How to Synchronize from diesel generator to Grid power system

There are already 2 threads active on this aspect (Voltage question and another one Feeding the grid)

The necessary details are already covered on these threads. The references for regulating and synchronisation is discussed and links are provided.

_{You have almost 3MW generator as per prelim calculations.}

Also check this thread http://cr4.globalspec.com/thread/32583 There are a few earlier ones also on this.

dear,

following precautions need to be incorporated...

1. Vector surge relay for isolating dg from grid during abnormal functions

2. pf control capacitors auto mode.

3. revrse power relay to protect grid / dg set

4. load control for constant power out put mode from dg set

5. fault levels to work out & accordingly, switch gear to install.

6. Earth fault / excitation failure / -ve sequence relays to incorporate

7. df/dt frequency relay to incorporate

regards

Dear Mr. Harry Potter,

I want to supplement your points.

The Droop Character of Voltage from No-Load Speed to Full-speed is also to be considered.

dhayanandhan.s

Aikhh,

May I suggest a much more cost effective way to do this?

Instead of running a Diesel genset, you should look into a flywheel based UPS (Uninterruptable Power Supply) system. I don't mean the inverters types.

They have several designs, but the basic idea is a flywheel running at some higher speed that allows time for a diesel genset to start up. Some can "filter" the Grid voltage and give much better and stable quality electrical supply, including power factor correction.

You only run the diesel once a month (or recommended by the manufacturer), instead of all the time. This achieves what you seem to be wanting to accomplish without having to waste fuel.

A Diesel genset will be several times more costly per KW than Grid power. Coal is 0.21 cents/gallon equivalent in the USA and diesel is $1-2.00/gallon, or about five-ten times in fuel cost. Diesel gensets are only efficient in a narrow band (75-95% of rated output depending on model), and if you need to supply for industrial electrical motors and varied demand, you may have to run the Diesel Genset down in a very inefficient range ( <50%) by sizing it much larger than average load, depending on the allowance needed surge demand. The grid is an infinite flywheel of sorts, and your diesel genset has to have enough beef to handle peak demand or at least critical processes.

The UPS guys will help you size it. They might also give you some perspective and some good ideas that may help you with your original idea...

Seaplaneguy

Dear seaplaneguy,

Thank you very much of your valued information.

Regards

it totally depends upon the company and make of genset to operate parallel or in synchronization. if u buy a diesel generator then u have to buy a synchronization system that will synchronize ur generator with grid in parallel operation.

faheem

electrical engineer

Guest,

The UPS usually has a synchronizer and is already and continuously synchronized.

Can the breakers be electrically closed or opened on your existing system? If the existing breakers can only manually closed, then you will have a problem trying to transfer back to main power once on generator. This could be your biggest problem.

I don't know if I'm an electrical specialist but here's my two "cents":

I guess you want to sync to the incoming power so you can generate your own power and shut down the generators when you need to. To do this you will need synchronizing equipment (automatic or manual) - this equipment will match your generator voltage and speed to the incoming (utility's) power and close your unit generator's breaker at the correct moment. Once you are synch'd to the main power you can do what you like with your generators (shut them down, share load, etc.). You can also operate the units isolated (you control frequency and voltage) and the load is constant; once you have assumed all your plant load on your generators you may open the utility breaker without the 4000 amps arc, ha ha.

A closed transition transfer switch will work too.

Dear hughes838,

Thank you very much of your reply.

I am from Glass manufacturing plant and i hv 13 production line with high air consumption from compressors,combustion and cooling system. So my essential loads about 4000A at 415v.

In order to prevent or avoid long start back time for each machine and other utilities system,i need a 'Seamless' electrical supply switch over from the grid system (If the power supply company keep us inform in advance).

I have make a record, we have interruption of power supply as high as 6 times per days. and we need few days to 'normalise' our product quality

Thank you

With 6 interruptions average per day, can you depemd at all on the supplu co ? Is it not better to run your plant on captive totally ?

Of course for the compressor, etc, depending on your requirements you may have on line buffer tanks that will get you a few minutes while you start the Gen sets.

But for the furnaces no such luck.

There is no point in having the grid synchronised if you are going to run all your gen sets to your required load.

Dear Aikhh..

There is another scheme also , which we have worked out successfully in other sophisticated plants....( high speed robotics)

1. Have UPS of 1 min. capacity for each 13 production lines

2. Have Automatic Mains failure DG start facility that whenever the plant mains supply failes, DG shall start within 6 seconds and feed power to selected feeders. Again, whenever Mains supply is resumed, DG shall automatically stop & plant shall run on mains supply. ( we had provided 4*500kva dg sets parallel ) with PLC.

