In looking at a previous relay setting table I came across something I was hoping someone could help me interpolate. The relay in question is a Westinghouse CO-8 style, that I understand now that belongs to the ABB product line as they purchased the Westinghouse CO product line. The table indicates C/T ration of 600/1 with a 2400A trip with the tap set at 4 and the time dial set at 5. However there is a column that indicates pick up at 6x tap equal to 92? What is the “pickup at 6x tap” and how is it calculated at 92?
Westinghouse CO-8 settings?
- Thread starter Mike01
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mayanees
Senior Member
- Location
- Westminster, MD
- Occupation
- Electrical Engineer and Master Electrician
That 6X pickup point is given as a timing mark for the tester, or for your TCC curve. Using the given tap of 4 and Time Dial of 5, apply 6*2400 and it should cross the curve you've developed at a time corresponding to the 92 number that's given.
Bugman1400
Senior Member
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- Charlotte, NC
To add, the tester would inject 6 x 4amps (24A) into the relay and make sure the relay trips in 92 cycles. Typically, there are at least 2 points on the curve that are tested....ie. 6X (6x4=24A) and 3X (3x4=12A).
mivey
Senior Member
I rounded before but the closer value is TD 4.56.
The times I had at 6x were (scaled off of computer screen):
Time Dial 5: 1.685 seconds at 6x
Time Dial 4: 1.340 seconds at 6x
Time Dial 4 to 5: 1.685 - 1.340 = 0.345 seconds
6x setting: 92 cycles or 1.533 seconds
Time Dial 4 to 6x setting: 1.533 - 1.340 = 0.193 seconds
Time Dial 4.x = 4 + 0.193/0.345 = 4 + 0.56 = 4.56
Bugman1400
Senior Member
- Location
- Charlotte, NC
if you've set CO-8 relays or any EM relay you know that 6x at 92 cycles could be at the 4.5 hash mark or anywhere in between 4.0 and 5.0. You typically set the timedial based on the trip time, not the hash mark on the timedial.
mivey
Senior Member
Of course. But we also note the time dial on the relay sheets in addition to the cycles to trip.
Bugman1400
Senior Member
- Location
- Charlotte, NC
Interesting......that is one way to do it. I guess it lets you know approximately where your time dial should be. We just list the time dial as 500% @ 30cycles. As you always hear..."That's the way we've always done it." Perhaps it is done this way to prevent the tech from setting the time dial without testing.....not sure though.
mivey
Senior Member
Knowing the approximate TD can make life easier in the field and in some coordination applications. There are many times I wished someone would have written it down so I did not have to go look it up or figure it out. For some applications I know a low TD on a ground relay does not coordinate with fuses as well as a high TD will. Can be a quick answer as to why a station breaker is tripping before a tap fuse and I don't even have to draw the curve to know the problem.
CO-8 instantaneous follow up?
CO-8 instantaneous follow up?
As a follow in looking at some with indicating instantaneous trip units, there are three taps available 6-20; 20-40 & 40-144. When the tap is in either of these [for example 40-144] how can you tell what value it is set at? There is a small “set screw” in the center that can be twisted [dialed up / down] I assume this sets the rating but how can one tell what that setting is without removing the whole CO-8 unit?
CO-8 instantaneous follow up?
As a follow in looking at some with indicating instantaneous trip units, there are three taps available 6-20; 20-40 & 40-144. When the tap is in either of these [for example 40-144] how can you tell what value it is set at? There is a small “set screw” in the center that can be twisted [dialed up / down] I assume this sets the rating but how can one tell what that setting is without removing the whole CO-8 unit?
Phil Corso
Senior Member
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- Boca Raton, Fl, USA
Mike...
You can if it's old-fashioned, i.e., in a withdrawable-case!
Regards, Phil Corso
You can if it's old-fashioned, i.e., in a withdrawable-case!
Regards, Phil Corso
mivey
Senior Member
You have to run a current ramp and see where it trips. Without that, the best you can do is get a rough estimate based on the screw position, probably a low-middle-high position in the selected range.
The further the screw comes out (up), the higher you are in the range. Some used to have a gauge with range marks. Without that, full range is roughly the height of the plate seen behind the screw plus a bit more. If you have a feel for the positions, you might estimate within 10-20%. Without that feel, you might be limited to a low-end vs. high-end observation.
I do have a copy of the Westinghouse I.L.41-100 type CO (Hi-Lo) Over current relay and am having difficulty trying to identify what is being referred to.
Check this document out, this is the one that I have:
https://www.google.com/url?sa=t&sou...QWHLiOiPQ2ffIvvGQ&sig2=Sye13v-8NBThlEK-FCc_aA
This is a second one:
https://www.google.com/url?sa=t&sou...r570NaWai52_T1YeaYsQ&sig2=dos1VCz5Blw6xjVGE5_
Check this document out, this is the one that I have:
https://www.google.com/url?sa=t&sou...QWHLiOiPQ2ffIvvGQ&sig2=Sye13v-8NBThlEK-FCc_aA
This is a second one:
https://www.google.com/url?sa=t&sou...r570NaWai52_T1YeaYsQ&sig2=dos1VCz5Blw6xjVGE5_
mivey
Senior Member
Inst. Value
Inst. Value
Correct, in the second link [page 3, figure 4] shows the image of the instantaneous trip unit with what I call the "ticker tape" type that actually indicates the trip setting on the indicating metal tape, however some of the newer ones installed [see attached image] do not have this and only have the indicating set screw and associated trip unit with no way to verify [visually] the actual inst. trip setting and I was not sure if there was a way to "visually" verify the setting without invasive investigation does not sound like it though...thanks
Inst. Value
Correct, in the second link [page 3, figure 4] shows the image of the instantaneous trip unit with what I call the "ticker tape" type that actually indicates the trip setting on the indicating metal tape, however some of the newer ones installed [see attached image] do not have this and only have the indicating set screw and associated trip unit with no way to verify [visually] the actual inst. trip setting and I was not sure if there was a way to "visually" verify the setting without invasive investigation does not sound like it though...thanks
Attachments
Thanks, now it appears to make some sense. The CO-8 is a very ommon relay used in med. Voltage swgr, one per phase, one for the neutrasl for a total 4 located on the front door of each breaker in FT1 drawout cases. There also should be a test plug that is jumpered for use to access the CT circuit for testing purposes. It's been at least 20 years since I saw one of these.
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