think you would want to rig a LOP as it would try to operate erroneously. It doesn’t happen often, but when it does the LOP doesn’t need to open anything. May be Better off with a 50/51. Besides, I believe the 50/51 will pick up MANY cycles before the LOP.

I don’t really think I would worry too much about a loss of one phase in that type of station. With the breakers, you lose all three or none. You problem with LOP may be more relay wiring than actual problems.

http://www.pes-psrc.org/kb/publishe...oltage_Considerations_for_Line_Protection.pdf
 
Hv&Lv said:
I finally found that paper..
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Big help again. :)

I don’t think you would want to rig a LOP as it would try to operate erroneously.
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What would cause inadvertent operation of LOP? Any real world encounters?


It doesn’t happen often, but when it does the LOP doesn’t need to open anything. May be Better off with a 50/51. Besides, I believe the 50/51 will pick up MANY cycles before the LOP.
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Thats my plan, have LOP activate 50/51 on the trafos. That way the faulty busbar will clear, but the trafos on the other side will not trip since step distance is still working and 50/51 is well above the 50/51 on the LOPing relays.

Sounds about right?



fetch




I don’t really think I would worry too much about a loss of one phase in that type of station. With the breakers, you lose all three or none. You problem with LOP may be more relay wiring than actual problems.

http://www.pes-psrc.org/kb/published...Protection.pdf
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In your own words, why so?

Don't get me wrong, you are way ahead of me. Digesting the paper as I type, will read it over a few more times.
 
mbrooke said:
In your own words, why so?
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There is always the problem of something silly, like a knife switch at a test point that isn’t tight, and arching.
(Guess how I know that??)

connections and terminations being bad. That’s a problem that has to be addressed on every relay.
theres the inadvertent transmission blink. While rare, it happens.

another instance of a real world experience... maintenance on some different relays, pull the voltage knife switches to cut voltage for relay change on a relay other than one that has a LOP setting... say a 734 revenue meter. Sometimes the switches are at a single point in a statin.
 
Hv&Lv said:
There is always the problem of something silly, like a knife switch at a test point that isn’t tight, and arching.
(Guess how I know that??)

connections and terminations being bad. That’s a problem that has to be addressed on every relay.
theres the inadvertent transmission blink. While rare, it happens.
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This! LOP doesn't seem like a good idea now.


another instance of a real world experience... maintenance on some different relays, pull the voltage knife switches to cut voltage for relay change on a relay other than one that has a LOP setting... say a 734 revenue meter. Sometimes the switches are at a single point in a statin.
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Not so much concerned about open test switches. I have the relay set such that loss of voltage will set off an out single which goes back to dispatch.
 
Question- and you don't have to answer, but what does your POCO typically call for when dealing with LOP? Just alarm? I think I might be ok with just alarming.
 
mbrooke said:
Question- and you don't have to answer, but what does your POCO typically call for when dealing with LOP? Just alarm? I think I might be ok with just alarming.
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Our 115kV stations alarm and email through SCADA. The last thing we want is for it to drop out on a blown CCVT fuse, or a transmission blink.
We had several blinks during the last few hurricanes.
I have to respond pretty quick to get it back up. One is in a place where the batteries charge from a CCVT.
 
Hv&Lv said:
Our 115kV stations alarm and email through SCADA. The last thing we want is for it to drop out on a blown CCVT fuse, or a transmission blink.
We had several blinks during the last few hurricanes.
I have to respond pretty quick to get it back up. One is in a place where the batteries charge from a CCVT.
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Basically, the LOP takes longer to dis-engage after the blink is over? Just want to understand exactly what happens.
 
mbrooke said:
Basically, the LOP takes longer to dis-engage after the blink is over? Just want to understand exactly what happens.
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No, the LOP is set to alarm and email through SCADA, as mentioned.
If we set it to open with LOP, then the breaker opens when the transmission line blinks, or a fuse blows between the CCVT and the relays for some reason. We don’t want that.
Also don’t want it closing with a voltage return...
if I get an alarm, I need to see why. Is a fuse blown? Is the CCVT out? Blade open?
I need to keep up with the alarm from our one remote station that charges batteries from the CCVT. Don’t want the batteries to run down.

On a a side note, if your using LOP on your project, are you also using UF? If so you may want to put a low voltage trip block on the UF logic.
Also undervoltage. If your using it you want to differentiate between UF, UV, and complete LOP with blocking logic.
 
Hv&Lv said:
No, the LOP is set to alarm and email through SCADA, as mentioned.
If we set it to open with LOP, then the breaker opens when the transmission line blinks, or a fuse blows between the CCVT and the relays for some reason. We don’t want that.
Also don’t want it closing with a voltage return...
if I get an alarm, I need to see why. Is a fuse blown? Is the CCVT out? Blade open?
I need to keep up with the alarm from our one remote station that charges batteries from the CCVT. Don’t want the batteries to run down.

On a a side note, if your using LOP on your project, are you also using UF? If so you may want to put a low voltage trip block on the UF logic.
Also undervoltage. If your using it you want to differentiate between UF, UV, and complete LOP with blocking logic.
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Oppps my bad, I meant when LOP is used in the relay. :ashamed1:

I'm going to be honest with you... While I can disable LOP here, I typically enable it. Once engaged it triggers an 50/51 set slightly above the lowest anticipated short circuit current at the busbar + the line impedance.

But you have opened my eyes in saying that most loss of potential events are single phase, not 3 phase.

Just seems to go against what senior EEs have taught me, but honestly, you make more sense. Don't tell them I said that :p



No UF, but I could enable supervision via UF and/or UV. Would that help for transmission blinks in any considerable way regarding LOP?
 
Also don’t want it closing with a voltage return...
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The breaker? I've done this think were I've set reclosing so that the breaker closes automatically for hot line hot bus--- basically one breaker cycles the other closes automatically if the lines holds for 15 seconds.
 
mbrooke said:
The breaker? I've done this think were I've set reclosing so that the breaker closes automatically for hot line hot bus--- basically one breaker cycles the other closes automatically if the lines holds for 15 seconds.
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Yes, it works for some places fine. The problem is in some places during hurricanes trees come down across transmission lines. If the breaker opens we want to see why, rather than try it and hope for the best.
if it opens on a pretty day, we want to see why rather than close it and hope for the best.

Hey, maybe that’s some of the reason why California burnt up last year....
 
Hv&Lv said:
Yes, it works for some places fine. The problem is in some places during hurricanes trees come down across transmission lines. If the breaker opens we want to see why, rather than try it and hope for the best.
if it opens on a pretty day, we want to see why rather than close it and hope for the best.

Hey, maybe that’s some of the reason why California burnt up last year....
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Trust me, I'm not touching Cali. I enjoy me reclosing :cool:

Anyway, did you get an answer to reaching half way through the trafo?
 
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