Calculating line impedance for distance relaying

[mbrooke]

You could also make use of google.. Hihi


Sent from Mars

Google is about as accurate as asking a fortunate to determine your health.

 

[rian0201]

Do you do that for new T-lines? If so, is the test performed and then the values are sent to the relay engineers?

Yep, they sent this sequence impedances to the relay engineers.

They can measure t line by shorting the line at the t connection, and measure the ends one at a time.

 

[rian0201]

Google is about as accurate as asking a fortunate to determine your health.

Maybe, if you provide wrong key words. When you ask the link, I just searched it, and i found it immediately, rather than waiting in the forum.

 

[mbrooke]

Maybe, if you provide wrong key words. When you ask the link, I just searched it, and i found it immediately, rather than waiting in the forum.

Because you know exactly what your looking for, and you know if its correct, dated, ect.

 

[rian0201]

Of course, but i said omicron in the previous post havent i? You could use that term or keyword..


Sent from Mars

 

[mbrooke]

Of course, but i said omicron in the previous post havent i? You could use that term or keyword..


Sent from Mars

I mean yes, there is this, but how do I find the tester out of so many?


https://www.omicronenergy.com/en/

 

[rian0201]

I mean yes, there is this, but how do I find the tester out of so many?


https://www.omicronenergy.com/en/

Hmm... They have a search engine within.

 

[mbrooke]

Hmm... They have a search engine within.

Lets just say Im internet challenged


Anyway, that measurement device looks really neat, and dare I say more accurate?

 

[Bugman1400]

Yep, they sent this sequence impedances to the relay engineers.

They can measure t line by shorting the line at the t connection, and measure the ends one at a time.

Have you been able to do a comparison between what was calc'd and what was measured to see how close they are?

 

[Bugman1400]

I have never seen a set of 3PH line VTs for a straight bus application. It would be much cheaper and more reliable to provide a backup up set. In the E-M days, a voltage balance relay would be used to switch between the two sets of bus VTs. Typically, LOP is alarmed on via SCADA. I would expect that whatever would cause a bus VT fuse to pop would cause ALL the line VTs to do the same.

Just saw a design by a large utility where they use 3-PH line VTs on a straight, double-bus application. Boy, this crow sure taste bitter.

 

[mbrooke]

Just saw a design by a large utility where they use 3-PH line VTs on a straight, double-bus application. Boy, this crow sure taste bitter.

Get with the times, everyone is doing it now!


Single breaker double bus or double breaker double buss? In dual breaker designs those 2 CT input relays actually require it, but optional for straight bus. If the latter I wonder if they have the same concerns as I do.

 

[rian0201]

I think they are using line vts on the double bus, so that there will be no changing of pt source to the relay.

This is the case for breaker and a half systems,.. The pts at connected at the lines for line protection. And we also placed another pts at the bus for the other protection requirements.

But for our single bus systems, we just placed the pts on the bus.


Sent from Mars

 

[mbrooke]

I think they are using line vts on the double bus, so that there will be no changing of pt source to the relay.

This is the case for breaker and a half systems,.. The pts at connected at the lines for line protection. And we also placed another pts at the bus for the other protection requirements.

But for our single bus systems, we just placed the pts on the bus.


Sent from Mars

How do you deal with a blown secondary CVT fuse in your case?

 

[rian0201]

Calculating line impedance for distance relaying

Change the fuse?

We are SEL311L using at that time. When the PT fails, for example, LOP alarms, schedule a shutdown. At that time we will rely on our line differential.

Sometimes, there will be duplicate systems, as per required in our utility. There will be two pts separate of each relays of different kind.

But still, it is a matter of preference, i think..

If we use two pts, we could always ask, what if two pts fail?


Sent from Mars

 

[mbrooke]

Change the fuse?

We are SEL311L using at that time. When the PT fails, for example, LOP alarms, schedule a shutdown. At that time we will rely on our line differential.

What happens when communication is out and the unit is under LOP? Not trying to be difficult, just genuinely curious.

