Power Plant Parallel Operation

The voltage is dropping probably because of overloading, your additional generation should overcome the shortfall and all will be well....

the national utility grid is overloaded by the load of the whole country. how can our small 25MW plant cope with all this load . our plant of 25MW will only cope our load and will inject a very small power (may 2MWe) into the national utility grid. this small injected power cannot rise up the national utility grid voltage so for as i think. regards

I think you will find that frequency is the first consideration of any power plant distribution concern.

You can correct for voltage drops with various types of auto-transformers, but if the frequency changes too much clocks become inaccurate. Auto-transformers do have their limits, so at some point they must also give up or burn up.

Voltage falls as a result of loading or overloading when the breakers trip out. The only solution I can think of at the moment is backup power in case of power failures. That may not be reasonable for some industrial customers, however, others generate their own power just to avoid failures on shared networks.

Network planning is the key. I'm sure it is loaded with pitfalls too.

as i already told , the OLTC of our consumers transformers fails below 118KV. we are presently getting power from national utility which has the problem of this undervoltage. that is why we are building our own 25MWe coal power plant. however if we are going to connect this coal power plant with the national utility, then the whole purpose of coal plant dies when the utility voltage will be falling to very low levels causing tripping of the coal plant generators.

the only solution in my mind is to trip the incoming breaker of national utility in case of undervoltage so that the coal plant will then operate in isolated mode on the bus. after the national utility power voltage rises to some stable value , then the synchronizer will sync the two sources and connect them in parallel mode. what do you think?

What will likely happen if the national grid voltage drops is that you will see high reactive currents as your generator tries to maintain the voltage. Your plan of disconnecting from the national grid when the voltage sags and to re-parallel when it recovers sounds reasonable to me.

Why on earth would anyone today build a new coal boiler for the steam to drive a 25 MW steam turbine? Coal produces so much ash and airborne pollutants that this plant will likely be quickly crippled in some fashion by regulators.

Oh and if you don't know how to deal with a 20% sag in provided power then I doubt you're qualified to install any kind of power generation.

Hire a qualified engineer.

can you tell me how to cope with a 20% sag and then i will hire you

Let me see, where might one find an explanation on AC voltage stabilizers?

Beginners can always start with Wikipedia.

To be fair, I work with some very high power devices but I'm not a power distribution electrical engineer. Then again, I'm not claiming to be selling a 25 MWatt generator to anyone either.

i have already told shortcoming of voltage stabilizer i.e. OLTC of transformers. but i think u do not have field experience.

One of the telephone companies here uses turbo jet engines to temporarily supply power in the event of a power failure. These (jet) engines start very quickly and shut down when the main power kicks back in. They

Capacity and load shedding is not a simple matter. A sag may very well be due to insufficient generation capacity in which case your plant is justifiable. The problem will be figuring out who gets what when the billing is all done. It will require a complex agreement with the other networked power plants.

Of the many details you left out, how long does the sag last? Is it daily or seasonal? There are many answers, all dependent on the existing issues.

the sag is seasonal i.e. severe in summer (from May to September) and lasts for may be 30 minutes or hour. in that time all our bulk load is cutoff due to undervoltage. we call the national utility company. the company then sheds some of the load on their grid and the voltage rises. this is a problem for our production. so we decided to build our own power plant of 25MWe. we will operate this plant in parallel with national power company and billing will be according to import/export scenario. billing is not a problem at grid stations. the import and export kwh meters will record every thing on incoming lines of grid.

I am NOT the "GURU", . . . but I know how to deal with problems you are referring to. Thus, . . . if you are interested, . . . you can send me an email.

By the way, . . I will be Bangalore on tuesday, . . .

Oleh Iwanusiw

Sorry, redfred, I cannot agree with you. The modern coal fired power stations are provided with

enough means in order to eliminate the ash, sulphur, carbon dioxide, carbon oxide, NOx and other,

so through the high stack the exhausted air is cleaner than polluted air from the atmosphere around.

Two advantages of coal are : infinite reserve at lowest price.

The fossil petroleum materials, gas and the nuclear combustible are more dangerous and limited

as reserve and at higher cost.

In my opinion, if the utility present such instability I'd prefer to work only on my own generator

if it is capable to sustain the load and only as emergency [or redundancy] to employ the utility service.

At least for vital consumers. You may use for non vital installation this service.

With the possible exception of not producing any NOX, all of the waste products produced must still go somewhere. They're just not going up a vent stack.

Don't get me wrong, I'm all for exhaust scrubbing technology being used on existing coal fired plants. I just question the wisdom of building a new coal plant when a virtual surplus of cleaner burning natural gas exists. Also since this application appears to be a supplemental production of power and not the continuous operation of a power plant utility, the lag time of getting coal to boil water into steam seems like the wrong approach. The relatively quick turn on time of a gas turbine to power an industrial island seems like a much better approach than running a tiny coal fired boiler.

