Basic protection scheme for 11kV industrial plant

[DrDrreeeaaa]

Hi All,

I am developing a concept design for 11kV power distribution system. It is a basic system with 11kV supply from the distributor (250MVA fault level) feeding 3-off 300 kVA 11/0.4kV TFs and 1-off 1.0MVA 11/0.4kV TF.
It's just a bus topology, no ring, etc.

I need to select the appropriate switchgears for the job. At the moment I have switch fuses for both the service isolator and protecting the TFs, but, the service isolator (100A) will blow when I energise the 1MVA TF.

How does one get around this problem? (this is likely a very elementary problem)...

 

[dpc]

One uses a larger fuse. The fuse has to be sized to withstand the transformer inrush.

I recommend you purchase the IEEE Red Book and read it as a starting point if you are trying to design an electrical system.

 

[LionelHutz]

The rated load of the 4 transformers you list adds up to 99.7A at 11kV. A 100A fuse is typically not used to service a 99.7A load.

Or, as dpc posted, use a fuse that will not blow. You have to take more than just the rated load into account when sizing this stuff.

 

[DrDrreeeaaa]

Thanks guys. I have the red book and I am reading.