Power Consumption

I would say an 85kVA genset or thereabouts. If you are already running four 14kVA welders, and allow 2 x 14kVA as a starting reserve for the fifth, that comes to 84kVA, which I rounded up to 85.

Tornado has given you good advice.

Since you indicate that you have no idea how to calculate the load, I'd advise strongly against trying to save money by buying less generator capacity than he recommends. In fact, I'd even buy some more reserve power for future growth.

Most of all, I'd suggest investing in a local consultant for a few hours to give on-site advice and council.

Actually given that it is highly unlikely that you would ever have all of the welding units maxed out at 100% output at the same time you should be able to get by on a 50 KVA gen set just fine.

I used to work as a service tech at a welding supply chain store and I do a fair amount of welding myself as well and I can assure you its rare to ever need to run a welding system at 100% capacity let alone 5 of them all at once.

I don't know about India, or your experiences, but here in the USA, if you are calculating the power required for a line of equipment, to meet code, it would be by taking the FLA of everything in the system as the power requirement.

I agree that it is unlikely to ever happen.

Depends on if this is a hard wired permanent system intended to be a full capacity backup power unit for a facility or if this is for a portable system intended primarily for on site applications.

He didn't specify so I went with that assumption that being the inverter welders are only 14 KVA input they are of the portable suitcase style and thusly this would be for a portable power plant intended for onsite work.

Fair enough.

Our customers used to scream when we gave them the power requirements we'd need BEFORE we could install our equipment.

A typical process line might have 8-10 7.5 HP pumps, then 4-6 5 HP pumps 10-20 1-3 HP pumps, a couple of 10 HP dryers and 10-20 conveyor drive motors.

Oh, throw in 10-15 electric sump heaters too.

YEa that may be true. I never have had much to do with new setups or permanently installed backup power systems.

As a service tech I tended to have to deal with the portable power systems far more often which is what I base my numbers on.

The Diesel Engine and 3 phase alternator will have to be sized separately.

To size Engine go as follow:

Rating each invertor = 14kVA

Quantity = 5

Total power = 70kVA

Power Factor = 0.93

Total kW = 70 x .93 = 65kW

Your information about DC output of Welding machine is confusing, could be that 72V is the Open Circuit Voltage and when the arc strikes, current being 400A, voltage is less (because 72 x 400 = 28.8kW which is more than double the input and is not possible).

Anyhow at 65kW output of alternator, assuming 90% efficiency of alternator, Output at flywheel of Engine shall be = 65/.9 =70kW or 94HP. You can select a Diesel Engine of Prime rating of approx. 85HP. This will have fuel stop rating of (110%, which is 94HP) and shall be sufficient for this application as your load is not continuous intermittent even duty of welding machines is intermittent hence Diesel Engine with prime power rating of 85HP at flywheel is adequate.

Next is selection a suitable synchronous alternator. Because it is invertor, assume it is 6 pulse, harmonics will be less but not low enough and alternator has to be oversized to prevent it from overheating.

Coming to rating of alternator to be coupled with the Engine:

Margin for Harmonics = 70/0.66

= 106kVA

Next when the arc of welding machine will strike it will result as a short circuit and the voltage of alternator will dip suddenly. AVR will take some time to respond.

The response time of AVR + Excitation system + alternator is more than 20 m sec. Hence beyond Transient time of reactance of alternator.

The transient reactance Xd' of salient pole alternator of rating being considered is approx. 30%.

Considering 3 out of 5 welders striking arc simultaneously, expected short circuit current approximately shall be 90A.

At 90A inrush current (equivalent of surge kVA of 65kVA) and 30% transient reactance the voltage dip for 105kVA alternator shall be very high of the order of 16%. This is acceptable limit (initial dip of up to 30% shall be acceptable for this type of job). (I have voltage dip calculations in excel sheet - not possible to type formulae here).

The above voltage dip is up to transient time of machine (less than a second), hence please do not worry for same.

Also harmonics will distort the voltage of alternator that will create problem in AVR. That means either select an alternator with PMG (permanent magnet generator) type pilot exciter or install a low pass filter in ac supply to AVR.

Summary: Recommended is 85HP (Prime Power) rated engine coupled to 105kVA, 3 phase Prime rated (Duty Class S1) brushless synchronous alternator having PMG pilot exciter.

Welding Inverter manufacturer has provided the technical broucher in their website .....http://www.adorwelding.com/site/pdfs/dl-ChampT400.pdf which would clarify ur doubts if any.

Manual says, Open circuit voltage in the DC output is 72volts & welding current range is 10-400 amps.

Welding Current (40°C 10 minute cycle) is 400 amps @ 60% duty cycle and 310amps @ 100% duty cycle.
As per cummins India, Diesel Generator is coupled with Permanent Magnet Generator. They recommended 82.5KVA genset.
Please confirm once...
Thanks..

Isn't there someone in your company who knows ANYTHING about welding and electrical power requirements of the equipment??????

I'm curious how your company can possibly stay in business.

"I'm curious how your company can possibly stay in business."

Oh heavens of all people you should know by now that any idiot can run a business.

If not then take my experienced word over it. I have seen far too many idiots running businesses.

Sad, but true.

I'd say that the requirements for the OP's job must have been the ability to read, with no requirement that logical thought accompany the exercise.

That is what I suspected that 72V is open circuit voltage of the welding machine and therefore did not consider same in my calculations.

To which Cummins Dealers you are talking to, Jakson, Sudhir or Powerica. I know there capabilities and doubt they have considered effect of harmonics and sudden short circuit in sizing the alternator. They are fine to size machines for normal applications, but doubt if can handle properly applications as yours.

Another problem is that when packaging DG Set for the first time, Torsional Vibration Compatibility of drive chain has to be carried out. Cummins would have done this for standard rating of Engines with their Stamford (Newage in India) alternators and given to these packager - these packager do not have the TVA Data and tools to check for non-standard packages. Hence these dealers will offer you a standard package.

You can go for 85kVA DG Set but take a written guarantee (not verbal - Jakson and Sudhir are in the habit of backing out) in clear wording that

". .......... has considered effect of harmonics due to welding machines in selecting rating of synchronous alternator and will be responsible in case alternator winding overheats of machines do not perform satisfactory due to sudden short circuit current occurring of striking a number of welding machines simultaneously."

Sorry for the error. Pl read 82.5 in stead of 85 in my last comment.

See #1↑

what he say ^

simple:

YMK ( YouMayKnow )

things happen; and no one asked if ALL would ever be achievably at FLA in practice in your field of any instantaneous daily activity, relatively, respectively

if not an idiot at the helm,

then truly regularly unknowing folks, politely ignorant, as I am of so much, make lots of money, and run well in terms of 'success'

(compared to all the leaflets in the books on the shelves of the global library, and books already removed, etc., and books arriving a week ago , yet to be shelved for access...)

Thank you all for ur suggestions & comments.....

Good Day....