Section 6 in Tamil Nadu Electricity Grid Code, 2005
6. Objectives.
(1)The objectives of the grid connectivity conditions are to ensure that (a) the basic rules for connections are complied with to treat all agencies in a non-discriminatory manner (b) any new or modified connections, when established, shall neither suffer unacceptable effects due to its connection to the transmission system nor impose unacceptable effects on the system of any other connected agency (c) the ownership and responsibility for all the equipments, shall be clearly specified in a schedule (Site Responsibility Schedule) and (d) a prospective user is well informed, in advance, of the standards and conditions his system has to meet, for being integrated into the existing power system, the standards and parameters of the existing system with which his system has to be interfaced and the electrical environment in which his system has to operate.(2)Scope: The connectivity conditions apply to all State / Central Government sponsored generating companies, captive power generators, IPPs, STU, transmission / distribution Licensees, Bulk Consumers and all the users seeking new connection with the intra state transmission system including the existing transmission licensees and the users who may be required to modify / upgrade their systems.(3)Procedure for connection: (i) STU shall identify opportunities for new connections and optimal locations after conducting the system studies in co-ordination with the organizations listed under the respective sections of the Act, namely Section 39(2)(b) for the STU and in conformity with the National Electricity Plan drawn by the Authority under Section 3(4) of the Act.(ii)STU shall furnish details of the prospective connection points in respect of their system on their web-site inviting initial application from the users.(iii)Connection may also be sought for locations other than those described in (i) and (ii).(iv)In all the cases covered by the points (i), (ii) and (iii) above, the users and transmission licensee shall forward their request for grid connectivity to the STU, as the case may be, in the proforma prescribed by the STU. Proforma for different categories of users shall be made available on STU's web-sites and shall inter-alia, include technical data pertaining to generating unit(s)/ transmission system / distribution system / load, single line diagram and topographical map showing the location of the proposed user's apparatus and equipment.(v)The prospective users shall be required to pay to the STU/transmission licensee the charges as (proposed by STU/transmission licensee) approved by the Commission, for the purposes of conducting initial interconnection studies, any additional studies as well as processing the application.(vi)On receipt of the request from the user & transmission licensee along with the prescribed charges, the STU / transmission licensee shall, within one month of receipt of the proposal, accept the proposal or suggest modifications thereto. In the event of user / transmission licensee requesting for any specific information / study / data from the STU / transmission licensee for the purpose of grid connectivity, the STU /transmission licensee shall make the same available to the user /transmission licensee(vii)STU shall be entitled to reject any application for connection lo/or use of State Transmission System if such proposed connect ion is likely to cause breach of any provision of its license or any provision of the Grid Code or any provision of 1EGC. In the event of any dispute with regard to modifications, not being acceptable to the user, the user may approach the Commission for dispute resolution.(viii)The STU/ transmission licensee and the user/ transmission licensee shall enter into a Connection Agreement within two months of acceptance of the proposal. The Connection Agreement shall contain time schedule for completion of the facilities of User and STU/ transmission licensee, both indemnifying the delays on the part of the other. Both the parties shall inform the progress of major milestones to each other. The lime limit for entering into the connection agreement may be extended, if both parties agree.(ix)Copies of the Connection Agreement shall be sent to the transmission licensee, load dispatch centre, Regional Powder Committee, Commission and the Authority.(x)Upon fulfillment of all the conditions, STU shall notify the agency that it can be connected to the STS.(xi)In respect of existing connections, the Commission may allow relaxation up to 2 years in respect of connection agreements. The process of renegotiation of the connection conditions of the STS should be completed within the above period. Due to any reason if this process gets delayed further, Commission may consider relaxation for a further period for which a petition will have to be filed by the concerned constituent along with STU's recommendations / comments. The present agreements may continue till such renegotiation and revised agreements are over.(xii)The cost of modification, if any, shall be borne by the concerned constituent. The STU shall normally make a formal offer to the agency within two months. The offer shall specify and take into account any works required for the extension or reinforcement of the Transmission System to satisfy the requirements of the connection application and for obtaining statutory clearances, way leaves as necessary.(4)General Connectivity Conditions: A prospective user and transmission licensee proposing a new connection shall comply with the following conditions:(i)The user shall meet the requirements in accordance with the provisions of Standards on Grid Connectivity and Grid Standards specified by the Authority and IEGC specified by CERC.