3. Advantage over grid synchronizing scheme is that 1. Complications of grid sync is eliminated, Cost of UPS is increased but cost of heavy switch gears / critical instrumentations for grid sync. is eliminated . With this, over all simplicity & user friendliness with the power. Fuel savings in operations and no need of every time communicating with supply authority ..... as 6 times per day, supply authorities may not be able to inform you well in advance every time.

regards

I too thought initially on these lines, But 5MVA UPS seems too much to me.

Hi Aikhh,

Sorry I "missed the boat" on your problem. Are all those power outages unscheduled? If the power company is having that many faults, they're probably not making any money. However, if the outages are scheduled (rolling blackouts) then you can be forewarned so you can sync your generators and go isolated until the outage is over. Another factor is: unless the fuel is excessively expensive, viewing the criticality of your operation, I agree with SB that until the commercial power system is normalized you should operate isolated (captive).

How many, and what types of generators/circuit breakers/PLC's do you have?

Has your company considered discussing the problem with the power utility? If those outages are scheduled then there's also a possibility that something can be negociated to provide more reliability.

I am now looking at your problem with the grid sync, but I thought I would provide some interim relief, ha ha.

hI hughes838,

Thank you very much of your reply,Normally the 1st outages is unschedules if the fault is came from underground HT cable or flash over at switch gear from the power company.They are the GLC (Govement link company) and the ONLY power producer & distributor,we cant do anythings, even we have wrote letter to enery minster ,call for regional power manager to hv a dialog,meeting etc. but in turn it came worsen.

We have suggest to lay a 'dedicated' HT (22Kv)power line from the nearest Main Sub station from Power company to our factory which is 4km away and the estimate cost is about USD 2Millons

Of caourse diesel is much expensive at USD 0.47 /Liter and our DG consumption is 200ml / kw

I am very confident to said the power outage is 100 % from power company and so far it never happen at my site (all the electrical equipments and system).

We have 2 block of DG power generation room.

1. 640Kva x 2 unit (Cummins ) / 1000 A / Cummins / Siemens S7 300

another power generation room is ( distance is 200m away from each generation room )

2. 875Kva x 2 unit (Simens ) / 1250 A / WardWood / Siemens S7 300

Glass industrial is highly energy orientated industrial so reliable electrical system is one of the key factor to make good profit.

Thank you

Looks like you are alomost in similar condition as over here. The electricity supply co cuts the power and says transoformer or cable or some other fault .

I still feel dedicated supply may be good for you, in case you can not have any outage. Normally here (I don't know about smaller industries what they do) but the process industries, that can not have interruption - where the total furnace load will be waste in case of power interruption, go purely captive for these applications and grid+ generator based systems where you may have some breathing time .

This way you can reduce the dependence on grid interruption as well as save on the diesel. Look at the economics of it. (average losses due to interruption vs going captive, vs going limited captive).

Air supply can be regulated through accumulator tanks to supply till the generators are switched on, this 1-2 minutes interval can be fed from this.

Lighting can be reduced for outages to limited nos fed by UPS.

etc.

Guru sb,

Thank you very much of your reply,we have lots of air tanks which distribute and regulate compress air everywhere before air operate machine but due to high air demand 300 to 450 NM³/min (with some diesel engine & NG engine driven compressors). The main air tank have the limitation of the physical size.

Regards

Hi All,

We have a similar situation where we tried to synchronise and tie in our generator 400kW to the 415V,3phase,4 wire(R,Y,B,N) busbar supplied by utility.

As soon as our generator is in synchronism with the busbar, the generator breaker was closed but immediately the generator breaker tripped by earth fault.

We suspected that it was due to the busbar's unbalanced loading at time of closing of the generator breaker.

Someone suggested that since our generator is with the star point solidly grounded, we must open the generator star point ground after the successcul closing of the generator breaker. Is this true? I'm doubtful about his suggestion.

However, i have some explanation about why the earth fault operated. Since there's unbalance load in the busbar, and that the earth fault protection is using a summation of the 3-phases(without the neutral) method at the generator side, this could cause the unwanted earth fault protection to operated under unbalanced load condition.

But my question is, can i place a Z-CT at the generator star point earth to detect the earth fault? Will this solution be table under the unbalnced load condition?

Hope someone could advice.

How did yo syncronise the gen set with the mains utility????

syncronising is verry importasnt firs tthta then close the breaker then no problmes...

Dear Sir,

As you said you cant stop incoming supply to your machines. I like to know few things to know. Considering your plant will not disturb 60 to 80 seconds interval. Because there are various coupling / synchronising logic.

a) You can use 3-4 numbers DG Sets in ideal condition and provide bus coupler in between main grid and DG.

b) Synchronise DG Sets along with main grid.

Note that option "b" will be costlier from operation cost point of view.

Thanks

Sudhanva Madhukar Mahamuni