Diversity

[James]

Good morning,

Just trying to get my head round a diversity issue.

Will be a new board fed from a panel board adj transformer

Have to feed 3 machines
Machine 1 140kw
Machine 2 80kw
Machine 3 80 kw

They are production machines (lathes) so will be in use at the same time but the ratings given are the theoretical maximum they can use, I.e all motors running at full load.
Prior experience tells me that none of these machines will draw even half their full load.

So approximate currents should be (max in theory)
Mc 1 250A
Mc 2 140A
Mc 3 140A

My thoughts are each machine should have a supply capable of providing the maximum current as per machine spec.

So 250A and 2 off 150A supply’s
New board will be required to feed them and I am thinking
100% of 250A + 50% of each 140A gives a board loading of 390A after diversity.

What are people’s thoughts to this?

These are expensive cables and breakers, just wanted a second opinion really that I am in the right ball park. It’s been a long time since I have done installs of this size.

 

[Lucien Nunes]

I agree a lot of machine tools run most of the time at a fraction of their nameplate power. Even if 40kW is being used to convey chips, pump coolant and load pallets, the remaining 100kW would rip its way through a lot of metal very quickly. But you would have to speak to the production engineers to get a clearer idea of how the machines are being used before estimating diversity, otherwise there are too many variables. One of our jobs starts out with a billet of 302 and proceeds to demolish it at a solid 80% spindle load until there's only a paper-thin bit left. Another job on the same machine pootles about for hours tickling a piece of ali here and there, with the pumps drawing more than the spindle.