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Portable Generator Volt drop concerns

Jones88

I want to get a diesel generator into an underground cavern to do some civil works. Unfortunately the generator will need to be situated 275m away from where the power supplies need to be (ventilation issues in cavern), and I'm concerned about the voltage drop. I've run some simple calcs, and the cable size recommendation is 10mm, however the standard size cable for a 10kVA transformer input cable plug can only accommodate a 6mm cable. It seems overkill to start thinking about a distribution board etc. for a job that will take a week, does anybody have any suggestions? I've included details of what i plan to use below: 

20kVA Diesel Generator

275m of cable (6mm) 

10kVA transformer (32A 3Ø input, 2 x 110v 32A and 4 x 110v 16A output)

Allowable volt drop: 5% (assumed)

Total Load is approx 9,500 W

The load at the end is a coring drill and some halogen lights. 

This is quite a unique issue. I'm hoping the 10kVA transformer can accommodate incoming voltages with up to 10% volt drop (investigating with supplier). Any ideas/feedback welcome.  

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  • 0

    well every 6m of 6mm2 core will be 16-19 milliohms. 275m of 6mm core is about 0.8 ohms.

    9500 watts split over 3 phases at 3000 watts each, call it 15A. Drop about 12v in each phase, neutrals should cancel. Should be OK.

    The transformer will not care, but the op will droop on load. The lights will probably flicker a bit as the drill starts.

    I suggest in this case you will be OK, so long as the loads are well balanced, you may want to wind the genset to nearer 240 than 230 when it starts, and  bring the loads on step wise, not with a bang, so iit has time to stabilize as the load changes.

    Mike

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  • 0

    well every 6m of 6mm2 core will be 16-19 milliohms. 275m of 6mm core is about 0.8 ohms.

    9500 watts split over 3 phases at 3000 watts each, call it 15A. Drop about 12v in each phase, neutrals should cancel. Should be OK.

    The transformer will not care, but the op will droop on load. The lights will probably flicker a bit as the drill starts.

    I suggest in this case you will be OK, so long as the loads are well balanced, you may want to wind the genset to nearer 240 than 230 when it starts, and  bring the loads on step wise, not with a bang, so iit has time to stabilize as the load changes.

    Mike

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  • 0 in reply to mapj1

    Hi Mike, Thanks for your feeedback. I came to the same conclusion i.e. it will probably be ok, but without knowing the spec of the equipment used, i didn't want to risk any issues. We've looked at the cost of hiring larger equipment, and it is not substantial, so have decided to play it safe to avoid any issues. Thanks

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