Grid stds
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This document outlines grid standards and operating procedures that must be followed by electricity grid entities in India. It details standards for frequency control, voltage limits, fault clearance times, contingency planning, maintenance planning, operating instructions, reporting of grid incidents, restoration procedures, and safety protocols. Entities must coordinate operations according to the guidelines and standards set by regional and state load dispatch centers to ensure reliability and stability of the national power grid.
Grid stds
- 2. 2 1. Short title and commencement and application •These are CEA (Grid standards) Regulations, 2010 •They come into force on their publication in official gazette I.e.June 26, 2010 •These shall apply to the entities, appropriate LDCs, and RPCs. 2. Definitions •Bulk consumer – means a consumer who avails supply at voltages of 33 kV or above •Entity - means a Generating company or a transmission licensee or a distribution licensee or a bulk consumer •Voltage Unbalance – Ration of the maximum voltage deviation of the phase voltage from the average phase voltage to the average phase voltage
- 3. 3 3. Standards for operation and maintenance of transmission lines a) Frequency Control • All entities • LDCs • RPCs Operating Range : 49.2 to 50.3 Hz or as per grid code
- 4. 4 b) Operating Voltage Limits S.No. Normal system Voltage (kV rms) Maximum (kV rms) Minimum (kV rms) 1 765 800 728 2 400 420 380 3 220 245 198 4 132 145 122 5 110 121 99 6 66 72 60 7 33 36 30
- 5. 5 c) Temporary over voltage range d) voltage unbalance limits S.No. Nominal System Voltage (kV rms) Temporary over voltage Phase to Neutral (kV peak) Voltage unbalance (%) 1 765 914 1.5 2 400 514 1.5 3 220 283 2 4 132 170 3 5 33 State grid code 3
- 6. 6 e) Max fault clearance time S.No. Normal system Voltage (kV rms) Maximum time in milliseconds 1 765 and 400 100 2 220 and 132 160 Time delay for Back up breaker operation 200 ms.
- 7. 7 f) Grid shall with stand one of the following contingencies without loss of stability • Outage of one single largest generating unit • Outage of a 132 kV double circuit line • Outage of a 220 kV double circuit line • Outage of a 400 kV single circuit line • Outage of a 400 kV single circuit line with series compensation • Outage of a 765 kV single circuit line without series compensation • Outage of one pole of HVDC Bipolar line • Outage of one interconnecting transformer
- 8. 8 g) N-1 criteria for system stability- system shall be stable for one of the following contingencies • Tripping of single largest generating unit • Transient SLG fault of a 765 kV line close to bus • A SLG Fault on 400 kV line and isolation of the line • A fault on one circuit of a 400 kV double circuit line in operation • A transient SLG fault in one of the 400 kV double circuit line when the second circuit is already under outage • A 3 ph fault in 220 kV or 132 kV line • A fault in one pole of HVDC bipolar in a HVDC Converter station
- 9. 9 h) Limits for harmonic distortion in Transmission systems S.No. System Voltage (kV rms) Total harmonic distortion (%) Individual Harmonic of any particular frequency (%) 1 765 1.5 1.0 2 400 2.0 1.5 3 220 2.5 2.0 4 33 to 132 5.0 3.0
- 10. 10 4. Operations planning • Regional Power Committee shall do the operation planning for good frequency profile, voltage profile, line loading, grid incident, grid disturbance, performance of protection schemes and protection coordination 5. Maintenance planning • The RPC shall do the maintenance planning for Gen stations, ISTS • Coordinate the annual maintenance plan for inter regional transmission system • Organise monthly operating committee meetings in the region • The SLDC shall do the above for intra-state constituents
- 11. 11 6. Coordination in operations • No entity shall introduce or take out the element of the grid without the concurrence of the appropriate LDC except in case of risk of safety of plant and personnel in which case it must intimate the appropriate LDC.
- 12. 12 7. Operating instructions • Every generating company and transmission licensee shall provide written operating instructions for each equipment and operating procedure for sequence of operations of power system equipment in their control room 8. Instructions of LD shall be recorded • All operating instructions given by RLDC and SLDC through phone, fax, email shall be given a unique operating code number and recorded . All conversations regarding operating instructions shall be recorded with voice recorder. • Above records shall be preserved for six months.