The economy of scale efficiency of a power utility only applies when one is producing enough power to be called a utility.

I must agree with redfred on this. One seldom sees such a diminutive coal-fired generation plant being constructed. It is not really economical to do so. Gas fired generation on this level of construction is (1)common practice, (2) fast dispatch (especially when the motive force is a gas turbine), and (3) relatively economical.

I agree with you. However, you'll need a gas source available and stable. Second, in order to be economical, indeed, you have to provide a combine cycle. It is not so cheap. The steam turbine need treatment as a fossil fired boiler supplied turbine. And a coal power station is in function 40 years-at least but a gas turbine about 10 years.

Of course, such a small coal fired turbine I never saw-me too. Usually it start from 300 MW up to 800 MW per unit.

A gas turbine using crude oil or heavy oil will be indicated in this case, in my opinion.

A new cycle has been commissioned in La Porte TX. It is the Allam cycle. In such a cycle, air separation plant upstream sells off the nitrogen (if not used), and keeps the oxygen. Oxygen is combined with high pressure gas in the header at the burners where super-critical carbon dioxide is injected (from the cycle low temperature end). The resulting high temperature, high pressure carbon dioxide and steam are sent through the turboexpander, then the water is condensed and pipe-lined out as pure water, and some of the CO2 is also condensed to be pipe-lined out as food grade CO2. Very favorable heat rate power cycle on a single turbine due to the high density of the operating fluid. SCC is very dense (about 43 lb/ft³) at the cold end of the cycle, thus the compressor looks more like a liquid pump than a typical Brayton cycle compressor.

Also, some other advances in gas turbine technology in the 100 MW class (GE for example) has resulted in low heat rate in a single cycle, no need for bottom cycle. This done through two-stage compression using an effective inter-cooler, along with advanced features of a turbine that resembles other aero-derivative types.

I really doubt that coal is readily available and abundant at this undisclosed site but I suppose it is possible. Therefore whatever fuel will be burned to supplement or isolate these consumers from the grid will have to be shipped in any way. As for the time line, if the grid is not expected to meet demand in the next 10 years then there is a much bigger problem beyond engineering.

Starts to make a case for DC transmission if the area is remote enough, and all the communities on this longer stretch are suffering the same or similar load and voltage issues. At least one manufacturer makes intermediate sized equipment for this, so the barn does not take up an entire county.

Build your new generation facility large enough to handle the load of your facility (with enough spare capacity) and keep the national grid as a backup in case you loose your own generation system.

yes you are very right. that is what we are thinking . but the problem is that our actual load is about 20Mwe. so we have a surplus of about 3Mwe ( 2Mwe will be internal consumption of the power plant.). we want to sell this 3Mwe to the national utility company by connecting in parallel with the national utility company. however the problem in connecting in parallel with the national utility company is the effect of the company voltage/frequency dip on our generators voltage/frequency. so how do we then cope with this parallel situation. i.e. how do i prevent my power plant voltage /frequency from dipping due to a dip in national company voltage/frequency in case of parallel operation ?

While not an expert on power plant operations (there are such folk here who may offer commentary)... I do not think you can do what you wish to do. As soon as you parallel your local distribution to the national grid, you become a slave to the national grids ability to deliver power to the connected load on that grid.

From the sounds of the stiffness of the national grid, 3Mw of additional power dumped to the grid will do nothing to help the national grid and will only expose you to the sags and swells inherent in that grid. Which is what you are trying to get away from by building your own generation system n the first place. Try to find another customer, not on the national grid, for your 3Mw.

You could always dump the 3Mw to a battery inverter system and feed the power to the grid that way, this will isolate your system from the national grid.

It is not a problem, it happens everywhere on essentially a daily or even hourly basis. Electric power wheeling and dealing is a lot like making laws and sausages, you really, really do not wish to know, just consume.

very true and practical.regards

I wouldn't think there's a need to dump any power. Steam supply can be modulated to match power demand.

By "dump" I meant send the excess 3Mw to a battery and inverter system to export to the national grid that is isolated from his local power system. That way... he sells his 3Mw to the national network and keeps his local stuff isolated from the swings.

OK, I see what you mean

No need to burn the extra fuel in the first place. These things have a turn-down of about 50%.

You will absorb that and more in producing the VARS needed to right the ship of sagging voltage.

What you mostly have is a situation where the "national" load is inductive, sufficiently at times to drop down the 132 kV interconnection to dangerously low (brown-out) levels.

What is lacking in the national grid is sufficient phase shifting capacity (cap banks) to correct phase angle, power factor, and raise the voltage back up.

Options:

1. Install your own capacitor banks locally, to raise the voltage when inductive loads dominate the grid. $$
2. Install a synchronous condenser unit (this is like a cap bank, only is linearly adjustable by controlling the exciter on a motorized generator).
3. Install your 25 MWe unit (who decided it must be coal when natural gas is cheaper right now in many places and easier to obtain permitting?), and be prepared to minimal load the unit, but when voltage begins to drop keep raising load and VARS to raise the power factor at your end of the grid.

