I have an application where a 112.5kVA 480v/400v star/delta Ydn transformer is to be used to step down the voltage from a wind turbine panel from 480v to 400v. The transformer is located near the supply authorities point of connection and is 280m away from the turbine panel.
Are there any guidlines in selecting the protection required for the transfomer and what uk regulations must be adhered to?
I would like to use circuit breakers if possible and I presume I would need one either side of the transformer, considering the transformer will see a supply from both the wind turbine panel and the supply authority mains.
I realise the protection would need to cover both the transformer and the cabling.

I would just use circuit breakers for a transformer of that size. If you wanted somthing a bit better you could use transformer differential it just depends on how much you want to spend.
How is the 400V side earthed? You say its dn?
Is this the main exoprt transformer for the turbine or to supply auxilary power?

The transformer is being used to step down the turbine panel voltage of 480V to the UK supply voltage of 400V. It is in line with the power from a 60kW turbine, once the power has gone through the turbine power/control panel.
The selection of the transformer is by the wind turbine manufacturer.
He is earthing the primary side which is connected to the turbine panel, but he has given me delta on the 400v side.
Since it is delta I have no star point to connect an earthing system.
Does this create a problem with our regulations?

From what you say, the transformer is YNd as your neutral is presented on the primary side (assuming that you are treating the 480v side as the primary). Having a delta secondary is only an issue if you are planning to run independantly of the DNO supply. With a star secondary, you would only earth the star-point when running split from the DNO.

As Arthur said, the protection you put on the transformer will depend on how important it is to you. You would have to use fuses or circuit breakers to prevent from overload anyway. The only other thing you could do, is use a differential protection round it to provide fast acting protection against internal faults. This will not prevent a fault developing, but may make the transformer repairable under some circumstances as well as limiting the chance of a catastrophic failure. Depending on the location of the CTs (if you decide to use this) you would also be able to protect your longish connecting cables. The protection would need a circuit breaker on either side of the protected zone to trip for a fault.

Regards,

Alan.