Transferring station loads between new / existing distribution systems.

[AlwaysLearnin]

Good Day. I am working on a project in a facility where the owners have several loads they have deemed "vital" to operations and cannot be in an outage for a prolonged period of time.

Our specific task in this project is the replacement of the upstream distribution equipment including transformers and Switchgear. We are fortunate enough where we can install the new equipment without impacting the existing equipment until the loads are ready for transferring. It is at that phase of the project that several members of my team come into conflict and I am looking for opinions from those more experienced then myself in matters of construction.

The majority opinion on how to rectify this is to install a temporary Motor Control Center and transfer the vital loads over to this temporary unit. The existing Motor Control Center can then be transferred to the new distribution network at leisure. Once the motor control center is transferred, the vital loads can be relocated back to that existing Motor Control Center and the temporary unit demolished. I have seen this method used on equipment were outages were be prolonged due to other schedule incompatibilities or construction phasing requirements.

The minority opinion disagrees with this approach on this particular project. As a disclaimer, I fall into the minority opinion on this matter. I feel that it would be quicker and require less outages of the vital equipment to simply transfer the entire MCC upfront and without construction phasing. I do not feel that the labor time associated with the disconnection and re-connection of a new feeder for an MCC would substantially exceed what is required to transfer the smaller compartments to the temporary unit. For arguments sake consider the MCC feeder to be 6-1/C 500 with ground. The greater portion of the raceway run and cable pull can be done prior to de-energization, leaving only the last few feet of cable dropping into the motor control center and of course making the final terminations.

Am I underestimating the effort required in re-feeding an MCC as compared to the temporary power scheme my peers have suggested?

Thank you for any assistance you can provide.

 

[davidbeach]

First you need to define what "cannot be in an outage for a prolonged period of time" actually means. How are you measuring time, cycles, hours, weeks? What voltage? How large is the load?

 

[AlwaysLearnin]

Davidbeach,

"Vital" loads are currently undefined. We have the Single Line Drawings available but the Owners are responsible for providing which of those loads cannot be in a sustained outage. In general the loads we anticipate being considered "vital" would include ventilation equipment (fans smaller then 75 HP) used to downgrade hazardous locations to a lesser hazard as per applicable NFPA standard. The remainder of the loads (less then 20 HP pumps) do not appear to to be vital to the overall facility process, however we have not ruled them out as of yet.

In regards to time and its measurement, the number being thrown around is thirty minutes to an hour for the vital loads. That would be our maximum outage time frame.

 

[crshears]

If I'm understanding the OP correctly, you are speaking of transferring vital loads off the existing MCC before the cut-over takes places and returning them afterward versus transferring over the entire MCC in one fell swoop.

On the equipment replacement jobs where I've been involved, the individual loads fed FROM an MCC typically use smaller and therefore more flexible conductors than the much heavier cables that supply the power TO an MCC. The outage times for the individual loads have typically proven to be much shorter than the outage time required to disconnect the entire MCC from its old supply and reconnect it to its new supply; time allowances in the order of four or more hours for the latter are quite common, simply due to the gruntwork involved, so in your situation Door #1 as suggested by the majority might be the better one of the two.

As to installing and demolishing a temporary MCC: depending on the geographic location of the project, it may be feasible to rent a mobile MCC instead, and at less cost.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[AlwaysLearnin]

Crshears,

You are correct in situation I attempted to describe. Based on what you are saying it would appear I am underestimating the time requirement for the main MCC feeder cut-over.

Just to be clear the minimum time allotment you indicate above is ONLY for the final few feet of feeder cable down to and inside the MCC (Placement and Termination)? Installing the raceway and cable up to the MCC in preparation for the outage would not decrease this time requirement?


If I could inquire further, do you also have an estimate for time to relocate a simple motor starter compartment? I am trying to gauge if "much shorter" would be thirty to sixty minutes maximum per starter compartment or more.