With or without the national grid, what is the local load you supply compared to the unit you are installing? If that load is more than about 3-4 times (i.e. 75-100 MWe) the coal unit, you may still have problems outputting sufficient VARS to control the situation, IMHO.

your options of cap banks and sync condensers are very appreciated and practical. the bulk consumers load is about 20MWe. internal consumption of coal plant is 2MWe. so there will be 3MWe surplus energy that we want to sell to the national utility company by connecting in parallel with the national utility company. however i want to prevent my power plant generators from tripping because of utility company low voltage/freq problem.

By all means, hire RAMconsult. He is good with this stuff. One other point. You will find that your 25 MWe (or any other capacity generator) will have a range of output power levels from its minimum firing load, to perhaps (intermittently) a bit more than nameplate rating.

Thus you will not always be sitting at peak load, and not always or maybe ever have to market the extra "3 MW ".

It is always a good idea to have your own captive generation when the load is substantial such as 20MW.

It is difficult to remain connected to the grid when the grid voltage drops to as low as 80% rated and generator may not be able to cope with it unless the generator is specially designed or some re-engineering is done to the existing power system.

Islanding the plant (along with captive generation) when there is low frequency or sudden drop in frequency in the grid is another requirement.

Hire a consultant.

I assume, perhaps incorrectly, that you DO know how to use a telephone.

We've seen ample proof that you can use the internet to solicit free technical advice.

Hire a consultant!

It would seem that you would do everybody a good deed by building a larger plant of say 50MWe...or even larger...or institute a rolling blackout strategy like everybody else has done....

I have dealt with similar situations before, and there are engineering solutions that will mitigate the 20% voltage sag problem. The first step involves a load-flow and transient analysis of your connection to the grid; based on my studies with that data it will be possible to determine which solution is best suited to your unique conditions. PM me with the system data and then you can hire me to solve your problem(s).

can you send me your email id and what data do you need for load flow and transient stability study?

You only have to click on a persons name to contact that person through email....

What you are wanting to do is essentially the same as is done at hospitals, airports, and other installations where continuous power is crucial, i.e., an emergency power backup system.

https://en.wikipedia.org/wiki/Emergency_power_system

Coolyaar are you related to Merle? He had grandiose plans for a high head hydro power plant (large size).

Given you past record I don't believe a word of your power plant story.

Dear Mr.coolyar,

Try to check the VOLTAGE DROOP CHARACTER of your AVR and also check the DROOP CHARACTER of the Governor of the Prime Mover.

Generally the Droop Character will be in the range of 5 to 6% for Governor and 5 to 6 % for AVR.

It is known that if the Droop Chaacter is small or narrow range, it will tend to share MORE LOAD and hence tripping may occur. The alteration of the Droop Character has limited scope only.

Pl. post the details of the VOLTAGE DROOP CHARACTER of your AVR and also check the DROOP CHARACTER of the Governor of the Prime Mover. The CR4 Members can study and suggest what you can do.

DHAYANANDHAN.S

as i have already stated that we are in the planning stage of the power plant design process . so at this time it is impossible to know what will the droop settings/ranges of governor and AVR. it will be known to us only after bidding process.

You need to write something to this regard within the bid specifications, based on the final recommendations of the consultant you should undoubtedly hire. Trust that it is very likely no one within your present organization really has the credentials to tackle that alone. Wise to seek counsel.

you are right but we must understand first if the bidder will actually be able to tackle this or not.

It comes down to knowing HV line droop at lowest load for your node of the system, along with the known droop at highest load at your node. That could be a strong indicator of the quantity of power (and VARS) needed to inject at the local node to prevent line voltage sag. If you could even test at a no load condition for a few minutes that could be helpful, although by communicating with the nearest generating node on the national grid as to their known output voltage, and how much load is on the system node your community is situated upon (other than community load) would be useful information as well.

Example: Your community is at minimum load and the line is at nominal voltage -3%, then something out there is pulling down this branch by that amount, perhaps a lumber mill or a paper plant, who knows? At peak load, all the communities on the branch are pulling high loads for HVAC (or if really cold climate, for heater fans), and the line droops to -10% (this is very bad). Knowing the entire branch load at this point in time tells you a lot. It may also tell you that you cannot independently raise the line voltage with that small a unit, although reducing local load that draws on line to near zero might allow to trick the grid. Electrons are unbiased, so they only travel where a conductive path and potential dictate.

"at this time it is impossible to know what will the droop settings/ranges of governor and AVR" and yet you want the forum to give you advice??

It you to bid on an undefined plant, you are certainly not qualified for this.

Hire a consultant and look for a less technical position.

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Arizonian wit trumps Finlandic sensibilities?

have u ever been part of a bidding process???? (i doubt that). do u even know what kind of two studies are needed for power system planning/interconnection? do u even known transient stability study?