Ground fault Current of Chiller feeder

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mohsan514

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I am facing issue with chiller , we have installed YORK chiller with Full load current of 1200 Amp. ,
Once we are running the chiller , main breaker from MDB is tripping dur to Ground Fault , the strangr thing is Chiller itself has Schneider Breaker and GF setting is at 300Amp , and upstream setting is 450 amp..
Also we disable the Ground fault protection from MDB breaker , chiller worked fine without any tripping.. And we monitor the Ground Fault current from MDB breaker it reaches to 600 Amp ... but chiller was working fine..
We called the experts from York and they confirmed that there is no issue in chiller site , they also Megger the main feeder cable it was OK...
What could be the reason of this??


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mohsan514 said:
I am facing issue with chiller , we have installed YORK chiller with Full load current of 1200 Amp. ,
Once we are running the chiller , main breaker from MDB is tripping dur to Ground Fault , the strangr thing is Chiller itself has Schneider Breaker and GF setting is at 300Amp , and upstream setting is 450 amp..
Also we disable the Ground fault protection from MDB breaker , chiller worked fine without any tripping.. And we monitor the Ground Fault current from MDB breaker it reaches to 600 Amp ... but chiller was working fine..
We called the experts from York and they confirmed that there is no issue in chiller site , they also Megger the main feeder cable it was OK...
What could be the reason of this??


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Click to expand...
Ground fault protection settings depend on the arrangement of electrical equipment and how they are connected when a ground fault occurs. The setting ranges from 10 to 100% of the phase current overcurrent protection setting. As mentioned above, if you have a lot electronics connected, these elements could have triplen harmonics that will cause higher leakage to ground and will cause a trip.
 
Is the upstream GFP tripping while the downstream GFP holds?

Is the problem GFP neutral sensor connected correctly?
 
topgone said:
Ground fault protection settings depend on the arrangement of electrical equipment and how they are connected when a ground fault occurs. The setting ranges from 10 to 100% of the phase current overcurrent protection setting. As mentioned above, if you have a lot electronics connected, these elements could have triplen harmonics that will cause higher leakage to ground and will cause a trip.
Click to expand...
Micrologic.jpg
 
Can you monitor individual phase currents with that MDB breaker? If so, then that might provide an indication of what's happening on the load side of the breaker.
 
Those line currents are reasonably balanced and there's no indication that they are feeding a significant ground fault current. And certainly no where near the large GF current that the breaker is displaying.
And so Jim's suggestion of a problem with a neutral CT or its connections sounds like a plausible reason for your indicated ground fault current.
 
synchro said:
Those line currents are reasonably balanced and there's no indication that they are feeding a significant ground fault current. And certainly no where near the large GF current that the breaker is displaying.
And so Jim's suggestion of a problem with a neutral CT or its connections sounds like a plausible reason for your indicated ground fault current.
Click to expand...
Since we are not using Neutral , Only 3 Phase for the chiller , We disconnect the Neutral CT , still the value is same
 
mohsan514 said:
I believe This issue is not due to harmonic.
We have two chillers both are having same issue . Harmonics are Less the 8%
Click to expand...
Yup, agree. If it is true that the THDi is only 8%, the computed neutral current will be around 24% of the line current --> 84 A! The setting of 450A is more than the expected harmonics current that will flow on the neutral. BTW, although you have tried to coordinate the current settings (450 vs. 300 A), if the actual neutral current is 700ish, it will just be a race between the two breakers as to which will trip first.
Maybe, something is causing that 700ish ground current in your system. We cannot put blames on the breakers as you have measured the Ig, which is really above the setting.
 
mohsan514 said:
Since we are not using Neutral , Only 3 Phase for the chiller , We disconnect the Neutral CT , still the value is same
Click to expand...
Your first post said you effectively had 2 breakers in series, feeder and equipment. Is the ground current the same at both breakers.

Have you looked at the phase currents and angles with a power monitor or are you just using the breaker display.

Is your breaker configured properly for a 3wire load? Some times you need to install a jumper when there is no neutral CT.
 
jim dungar said:
Your first post said you effectively had 2 breakers in series, feeder and equipment. Is the ground current the same at both breakers.

Have you looked at the phase currents and angles with a power monitor or are you just using the breaker display.

Is your breaker configured properly for a 3wire load? Some times you need to install a jumper when there is no neutral CT.
Click to expand...
We have checked the phase current with another Meter , It is same as shown in breaker display. But for Ig we could not verify from another instrument.
Also Breaker is configure as 3P 3Wire system. Yes we jumper the Neutral CT Terminal. Still Ig is same.
 
topgone said:
Yup, agree. If it is true that the THDi is only 8%, the computed neutral current will be around 24% of the line current --> 84 A! The setting of 450A is more than the expected harmonics current that will flow on the neutral. BTW, although you have tried to coordinate the current settings (450 vs. 300 A), if the actual neutral current is 700ish, it will just be a race between the two breakers as to which will trip first.
Maybe, something is causing that 700ish ground current in your system. We cannot put blames on the breakers as you have measured the Ig, which is really above the setting.
Click to expand...
Sir if the cables are single core , unarmored and not laid in Trefoil arrangement , Each phase is laid separately , This Scenario has anything with Ground fault current?? Just to clear my doubt.
 
I'm not at my best in the morning, but....

If the currents in #8 were reported by the breaker, have them been confirmed by separate measurements?

mohsan514 said:
We disconnect the Neutral CT ,
Click to expand...
That troubles me a little- if that CT input isn't being used, is the input shunted or left open? I don't think it should make a difference, but might on that breaker design. If it isn't shunted, I'd do that or connect an appropriate CT without any wire through it and see if the readings change.
 
mohsan514 said:
We have checked the phase current with another Meter , It is same as shown in breaker display. But for Ig we could not verify from another instrument.
Click to expand...
How did you measure the Ig? Did you put a Rogowski coil or other current probe around all three phases of the feeder to see what it indicates as a zero sequence current (which would presumably be a ground fault if there's no neutral)?
If you turn off the chiller, and then its Schneider breaker, how does the indicated GF current change?
 
mohsan514 said:
We have checked the phase current with another Meter , It is same as shown in breaker display.
Click to expand...
Did you use a 3-phase power monitor that measures and records phase angles, or did you just measure current magnitudes one at a time?
 
mohsan514 said:
Sir if the cables are single core , unarmored and not laid in Trefoil arrangement , Each phase is laid separately , This Scenario has anything with Ground fault current?? Just to clear my doubt.
Click to expand...
Please pardon me if I didn't get that. What do you mean by "Each phase is laid separately"? IMO, you don't lay down power cable phases separately! If they are multi-conductor runs, you have to lay all three phases in a conduit; if it's a 3-conductor per phase, you will have all 3 phases in one conduit, have three conduits all in all.
 
Please see the pictures, all phases are laid in a Cable tray..
e45beca8d95e542188fc2be90f35c699.jpg


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mohsan514 said:
Please see the pictures, all phases are laid in a Cable tray..
e45beca8d95e542188fc2be90f35c699.jpg


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Click to expand...
Gotcha! Your cable layout is not the optimal arrangement for flat multi-cable runs. Here is the proper arrangement:
1648447819540.pngOr you could arrange your cables in A1B1C1 A2B2C2 A3B3C3 with intra-phase spacings of 2 cable diameters apart, cable groups (1 to 2 and 2 to 3) with 3 cable diameters apart. But definitely not the way you did as shown in your sketch.
Hope that helps!
 
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