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Transmission Operating Standard


    These standards shall serve as guidelines for the Licensee to operate its Transmission System for providing an efficient, coordinated and economical system of electricity transmission.


    2.1 The Licensee shall acquire, store and manage following data relating to its Transmission System and Generating Units of Generators.

    1. Line data

    2. Transformer data including Generation Transformers

    3. Bus data including that of Generating Stations

    4. Generator data (inclusive of Captive Power Plant)

    5. Demand data for each EHT sub-station

    6. Real Time Data

    2.2 Details of data shall be as specified in Annexure - 1.


    3.1 The Licensee shall establish a State Load Despatch Centre and run round the clock for the purposes of

    1. Daily Generation Scheduling and issuing despatch instructions.

    2. Monitoring line MW and MVAR drawls, EHT Bus Voltages, Frequency.

    3. Monitoring Generation out-put.

    4. Coordinating restoration process after total or partial blackouts in the Transmission System or Regional System.                                                                                        


    4.1 The Licensee shall establish reliable and efficient point to point voice and data communication links between SLDC, ERLDC, Generating Stations and EHT sub-stations.

    4.2 All operational communications/instructions transmitted by SLDC or transmitted to SLDC shall be recorded as evidence of the communications/instructions.


    5.1 The Licensee shall ensure that its plan for outage of circuits / Transformers required for maintenance, construction, modification, diversion, etc. does not violate the security standards of Transmission system.


    6.1 The Licensee shall carry out system studies including Load flow, short circuit and Transient stability studies as often as required but at least once in a year.

    6.2 The Licensee shall endeavour for optimal use of existing reactive resources and the reactive reserves in the system to meet the steady state voltage limits at all Buses in the Transmission System as set in "Planning and Security Standards for Transmission System".

    6.3 The Licensee shall coordinate the settings of the Relays in the Protection Schemes of its Transmission system with those of the Generators, PGCIL and grid system of neighbouring States at respective points of interconnections.

    6.4 As a routine measure, the Licensee shall intimate all users of the Transmission System, the approximate fault level of the Transmission system at each point of interconnection both at EHT Bus and at H.T. Bus.

    6.5 The Licensee shall prepare schedule of operation of on-load Taps of load-transformers and interconnecting transformers at each EHT sub-station in the Transmission System under different Generation and load despatches as simulated in the system studies and enforce its implementation under similar situations obtained in practice.


    7.1 The Licensee shall monitor MW/MVAR loading of each EHT line and each interconnecting transformer on real time basis at SLDC. Similarly, the loadings on each load transformers at EHT sub-station shall be closely monitored during peak load hours.

    7.2 If any system component is being over loaded/over heated, the load on the same shall be reduced by following suitable procedure.


    8.1 The Licensee shall monitor voltage levels at all EHT sub-stations of its Transmission System on real time basis at SLDC.

    8.2 Since voltage is affected both by frequency and reactive power flow, system voltage shall be regulated by taking all possible measures to regulate system frequency and reactive power flows.

    8.3 All local voltage problems shall be addressed by attending to local transformer taps.

    8.4 In case of system High Voltage, Licensee shall take following measures :

    1. Address high frequency problem.

    2. Request Generating Plants to increase MVAR absorption in accordance with machine capability curve.

    3. Switch in bus reactors where provided.

    4. Switch out capacitors where provided and switched in.

    5. Reduce taps of 400/220kV and 220/132kV interconnecting transformers.

    6. Switch out one circuit of lightly loaded double circuit Transmission lines.

    8.5 In case of system low voltage, Licensee shall take following measures :

    1. Address low frequency problems.

    2. Request Generating Plants especially nearer to load centres to increase MVAR generation in accordance with machine capability curve.

    3. Switch out bus reactors.

    4. Switch in capacitors.

    5. Increase system voltage by tap changing of 400/220kV and 220/132kV interconnecting transformers.

    6. Restoration of circuits under outage.

    7. Demand reduction.                                                                                                       


    9.1 The Licensee in consultation with users of Transmission system shall identify H.T. Feeders emanating from EHT sub-stations to drop automatically and sequentially loads in blocks when the system frequency begins falling from 49 Hz. Quantum of loads to be shed in blocks from EHT sub-stations at each of the following stages of under frequency shall be determined.

    Stage I   : 49.0 Hz
    Stage II  : 48.8 Hz
    Stage III : 48.6 Hz


    10.1 To avoid total black out of the grid, during system disturbances and for early normalisation, an islanding scheme involving major generating stations and part/parts of Transmission System shall be developed in consultation with ERLDC.


