To install black start generator for 2 power generators 45 MW

[SA07]

Hi
We have 2 turbo alternators 45 MW 11 kV 50 Hz each exporting to the utility grid. We intend to install a stand by generator to do black start of a turbo alternator in case of total black out of the national grid and then export some MW on the grid.

The auxiliary consumption of one plant before synchronising is about 2 MW.

We have a series of 11 kV circuit breakers next to each other for each unit and a common busbar as shown in the attached doc. After each unit are synchronised with the network, we want the std by generator to export some power to the grid.

Our biggest single motor is the boiler feed pump of 1 MW.

What rating of std by generator do we need? Will a 5 MW be enough?

Then after synchronising both units, will we be able to export an additional of 5 MW on the grid?
Is there a 5MW 11 kV std by generator on the market?
There is a request from the national grid company to increase our production because of some issues on the grid.

 

[RRaghunath]

For a DG set to have black start capability, its auxiliaries should be minimum and / or should be able to start on DC battery.
I am afraid 5MW could be large to be able to start on its own. You may discuss this with a reputed manufacturer before making a decision.
Since the black start power requirement is 2MW only, a 2.5 or 3MW set could be good enough. To cater to the starting power requirement of BFP, the generator alone can be of higher MVA rating. This is because 1MW motor may take 5MVA power during start @ a power factor of 0.2 (say). This is to say a DG set comprising 3MW Diesel Engine and 5MVA Generator.
Optionally, if a Soft starter can be added to the 1MW motor, the starting current can be limited to 2x the rated current.

 

[waross]

What is the energy source of the proposed standby generator?
If diesel powered, you probably can't afford the fuel to export power.
Size the standby to black start the most demanding power generator.
After starting one or both power generators, leave the standby online and advance the frequency setting until it is exporting the load that you desire.
Governor droop will cause the frequency setting to control the loading for export.
For a diesel set exporting power, make prior arrangements with your banker before refueling.

 

[edison123]

Black start is an emergency for which hydro generators and GTG's are more suited than STG's which take anywhere from 10 to 18 hours to synchronize.

 

[wcaseyharman]

My recommendation is Install a PQ meter and trend your plant load during startup. Your standby set will only need to carry the load until one of the 45MW generators sync and begins to share the load.
There’s a chance that a 2.5MW generator would work because your aux loads might relatively low during startup, but the only way to determine that is to measure.
We blackstart a 75 MW gas turbine site with a 2 MW gen, but the aux loads on gas turbines are relatively small other than the .5MW starting motor.

 

[bacon4life]

In my region (Washington state, USA) the emissions limits for emergency generators are much less stringent (tier 2) than for generators intended to export power to the grid (tier 4). It extremely rare for folks in my area to buy a tier 4 engine for an emergency generator, so we could not legally sell power from an emergency generator to the market. Other regions have very different rules. I think Minnesota has a utility sponsored programs to run customer owned emergency generators at peak demand times.

 

[SA07]

We just got some updated information.
In fact, the main purpose is to supply power to the utility grid during peak demand hours.
We intend to use the diesel generators also for black start of our plant.
We have 6 auxiliary transformers :

2x2.5 MVA 11kV/400V

2x3.63 MVA 11kV/400V 630 kVA 690V/3MVA

2x2 MVA 11kV/690V


Can we connect 6 diesel generators approx 1.5 -2 MW 400 V and 690 V with synchronising breakers directly to the secondary of each auxiliary transformers ? Will the diesel generators be able to push excess energy through secondary of the auxiliary transformers to our 11 kV busbars and up to the utility 66 kV network?

 

[wcaseyharman]

At a high level, I don’t see why not.
Some complicating factors:
- Do you have transmission contracts or requirements in your area that would require new transmission contracts? Have you consulted with your transmission operators engineering groups? They maybe have concerns and need to review from a transmission perspective. We have FERC processes in the US that would complicate this, and in my area in Washington State would likely be the most difficult as transmission regulation seem to be the most onerous these days.
- Have you reviewed regulations regarding emissions for standby generators and operating to support transmission needs? You might need to amend your air permit if your area requires one.
- You will need to do electrical studies, since you are adding sources to the auxiliaries: in the US this would at least be arc flash, fault studies (to determine the existing equipment has sufficient fault withstand ratings), and protection coordination.

My $0.02 anyway.

 

[waross]

2x2 MVA 11kV/690V


Can we connect 6 diesel generators approx 1.5 -2 MW

Unmatched units.