SWA Cable Calculation Help

[CamplingM]

Dear Forum Members,

I am hoping you maybe able to provide some cable sizing help. We have a 450KVa generator which has a 400amp Main Switch going to a Dorman Switchgear. Only around 50% of the generator power is currently being used. We had a second generator (170Kva) generator which has recently gone pop. We are wanting to move the services off the knackered generator onto the 450 generator.

The two locations are 120m apart. The SWA Cable will be buried for around 60m and clipped the balance.

We were intending to put a 160amp MCCB in the Dorman Smith Board.

Please could you advise on the recommended cable size? We are hoping to use a five core SWA or 4 Core and Earth.

Regards Matt

 

[Sintra]

Have you done any calcs on this yourself?

 

[Engineer54]

So you're replacing a 170 KVA generator with a 450 KVA generator, who came up with that bright and potentially disastrous idea?? One of the biggest and most common mistakes made by those that have little experience of working with generators is to oversize them. Generators are far happier working at loadings approaching rating than working way below it's rating. As a rule of thumb the minimum loading of a prime power generator is 70%, anything below that, really needs an in line resistive load bank to bring the load back to 70/80% of it's rating. Preferably auto stepping that adjusts with load.

Running a generator with minimal loading is like running the engine at idle hour after hour. What it will go is reduce it's life expectancy by cokeing up everything the valves and head etc etc, shorten periods between scheduled maintenance times, and overall increase the running costs by not an insignificant amount. I've seen damn good but oversized generators, that have destroyed themselves in a matter of a couple of years running at less than half their rating!!

 

[davesparks]

If I've read it right the 450Kva is already in use with a 50% load and they now want to add the load from the knackered 170Kva onto it.

 

[Knobhead]

Something doesn’t add up here. A 450KVA set with a 400A main switch? You’d have to be running at 660V for that to work.

As for the cable size, are you going to pay a member to calculate it for you? Post your calculations and someone will check them for you.

 

[Engineer54]

If I've read it right the 450Kva is already in use with a 50% load and they now want to add the load from the knackered 170Kva onto it.

That may be me then, not reading the post too well.... Need another coffee me thinks!!