Grid Connectivity Standards, Grid standards

1. Grid Connectivity Standards,Grid standards alka NPTI, PSTI Bangalore

2. CEA’s Standards for Grid Connectvityapplicable to the transmission systems

3. 1.Transmission system Planning & Design i. The transmission licensee shall plan and design the inter state/ intra state transmission system based on the following • CEA “Manual on Transmission Planning Criteria: 1994” • CEA “Report of the Committee for Updating the Best Practices in Transmission System for the Country: 2002”. • Latest Issue of CBIP Manuals on: Layout of Substations, Transmission Towers • Grid code • State Grid code

4. 1.Transmission system Planning & Design • The integrity of the regional grid is not affected under various operating conditions including stipulated system contingencies • all elements of the transmission system shall be designed taking into account the specified factors of safetyin regard to electrical, mechanical and civil aspects in the respective standards • optimal system to be chosen after performing load flow, short circuit, stability studies of the various transmission alternative • The system designed shall not impinge on the rating of the substation equipment in any other sub station in the vicinity.

5. 2. Overhead Transmission Lines • The transmission line proposed to be connected shall be comply with the following • Tower design shall be based on the technical standards for the construction of electrical lines specified by the authority under section 73(b) of the Act • Foundation design for the tower to be developed by the transmission licensee for various soil categories. • Use of multi circuit and narrow based towers wherever ROW constraints exist • Each type of tower to be type tested for mechanical strength ii.Clearance from PTCC shall be obtained

6. 3. EHV/HV Underground Cables i. Cables proposed to be connected to the system, shall comply with the following • Shall be of XLPE typecorresponding to IS 7098 • Cable conductor to be of adequate sizeconsidering continuous current, short circuit current, voltage drop etc, & shall correspond to IS-8130 • Cables to be provided with proper sheathing, armoring & screening • Prior permission from appropriate authority to be obtained for digging trenches, precautions to be taken • Route maps to be kept at Substation & markers shall be fixed to trace the cables • Road crossing to be carried out by providing Hume pipes or GI pipes • Jointing & termination to be carried out as per relevant standards ii. Clearance from PTCC shall be obtained

7. 4. Substations Planning and design of substations to be based on the following • Security of supply, extendibilty, maintainabilty and operational flexibility • Statutory safety requirements • Protection from direct lightening stroke • Switching scheme:- 765 kV Substation: Double bus double breaker 400 kV Substation: One and half breaker scheme/ double main and transfer bus bar scheme 220 kV Substation: Double main and transfer scheme/ double main with breaker by-pass scheme 132kV Substation: Main and transfer scheme below 132 kV Substation: as decided by licensee

8. 4. Substations Planning and design of substations to be based on the following • All EHV circuit breakers to be of SF6 type • Isolators to be pneumatic or motor operated • ICTs to be provided with OLTCs • Surge arrestors to be of metal oxide type (as per IEC 60099) • Control room to be extensible • All substation structures to be of lattice steel. Structures to conform to IEC 865, IS-875, IS-802, IS-800 • Electrical, mechanical and civil designs to be standardised to the extent possible

9. 4. Substations Planning and design of substations to be based on the following • Power Supply to the sub station auxillaries a. AC Supply; 2 HT supplies shall be arranged from independent sources. In addition, a DG set of suitable capacity to be provided b. DC Supply: 2 sets of 220 V batteries each equipped with own charger for substations of 220 kV & above. 2 sets of 50 V batteries for PLCC system. for substations of 132 kV & below, 1 set of battery each to be provided • For high current, XLPE cables to be employed. For LV/MV systems, PVC cables corresponding to IS-1554, can be employed

10. 4. Substations Planning and design of substations to be based on the following • Reliable communication link shall be provided on all EHT lines for voice, Fax, protection, telemetry & SCADA • Substation grounding shall be done in accordance with IEEE-80 • Size and no. of ICTs to be selected such that outage of one shouldn’t overload the remaining ICTs or the underlying system • The stuck breaker condition in the substation shall not cause disruption of more than 4 feeders in 132 or 220 kV system, more than 2 feeders in 400 kV system and more than one feeder in 765 kV system • In substations of 220 kV and above, control room, PLCC room, Relay testing room and electronic laboratory shall be air conditioned

11. 5. Earth Fault Factor In the event of a point in the EHT system of a transmission licensee being earthed, the Earth fault Factor shall be less than 1.4 6. Electromagnetic Compatibility A line or equipment in the transmission system shall not generate excessive electromagnetic field and the RIV (radio interference voltage) shall be within permissible limits as per relevant standards

12. 7. Insulation coordination • For new connections, the CTU/ STU/ transmission licensee, shall inform the transmission users seeking connectivity, the BIL and important parameters of the equipment and ratings of the surge arresters in its system adjacent to the connection point. • The transmission users and licensees seeking connectivity shall furnish to the CTU/ STU, the BIL of the proposed system/ important items of the equipment and the rating of the surge arresters adjacent to the connection point • The CTU/ STU/ transmission licensee shall determine the ratings of the surge arresters to be installed at the connection point • Requisite insulation coordination to be done by the CTU/ STU/ transmission licensee.

13. 8. Grid standards The transmission utility, transmission licensee and the load dispatch center shall comply with the CEA’s Grid standards

14. Grid Standards

15. 1. Short title and commencement and application 2. Definitions These are CEA (Grid standards) Regulations, 2010 These regulations came into force on their publication in official gazette i.e.June 26, 2010 These shall apply to the entities, appropriate LDCs, and RPCs. • 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 – Ratio of the maximum voltage deviation of the phase voltage from the average phase voltage to the average phase voltage

16. 3. Standards for operation and maintenance of transmission lines • All entities • LDCs • RPCs • Frequency Control Operating Range : 49.5 to 50.2 Hz or as per grid code, except during the transient period following tripping.

