NATIONAL ALUMINIUM COMPANY LIMITED - Rites

4.7.3 Winding
The coils used for transformer winding shall be made of insulated, continuous and smooth
electrolytic copper conductors of high conductivity and of 99.9% purity. Similar coils shall be
connected by accessible joints brazed or welded and finished smooth. No corona discharge
shall result on the winding during induced voltage test as specified in applicable standard.
The insulating materials for dry type transformers shall be of type not inferior to Class “F”. All
insulating materials shall be of proven natu nature re and shall be suitable for the suitable for the
limits indicated in the applicable standards as well as the maximum possible winding
temperature and shall not deteriorate when the transformer is operated continuously at its
specified rating at the specif specified ambient temperature.
The inter-turn and inter-coil
coil insulation shall be so designed that the dielectric stress is
uniformly distributed throughout the winding under all operating conditions.
The windings shall be dry cast resin type.
The transformer er windings shall be designed for basic Impulse insulation level not lower than
those specified above.
4.7.4 Protective Housing for Dry type Transformer
Dry type transformer shall be provided with suitable protective sheet steel housing, with
minimum IP P 23 degree of protection for the enclosure. The housing shall have ventilation
louvers provided with wire mesh screens and shall be supplied with suitable lifting lugs. Safety
limit switches shall be provided and wired in such a way that the incoming supp supply may be
disconnected whenever any one of the sides of the enclosures are opened with the
transformer in energized condition.
Sufficient precautions shall be taken so that doors are closed fully. Door locks shall be
provided and keys shall be universal type.
4.7.5 Off-Circuit Circuit Links
The off-circuit circuit tapping links shall be provided on the HV side with appropriate register plate to
show the link location. The links shall be provided with a separate door for access. The door
shall be provided with appropriate safely limit switches which will trip the transformer HV / LV
sides in open condition.
4.7.6 Cooling
The cooling system for or dry type transformers shall have Air Air-Natural Natural (AN) cooling.
4.7.7 Neutral Bushing Current Transformers
Technical Specification:Sec-6, Electrical
Page 34 of 97