NATIONAL ALUMINIUM COMPANY LIMITED - Rites

stress, noise on communication system and undesirable circulating currents between the
neutrals ls at different transformer stations.
The Transformers shall operate with minimum noise and vibration. The cores, protective
housings and other structural parts shall be properly constructed and windings properly
braced so that the mechanical vibrations are kept to the minimum, thus reducing the noise. To
this effect, the laminations shall also be bonded together with appropriate resin. The core core-coil
assembly shall also be fixed in such a manner that no shifting or deformations occur during
shipment or installation.
Each transformer shall be designed for minimum no no-load load and load losses within the economic
limit.
All electrical connections and contacts shall be of ample section for carrying the rated current
without excessive heating.
All mechanism shall all be of stainless steel, brass, gunmetal or other suitable material to prevent
sticking due to rust or correction. If any temporary fitting is fixed to the protective housing of
the transformer for transporting / handling purpose, these shall be identica identical as well as
instructions and illustrated drawings shall be furnished to facilitate their removal at site after
erection.
4.7.2 Core
The framework, clamping arrangement and general structure of the cores of each transformer
shall be of robust construction and shall be capable of withstanding any shock to which they
may be subjected during transport, installation and operation. The assembled core shall be
securely clamped on the limbs and the yoke to build up a rigid structure. The clamping
pressure sure shall be uniform over the whole of the core and so adjusted as to minimize noise and
vibration in the core when the transformer is in operation. The framework and the core bolts
shall be effectively insulated from the core so as to reduce the eddy eddy-currents rents to the minimum.
The magnetic circuit shall be built of high quality, low loss, non non-ageing. ageing. Cold rolled, grain
oriented, silicon steel laminations (CRGO Prime Grade) having excellent magnetic properties
and specially suitable as core material. Lamina Laminations tions shall be insulated from each other with
material having high inter inter-lamination lamination insulation resistance and rust inhibiting property and
also capable of withstanding stress and mechanical vibration.
Necessary cooling ducts shall be provided for heat dis dissipation sipation from the core so that the
anticipated maximum hot spot temperature in the core shall not be injurious to any material
used in the core assembly.
The core-clamping clamping frame shall be provided with lifting eyes having ample strength to lift the
complete te core and winding assembly.
Suitable provision shall be made in the dry type transformers for effective core earthing.
Technical Specification:Sec-6, Electrical
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