Storm water pump

[a1guvner]

Hi Guys,
Got to go and visit one of our customers this afternoon, they have a storm water storage system that has three separate pumps that work independently of each other (not to sure of the setup). Had a call from them this morning when they had found the mccb feeding this equipment had tripped which does apparently happen now and then, when they reset this mccb it took out the main mccb for the incomer (around 800 amp supply). They have called again to say the storm water pump supply has tripped again and they cant risk turning it back on if it takes out the main MCCB, obviously the initial fault needs looking into but has anyone had any experiences where a small submain mccb can trip the incomer when reset

 

[telectrix]

possibly a spike or inrush when resetting. you need to start with the pumps and work back to find any faults.

 

[a1guvner]

possibly a spike or inrush when resetting. you need to start with the pumps and work back to find any faults.

I was thinking along those lines, just got me thinking for what i believe not to be massive pumps to take out the incomer seemed strange, but i guess i shall see later on

 

[Bobster]

Windings in the pump could be down to earth. I've seen it a few times, relatively small motors 50KW - 132kw take out the upstream ACB rather than its own fuses.

Basic testing will probably show the fault quite quickly.

 

[a1guvner]

Windings in the pump could be down to earth. I've seen it a few times, relatively small motors 50KW - 132kw take out the upstream ACB rather than its own fuses.

Basic testing will probably show the fault quite quickly.

Definitely, time shall tell,

 

[Marvo]

You haven't given much info but working on the theory that all 3 pumps are similar sizes and all are fed from the 800A incomer I'd suspect a large short circuit or earth fault is most likely rather than inrush on reset. I think even an LRA fault is pretty unlikely if the main 800A incomer is tripping. A couple of minutes testing at the control panel with a mega tester and a multimeter would probably localise and ID the problem.

 

[Engineer54]

Don't rule out a faulty 800A MCCB/ACB either!! Also if this incoming 800A breaker has adjustable setting parameters, check that they are all set correctly for installation....

 

[PEG]

Most been said,but do not rule out two problems! Initial one,and what what may have occurred due to "persons unknown" repeatedly re-setting fusing device. What i have noticed,over the years,is if someone appears to have "fixed" an outage,by re-setting a breaker,they will repeat that tactic in ANY multiples,in order to attempt a result. One memorable occasion,a damaged cable was blamed for the melted Breaker,when really,it was Steve from the workshop,re-setting 60+ times,until the poor little breaker dissolved!:conehead:

 

[Knobhead]

You don’t say what size the motors are. Several motors starting simultaneously can take out the main MCCB without there being a fault.
I’ve lost count of the times it happened on my shift with the production guys starting multiple drives to quickly. It used to take the 11KV OCB out.

Try each one separately and work from there.

 

[a1guvner]

Hi Guys,
Thanks for the replies,
When I attended the pumps are quite small 2.5hp, tested the windings and all were clear at the time of testing, re-energised and started one pump at a time individually and all was fine, then started all pumps and all was fine at that time. looked at the setup a bit closer and found the main mccb that tripped fed the main panel, this panel feeds various submains to different parts of the building, there is a 250a submain that feeds a plant room db, this db via 100a terminal block feeds 63a mccb which then feeds the pumping station control panel. if there was an inrush you would think the next mccb in the main panel would of let go instead of the main one............
the next morning the client called to say it had tripped the 63a mccb again but the main switch was still fine, going through a process of elimination now and leaving one pump isolated at a time...........

All ideas welcome

 

[a1guvner]

The plot thickens

On enquiry to the system manufacturer who advised the startup current of these pumps would be 25a each giving a total of of 75a, i am starting to question the fact that as the two mccb's immediately upstream being the 63a and 250a respectively are holding that the issue maybe the main 800a mccb is letting go when the motors start is pushing it over the edge if the switch is possibly set to low or working at its limits, i am now thinking of on delay timers for each of the motors along with assessment of the total load via a data logger.
Has anyone else had a similar experience.

