Stepping up from 480Y/277V to 12470Y/7200V

[Shujinko]

I have a project with a campus loop type electrical distribution system. The campus loop is fed from a 15kV Medium Voltage (MV) Switch. The MV Switch can be fed from either the electric utility or a client owned Tier 3 emergency generator. The generator is a 1400KW, 480Y/277V, diesel engine, and the voltage system is stepped up on the emergency side of the MV Switch. The voltage system is stepped up via a 1500KVA transformer from 480Y/277V to 12470Y/7200V.

The client is part of an Emergency Back-up Generator Program with the utility company, where they get monthly rebates in exchange for the utility company being able to switch the generator on to feed the campus loop when necessary. The utility company is requiring the generator to be replaced from a Tier 3 to a Tier 4 generator in order for the client to stay in the rebate program. The client just wants to replace the generator only, without making any upgrades or system changes. The generator is currently located in a very basic aluminum building shed.

My question is, it seems impractical to get a new 480Y/277V generator and step up the system voltage to 12470Y/7200V. Is this stepping up a voltage commonly done at the electrical distribution level? What upgrades would need to be done with the system and the building if we did look at going with a 12470Y/7200V generator? What codes besides the NEC and NESC should I be looking to comply with for the Medium Voltage (124700V/7200) generator? What upgrades would need to be made to the basic metallic building shed if we did change to a 12470Y/7200V generator and didn't go with the step-up scenario?

All help is appreciated. :thumbsup:

 

[Jraef]

A) It's done all the time, because....

B) The owner of the generator must only deal with the 480V class control / metering / protection / maintenance, the MV step-up transformer and switchgear then becomes a different system falling under a different jurisdiction (whether internal or external).

If you generate at 12.47kV, ALL of the switchgear / protection / metering etc. is going to cost a WHOLE lot more and the same people who are qualified to work on other 480V systems in your facility can likely no longer work on the generator.

 

[Ingenieur]

a couple of things to check
genset price: 12470 vs 480
is the utility going to require a 1:1 iso xfmr or are you allowed direct tie to their grid

it seems like all your ats, relaying, synchronizing gear is on the 12470 side
so all you need is the genset

 

[ron]

It seems very practical just to replace the 480V gen and leave everything else alone. The step up process and protective relating is already there to grid tie, so just replace the gen.

The Tier 4 emissions will be bigger than the Tier 3 emissions equipment, so the very basic aluminum building shed will become bigger. You will likely want to just buy the generator in an enclosure from the vendor with all the accouterments. Be sure it comes from the vendor Tier 4 fitted out and tested and not modified by a local person as Tier 4 modified so the EPA will not give you a hard time.

 

[drktmplr12]

got a one line you are permitted to share?

 

[smoothops10]

I agree sticking with LV is probably the better route. Note, your transformer is slightly undersized and will limit the generator from providing full output. Almost all generators are rated with 0.8 pf so it has 1750kVA rating. I'm sure your actual load power factor is higher but worth noting and reviewing the tranformer protection. You should be also be able to talk with the generator manufacturer to limit excitation to not overload the transformer.
If you go the MV route, there are generators available in that voltage though it is at the upper end of available units. Above 13kV, the stator insulation gets too thick that it is not practical. Also an MV generator would not be solidly grounded like the existing LV generator. You would have to use a resistor and/or reactor impedance ground and provide the proper protective relaying. It is more difficult than specifying a mccb but I'm sure the gen mfr can help.
One thing I've heard on the Tier 4 is that many are specifying the emissions package as a 3rd party piece of equipment. This is so inducement controls are not hard programmed in to the generator ECM. I won't say more than that, I'm sure you can come up with the reason.
"Emergency Operation—To facilitate the use of certain nonroad engines in temporary emergency situations, the engines can be equipped with an AECD to override performance inducements related to the emission control system—for example, to allow engine operation without urea in the SCR system during an emergency [EPA 2014]. This flexibility is intended primarily for engines used in construction equipment and portable equipment used for temporary power generation and flood control." https://www.dieselnet.com/standards/us/nonroad.php

Also note the UREA or diesel exhaust fluid DEF consumption rates can be signifigant. You'll likely have to provide a chemcical storage tank and consider a containment area around the tank for the bulk storage necessary. Coordinate tank volume with local delivery service truck volumes and schedule. If it is outside, heat tracing is required as UREA freezes fairly low. Hope that helps - good luck.