Sometimes, there will be duplicate systems, as per required in our utility. There will be two pts separate of each relays of different kind.

But still, it is a matter of preference, i think..

If we use two pts, we could always ask, what if two pts fail?


Sent from Mars

2 3 phase PTs? Well its less likely two will fail at the same time imo. And I just want to share that I've moved on the secondary PT fuses blowing rather than the PT short circuiting. A shorted PT will clear a breaker or bus.

 

[rian0201]

What happens when communication is out and the unit is under LOP? Not trying to be difficult, just genuinely curious.

Hmmm.. No choice, overcurrent, i think. But that's the only contingency we anticipated. If you want your system to be reliable on that condition, you have have to design it solving that problem.

It is like saying, what if the dc supply fails? Or relay failure?

Haven't experienced it though, but i think if the above happend, LOP and comm out, it will alarm SCADA it could immediate shutdown of the line or hope for the backup at the adjacent line. But over current is still there. Or install a separate relay with separate comm..

But still a question is ask, what if both comm and LOP? Well, lets pray it happen. Hehe..

2 3 phase PTs? Well its less likely two will fail at the same time imo. And I just want to share that I've moved on the secondary PT fuses blowing rather than the PT short circuiting. A shorted PT will clear a breaker or bus.

In my experience, PT shorting resulted in an explosion of PT, it was blue fire, pity i did not filmed it.

 

[mbrooke]

Hmmm.. No choice, overcurrent, i think. But that's the only contingency we anticipated. If you want your system to be reliable on that condition, you have have to design it solving that problem.

Which IMO would involves line connected VTs. That way if a VT open circuited it would at remove the step distance protection from only one line instead of say 12 of them.

It is like saying, what if the dc supply fails?

Backup supply takes over.

Or relay failure?

The other relay takes over as designed.

Haven't experienced it though, but i think if the above happend, LOP and comm out, it will alarm SCADA it could immediate shutdown of the line or hope for the backup at the adjacent line. But over current is still there. Or install a separate relay with separate comm..

But still a question is ask, what if both comm and LOP? Well, lets pray it happen. Hehe..

Well, one day it will happen. It only a matter of time as experience has taught me.

In my experience, PT shorting resulted in an explosion of PT, it was blue fire, pity i did not filmed it.

That must've been one of those days :lol::rant: How many Kv primary was the PT?

 

[Bugman1400]

Multiple element failures like an LOP with a loss of comm on a 311L would typically result in a line outage. I rarely see phase overcurrent protection used on a networked line. An alternative would be to see if the line is protected by upstream/remote relays in a Zone 2 or Zone 4 (depending on how long the line is). However, that is typically not enough to persuade the Transmission Planning folks to allow the line to stay in-service.

 

[mbrooke]

Multiple element failures like an LOP with a loss of comm on a 311L would typically result in a line outage.

In practice, yes. The relays can be programmed to do anything the user desires.

I rarely see phase overcurrent protection used on a networked line. An alternative would be to see if the line is protected by upstream/remote relays in a Zone 2 or Zone 4 (depending on how long the line is). However, that is typically not enough to persuade the Transmission Planning folks to allow the line to stay in-service.

But if you want to keep the line in service while not taking out an entire substation for a fault, over current is the only reasonable solution. My understanding is that remote zone 2 or zone 3 will clear all the lines feeding into that station in question. The only risk with over current is misscordination (nondiscrimination); nothing more.

 

[mbrooke]

Multiple element failures like an LOP with a loss of comm on a 311L would typically result in a line outage. I rarely see phase overcurrent protection used on a networked line. An alternative would be to see if the line is protected by upstream/remote relays in a Zone 2 or Zone 4 (depending on how long the line is). However, that is typically not enough to persuade the Transmission Planning folks to allow the line to stay in-service.

Which brings me to this: a 311C or 421 without differential or communication. For an LOV you can either trip the line, switch to over current protection only, or do nothing (no line protection). Correct? With line VTs only one set of relays have to make this hard choice, but with bus VTs either all of group A or group B (if not both) must decide.