(ii)Requisite protections shall be provided in the user's system to protect the Grid from the faults originating in the user's systems.(iii)Notwithstanding the protection systems provided in the Grid, the user/transmission licensee shall provide requisite protections for safeguarding his system from the faults originating in the transmission svstem / Grid.(iv)No user of the Grid shall exceed the Harmonic Distortion Level specified in the CEA (Grid Connectivity) Regulations.(v)The user shall furnish requisite data to the STU / transmission licensee for enabling it to conduct interconnection studies.(vi)The user is obliged to cooperate with the STU, transmission licensee and load dispatch centre in respect of the operational matters listed below, but not limited to: -(a)Carryout the modifications in his equipment considered necessary, whenever the power system is upgraded or modified.(b)Protection coordination (relay settings).(c)Provide on line data to the appropriate load dispatch centre.(d)Participate in contingency operations such as load shedding, is landing, black start, providing start-up power and restoration.(e)Furnish data to the STU / transmission licensee, SLDC and any committee constituted by appropriate Government or Authority for disturbance analysis and other studies.(f)Coordinated outage plan of the State/Region.(g)Prompt implementation of instructions of load dispatch centre.(vii)The user's equipment at the site owned by the transmission licensee shall be maintained promptly and properly by the user and vice versa so that the equipment and personnel of the site owner are not jeopardized by the neglect of the other entity.(5)Connection Agreement: Every connection of a user's system to the transmission system shall be covered by a Connection Agreement between the user and the transmission licensee. The Connection Agreement shall contain general, specific, technical and financial conditions, applicable to that connection. A connection agreement shall include (but not limited) as appropriate, within its terms and conditions, the following:(i)A condition requiring both parties to comply with Indian Electricity Grid Code and Tamil Nadu Electricity Grid code, provisions under the Act, other Codes and regulations issued by the Commission / CEA.(ii)Details of connections, technical requirements and commercial arrangements.(iii)Details of capital expenditure if any required to be met before extending open access to the open access consumer.(iv)Site responsibility schedule.(v)Details of the protection arrangements made and its coordination with the Grid. This includes short circuit protection and insulation coordination.(vi)Procedure necessary for site access, site operational activities and maintenance standards for STU equipment at the premises of the users and vice versa.(vii)Specific clause to the effect that necessary guidelines for insulation coordination in live working shall be followed by the STU / Agency.(viii)Commitment to provide the data requirements as per Annexure B-l.(6)Metering and Communication (i) The user shall provide meters for accounting and audit purposes as per the standards specified by Authority under Section 73(e) of the Act. The agency who has to provide, operate and maintain the metering arrangements at various locations will be stipulated by the STU in the connection agreement. STU shall be responsible to formulate the metering procedure and implement it with other Users.(ii)The user shall be required to provide the voice and data communication facilities as decided by SLDC.(iii)The user shall make arrangements for integration of the controls and telemetering features of his system into the Automatic Generation Control, Special Protection System, Energy Management Systems and SCADA system of the STU / SLDC.(7)Connection Points(i)Generating Stations including IPPs: Generating stations Switchyard Voltage may be at the level of 400,230 and 110 kV or as agreed to by the STU. Unless specifically agreed with the STU, the connection point shall be the outgoing feeder gantry of the Power Station switchyard. All the terminal, communication, protection and metering equipments owned by the generating agency, within the perimeter of their site shall be maintained by them. From the outgoing feeder gantry onwards, all electrical equipments shall be maintained by the STU.(ii)Distribution Licensee: The Voltage may be at the level of 110,33,22 and 11 kV. The connection point shall be the outgoing feeder gantry of the STU's sub-station, if the sub station is owned by STU, else, the connection point shall be the terminal structure feeder gantry at the entry into the sub station.(iii)Inter-State transmission System: For the Southern Regional Transmission System, the inter state transmission link to the intra state system, the connection point, protection scheme, metering scheme, meteYing point and the voltage shall be in accordance with the mutual agreement between CTU and the STU.(8)Captive Generators, Co-generators and HV consumers: The voltage level maybe at 230,110,66,33,22,11 kV or as agreed to by STU. Sub-stations shall be owned by Co-Generators, CPPs and the HV consumers. The connection point shall be the feeder gantry on their premises.