GAIL (India) Limited

21CHAPTER 5SUB-STATION1. SCOPE:This specification is intended to cover the requirement of supply, testing at manufacturer’s works,installation, testing and commissioning of various sub-station equipment such as HT switchgear &transformer.2. Standards:All the sub-station equipment shall comply with the latest relevant Indian Standards. National ElectricalCodes and IE Rules.2.1 SINGLE POLE STRUCTUREThe single box Pole Structure shall be fabricated with 2 of 9.5 Mtr long RS Joist (150 x 75mm size) pole,as specified by AP TRANSCO. The pole shall be erected sturdily in Ground by excavating the soil.Providing foundation and coping with PCC of 1: 2: 4, The pole shall have a Channel using 75X 40 X 40mm MS angles for fixing of strain discs/ Lightning Arresters/ AB switch & HG fuse set. The pole shall besupported with stay wires & stay insulators and anchored properly in ground.The AB switch, HG fuse shall be mounted at the height as per drawing. The interconnections betweenIncoming line & AB switch/ HG fuse set shall be made using suitable size Copper wire. All currentcarrying parts shall be earthed using GI strip of 50 X 6mm size and Lightning arresters shall be earthedusing 25X 3mm Copper strip. All the earth strips shall be clamped to the RS Joists and interconnectedwith earthing stations.All metal parts shall be painted with two coats of Zinc chromate Primer & two coats of Aluminum paint.2.2 HT SFU:The HT SFU is latest and occupied less space. For maintenance & operation is easier / safe.The HT 630A ,11KV interior switch and 40A HT HRC fuse units shall be fitted in the enclosure.The enclosure shall be made dwith 14SWG CRCA sheer steel fabrication , floor mounted, double door,weather proof.The operation with spring charge mechanism and fuse trip mechanism. If fuse blam off it will hit the offcircuit lever and switch got off. Also with earth switch for earthong of any maintenance work carriedout.3. Transformer:3.1 Technical Requirements:The transformer shall conform to the specification as given below:i. Capacity: As per Scheduleii. Voltage Ratio: I1KV/433Viii. No. of phases: Three phasesiv. Supply of Voltage: 11 KV 3phase. 50Hz.v. Rating Suitable for continuous ratingvi. No. load voltage: 11000 V on HT side and 433V on LT sidevii. Connection: Delta on HT side and star on L.T side with neutral terminal brought out for solidearthing.viii. Vector group : Dyn-l1ix. Percentage impedance: shall not exceed 5%