Electrical

Look for "loops" in the conductors and the supports that might induce currents in the steel, which is magnetic.

I would suggest you analyze the bus for a loose connection at the point of high temperature and also check the support insulators for cleanliness and condition.

A high resistance joint can cause heating.

The support insulators may be dirty and/or breaking down allowing current to leak to ground causing heating. A meggar or DC Hypot can be used to determine if the insulator is breaking down.

1. Certainly it is the case of partial failure of insulator, which allows current to flow through the MS angle. This will continue until the insulator totally fails and draw high current till the breaker trips.

DHAYANANDHAN.S

You have the equivalent of an induction cooker.

Induction cooking - Wikipedia, the free encyclopedia

In an induction cooker, a coil of copper wire is placed under the cooking pot and an alternating electric current is passed through it. The resulting oscillating magnetic field induces a magnetic flux, producing an eddy current in the ferrous pot, which acts like the secondary winding of a transformer. The eddy current flowing through the resistance of the pot heats it.

This is due to eddy currents in the magnetic path. The brackets which supports the FRP supports acts as magnetic path. You have to break the path by introducing non magnetic material say aluminum strips and also stainless steel hardware for fixing the brackets.

I agree with the opinion that could be steel losses some where to rise the local temperature.

However, in my opinion if the phase currents are balanced and no neutral -or grounding wire-current will flow through the steel enclosure the steel losses have to be minimal influence.

First of all we don't know what represents 90oC and 50oC.Is it the air temperature or the equipment temperature? Equipment temperature of 90oC could be a normal temperature-mainly the cable connection.