Hi guys

I've a bit of a problem here at work I need to get a costing for the hourly run of a 3 phase plant, with all motors added together the full load current is 75.9A, £0.05/kwh. What is the calculation?

Thanks

sorry guys just found the calculation.

it is (voltage x current x root3) / 1000 = KVA

KVA x Hours run x Unit cost = Cost

Motors have a high peak current when you first switch them on that drops as they get up to speed. Don't use the rated current of the plate as a guide to running cost.

The power that a motor will consume is dependant on load. A 1kW motor can run at 1kW, basically for ever. If your load varies between 100W and 500W, you'll never draw the full power or current.

Watch out for power factor and peak load metering on industrial power supplies this can increase costs a lot!

Caber

I had the full load current from a motor spec sheet so was able to work out the total max current being used at any one time. The start up procedure of the plant means that once it is up and running nothing speeds up or slows down so taking the peak into account is not neccessary. It is a waste recycling plant which is basically a couple of converyors, magnets and trommels etc. The buyer wanted a rough price so i gave him what we think is the worst case scenario. It worked out to be £140/week!