Thank you very much for the input thus far!

 

[ScottyUK]

Getting the motor cable across is the easy bit in most cases. An LV resin joint can be usable fairly soon after pouring, and I've seen one poured while the circuit passing through was energised although it wasn't my job and I didn't sanction it.

Proving control functionality can take a lot longer, epsecially if things don't want to play nicely or if there has been undocumented meddling field repairs by maintenance techs. Have you installed new motor control circuits and pre-commissioned them? I think that's the only way you'll meet your 1-hour target per circuit.

 

[crshears]

Hello again Always,

First, I agree with Scotty's observation.

Second, re: placement and termination, you are correct in what I'm suggesting...but I'm not at the jobsite, and I may well be missing something crucial. Your best bet at a time allocation is from those who will be performing the work.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[AlwaysLearnin]

ScottyUK / Crshears,

We are still in the design phase and no construction contract has been awarded. I apologize if I implied we were that far along.

Our plan of action would have the contractor do as much pre-outage work as possible. When you ask, "Have you installed new motor control circuits and pre-commissioned them?", are you suggesting we run all new cable back to load and signal sources?

I can see where that has advantages, but the plan presented from my colleagues was to just extend the existing cable to the temporary MCC. Following that train of thought we would need to find a suitable location to pull the existing cables back too such that a splice for extending the cables could be cleanly and securely made.

At the same time I see where pulling back the cable and making those types of splices could significantly increase the outage time. I generally do not like lifting cables unless necessary either as they never seem to find their way back home the first time around. Running new cable does appear to make sense.

Am I on still on track with that monologue / rant?

(And I appreciate the continued assistance. As it is near closing time, enjoy the Holiday to those American's out there if you celebrate!)

 

[ScottyUK]

We did a series of large MCC replacements a couple of years ago in similar conditions and I guarantee that control was by far our biggest headache. We had the new boards in place with pre-glanded, pre-terminated tails ready to splice onto the motor feeders as they were made available to transfer, but the control cables were renewed up to a known good point in advance of the transfer day. We nominally said we'd renew to 'the first terminals it meets outside the MCC' although we did renew quite a few cables end-to-end where this was easier than jointing and testing.

Sort your permit to work system in advance so it is ultra slick: securing isolations then issuing permits and sanction-to-test documents devours time.

 

[tinfoil]

Whichever method you decide on, you should also develop a Contingency Plan to react to a situation where you are approaching or exceeding the 'maximum allowable time'.

You may need to plan for an emergency shut down, a partial or total facility evacuation, a lawyer standing by, or whatever.

Just make sure that you understand your 'worst case' risks, and have a plan IN PLACE, just in case.

 

[ScottyUK]

tinfoil,

You missed "up-to-date resume" and "resignation letter" from your list.

 

[AlwaysLearnin]

Thank you both for the words of encouragement!

No need to fear though. My organization provides a complimentary tanto upon starting employment.

 

[crshears]

What's a "complimentary tanto"?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[stevenal]

tan·to
/ˈtän(t)ō/
noun
noun: tanto; plural noun: tantos
a Japanese short sword or dagger.

At least it's complimentary.

 

[resqcapt19]

If you have the conduit run and the cable pulled to within a few feet of the MCC, I think it can be done in an hour. I would suggest that if possible you plan on installing a wireway between the conduit and the MCC, use DLO/RHW cables and, if you have very good information, have the termination lugs crimped on the conductors before the outage. The wireway will give you some space to work with if the cables are a bit long, and the very finely stranded DLO cable really reduces the termination time. You may have to increase the raceway size because the DLO is a bit larger. The insulation is thicker than standard cables, and the actual copper size will 535.3kcmil.

 

[ScottyUK]

Ah, conduit. A creation of Old Nick himself. I hand't even considered that - over here most of our industrial cabling is single wire armoured. If you're using conduit then my earlier suggestion of jointing cables away from the board wouldn't make so much sense.