FIBRE GLASS CROSS ARMS FOR 33 KV LINES

Transcription

1 REC Specification No Page 1 of 5 REC Specification No. 42/1987 (Revised 1997) FIBRE GLASS CROSS ARMS FOR 33 KV LINES FOREWORD Many countries are now extensively using line cross arms and other hardwares made of Fibre glass Reinforced Plastic (FRP) as substitute for steel. FRP cross arms have the following advantages over steel cross arms :- i) FRP cross arms being light in weight (about one-fifth of steel ), transportation costs are reduced and the cross arms are very easy to erect on poles. ii) Due to good insulating property of FRP, the birdage problem is eliminated and flashing of insulators (particularly in coastal areas) is minimised. iii) No painting is required, saving periodical costs and labour. iv) The cross arms are especially suitable for coastal areas due to their corrosion-resistance properties. v) Earthing of pins can be dispensed with, resulting in saving of time and money. Adoption of FRP cross arms for 11 KV lines was discussed in the 11th Standardisation Conference held in September, 1984 and accordingly REC Specification No.40/1985 was issued earlier. Subsequently, on the request of some of the SEBs, a Specification was prepared for 33 KV Cross Arms, which was considered in the 12 th Standardisation Conference held in July, A Specification was issued in 1987 on the basis of the decision taken by that Conference. The present revised specification includes the various tests to be conducted on the cross arms and on the raw materials as per the relevant Indian Standards. It has been reported by TNEB & GEB that the FRP cross arms develop cracks at the places where the bolts are tightened. This is due to the excessive pressure applied by the line staff who are not used to FRP cross arms. To overcome this problem, provision of polymeric ferrules as packing material for improving the mechanical strength of the cross arms at the places of tightening of the bolts have been incorporated in this revised specification. The revisions in this specification have been approved in the 14 th Conference on Standardisation and Technical Development. 1. SCOPE This specification covers details of Fibre Glass Reinforced Plastic cross arms to be used on 33 KV overhead lines in rural distribution system. 2. APPLICABLE STANDARDS Unless otherwise mentioned in this specification, the raw materials used shall comply with IS : and IS : or their latest version.

2 3. SHAPE & SIZE 3.1 The cross arms shall be of either channel or rectangular hollow section with an overall length of 1605 mm and a minimum top width of 50 mm. 3.2 The cross arms shall have two holes of 26 mm dia for fixing of pin insulators. The centre-to-centre distance between the holes shall be 1525 mm and holes shall be in the middle of the top width of cross arm. 3.3 If required by the purchaser, holes of specified size and spacing shall also be provided for fixing of pole back clamp to suit the pole. 3.4 The enclosed drawing gives the general details of a typical rectangular cross arm showing various dimensions, size of holes, mounting arrangement etc. These details shall also apply to channel cross arms. 4. GENERAL REQUIREMENTS 4.1 The cross arms shall be made from good quality fibre glass and plastic ingredients conforming to standards laid down in this specification in Clause 2 suitable for outdoor application and shall be manufactured by automatic pultrusion process. 4.2 The cross arms shall have smooth surface finish and the cut cross-section shall give a homogeneous appearance. 4.3 The cross arms shall be of light colour so as not to attract birds. It shall not corrode while in contact with steel fittings/fixtures, P.C.C. poles and aluminium conductor. 4.4 Supply of cross arms with Ultra Violet resistant Poly Urethene coating is optional for which the SEBs may have to specifically mention in their tender specifications. 5. MECHANICAL PROPERTIES 5.1 The cross arms shall be able to withstand a vertical load of 400 kg applied at each of the two points coinciding with the centre of the pin insulators on both sides as shown in the enclosed drawing. For the purpose of this test, the cross arm shall be mounted on a support with 230 mm centre-to-centre distance between clamp bolts (16 mm dia). With the application of this load, no damage should occur to the cross arm and it should remain serviceable. 5.2 In the other direction, the cross arm should be able to withstand a load of not less than 135 Kg. applied on both sides as shown in the drawing. 5.3 For improving the mechanical strength, rectangular solid polymeric ferrules may be provided as packing material at both ends of the cross arms (F-2) where 33 KV pin insulators are bolted to the cross arm and also in the middle where the cross arm is fixed to the PCC pole (F-1), to prevent development of cracks in the cross arm

3 at the place of tightening of bolts. Note :The polymeric ferrules will be made out of formulation of fire retardant thermoset resins. The ferrules will be resin cast of the shape and sizes of solid rectangular bars as per the drawings. The polymeric ferrules shall be fixed inside the hollow portion of the cross arm to provide mechanical support while fastening the nuts and bolts at the pole back clamps and the 33 KV pin. 6. TESTS The cross arms shall be subjected to the following tests as per IS : and IS : Type Tests The following tests shall constitute the type tests : a) Visual Inspection b) Dimensional check c) Load test d) Impact Strength e) Tensile Strength f) Comparative Tracking g) Specific Gravity h) Water absorption ( As per IS : ) i) Cross Breaking strength j) Compressive Strength k) Insulation Resistance l) Flammability ( As per IS : ) 6.2 Acceptance & Routine tests The following tests shall constitute the Acceptance & Routine tests :- a) Visual Inspection b) Dimensional check c) Load test d) Specific Gravity test e) Water absorption test f) Cross Breaking strength ( As per IS : ) g) Compressive Strength h) Insulation Resistance i) Flammability ( As per IS : ) The routine and acceptance tests should be performed on one sample chosen at random out of every 20 samples subject to a maximum of 2% of the supply

4 batch. 7. MARKING The following information shall be marked on each cross arm : a) Manufacturer s name or trade mark b) Year of manufacture 8. PACKING The FRP cross arms will be packed in quantities of 10 to 20. Each cross arm will be covered with stretch wrapping film on the winding machine. The items so wound will be grouped as per numbers per packet. The information like product quantity should be mentioned on the packets.

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