This document is applicable to ceramic insulated outdoor bushings for highest voltages for equipment of 24 kV and 36 kV, with rated currents of 5 kA and 8 kA for insulating liquid filled transformers and frequencies from 15 Hz up to 60 Hz.
This document establishes dimensions to ensure interchangeability and adequate mounting of bushings.
Two types of construction are specified, type A and type B, both types for highest voltages for equipment 24 kV and 36 kV and rated currents of 5 kA and 8 kA. The mechanical stresses of the conductor tube define the difference between type A and type B. The conductor tube of type A is axially and radially fixed in the top of the bushing. The inner line terminal of the transformer can be flexible and without any special support for the lower end of the conductor tube.
For new installations bushings of Type A are expected to be used. Type B bushings can be supplied at the request of a customer.
In case of type B, the conductor tube is only radially fixed in the top of the bushing. In that case, a rigid support is mounted to fix the lower end of the conductor tube (for example, in combination with a drip proofed sealing end). The drip proofed sealing end is often required in the service requirements. In this case, it is not possible to use type A because of the existing double fixation. Therefore, both bushing types A and B are be specified.
The condition for the usage of type B is that the drip-proof sealing end is able to withstand the mechanical stress in axial direction.