(9)Site Responsibility Schedule: A Site Responsibility Schedule (SRS) shall be prepared for every connection. At the connection site where equipment of both entities, i.e., the Transmission Licensee and the user are installed, the user shall furnish required data to the Transmission Licensee and the Transmission Licensee shall prepare SRS. At a generating station, the transmission licensee shall furnish the necessary data to the generating company who shall prepare SRS. A SRS format is given in Annexure -B1(10)Access at Connection Site: The user owning the Connection Site shall provide reasonable access and other required facilities to another User / Licensee whose equipment is proposed to be installed / installed at the Connection Site for installation, operation, maintenance, etc. Written procedures and agreements shall be developed between entities to ensure that mandatory access is available to the entity concerned, at the same time safeguarding the interests of both entities at the connection site.(11)Site Common Drawings: Site Common Drawings shall be prepared by the owner company (transmission licensee or User) using the information furnished by the other company (user or transmission licensee) containing the following information:(a)Connection Site Equipment Layout(b)Electrical Layout(c)Common Protection and Controls(d)Common Services (water, compressed air, telephone, LT electricity for lighting and other appliance, etc.,)The site common drawings shall clearly show the gas insulated parts and gas/air boundary in the case of gas insulated sub-stations. If any change in the drawing is found necessary, either by agency or STU, the details will be exchanged between agency and STU as soon as possible.(12)Site Operational and Safety Procedures: (i) The transmission licensee and the user shall ensure that staff is available to take necessary safety precautions and carry out operational duties at the site. Written operating and safety procedures as approved by competent authority shall be made available at each site. The telephone numbers and addresses of the officers of each entity responsible for operation at the connection site shall be furnished to the other entity.(ii)The CEA (Safety) Regulations and CEA (Safety) Standards shall be complied with by all the Users and Transmission Licensees.(iii)Fire Protection Systems shall be provided at the generating stations and sub-stations as per prudent utility practices.(13)Boundaries between Systems of Entities: (i) Boundary between a Generating station and the Transmission System: The boundary shall be the line isolator of the feeder, which injects power into the transmission system. The isolator shall be in the jurisdiction of the generating company.(ii)Boundary between the Transmission System and the Distribution System: The boundary shall be the line isolator of the outgoing feeder injecting power into the distribution system. The line isolator shall be in the jurisdiction of the transmission licensee. Alternatively the boundary may be the isolator between the LV side circuit breaker of the Extra High Tension (EHT) Transformer and the 33kV bus-bars at the EHT Sub--Station. The actual boundary shall be decided jointly by the transmission licensee and the distribution licensee.(iii)In respect of case (i) and (ii) above, at particular inter-connections both parties may jointly agree on a different boundary. In such an event the written agreement shall be submitted to the RPC /STU.(iv)Boundaries between Transmission / Distribution Licensee and Captive Generators, Co-generators and HV consumers: The boundary between the transmission / Distribution licensee and Captive Generators, Co-generators and HV consumers is the isolator in the consumer's or Captive Generators or Co-generators system, which is also the point of commencement or injection of supply.(v)Boundaries between Inter-State Transmission System and Intra State Transmission System For the Southern Regional Transmission System, the inter state transmission link to the intra state system shall be in accordance with the mutual agreement between CTU and the STU. In such an event the written agreement shall be submitted to the RPC.(14)Standards and Codes of Practices: (i) The equipment to be installed by the users and transmission licensees shall conform to the relevant construction standards specified by the Authority, the relevant Indian Standards (IS), the relevant British Standard, IEC Standard, Standard of American National Standards Institute (ANSI) or any other equivalent International Standard(ii)Where neither an Indian nor an International Standard or Code of Practice exists, an entity shall develop its own Interim Standard or Code of Practice acceptable to Prudent Utility Practices. The Standards and Codes of Practice shall be similar to the existing standards for similar equipment. The aim of each Standard or Code of Practice shall be to achieve quality and reliability in performance and safety and compatibility with other equipment in the same system. The Interim Standard developed by an entity shall be replaced by an Indian or an International Standard when it is published.(iii)Wherever an International Standard or IEC Standard is followed, necessary corrections shall be made for different system frequency, nominal system voltage, ambient temperature, humidity and other conditions prevailing in India before actual adoption of the Standard.(15)Basic Insulation Level and Insulation Coordination: (i) For Basic Insulation Level and Insulation Coordination, the Grid Connectivity Standards formulated by CEA shall be followed.(ii)The following criteria shall be applied in the same order of priority in determining Basic Insulation Level (BIL) of various items of equipment and ratings of surge diverters at generating stations, lines and substations:(a)Ensure safety to public and operating personnel.