    11.1 The Licensee shall observe the General Safety Requirements as laid down in I.E. Rules for construction, installation, protection, operation and maintenance of electric supply lines and apparatus.

    11.2 The Licensee shall designate suitable control persons as specified in GRID CODE for coordination of safety procedures before work is taken up, during work, and after work is completed till the concerned system component is energised, both inside its own Transmission System and across a control boundary between Licensee's Transmission System and that of any User.

    11.3 The Licensee shall develop its own Safety Manual for the purpose of Safety Coordination.


    12.1 The Licensee shall monitor all abnormal occurrences or events affecting the operation of system requiring attention, outlined in GRID CODE.

    12.2 The Licensee shall ensure that within ten minutes of an occurrence, verbal/telephonic communication shall be made to a designated officer by Shift-Manager, SLDC, who shall be in position and authority to initiate follow up action as deemed fit. The Shift Manager, SLDC must, however, give utmost priority in safeguarding the system before initiating the reporting procedure.

    12.3 Within 30 minutes, a preliminary report shall be prepared in a Form to be standardised by Licensee and communicated to the designated officer/officers.

    12.4 Within 48 hours, detailed report shall be prepared in a Form to be standardised by Licensee and communicated to the designated officer/officers.


    13.1 All major grid disturbances causing tripping of Generating Units (110 MW and above), tripping of EHT lines (220kV and above) causing full or partial System Black out, break down of Inter connecting Transformers (100 MVA and above), break down of EHT lines causing prolonged interruption and load restrictions shall be immediately discussed and analysed in the GRID CODE REVIEW PANEL. This shall promptly be done following discussion and analysis in any Sub-panel that may be formed by the panel for the purpose.

    13.2 Disturbance Reports and recommendations made in such meetings shall be compiled and circulated to all members of GRID CODE REVIEW PANEL for its implementation.


    14.1 The Licensee shall develop maintenance schedules of lines and sub-station equipment in conformity with I.E. Rules and relevant CBI & P manuals.

    14.2 The Licensee shall establish a hierarchy for implementation of the maintenance standards and its monitoring.

    14.3 No EHT line shall suffer total interruption for more than 175 hours in a year including planned outages but excluding Force Majeur causes.

    14.4 No HT supply at points of interconnection shall suffer total interruption for more than 310 hours in a year including planned outages and excluding Force Majeur causes.

    14.5 For the purposes of reducing inventory, procurement time, installation time, the Licensee shall adopt standardised designs for Transmission Line Towers, Structures for sub-stations, standardise layouts for sub-stations, sub-station lighting, Control Room lighting and ventilation, sub-station earthing, prepare standard specifications for line materials, transformers, sub-station equipment, Cables, Bus bar accessories, insulators and hardwares, etc.

    14.6 For convenience of maintenance, repairs and replacement, of line equipment and sub-station equipment, the Licensee shall develop and observe a policy on spare parts.

    14.7 The Licensee shall establish Electrical Testing Laboratories of its own, equipped for Routine Testing of Relays, Meters, Current-Transformers, Potential Transformer, Condenser Bushing, and other electrical accessories used in sub-stations in accordance with relevant Indian Standards and Manufactures instructions.

    14.8 The Licensee shall establish testing organisations under its control, staffed with qualified, trained and skilled persons and equipped with all necessary testing equipment, power supply etc. for conducting field tests and Commissioning tests of sub-station equipment such as Transformer, Circuit Breaker, Current Transformer, Potential Transformer, Station Battery, relays and meters, Control Wiring, Cables, Lightning Arrester, sub-station earthing, etc.

    14.9 The Licensee shall maintain in good order and condition all necessary equipment, tools, tackles, etc. for carrying out maintenance of lines and sub-stations equipment and ensure their availability at all sub-stations.

    14.10 The Licensee shall carry out periodical inspection of all lines and sub-stations in its Transmission system, through an independent inspection team, qualified for the purpose, to ensure that maintenance of lines and sub-stations are carried out as per maintenance schedules.



    Data for Operation and Studies
    (With reference to Para 2 of Section-4)

    All data should be on 100 MVA base.