 

[Knobhead]

What'sthe base loading onthe 800A MCCB

 

[shanky887614]

The plot thickens

On enquiry to the system manufacturer who advised the startup current of these pumps would be 25a each giving a total of of 75a, i am starting to question the fact that as the two mccb's immediately upstream being the 63a and 250a respectively are holding that the issue maybe the main 800a mccb is letting go when the motors start is pushing it over the edge if the switch is possibly set to low or working at its limits, i am now thinking of on delay timers for each of the motors along with assessment of the total load via a data logger.
Has anyone else had a similar experience.

did you check the total load on mccb from other possible sources

 

[Marvo]

As per the last 2 posts, if it's taking out the 800A MCCB then it's almost certainly a wider issue that includes the other loads it's supplying. I assume you already checked the adjustment of the settings of the 800A MCCB and checked for obvious things such as overheating terminations which could cause this kind of tripping.....?

 

[a1guvner]

As per the last 2 posts, if it's taking out the 800A MCCB then it's almost certainly a wider issue that includes the other loads it's supplying. I assume you already checked the adjustment of the settings of the 800A MCCB and checked for obvious things such as overheating terminations which could cause this kind of tripping.....?

That is next on the agenda, we just have to get past the stringent permit to work system that is in place even though they push for a resolution, love the red tape that blocks their own needs..... one does try

 

[a1guvner]

UPDATE.......
Problem solved, in the end.

The main MCCB ended up being set to 0.4 of its rating so in effect it was sitting at 320a, adjusted correctly and that issue was resolved.

Moving on to the pumping station we found various issues, found incorrect overloads on the contactors, replaced with correct ones.
Found on the 63a circuit that the pumps were peaking at 75a on start up and we believed pushing the MCCB over its limits, checked calculations on the circuit and the design allowed to uprate the MCCB to a 100 amp one. Problem solved or so we thought. some 6 weeks later we get another call to say the MCCB had tripped again just after we had some rain. Attended and disconnected the 2 ends of the cable and tested again and although previously the cable had tested clear on this occasion it was failing on various cores on IR. Used a TDR on the cable and it showed a short on the cable at 110m and on another core at 130m which coincided that ground works had occurred in the previous couple of years so we used a cat scanner and genny to trace the cable across the fields. The decision was made to dig at 2 positions either side of the possible fault and to cut the cable and hopefully test back to the building and out to the pumping station and the cable shows as clear. Unfortunately the cable still showed faults so more test holes were made to try and locate where the fault was. Five holes later and various cuts of the cable still showed faults on IR on the cable. During this time we found where the cable was being cut the cable was actually dripping water out of it but not just inside the PVC outer sheath but actually dripping out of the cores. the cable was around 250mtrs long and only ducted in one section under a pitch on a playing field. The
We ended having to replace the cable and running back to a different location that was a shorter run but still quite a job.
After we had finished we spoke with an electrician that was involved with the installation when the building went up and apparently this cable was having problems snagging on something as the cable tried to leave the building and in the end they used a tractor to pull the draw rope and we now believe the cable was damaged in various places causing numerous faults especially when the water table raised.

Finally the mystery is solved.

 

[Bobster]

Thanks for the update. Not uncommon for a small nick in a cables insulation to draw water through capillary action.

First time I saw it I was an apprentice, opened the panel up and water was coming up through the SWAs inner sheath like a spring.

 

[a1guvner]

It was very strange even though we pulled out the section that was in a duct and found no physical damage that the water must of tracked that far, we did find on one of our test pits on the 4c70mm 2 cores were nice and bright as you would expect and the other 2 were tarnished.

 

[Engineer54]

After we had finished we spoke with an electrician that was involved with the installation when the building went up and apparently this cable was having problems snagging on something as the cable tried to leave the building and in the end they used a tractor to pull the draw rope and we now believe the cable was damaged in various places causing numerous faults especially when the water table raised.

A lesson for everyone there, ...NEVER use machinery to pull a cable, unless it has been specifically made for the job!!

At the very least you will almost certainly end up with a stretch damaged cable, and at worst, well a stretched cable that also ripped to pieces!! lol!!

 

[Jonspark]

seen a 185 pulled in with a JCB by some Irish workers that snapped and whipped across a play ground, luckily no one was occupying it at the time.