- 13. 13 9. Under frequency relay settings • All entities shall set their UF relays and DF/DT relays in accordance with RPC plan to provide load relief for grid security and ensure the operation of these relays at the set frequencies. • All entities shall include the Fr relay details in their daily report and the RPC shall inspect the relays as and when required. 10. Islanding schemes • The RPC shall prepare islanding schemes for separation of systems with a view to save healthy system from total collapse in case of grid disturbance. All entities shall ensure proper implementation of the islanding schemes.
- 14. 14 11. Categorization of Grid incident and Grid disturbance based on severity • Severity of grid incidents – GI 1: Tripping of one or more power system elements resulting in no loss of supply at a substation or loss of integrity of grid at 220 kV level – GI 2: Tripping of one or more power system elements resulting in no loss of supply at a substation or loss of integrity of grid at 400 kV level and above. • Severity of Grid disturbance – GD 1: when Generation or Load loss in a region < 10% – GD 2: When Generation or Load loss in a region is between 10% to 20% – GD 3: When Generation or Load loss in a region is between 20% to 30% – GD 4: When Generation or Load loss in a region is between 30% to 40%
- 15. 15 12. Reporting of events affecting grid operation • Any tripping of generating station or transmission element shall be promptly reported by the respective entity to the appropriate LDC in the prescribed format. • The appropriate LDC shall intimate the SLDC and RLDC for further dissemination to all concerned. 13. Reporting of grid disturbance • The RLDC shall inform occurrence of the grid disturbance to the constituents and RPC at the earliest • The disturbance resulting in failure of power supply to large areas shall also be reported by RLDC to Authority within 24 hours. • The RLDC shall also post on its web site a brief grid disturbance report indicating the affected area or the system, extant of outage and the likely cause of initiation.
- 16. 16 14. Restoration of grid following incidence or disturbance • The RLDC in consultation with RPC shall develop procedures for enabling restoration and normalization of the grid for inter- state system. • The SLDC shall also develop restoration procedures for intra- state system. • The restoration procedures shall be reviewed following addition of generating station or transmission line or at least once in two years. • The above procedures shall be made available to, and be followed by all concerned.
- 17. 17 15. Operational data during normal and grid disturbance conditions • All real time data as required by the appropriate LDC shall be furnished by the entities. • All data required by RPC, in discharge of the responsibilities to it, shall be furnished by RLDC. • All operational data, including disturbance recorder and event logger reports, for analysing grid incidence / disturbance shall be furnished by all entities to RLDC and RPC. • The RPC shall recommend remedial measures to be taken on the disturbance report of RLDC to prevent recurrence .
- 18. 18 16. Operational data records • Operational data logged manually and electronically shall be preserved for at least three years. • The unmanned sub-station data shall be maintained by the concerned SS or LDC responsible. • All observations shall be in chronological order. • The observations made during inspection including important parameters and deviation of parameters outside permissible tolerances also be recorded in the log book. • The RPC shall keep the record of grid incidences and grid disturbances for each financial year. It shall include sequence of tripping, the cause, and the sequence of restoration, remedial measures taken to avert such incidents and disturbances.
- 19. 19 17. Communication facilities • The communication facilities installed by the transmission licensee shall be in accordance with CEA Regulations, 2007 and shall be maintained in good condition. 18. Safety procedure • The entity shall prepare contingency procedures for use of operators at each sub-station and switchyards and these shall be regularly updated. • All operating personnel shall be trained in contingency procedures and they shall follow the procedures. • The fire fighting equipment shall be made available at all sub-stations, switchyards, etc and shall be checked periodically for its upkeep and mock exercises in fire fighting shall be carried out at least once in a year.
- 20. 20 19. Maintenance of tools and equipment • The maintenance staff shall be made aware of the list of tools, devices and equipment for various maintenance and rectification works on Tr lines, SSs, switchyards and converter stations and the tools shall be made readily available and certified for usage. The entity shall prepare maintenance procedures for each equipment in line with the manufacturer’s recommendations and prudent utility practices. 20. Maintenance procedures
- 21. 21 21. Hot line methods • Each transmission licensee shall have an arrangement for restoration of transmission lines of 400 kV and above and strategic 220 kV lines through the use of emergency restoration system in order to minimise the outage of the tr. Lines in case of tower failures. 22. Emergency restoration system • The hot line techniques for maintenance of critical transmission lines and sub-stations shall be adopted where ever possible • Only trained staff shall be used for the hot line techniques and the tools employed shall have necessary certification from a national or international laboratory before use.
