Eaton's microprocessor programmable relay EDR-5000, Measured and Calculated Neutral current 3

[Pdave6]

We are using Eaton's Microprocessor programmable feeder protection relay EDR-5000 as attached. The swgr factory had switched relay coil B connections as shown in the attached.
We are using the relay as simple phase and ground overcurrent relay. No voltage input and no directional settings.
The relay measured large ground current IX, and showed large calculated ground current IR. The relay tripped the breaker 3 times with timed ground measured current IX, during magnetizing inrush during commissioning. IR trip was deactivated, so that did not operate relay.
It was surprising that once we found and switched the B coil connection to make it right, both IX and IR magnitude dropped considerably during magnetizing inrush and breaker did not trip for next 7 to 8 operations until now. No relay settings were altered.
It is understood that magnetizing current will keep on changing depending on where the breaker contact closes in the sine wave cycle. The IX and IR value will also change with this during magnetizing inrush. But I do not think that the IX magnitude is the reason (or only reason) for breaker tripping.
Question: The big change in IR, calculated ground current, is understandable. But I cannot understand the big change in IX measured value, after B coil connections were switched to make it right. It seems IX value should not be impacted much whether relay B coil is connected right or reversed as shown. Somebody familiar with relay internals can explain the relay behavior.
Thanks in advance.

 

[davidbeach]

Given that drawing Ix would have always been correct and would not have been affected by correcting the B-phase connection. If it did change I would suspect that either the drawing isn’t correct or the correction was something other than described.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Kiribanda]

I am not 100% sure wether I understood your question. All what I can say is, if the B phase coil is
reverse connected then there is a polarity issue and therefore as a result of that reverse polarity
a large zero seq current will flow through the X coil, thereby tripping the relay on residual current.
When it is properly connected the resultant zero seq current is very small and cause no trip.
During energizing there is a possiblity of creating a similar residual current in the X coil but that
spill over current is very small unless the three CTs are not matching. Also the pick-up may be low.

 

[thermionic1]

My first guess would have been a setting difference between the phase CT's and the neutral CT inputs (both should be the same in your case). Then I checked the manual and it looks like that decision is made by wiring and a setting in the relay. Then looked closely at the wiring diagram. I would verify that the polarity terminals from your CT's for both phase and the neutral CT input are all wired correctly, which should be the 5A input in your case. The manual appears to be wrong. Further in the manual a 1A CT is shown going to the correct terminal. If all your CT's are not wired to the 5A input terminal on the relay you will have a problem. Now if your magnitude dropped after a wiring change, that would suggest whomever made the wiring changes understood that the manual was wrong and made the change to the 5A input. This would explain the difference in what you measured. If your system is balanced, Ig or(IR)(Calculated residual) and In or IX (measured residual) should be zero, or close.

 

[Pdave6]

Thank you all for taking time to read and respond.
1. Trips were during magnetizing inrush which has unbalanced current flowing thru neutral. The load is balanced and after magnetizing there is zero or close to zero current expected in neutral.
2.I did not mention earlier that recently we had changed IX from Extreme Inverse to very Inverse as a precaution. But this was done after about 5 successful breaker closings, and as a precaution only.
3. I have the downloaded waveform files for Magnetizing with Trip, and Magnetizing without trip later. I have converted these two files to text files. I have also downloaded Fault file which goes with Magnetizing with Trip file. See the difference that IX drops from instantaneous 600+ Amp to about 62 Amp after B coil connection was corrected.

My question : Why the relay has both Measured and Calculated ground current ? (Although we have only IX active, probably one can keep both IX & IR active. ) There may be some program routine the relay may have, when there is a big discrepancy bet IX and IR. Ideally both should be same or close to same, all the time. This can only be answered by someone familiar with relay internal program. I do not know if Eaton can create this condition on a bench and verify, with 3 phase transformer. I tried to speak to Eaton's technical support but so far I need more convincing answer.
BTW,I could not upload more than one file, at a time. I do not know why? I will upload 2 more files.
Thanks.

 

[Pdave6]

Please see magnetizing current file, after B coil connection was corrected, with no trip. The neutral current instantaneous dropped from appro. 600+ amp to about 60A.

 

[Pdave6]

Please see fault record file created by Eaton's EDR-5000 relay, for Magnetizing Trip condition. You can see RMS and fundamental current values.
I forgot to mention earlier that relay takes 32 samples per Cycle. (Applicable to earlier uploaded files.) Thanks.