(b)Avoid permanent damage to plant..(c)Prevent failure of costly equipment.(d)Minimize circuit interruptions.(e)Minimize interruptions of supplies to consumers.(iii)For determining BIL, the following factors shall be taken into account:(a)Over voltages due to switching and transients occurring under the highest permissible steady state system voltage conditions.(b)Lightning surges.(c)Type of earthing of the system - solidly earthed or earthed through resistor/reactor or isolated neutral.(d)Weather conditions prevailing at site.(e)Effects of pollution.(iv)Computer-based optimisation studies may be carried out to finalise the BIL. The recommendations of IEC - 71 may be taken into consideration while carrying out the above studies.(v)Each user/transmission licensee shall calculate optimum BIL for various items of equipment and lines in his system and ensure that the equipment used / proposed to be used is manufactured to the required BIL. It shall be the responsibility of the user / transmission licensee to ensure through appropriate tests that the equipment procured has the required BIL.(vi)Insulation coordination of equipment and lines on both sides of a connection point belonging to different entities shall be accomplished and the co-ordination shall be done by the transmission licensee.(vii)To protect the costly equipment like Generator and Transformer against lightning, switching and other surges, surge diverters shall be provided as near the equipment terminal as possible.(16)Disturbance Recorders and Event Loggers: Every generating station connected to the Grid at 230 kV or above, 230 kV sub-stations with transformation capacity more than 200 MVA, all substations of voltage 400 kV and above shall be provided with disturbance recorders and event loggers and shall be synchronized with a common time reference of Global Position Satellite (GPS) System.(17)Schematic Diagram: (i) The user and transmission licensees shall prepare single line schematic diagrams in respect of their system / facility and make the same available to the transmission licensees and the users in order to enable both of them to have requisite information about the system with which they are to get connected.(ii)The following details shall be included in the single line diagrams:(a)HT and EHT equipment, bus bars, incoming and outgoing feeders, control, protection, metering arrangement, length of feeder, size of the conductor and name of the station at the other end of the feeder.(b)AC and DC auxiliary power supply systems. Standby supplies and sources.(c)Connection of distribution systems at El IT sub-stations, showing the areas served by each outgoing feeder.(iii)State Grid Maps showing the complete network of transmission lines shall be prepared, updated and maintained by STU and supplied to the entities requiring the same.(18)Protection System and Coordination: (a) Protection in general(i)Every element of the power system shall be protected by a standard protection system having the required reliability, selectivity, speed, discrimination and sensitivity. Where failure of a protective relay in the system of one entity has substantial impact on the system from which power is drawn by it, it shall connect an additional protection as standby. The entity supplying power to another entity shall provide back-up protection to the system which receives power.(ii)Protection coordination shall be done at State level by STU in consultation with RPC. Each entity shall develop protection manuals conforming to various standards for the reference and use of its personnel in consultation with STU. The System Fault Dependability Index shall be as stipulated in CEA (Grid Standards) for the systems of all entities.(iii)Over current, short circuit, earth fault over voltage and other types of protection systems are generally required to be provided by all Licensees and other agencies connected to the Grid. These protective systems are essentially required for the quick isolation of faulty equipments, lines and UG Cables and protection of the network and its healthy equipments and lines and UG cables from the severe impact of the fault, with the appropriate reliability, sensitivity and selectivity.(b)Fault clearance Time(i)The fault clearance time, for a three phase fault (close to the bus-bars) on agencies equipment directly connected to STS and for a three phase fault (close to the bus-bars) on STS connected to agencies equipment, shall not be more than:(a)100 milli seconds (ms) for 400 kV and above(b)160 milli seconds (ms) for 220 kV & 110 kV(ii)Back-up protection shall be provided for required isolation / protection in the event of failure of the primary protection systems provided to meet the above fault clearance time requirements. If a Generating Unit is connected to the STS directly, it shall withstand, until clearing of the fault by back-up protection on the STS side.(iii)All agencies connected to the STS shall provide protection systems as specified in the connection agreement.(c)Generating Unit Requirements The guidelines mentioned in the "Manual on protection of Generators, Generator Transformers, and 220 kV and 400 kV networks" vide publication No: 274 of CBIP shall be kept in view. All Generating Units and associated electrical equipments connected to the Transmission System shall be protected by adequate protection so that the Transmission System does not suffer due to any disturbance originating from the Generating Unit. The generator protection schemes shall cover at least differential protection, back up protection, stator earth fault protection, field ground/field failure protection (not applicable to brush-less excitation system), negative sequence protection, under frequency, over flux protection, back-up impedance protection and pole slipping protection (applicable to units above 200MW), loss of field protection, reverse power protection etc.