    1. Line data for all lines of 132 kV level and above

    From Bus No. :

    From Bus Name :

    To Bus No. :

    To Bus Name :

    Volt. Level (kV) :

    Ckts No. :

    Line length (KM) :

    Conductor size & No. of conductors per phase :

    Pos. seq Resistance/KM (in p.u.) :

    Pos. seq Reactance/KM (in p.u.) :

    Pos. seq Half Line susceptance/KM (in p.u.) :

    Zero seq Resistance/KM (in p.u.) :

    Zero seq Reactance/KM (in p.u.) :

    Zero seq Half Line susceptance/KM (in p.u.) :

    Line Capacity (AMPS) (specify Amb. Temp °C and Temp rise over amb. in °C):

    Line Reactors (if any) (at both ends) MVAR :

    Year of commissioning :


    2. Transformer data for all 400/220 kV, 400/132 kV and 220/132 kV auto transformers and Generator Transformers.

    From Bus No. :

    From Bus Name :

    To Bus No. :

    To Bus Name :

    Voltage on HV side :

    Voltage on LV side :

    No. of Transformers :

    Resistance (in p.u.) :

    Reactance (in p.u.) :

    Tap setting :

    Nominal Tap :

    Tap step :

    Tap range :

    Transformer Type (2 or 3 wdg. Vector Group) :

    Rating of transformer (MVA) :

    Year of commissioning :

    Special data for 3 winding transformer

    Impedance between (p.u.)
    HV-MV :
    MV-LV :
    HV-LV :

    Voltage on HV side :

    Voltage on MV side :

    Voltage on LV side :

    Loading capability of tertiary, (if any) :

    Grounding impedance in p.u. :
    (if the neutral of the star is grounded)


    3. Bus Data

    Bus No. :

    Name of Bus :

    Bus Voltage (kV) :

    Gen. Bus/Load Bus :

    Pgen (MOO) :

    Qgen (MVAR) :

    Pload (MOO) :

    Qload (MVAR) :

    V obtained for Gen. Bus :

    MVAR Capability Curve for generators :

    Shunt Reactor, if any :

    Shunt Capacitor, if any :


    4. A) Generator Data :

    1. Capacity - MVA*, MW, MVAR (Minimum) & MVAR (Maximum)

    2. Generator voltage in kV Nominal, minimum, maximum

    3. Sequence impedances of winding on its 'OWN' base/ Grounding impedance

    4. Direct axis
      - Synchronous reactance
      - transient reactance
      - sub-transient reactance

    5. Quadrature axis
      - Synchronous reactance
      - transient reactance
      - sub-transient reactance

    6. Inertia constant in MW-SEC/MVA

    7. Damping constant

    8. Armature resistance

    9. Armature leakage reactance

    10. Direct axis
      - transient time constant
      - sub-transient time constant

    11. Quadrature axis
      - transient time constant
      - sub-transient time constant

      * Maximum Continuous Rating

    B) Turbine

    1. Type of Turbine i.e. Hydro/Steam, Francis, Kaplan etc.

    2. Block diagram of turbine model along with the values of gain constants & time constant.

    3. Turbine damping constant Kd.

    4. Speed of machine, nominal speed.

    5. Any other constants/specifications as described in the block diagram of turbine model.

    C) Exciter

    a. Block diagram of Exciter model along with the values of gain and time constant like :

    Voltage regulator gain and time constant
    Main Excitor gain and time constant
    Stabilising loop/closed loop gain and time constant.

    b. Power system stabiliser data.

    D) Speed Governors

    1. Block diagram of Speed Governor model (hydro/steam) along with the values of gain and time constant.

    2. Max. & Min. Valve position limits

    3. Effective speed governing system gain

    4. Valve Servo time constant


    5. Demand Data for all 220 kV & 132 kV sub-stations

    1. Weekly MW/MVAR load details

    MW/MVAR loadings should indicate the percentage of Agricultural load, Industrial load, domestic load & Commercial load separately.

    • Restrictions imposed

    • Assessed reduction in demand due to the restrictions

    • Unrestricted Demand
      : MW
      : MVAR

    2. Name of sub-station :

    Typical Daily Load Curve (for week day and weekend)

    • Under restricted demand

    • Under unrestricted demand



    Each Generating Units - Generation MW

    All 400/220 kV Line flow - MW and MVAR

    All 400/220 kV Transformer flow - MW and MVAR

    All 220/132 kV Transformer flow - MW and MVAR

    Bus Voltages at 400 kV, 220 kV buses

    Tap positions - 400/220 kV, 400/132 kV & 220/132 kV Transformers.

    Status of Circuit Breaker positions of all 400 kV, 220 kV and 132 kV lines, transformers, generators.