Section 6(5) in Tamil Nadu Electricity Regulatory Commission Tamil Nadu Electricity Distribution Code
(5)Planning Criteria and performance bases: The planning criteria for the distribution system as specified [by the Commission] [Substituted for the expression 'by Commission' as per Commission's Notification No. TNERC/DC/8-8 dated 8.2.2008 (w.e.f. 27.2.2008).] shall form the basis. The performance bases to be considered in the system planning are as follows:(a)The Distribution performances established herein shall be implemented in a manner so as to ensure that no entities are forced to achieve goals beyond the capability and limitations of the current system in the immediate future while continuing to strive for the higher standards by improving their system in the long term. As for the existing arrangements, the implementation can be in stages and shall be determined by the Commission.(b)The capacity of step down transformers used in the distribution system and the layout of bus bars, switchgear, transformers, capacitors, earthing system, surge arrestors, control panels, station battery, fire extinguishers and other accessories required for the protection and safe operation of the substations shall as far as possible be standardized by the Licensees and shall conform to the guidelines and principles contained in the Code. The Commission, in specific cases and to ensure uniform adoption, can however specify the standards to be adopted.(c)While planning the distribution system, the Licensee shall examine the cost effectiveness of loss reduction measures without compromising the security standards. The Licensee shall take measures to reduce the length of low tension bare conductor, overhead lines, wherever cost effective and these shall include but not limited to the following:(i)Achievement of HT: LT ratio to the level of 1 to 1.5(ii)Laying of underground cables(iii)Increasing the number of low loss distribution transformers.(d)Substation Design Criteria: HV substations, Sub transmission, primary and secondary distribution shall be designed taking into account the following factors:(i)Safety of Operating Personnel(ii)Adequate cross section of Busbar to meet the electrical and mechanical requirements.(iii)Mechanical and electrical interlocks to prevent inadvertent operation of equipments including switch.[iii-a) Adequate Protection System with proper insulation co-ordination] [[Substituted as per Commission's Notification No. TNERC/DC/8-8 dated 8.2.2008 (w.e.f.27.2.2008).before substitution it was as under:The distribution system shall be properly earthed in accordance with the Indian Standards in force, substation earth mats shall be designed to provide the required earth resistance and limit the ground potential rise limited by Touch and Step potential criteria as per standards]](iv)Adequate Flexibility in operation and maintenance.(v)Operation and Maintenance needs.(vi)Space for future expansion(e)Distribution Line Clearances: Overhead lines shall comply with the safety measures specified by the Authority under section 53 of the Act.(f)Earthing : The distribution system shall be effectively earthed in accordance with the [Indian Standards in force, substation earth mat shall be designed to have a low overall impedance / resistance and to have a minimum transient ground potential rise (TGPR) during fault, giving rise to only permissible safe touch and step potential] [Inserted as per Commission's Notification No. TNERC/DC/8-8 dated 8.2.2008 (w.e.f. 27.2.2008).]. All individual earth electrodes, earthing pits and interconnection arrangements shall be correctly installed and maintained. The bodies, cases, trucks and enclosures of all equipment shall be properly earthed in accordance with the system requirements and equipment ratings. Metallic line supports of overhead lines, cable sheaths and shields shall also be earthed in a proper manner. Connections may be compressed using crimping tool, welded, braced, or bolted using suitable lock washers/locknuts. Bolts should not be used for buried connections
