Small DG and EPS connection 1

[HamidEle]

have a question. We purchased a generator with a switchgear ( 4160V ), with two supplies, one is from Utility, the other is from 2x2.5MW generators. The utility is stepped down from 115KV transmission line. Under normal conditions, the generators will be standby. We will need to turn on the generators for periodic testing and maintenance, running in parallel with the grid ( no tie breaker). The sizes of the generators are small compared with the grid capacity. Wonder if we need to file an application to the grid for approval in this case. Is there any way we can get away from going to utility company for approval? Cause it would be a pain to go through all of these in the middle of commissioning the plant. Thanks in advance!

 

[stevenal]

No.

 

[waross]

Your plant must be disconnected from the grid before you power the plant with the generators.
Smaller sets use an Automatic Transfer Switch.
In a 5 MW installation you may use interlocked power circuit breakers with a suitable control circuit to do the work of the ATS.
Your switch-gear should include synchronizing gear to sync the generators together if they are intended to share the load.
You need a load bank for load testing.
Back in the day we did acceptance load testing with a liquid load bank.
Rent a large dumpster.
Use 5 or 10 tubes of RTV silicon to seal the door and fill it with water.
Throw in 20 or 30 kilograms of salt.
Lower three electrodes made of scrap metal into the water, suspended from a picker truck.
Fence and flag the area to the satisfaction of the safety department.
Arrange for lots of makeup water.
You do the math.
How many BTUs will 2.5 MW or 5 MW generate in an hour?
How many liters of water will that many BTUs boil in an hour?

Your plant must be able to recover from a short outage between the time that the grid fails until the generators come on-line.
Small sets will make it in under 10 seconds.
For your sets I would plan for 30 to 60 seconds.
Going from standby to the grid may be much quicker.
It may be as fast as you can drop out one breaker and pull in another breaker,
BUT
You may not want to re-energize large spinning motors that quickly.
An option that may be possible depending on the utility is going in parallel with the grid for testing.
If the utility agrees the utility will want anti islanding protection.
It may be cheaper than a permanent load bank for testing, but you must involve the utility.

By the way, are the generators redundant or are they intended to work in parallel?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[HamidEle]

Thanks, Waross,

You are right to the points. They are what we are planning to do with the essential gensets. We don't have ATS but we have Synchronization within the switchgear to allow the generators running in parallel with the grid. With the load bank running, there will be less impact on the plant system. the impact on the PCC will be negligible. Do we need to apply to the grid for the paralleled generators event though the grid nextwork might not notice the generators are on line?

 

[xnuke]

Yes, you'll need some sort of interconnect agreement with most utilities. They'll want to review the connection, protection, controls, etc.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[waross]

Are you allowed to post a diagram Hamid?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[HamidEle]

Here it is, Waross. The PCC is at 115KV. it is a single bus bar substation without main incoming breaker.

 

[HamidEle]

Hi, Waross,
There are no large spinning motors that quickly.
Generators are not redundant and they are expected to run in parallel.

 

[crshears]

"Utility companies" like the one I work for would be very irresponsible and in violation of numerous policies and agreements if they did not insist on connected generators having the appropriate permissions, relaying schemes, and so on in place and current at all times; there are many factors that must be taken into consideration during the planning stages of such projects, and on the face of it it seems this was not done in you case.

That being said...

My utility has its own back-up generators in various locations, and when their installations were being planned it came to my attention that the switching schemes would be as Bill described, with ATSs, break-before-make connections, etc., etc., including permanently installed ghost load banks [in our case, huge toasters that would never see a slice of bread in their lifetime].

I decried the deliberate and planned burning of Brobdingnagian quantities of non-renewable fossil fuels to produce nothing but heat and greenhouse gases, appealed to the company's own policy statements about the efforts it makes to be environmentally responsible, and suggested they investigate what it would take to provide these generators with the capability of synchronizing to the grid and going to full load, their outputs being used to displace transformer and switching station site loads and the balance if any being exported to the grid. My reasoning was that even if we were paid nothing for any power exported, the electricity would at least be used and provide at least some tangible return...

The idea was kiboshed by one upper-middle manager who stated dismissively: "We are not in the generation business." Very environmentally friendly way of thinking, indeed.

CR

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

 

[waross]

First thought;
Are you in the profit business?
Second thought;
It's much easier to say not to something that you don't clearly understand.
But on further reflection I realized;
As a regulated utility you are limited to a fixed return on your capital costs.
If the load banks cost a lot more than a grid connection they will be able to recoup their costs plus an ongoing profit.
Likewise the cost of fuel will become a cost that they will be able to recover through their rate structure, plus a profit.
He has not only maximized profits but he has done so in a way that makes him appear too obtuse to argue with.
In someone's world that is excellent management.
You have my sympathy.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crshears]

Thanks, Bill; the harsh reality of business-only-minded thinking can be really depressing sometimes...

Addition via edit begins...

I've finally had a chance to look at the OP's SLD, and clearly some equipment is missing / not shown...

If a firm commitment is made to never synchronize these units to the grid, the utility and/or AHJ [ Authority Having Jurisdiction ] will not certify the site for operation unless a satisfactory interlock system is in place to ensure that transfer of loads will always and only ever take place on a break before make basis. In this scenario, the 2 x 2.5 MW generators will not be classified as Distributed Generators.

Granted that the units are small compared to the capacity of the grid or the power consumption of the site, if synchronization to the system is pursued, licencing of the units as not only distributed generators but also as "displacement generators" [meaning they will never export power to the grid] will have to be obtained from the utility and/or AHJ.

Addition via edit ends...