(d)Transmission System Requirements: All HV lines taking off from a power station or a sub-station shall have appropriate over voltage protection and distance protection and back up protection schemes. The STU shall notify the users of any change in its policy on protection from time to time.(i)400 kV Lines / UG Cables: Two independent protection systems (Main I & II Protection) with separate DC Battery supply shall be arranged. Main-I Protection shall be preferably with three-zone static non-switched numerical distance protection with appropriate carrier protection and back up protection.Main-II Protection shall be a fast protection scheme using direction comparison or phase comparison carrier relaying scheme. In addition, single pole tripping and single shot, single pole auto-reclosing after an adjustable dead time shall be provided.(ii)230 kV Lines/UG Cables: The main protection shall be through three-zone static, non-switched numerical distance protection with suitable carrier protection. The back up will be micro processor based switched distance protection scheme. One pole tripping and single shot single pole auto-reclosing with adjustable dead time shall be provided for both schemes.(iii)110 kV ami 66 kV lines/UG Cables: Static/micro processor based distance protection with suitable backup protection shall be provided as the main protection scheme. The back up will be directional three phase over current and earth fault protection scheme.(iv)General: For short transmission lines and sub transmission system at or below 33 kV, appropriate protection schemes may be adopted. Relay Panels for the protection of lines of STU taking off from a Generating Station shall be owned and maintained by the STU. Generating Companies shall provide space, connection facility and access to the STU for such purpose.(v)Generator, Auto and Power Transformers: All windings of Auto Transformers and Power transformers of 400, 230 and 110 kV class shall be protected by differential relays and REF (Restricted Earth Fault) relays. In addition, there shall be back up time lag over current and earth fault protection. For parallel operation such back up protection shall have directional feature. For protection against heavy short circuits, the over current relays should incorporate a high set instantaneous element. In addition to electrical protection, gas operated relays, winding temperature protection and oil temperature protection shall be provided. For smaller transformers of FIV class, differential protection shall be provided for 10 MVA and above along with back up time lag over current and earth fault protection (with directional feature for parallel operations). Transformers of 1.6 MVA and above but less than 10 MVA shall be protected by time lag over current, earth fault and instantaneous REF relays. In addition, all transformers of 1.6 MV A and above shall be provided with gas-operated relays, winding temperature protection and oil temperature protection.(vi)Bus bar protection: Suitable (high impedance) bus bar protection shall be provided for the speedy clearance of bus faults at all the generating stations and 400 kV and 230 kV Transmission substations.(vii)Over voltage protection: There shall be proper "Insulation Coordination" studies before implementing the over voltage protection scheme. All the operating equipments, lines and UG cables shall be protected against direct lightning strokes by the use of masts / ground wires. In respect of protection against system generated surges (switching surges) and indirect lightning strokes/ back flash-overs, co-coordinated protective gaps and Metal Oxide Arresters (Gapless Arresters) shall be provided. These protective gapless arresters shall be placed at the entry point of OH lines/Under Ground Cable, at the power/ substation (Line Entrance Arrestors) and at a location very close to Auto/Power Transformers and other protected equipments including shunt capacitor banks. Gapless surge diverters shall be provided at the interface of OH line - UG cable in a composite circuit and also its entry at the power station / substation. To the extent possible, the mixing up of gapped and gapless arresters shall be avoided. Gapless arresters should not be placed on the LV side of a Auto/Power Transformer, when a gapped surge diverter already exists on its HV side. When IIV lines (110 kV or 66 kV) are used for feeding lower voltage substations (33,22 and 11 kV) after its degradation, its insulation level should be brought down to the level required by the substations fed i.e derated HV lines should not be employed directly for feeding lower voltage substations.All power system equipments should withstand twice its rated power frequency voltage for one minute so as to withstand the rigors of temporary over voltages generated in the systems, as a consequence of faults.(19)Protection against environmental contamination: STU and other agencies connected to the Grid shall take appropriate protective measures against the outage /tripping of lines and equipments triggered by environmental pollution especially at locations exposed to Saline Pollution, Industrial Pollution, Coal-fired Thermal Power Station, Chemical and Cement Dust Pollution or a combination of these contaminations.
