Our firm recently did an Arc Flash Study for a new lineup of 4.16kV switchgear equipped with Eaton FP5000 relays. One Main, One Tie (to an existing lineup) and 8 Feeders make up the lineup. In addition to the normal selective coordination, we enabled the Zone Interlock function and tested this week. A Fault on the feeder should hold off the fast trip of the main, but its not. Has anyone else had issues with this application?
Zone Selective Interlocking for Arc Flash reduction
- Thread starter dball
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- Wisconsin
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- PE (Retired) - Power Systems
Sounds like an installation error, not an application one.
zog
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- Charlotte, NC
Do they have everything hooked up for the ZSI? Pretty common for plants to have relays for ZSI functions available but not as common for all the cables to be ran and connected. How did you do your ZSI tests? All the ZSI jumpers removed?
Yes, we verified continuity of twisted pair connection between all of the relays. The (8) feeder relays have their outputs paralleled into the inputs of the main relay and tie relay. The main and tie are electrically interlocked, so either the main or the tie will act as the (Upstream Zone 1) device.
To test, we applied current (above the feeder relay pickup value) to both the Main and Feeder phase elements, through the relay test switches. We connected the trip output of the feeder relay to our test set so that the test current would interrupted when the feeder trips. Everytime, the Main tripped first. I have called Eaton, but apparently even they have no explanation. Eaton's relay sends a blocking signal (5V) when the feeder's pickup is reached, otherwise the selective coordinated settings reign.
I'm not sure which jumpers you are referring to. There are no jumpers on the relay's Zone interlock terminals.
SG-1
Senior Member
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- Ware Shoals, South Carolina
If I am remembering correctly the 5V signal just tells the upstream device to use its programmed settings, which should be above or longer than the downstream device.
When the upstream device sees fault current & does not receive the 5V signal & the zone interlocking is enabled, then the upstream device fast trip should activate, to mimic a bus differential relay. I will try to verify this later today.
Please check the trip settings in both FP5000 relays.
You can force the 5V signal out through the front panel & measure it at the upstream relay.
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SG-1
Senior Member
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- Ware Shoals, South Carolina
My memory banks seem to be operating within normal parameters.
Do you have the application notes ?
http://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/ap02602002e.pdf
With the zone interlock system off, which breaker trips first ?
Do you have the application notes ?
http://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/ap02602002e.pdf
With the zone interlock system off, which breaker trips first ?
I have had the Application Notes and have read them over and over. There is some rather ambiguous text in there that mentions a jumper on the last device in the final zone. I'm not sure if this applies to the FP-5000 and our scenario. The guys at Eaton are not sure either, and we haven't tried that.
With the ZI disabled, the main and feeders trip as expected. Feeder clears the downstream faults and the Main (or Tie) clears the bus faults.
One thing worth mentioning; This lineup is currently not energized. We are testing with the breakers racked-out, but with the control harness engaged so the breakers actually trip. This is GE Powervac gear. Thanks for the replies. Hopefully a light bulb will go off soon.
I believe we have an explanation. I was wrong when I said the feeder tripped first with ZI disabled. We have made an embarrassing error in our test procedure. Since the Main CT ratio is 3000:5 versus 600:5 on the feeder, the Main is seeing 5 times the current, so even though the Zone-Interlock signal is active from the Feeder output, it only blocks the main's ZI instantaneous trip, not the normal overcurrent trip. So here's what is happening;
With 40 amps (secondary) injected into the test switches of the feeder and main we are basically getting 5 times the primary current in the main. In which case the main trips slightly before the feeder. Even though this cannot physically happen, the results are as expected based on our curves. The Main relay target shows normal 51 trip, while the feeder relay shows a ZI trip. We plan to test it now for the ground elements, and see if the ZI operates as expected. Since the ground CT ratios are all 50:5, we should get the same current through both relays.
Normally when we test relay settings, we dont inject into two relays simultaneously, hence our mistake.
Thanks for asking the right questions to make the light bulb go off, or on, depending on how you look at it.
With 40 amps (secondary) injected into the test switches of the feeder and main we are basically getting 5 times the primary current in the main. In which case the main trips slightly before the feeder. Even though this cannot physically happen, the results are as expected based on our curves. The Main relay target shows normal 51 trip, while the feeder relay shows a ZI trip. We plan to test it now for the ground elements, and see if the ZI operates as expected. Since the ground CT ratios are all 50:5, we should get the same current through both relays.
Normally when we test relay settings, we dont inject into two relays simultaneously, hence our mistake.
Thanks for asking the right questions to make the light bulb go off, or on, depending on how you look at it.
SG-1
Senior Member
- Location
- Ware Shoals, South Carolina
The signal to the upstream FP5000 tells it to use the normal trip settings. The downstream relay is saying, " I got this ". If the downstream breaker does not trip, then the upstream breaker will still trip using it's normal settings.
If the down stream FP5000 does not send a signal that it "sees" the fault then the Main relay is thinking " bus fault" because it alone is sensing the over current & should override the normal settings for a fast trip.
You could change the Mains CT ratio to match the feeder for the secondary injection test, then change it back.
Sounds like you are making progress, good luck !
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As I recall it appears that hasn't changed since the old Westinghouse zone interlocking method. In my younger days I used to have the ability to call the engineer who designed it ask him directly. But as I recall you have described it very well.
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