standards / manuals / guidelines for small hydro development - AHEC

disconnect switch contacts in such substations is more difficult as the contacts are noteasily accessible.3.3 Isolator InsulationInsulation to ground, insulation between open contacts and the insulation between phasesof the completely assembled isolating switch should be capable of withstanding thedielectric test voltages specified as per IS: 2026. Insulation between open contacts of apole should at least 15% more than the insulation between the live parts of a pole toground so that if any flashover occurs when switch is open, it should be to the ground.The post insulators should consist of no. of stack units conforming to IS: 2544. Theinsulators selected should be suitable for use in the type of normally polluted atmosphereof the area as per relevant IS and should be specifically suited to meet the particularrequirements of ultimate torosional strength and cantilever loads which they will becalled upon to resist during service at the rated voltages. The guaranteed data andparticulars of the insulators adopted for the equipment should be obtained from thesupplier.The porcelain should be homogeneous and free from all cavities and flaws.Design of the insulators should ensure ample insulation, mechanical strength and rigidityfor satisfactory operation under site conditions. The design should also ensure that thelosses caused by capacitive currents or conduction through dielectric are minimum andthat the leakage due to moist and dirty insulator surface is least.3.4 Arcing Horn & Arcing ContactsA set adjustable arcing horns should be mounted on each insulator stack of the isolatingswitch.Besides above adjustable arcing horns which are required for the purposes of insulationco-ordination, the isolators may be provided make before and break after arcing contactsif considered necessary by the manufacturers.A graph showing impulse and power frequency spark over voltages for various gapsettings of the arcing horns be obtained from supplier.3.5 Load Break SwitchesLoad break switches for sectionalizing or for selection of bus if required may be used asper following specifications.i) 12 kV REC Specification 43; IS: 9920 Part I to IVii) 36 kV REC Specification 54; IS: 9920 Part I to IV2-4