17. b) Operating Voltage Limits

18. c) Temporary over voltage range d) voltage unbalance limits

19. e) Max fault clearance time

20. 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

21. g) N-1 criteria for system stability- system shall be stable and sustain integrity 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

22. h) Limits for harmonic distortion in Transmission systems

23. 4. Operations planning • Regional Power Committee shall periodically review the performance of the grid for the past period • RPC shall plan stable operation of the grid for future, considering various parameters and occurrences such as • frequency profile, • voltage profile, • line loading, • grid incident, • grid disturbance, • performance of protection schemes and • protection coordination

24. 5. Maintenance planning • The RPC shall prepare annual maintenance plan for Generating stations, ISTS • Coordinate the annual maintenance plan for inter regional transmission system • Organise monthly operating committee meetings in the region to review and revise the coordinated generation and transmission system plan • The SLDC shall do the above for intra-state constituents in consultation with the concerned transmission licensees • The generating company/ transmission licensee shall obtain approval of the appropriate LDC before actual shut down

25. 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. • The appropriate LDC shall inform all affected parties of the outage

26. 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 These instructions to be consistent with the manufacturers’ instructions Instructions and procedures to be reviewed and revised by generating company/ licensee.

27. 8. RLDCs and SLDCs Instructions’ to be recorded • All operating instructions given by RLDC and SLDC through phone, fax, email shall be given a unique operating code number and recorded . Voice recorder to be maintained for recording and reproduction of conversation with time stamp/ tag. • Above records shall be preserved for six months.

28. 9. Under frequency relay settings All entities shall set their UF relays and DF/DT relays in accordance with RPC plan to provide adequate 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 to the RLDCs and RPCs. RPC shall carry our inspection of the relays as and when required.

29. 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.

30. 11. Categorization of Grid incident and Grid disturbance based on severity • “Grid Incident” means tripping of one or more power system elements of the grid, which requires rescheduling of load/ generator, without total loss of supply at the substation or loss of integrity of the grid at 220 kV and above (132 kV in case of NE region) • “Grid Disturbance” means tripping of one or more power system elements of the grid, resulting in total failure of supply at the substation or loss of integrity of the transmission system at 220 kV and above (132 kV in case of NE region)

31. 11. Categorization of Grid incident and Grid disturbance based on severity (contd…) • Severity of grid incidents • GI 1: Tripping of one or more power system elements which requires rescheduling of generator/ load, without loss of supply at a substation or loss of integrity of grid at 220 kV level(132 kV in NE region) • GI 2: Tripping of one or more power system elements which requires rescheduling of generator/ load, without loss of supply at a substation or loss of integrity of grid at 400 kV level and above (220 kV in NER). • 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% • GD 5: When Generation or Load loss in a region is between 40% to 50%

32. 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 event to the SLDC and RLDC of the affected regions for further dissemination to all concerned.

33. 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 in a state shall also be reported by RLDC to Authority within 24 hours of the occurrence of the grid disturbance. • The RLDC shall also post on its web site a brief grid disturbance report indicating the affected area or the system, extent of outage and the likely cause of initiation.

34. 14. Restoration of grid following incidence or disturbance The RLDC in consultation with RPC shall develop proceduresfor enabling restoration and normalization of the grid for inter-state system at the earliest. 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 and revised if considered necessary. The above procedures shall be made available to, and be followed by all concerned (entities, RLDCs and SLDCs).

35. 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 incident / disturbance shall be furnished by all entities within 24 hrs to RLDC and RPC. All equipments such as disturbance recorders and event loggers shall be kept in healthy conditions. The RPC shall recommend remedial measures to be taken on the disturbance report of RLDC to prevent recurrence of GI and GD.

36. 16. Operational data records Operational data (including equipment and system parameters) logged manually and electronically shall be preserved for at least three years. Logbooks to be maintained by every by every manned switchyard and substation. The unmanned sub-station data shall be maintained by the concerned control centre. 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.

37. 17. Communication Facilities The communication facilities installed by the transmission licensee shall be in accordance with CEA(Technical Standards for Connectivity to the Grid) Regulations, 2007 and shall be maintained in good operating condition.

38. 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 at regular intervals 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.

39. 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 Transmission lines, Substations, Switchyards and Converter stations and the tools shall be made readily available and certified for usage.

40. 20. Maintenance procedures The entity shall prepare maintenance procedures for each equipment in line with the manufacturer’s recommendations and prudent utility practices.

41. 21. Hot line methods • 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.

42. 22. Emergency Restoration System • 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 Transmission Lines in case of tower failures. ( “Emergency Restoration System” means a system comprising of transmission towers or structures of modular construction, complete with associated components such as insulators, hardware fittings, accessories, foundation plate, guys, anchors or installation tools and the like to facilitate quick restoration of damaged or failed transmission line towers or sections)

43. 23. Inspection and patrolling • All essential parameters which indicate the healthiness 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 and most vulnerable terrain . • 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 shall be carried out immediately after patrolling wherever required.

44. 24. Maintenance schedules • 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 substations located 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 onset 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.

45. 25. Use of diagnostic Techniques for Condition monitoring of equipment • The diagnostic methods of maintenance shall be preferred over traditional time based maintenance.

46. 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.

47. 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 relevant 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.

48. 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.

49. 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 corrective action, if any.

50. 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, manufacturers’ instruction or industry best practices and suitable remedial action for breach of the same shall be taken by the management of the entity.