standards / manuals / guidelines for small hydro development - AHEC

The tank shall be provided with two separate earthing terminals.The unit shall have rating and diagram plate and will have suitable base channels tofacilitate mounting of the equipment on the structure.Terminals: The voltage transformers shall be provided with bolted type terminals on the11 kV side to receive ACSR conductors upto 8 mm dia (without requiring use of lugs)both in vertical and horizontal directions. The terminals shall be such as to avoidbimetallic action.Indoor TypeThe voltage transformer shall be of resin-cast type suitable for indoor installation andshall be normally mounted on one of the 12 kV incoming circuit breakers.5.4 Coupling Voltage Transformer (36 kV & Above)These transformers should be suitable for use on transmission line to pass through thecarrier frequencies for communication and low voltage for protection and metering. Thesingle phase CVTs should be of suitable ratio (say 66 kV/√3/110V/√3 for 66 kV line)suitable for outdoor installation on steel structures. The equipment should be suppliedwith terminal connectors suitable for vertical take off from line conductor and hot dipgalvanized base fasteners. Other details should be in accordance with the specificationsfor potential transformers. The secondary terminals should be provided duly marked forabove requirements.The wave traps should hanged underneath feeder bay structure. The carrier frequenciesand wave trap capacity should be decided in accordance with the other ends of thetransmission lines terminating at sub station.6.0 TransformersSelection of power transformer is discussed in section 3. Layout of transformer isdiscussed as it is the largest piece of equipment in a substation and it is, therefore,important from the point of view of handling and station layout. In small hydro stationstransformer are installed in the switchyard and the bay width is determined bytransformer dimensions. Handling of transformer is normally done by the powerhousecrane and for large transformer rails are laid from powerhouse to the site of installation inswitchyard. For this purpose bi-directional rollers are provided on the transformers.Arrangement for removal of transformer in case of repair/maintenance without disturbingother equipment is required and also affects layout. In order to reduce the chances ofspread of fire, transformers are provided with a soaking pit of adequate capacity tocontain the total quantity of oil. Sometimes where feasible drainage arrangements areprovided to drain the oil away from the transformers in case of fire. Besides, separationwall are provided in between the transformers and also between the transformer androads within the substation.2-13