standards / manuals / guidelines for small hydro development - AHEC

(iv)Electro magnetic type interlocking should also be provided to avoid wrong localoperation of the isolator (manual or motor) when the corresponding circuit breaker is inclosed position. Operation of isolator may be categorized manual or motorized withremote facility according to facilities provided in the system.Isolators and earth switches should be so designed that the above noted requirements canbe conveniently met.3.8 Supporting Structures3.9 TestsAll isolators and earthing switches should be mounted rigidly in an upright position ontheir own galvanised steel supporting structure and not on the bus-bar structures.Each isolator and earth switch should strictly comply with the requirements of all the typetests and should be subjected to all routine tests stipulated in the latest edition of relevantIndian standard.Copies of the type tests already performed on similar type of isolators must be obtainedand scrutinized for adequacy.4.0 Current Transformersa) 12 kV and AboveCurrent transformers may be either of the bushing type or wound type. The bushing typesare normally accommodated within the transformer bushings and the wound types areinvariably separately mounted. The location of the current transformer with respect toassociated circuit breaker has an important bearing upon the protection scheme as well aslayout of, substation. Current transformer class and ratio is determined by electricalprotection, metering consideration.Outdoor Type: The outdoor CTs shall be either oil filled type or of resin cast type whichshall be enclosed in a sealed housing to avoid direct exposure to sun and otheratmospheric effects.Indoor Type: The CTs shall be of resin-cast type suitable for indoor installation.Current ratings, design, Temperature rise and testing etc. should be in accordance withIS: 2705 (Part I to IV). Unless otherwise specified in these specification.12 kV current transformers should conform to REC specification 59/19932-6