- 22. 22 • All essential parameters which indicate the health of the equipment in a sub station, shall be inspected by the shift engineer once in each shift and periodically by the officer in charge. • Overhead lines shall be patrolled at periodicity decided by the transmission licensee and different patrolling schedules shall be implemented by the transmission licensee for normal terrain, vulnerable terrain etc. • The important lines shall be inspected by senior engineers after patrolling by junior staff and maintenance works such as tree cutting, replacement of damaged insulators, etc shall be carried out immediately after patrolling. 23. Inspection and patrolling
- 23. 23 • Entities shall identify critical equipment and as far as possible, practice condition based maintenance for such equipment in place of time based maintenance. • In case of time based maintenance, the periodicity of maintenance of lines and SSs in polluted area or coastal area shall be more frequent. • The maintenance of lines passing through and sub-stations located in such areas should be completed before on set of winter so as to minimise tripping under conditions of fog or due to salt deposit on insulator discs in coastal areas and once before onset of summer. • The maintenance work on various items of equipment may be advanced depending on the condition of the equipment. 24. Maintenance schedules
- 24. 24 25. Condition monitoring • The diagnostic methods of maintenance shall be preferred over traditional time based maintenance. 26. Thermo-vision scanning • The thermo-vision scanning for hot spots on all overhead lines and sub station equipment at voltage level of 220 kV and above shall be carried out at least once in a year and necessary remedial measures shall be taken where hot spots are detected.
- 25. 25 27. Failure analysis • All failures of the equipment and tower collapse shall be analyzed by the entity to avoid recurrence and a copy of the report shall be submitted to the RPC and Authority • The authority may appoint a group of experts for investigation and analysis and the representatives of the manufacturers may be invited to participate in such analysis. • All data which may help the group of experts in analysing the failures shall be furnished by the respective Entities. • The recommendations of the group of experts shall be submitted to the authority and the recommendations accepted by the authority shall be implemented and circulated to all within the organisation and to other organisations to prevent recurrence of such failures.
- 26. 26 28. Inventory control and spare parts management • The required spare parts shall be kept in stock, to ensure speedy maintenance of the equipment. • Computerised materials management system shall be developed by the entities to optimise inventory. 29. Maintenance audit • An internal audit committee may be established by the entities to verify whether actual maintenance works are carried out at site in compliance of the procedures and the policy of the transmission company. • The observations of the committee shall be put up to the management of the entity for perusal and taking action, if any.
- 27. 27 30. Residual life assessment • The RLA shall be carried out for all major equipment including transformers, reactors, breakers, etc as envisaged by relevant standards specified by the Bureau of Indian standards, manufacturer’s instruction or industry best practices and suitable remedial action for breach of the same shall be taken by the management of the entity. 31. Disaster management • The maintenance staff shall be trained in disaster management and a detailed procedure for the same shall be developed by the entity and displayed prominently. • The detailed procedure shall be reviewed periodically and also based on mock exercises carried out by the entity. • The equipment including vehicles, diesel gen sets and fire fighting equipment, etc shall be kept at sub-station or at appropriate location for disaster management.
- 28. 28 32. Maintenance records • The records of all maintenance carried out for each equipment shall be kept in the table and formats in electronic form and hard copy and the next due date for maintenance of each item of work shall be clearly marked in such tables and formats. 33. Training • Every person involved in O&M of transmission lines shall be trained at the induction level and at least once in a year. • The shift staff shall be trained to make them through in carrying out operations at each SS and every person concerned with real time operation shall be trained. • Every grid operator shall undergo training in real time digital simulator and a refresher course at least once in two years. • The maintenance personnel of every entity shall also be trained in preventive and breakdown maintenance of various equipment and the personnel shall be trained in detailed maintenance procedures.
- 29. 29 Thank you