Off Grid Start-Up

I like you're sentiment but the collateral costs would be astronomical in relation to the savings recouped. It's not just the cost of the generator, the switch gear to control the set up would be a substantial investment.

Keep trying on the cost saving.

I wish you all the very best.

Rather than clutching at straws like this one, concentrate on the basics of loss prevention first:

"A place for everything and everything in its place. Nothing there that shouldn't be there." - Anon

Some call it "housekeeping".

Have you installed PFCC?. During starting as there is more VD fix another capacitor via a timer only during the starting period.

We are billed according to our max demands on the grid. It's the start up we pay for. If it cost 100K to set this up and we cut our costs by even 15% it would be a viable alternative.

Our soft starts are fairly state of the art. I'm thinking the capacitors are pretty close to what they need to be but I'll learn more about that and see.

Thanks all for your input

Great Idea, this is what our local Cement company does when they re-start their kiln.

Volts: 34000, 3Ph 7200A, HP: 760 Line drop, 23% on each start up, 4 kilns. Recovery time: 37 mins. Power company jumps through many hoops. Amazing site. You have to see it to appreciate it. All happens in the middle of the night and only the clocks take a hit from the 60Hz. Over time you will need to reset your clock. Only happens a few times a year when the Kiln has to be re-Lined.

From the rough estimations you give, I assume that these motors start a huge inertia system. Also assume you can reduce or even eliminate the actual load (apart from the load due to inertia at start) If both those conditions apply, I believe you can double or triple the soft starting time and significantly reduce starting current, even close to normal working current. But do verify your billing system details before doing anything. S.M.

a battery bank and a 3 phase UPS of the line following type as used to run large data centers would work here.

You would need to inspect the cost from suppliers of large UPS equipment. I know it can be done, but there needs to be a detailed cost out for it, someone else commented that the cost of the switching and line phase matching equipment may well kill the concept.

200 Hp = 150 Kilowatt hours per hour, at 10 cents per KWH (what is your rate?) = $15 per hour each

ten motors = $150 per hour, if you have 150 workers per shift = $1 per hour per worker, more or less, as the number of workers differs from my guess.

So management might be engaged in driving the workforce with lies?

What will be the voltage drop in UPS battery when you start a large motor of given capacity,how long will it take to recharge?.

What about synchronizing a smaller size with the grid say half the rated for a 200hp motor and retransfer the total load to the grid once it reaches it's operating speed.

Hello,

You could look into 'variable speed drive' for each motor to save energy cost. Please see "en.wikipedia.org/wiki/Variable-frequency_drive" for more information.

Yes, you can use one large enough(500 kw) genset to start up the 200hp motors

individually, then synchronize the genset to the grid and smoothly transfer the motor

to the grid, then repeating the process for the other motors. BUT big BUT, CONSIDER

THE COST OF OPERATING THE DIESEL GENSET AND OF THE PROCESS OF THE MOTOR

TRANSFER TO THE GRID. WILL IT OFFSET THE GRID BILLING?

Posts #6 and #7 make good sense.

I note on #6, J. Raef's, point that 10 motors at a minute each, started at 90 second intervals would fill up the 15 minute window, while 9 motors running plus the last starting may be 150% of the steady final load current if your start is not very "soft".

So could automating the starts sequence (minimum time between starts) to reduce overall start time or breaking up start into two groups of 5, spaced 5, 10 or 15 minutes apart dodge the charge rules?

Capacitor Power factor compensation to unity of each of 10 motors, gives a capacitor current enough to cancel the lagging current of one motor starting compared to no-compensation.

So lots of thinking time on charging rules and operating practice could be imminent!

I think JRaef nailed it and others have concurred. I need to find out for myself how the billing actually works instead of going on hear-say from someone who is supposed to know because it's their job.

But a HUGE thanks to all you guys! Some posting for their first time(like me) You really have an awesome forum here and have given me a lot of incentive to keep learning.

Pnaban, check out Corvus-energy.com They could meet this discharge with a bank of Lithium Ion batteries that would re-charge in 30 min. Awesome!

Scandrews, two of our crushers do just that. They have two motors. One starts the bowl then the other joins in.

You could use a large flywheel storage system coupled to a motor which could rev it up in say 15 minutes. Once it is running at peak speed, a generator coupled to this flywheel could be synchronised with mains. Starting your 200HP motor on this setup will eliminate your starting peak due to flywheel feeding the energy. Flywheeel energy storage systems upto 1000KVA are available. You may read more about it in:

http://en.wikipedia.org/wiki/Flywheel_energy_storage