Erratic Tripping of Breakers

[greggs007]

Could someone help me with this.

In my building there is PDU (fed from UPS with solid ground neutral) having 125A TPN MCCB, which is followed by four 63A TP MCBs downstream. Each 63A TP MCB feeds one 8-way DB. Each 8-way DB has 32A TP Incomer, followed by 03 R-Y-B DP isolators of 20A each. Further, each DP isolator is followed by 16A SP MCBs.
One fine day, one particular 8-way DB, which feeds the various workstation, printers and LCD TVs in a floor, started experiencing erratic trips along with 125A upstream MCCB. On the first instance, the 8-way DB incomer tripped along with 125A MCCB. On second instance, Y-phase DP isolator tripped along with 125A MCCB. On the third instance R-phase DP isolator tripped along with the 125A MCCB.
Each subsequent trip occurred within the duration of 30-60 minutes. During the first and third instance, the 125A MCCB Ground Fault was set to OFF. On the second instance the ground fault was set to 20%.
Post restoration of circuit and after having switching ON all connected load on the PDU, the current measured on each line was 14, 9, 20. Using power clamp meter, I also found the net current at the output terminal of PDU to be between 1.2 to 1.5 Amps, and the total harmonic distortion (THD) in each line was between 40% - 60%.
Since last 10 days we did not have any trip after the initial incident.
We know there is need for coordination checks. Besides that what could have caused erratic tripping behavior. Could harmonics be the culprit or any spurious load or neutral.

 

[fmtjfw]

Coming from a software engineer who is used to using acronyms

Coming from a software engineer who is used to using acronyms

Please explain what the following mean:

PDU
TPN
MCCB
TP
MCB
DB
R-Y-B
DP
SP

I assume UPS means uninterrupted power supply.

 

[John120/240]

Please explain what the following mean:

PDU
TPN
MCCB
TP
MCB
DB
R-Y-B
DP
SP

I assume UPS means uninterrupted power supply.

fmtjfw For clairity start a new thread with your new question.

MCCB Motor Control Circuit Breaker ??

MCB Main Circuit Breaker ??

DB Direct Burial ??

R-Y-B Red Yellow Black or Red Yellow Blue ??

DP Double pole ??

SP Single pole ??

Not 100 percent certain on definitions not knowing the area you are working in. Industrial

maybe ? Others will chime in hopefully.

 

[ActionDave]

fmtjfw For clairity start a new thread with your new question.

I don't think he needs to do that since the list of acronyms came from the OP.

 

[hurk27]

I would be looking at the neutral and its connect ons all the way to the transformer, a bad neutral connection can cause many circuits tripping, this is because if you have many SPDs protecting equipment on multiwired circuits or even single circuits without shared neutrals, the combinations of all these SPDs can have enough clamping to load the breakers down trying to protect the circuits, I have experience this when our area was hit by a 915 volt surge from the utility when a 69kv line came into contact with a 7200 volt line, my 100 amp main opened and I didn't loose one piece of equipment, that day and a couple of days after I fielded many calls to houses and a couple business that gave me a great inside on how even surge strips can offer some protection against long term high voltage surges if enough SPDs are connected to each phase, house that had more then 3 surge strips on each phase had the main trip yes even a 200 amp main, while those that only had one or two on each phase had the strip burn up, two even caught fire, and one just tripped the branch OCPD, one of the business had between 40 to 50 work stations and a full network servers that was well protected, the had so many SPDs that even the 800 amp main to the building tripped and like my house they didn't loose any equipment once we reset the main.

I'm not saying this is what it is, but it would be worth looking at, and maybe installing a recorder to monitor what is happening, it might be found the utility might be having a transformer starting to fail, but that would not be intermittent and should just fail all at once. that is why I thought about a bad neutral connection.

 

[John120/240]

I don't think he needs to do that since the list of acronyms came from the OP.

Thank You for the heads up Action Dave

 

[greggs007]

Thanks for replies. Regret acronyms.

MCCB = Moulded Case Circuit breaker
MCB = Miniature Circuit Breaker
TP = Triple Pole Breaker (for three phases)
DP = Dual Pole Breaker(for one phase and one neutral)
SP = Single Pole Breaker(for any one phase)
R-Y-B = Red - Yellow - Blue (Phases)

Yes there are around 3 to 4 SPDs on each phase. The neutral conductor is shared. A bad neutral could mean loose connection or nick somewhere. Can a nick on neutral and it grounding somewhere cause a trip, though they are supposed to be at same potential. We have recorded presence of ground fault current, when measuring net current at the PDU.

Besides, what recorder could be best suitable to monitor and record such spurious trips.

Thanks for your responses.