 

[Shujinko]

got a one line you are permitted to share?

One-Line As-built of Existing System

 

[smoothops10]

If it were me I'd consider replacing the 1500kVA generator step up transformer with a 2000kVA wye grounded HV side and delta LV side. Talk to mfr's like Virgina Transformer Corporation, Howard Industries, etc. not the standard distribution transformer mfrs. Would also recommend having the impedance of all these transformers on the drawing as well. I would consider upsizing all of the MV distribution conduits from 4" to 5". Why no ground conductor in MV conduits other than the two main feeds from the main gear?

Recommend you get a copy of and review:
T-030 - Cummins Application Eng Guide Chapter 5
ieee_c57-116_1989-transformers-directly-connected-to-generators
ANSI-IEEE C37.102-1987 GUIDE FOR AC GENERATOR PROTECTION

 

[Shujinko]

If it were me I'd consider replacing the 1500kVA generator step up transformer with a 2000kVA wye grounded HV side and delta LV side. Talk to mfr's like Virgina Transformer Corporation, Howard Industries, etc. not the standard distribution transformer mfrs. Would also recommend having the impedance of all these transformers on the drawing as well. I would consider upsizing all of the MV distribution conduits from 4" to 5". Why no ground conductor in MV conduits other than the two main feeds from the main gear?

Recommend you get a copy of and review:
T-030 - Cummins Application Eng Guide Chapter 5
ieee_c57-116_1989-transformers-directly-connected-to-generators
ANSI-IEEE C37.102-1987 GUIDE FOR AC GENERATOR PROTECTION

This is an as-built drawing of their current instalaltion. I have not started the design yet.

 

[Ingenieur]

based on the single line
why the 480 xfer switch since the 12.47 gear has one too?
the only thing that feeds it is the gen?

me: get rid of the gen, ats, xfmr and get a 12.46 gen as long as the cost delta is not too large and they do not require a 1:1 iso xfmr

 

[drktmplr12]

OP: smoothops makes very good points.

we have 2 vendors out here that will provide t4 as part of the generator package, but there are modified after the fact and the vendor, not the manufacturer, takes responsibility.

One-Line As-built of Existing System

View attachment 19301

off topic, but that loop arrangement, ugh! owner can't inspect dead switches without shutting down the entire lineup cause there isn't a tie on the bus!! :happyyes: perhaps they can withstand a couple hours of down time.

 

[Shujinko]

based on the single line
why the 480 xfer switch since the 12.47 gear has one too?
the only thing that feeds it is the gen?

me: get rid of the gen, ats, xfmr and get a 12.46 gen as long as the cost delta is not too large and they do not require a 1:1 iso xfmr

You have a great question, why is there an ATS on the load side of the generator? This is an existing installation, but it's not clear why it was done as this ATS is only being fed from the generator. Maybe they installed this as a way to isolate the generator from the transformer, if the generator or transformer ever need to be taken offline for maintenance. I will have to investigate the history of this installation.

The previous poster makes a great point, a 12470/7200 gen won't be able to be kept in a simple aluminum shed and additionally the maintenance staff at the site only includes electricians trained to deal with 600V and below systems not MV systems.

Any idea on the construction requirements of a building that would house a 12470/7200 generator? What standard or code covers this? I think the 12470/7200 gen will add cost and other complications that my client might not be willing to entertain.

 

[Shujinko]

OP: smoothops makes very good points.

we have 2 vendors out here that will provide t4 as part of the generator package, but there are modified after the fact and the vendor, not the manufacturer, takes responsibility.



off topic, but that loop arrangement, ugh! owner can't inspect dead switches without shutting down the entire lineup cause there isn't a tie on the bus!! :happyyes: perhaps they can withstand a couple hours of down time.

This client's main interest is to continue getting the rebate from the utility company for the Back-Up Generator Program. I think that it wouldn't be economically feasible to change the entire loop system based on what the client is looking to achieve.