Why would there be a different relay settings on Each incoming phase?
Why would there be a different relay settings on Each incoming phase?
(OP)
I'm drawing the SLD for an existing wheat terminal facility that was designed in the early 70s and they have ABB CO-9 (Westinghouse) relays protecting the the incoming 12.5kV service feed.
There is three relays as each relay protects one phase.
However, I noticed this odd observation.
The middle relay is marked "Neutral." It has the following settings:
4 (pickup)
.5 (Time Delay)
The left and right relays have:
10 (pickup)
1 (Time Delay)
Any speculation as to why the middle relay is labeled netural and has different settings? Different CT ratio maybe?
I'm sorry, I don't have any other info, I don't even know what the CT ratio is, but the incoming line is measuring 28A and it is feeding a D-Y Step down Dry Type XFMR.
This might be a dead end as more information might be needed, but I would be curious to read what it could be.
There is three relays as each relay protects one phase.
However, I noticed this odd observation.
The middle relay is marked "Neutral." It has the following settings:
4 (pickup)
.5 (Time Delay)
The left and right relays have:
10 (pickup)
1 (Time Delay)
Any speculation as to why the middle relay is labeled netural and has different settings? Different CT ratio maybe?
I'm sorry, I don't have any other info, I don't even know what the CT ratio is, but the incoming line is measuring 28A and it is feeding a D-Y Step down Dry Type XFMR.
This might be a dead end as more information might be needed, but I would be curious to read what it could be.






RE: Why would there be a different relay settings on Each incoming phase?
RE: Why would there be a different relay settings on Each incoming phase?
RE: Why would there be a different relay settings on Each incoming phase?
I love you guys :)
That does make sense as all phases are protected anyhow. If it was a Phase to Gnd fault, then the gnd relay would protect the phases and if it was a phase to phase fault, then the other two relays would still provide protection. Why did they stop doing it this way?
Lack of redundancy?
RE: Why would there be a different relay settings on Each incoming phase?
RE: Why would there be a different relay settings on Each incoming phase?
Then this must also mean that they are protecting the Low Side as the H.V. service is connecting as Delta and assumed ungrounded.
RE: Why would there be a different relay settings on Each incoming phase?
If there is an analog ammeter, the range of ammeter is probably the same as the CT ratio.
RE: Why would there be a different relay settings on Each incoming phase?
Yeah you are right, I didn't consider that it can be feed from a grounded substation upstreams some wheres. I wish we can edit our posts, but this option seems to be unavailable in the Eng forum.
RE: Why would there be a different relay settings on Each incoming phase?
That is wicked! Thanks a lot DPC! :)
RE: Why would there be a different relay settings on Each incoming phase?
respectfully
RE: Why would there be a different relay settings on Each incoming phase?
RE: Why would there be a different relay settings on Each incoming phase?
Agreed. When I said amazing rule to know... I meant to say "rule of thumb." Not always true, but most times.
RE: Why would there be a different relay settings on Each incoming phase?
I have another incoming service at the opposite side of the same factory. About 20ft up, the cable comes out of the wall (3 conductors only, no fourth conductor ie no gnd, no neutral) and it then becomes a bare HV 12.5kV bus bar.
http://i4
(The Incoming 12.5kV service is red and shown in the background.)
The buses go into a CB switchgear, back out, two phases then go through CTs (one phase does not have high side CT) and then into a delta to delta 12.5kV/600V transformer.
The CB switchgear also houses these OLD ASEA RI relays. http://
The top relay is different than the other two, it has a faster time setting and a smaller current pickup. As we discussed, it is probably the gnd relay, and the other two are protecting the HS phases into the Step down XFMR. What I do not understand is how is the gnd relay setup? How can the system tap into the ground path? The incoming service is just three wires. Thus, the only way to provide gnd protection would have to be a zero sequence CT somewheres on the HS bus bar that I haven't seen. My reasoning is that even if the incoming service provides a gnd return conductor and there is a relay on it, it may not provide any protection. If one of the bus bars breaks and falls to the ground, the current can bypass the gnd relay as the current may not flow through the ground conductor but through the ground itself back to the substation upstream XFMR which is about 1.5km away. I've seen GND relays just before the GND point on upstream XFMR, but this location is so far from the feeding substation, thus a Zero sequence CT is the only possibility.
RE: Why would there be a different relay settings on Each incoming phase?
I'm sure, that Dpc explanation is true.
( After some old BBP, that we see in the forum, I don't know, maybe you found for us new type of connection with intr CT into protection cubicle)
You cancelled two possible connection:
1. ZS CT on bus bar.
2. Connection to ZC CT on the neutral point of upstream xfr.
As I understand , you haven't design of protection cubicle.
You need open cubicle with ASEA relays and check connection of current wiring.
On this way possible found something in old configuration.
Regards.
Slava
RE: Why would there be a different relay settings on Each incoming phase?
Today I found manual of this RI relay, may be it will be intresting for you (I looking for some old ASEA distance relay and found both of them).
Attached.
htt
Regards.
Slava