Black start load requirement 90 MW Gas Turbine

[HamidEle]

We are trying to calculate the black start load requirement for a 90MW Gas turbine unit. Based on the mechanical information, the black start demand load is almost 4MVA, which seems to be a bit higher based on my experience. It should be just below 2MW. It may vary between vendors. Since I am relatively new in Cogen field, I would appreciate it for any comments.

 

[7anoter4]

I am not familiar with Cogen power station [CHP] and 90 MW gas turbine.
But for let's say 120-130 MW CC the low voltage power required for turbine only it is about 1500-1800 kW.
You need also some MV supply for excitation and start motor. So 4 MVA could be the required power for Black Start.

 

[GTstartup]

4MW seems reasonable, 1.5MW for the starting device, the rest for auxiliaries and some margin to prevent harmonic isssues, plus selecting the next standard size of black start gen.

 

[ScottyUK]

What's the starting device - motor & torque converter, or LCI drive through the generator? A big LCI is not the most generator-friendly load imaginable.


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If we learn from our mistakes I'm getting a great education!

 

[HamidEle]

Confirmed with our mechanical, the black start demand load is about 3MVA. The startting device is a cranking motor. Thank you all for the interests and discussions.

 

[rmw]

If it is "black start" where are you getting power to run a cranking motor? Most black start units I have seen are "other than electric" start, diesel engines, gas driven (steam) turbines, etc.

rmw

 

[racookpe1978]

Are your control room loads and services (lights, computers, control consoles) power included in that startup estimation? Or is one assuming they will be needed, and the other group only looking at the CT itself?

Can you trim the reserve power margins (starting surges) if you start different loads up (lube oil, control air compressors, etc.) at slightly different times so the surges are separated out? If you are not going to be starting from a near-freezing condition, will your startup needs differ?

Can you put some startup loads like a turning gear motor on an air-operated system - but then can you always assume all of the air-operated systems are actually going to be pressurized when you need them?

 

[rmw]

I saw a "black start" FR 5 gas turbine once - air start Detroit Diesel engine cranked to 'black start' the islanded municipal utility defeated because the air source for the engine starter was plant air and guess what - when they went black, they lost their electricly driven plant air compressors and their plant air went down too rapidly to start the CT.

I still have a clear mental picture (not many of those left these days) of the city's sewer department truck coming through the power plant's gate with a Smith 75 engine driven air compressor trailer up on one wheel as he took the curve too fast.

rmw

 

[HamidEle]

We are planning to add a diesel generator to supply power to the black start as well as other auxilary loads. Can a gas turbine generator serve as an emergency power supply? I doubt it since it takes 5-30 mininutes to start any turbine generator, which is probabally too long under some emergnecy situations.

Suppose one plant has Utility supply as well as two on-site co-generators. Do we need to run one or both of them in parallel with the grid? I don't have a lot of operation experience. I am assuming we would need to run one or two if the plant needs more steam or power factor correction.

 

[racookpe1978]

You've GOT to get some experienced operator-side help on your design and planning team.

What "black start" contingencies are you facing now? How often to do they happen, and what happens to you - your facility - when they do occur? How do you recover now, and what time limits affect you as you recover under what circumstances?

Then ... start thinking: What do you fear? How long a blackout do you think will happen at what regularity? (A 3 hour loss happening once a year is one thing. A 3 day loss happening once every thirty years is another. A 5 minute blackout happening twice a week is a very different problem with a very different solution!)

So, assume you WILL face frequent area blackouts - not just to your plant - and that YOUR facility will be relied on by others to be the first one back up so they can startup safely. See the difference? On the other hand, that may mean you don't need a 5 minute automatic-hands-off immediate restart ability, but DO need to be able to start up in a controlled manner from nothing. A nuke genrating pkant or hospital needs elaborate and expensive auto-start diesels and air-pressurized fuel and oil systems because lives depend on it immediately coming up. That also forces them to buy elaborate auto-switching switchgear duplexed between primary and backup power, plus battery backups and APS systems for all systems that can't even switch from one AC source to another.

You may be able to get by with battery-backed APS systems for your computer, control room, and controllers so they are good for 1/2 hour before AC is restored and so you CAN restart other systems. A small diesel (kilowatt-sized) for building emergency lights and startup pumps like oil. An air-operated starter motor and electric switchable service pumps.