Chapter-3

 TRANSMISSION OPERATING STANDARDS

1.          OBJECTIVE

These standards are laid down for operating the transmission system so as to provide an efficient, coordinated and economical system of electricity transmission.

2.         DATA MANAGEMENT

The following data relating to the Transmission System shall be recorded and maintained by the licensee. The data where ever possible shall be online or recorded at an interval of half an hour (or as per the IEGC requirement).

1. Line data

2. Transformer data including Generation transformers

3. Bus Data including that of Generating stations

4. Availability and outage data of important transmission elements e.g. transmission line, transformer etc.

5. Generator data including that of Captive Power Plant running in parallel with the grid

6. Demand data including loading and power factor for each EHT sub-station

3.      LOAD DESPATCH

3.1   The State Load Dispatch Center (SLDC) would run round the clock for the purposes of :

   i.          Daily Generation Scheduling and issuing of despatch instructions.

  ii.          Monitoring line MW and MVAr drawals, EHT Bus voltages for important lines /substations, system frequency and other system operation parameters.

 iii.         Monitoring Generation output.

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

 v.           Giving direction and exercising such supervision and control as may be required for ensuing the integrated grid operation and for achieving the maximum economy and efficiency in the operation of power system of the licensee.

vi.           Ensuring that all directions issued by SLDC/Regional Load Dispatch Center are duly compiled with.

vii.        Enforcing the decisions of Regional Electricity Board.

4.        COMMUNICATION

4.1   A reliable and efficient point to point voice and data communication links would be set up between the SLDC, NRLDC, Generating Stations and grid sub-stations.

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

 5.      OUTAGE PLANNING

The plan for outage of circuits / Transformers required for maintenance, construction, modification, diversion, etc. would not violate the security standards of Transmission system.

Overall outage Planning for the Region is coordinated by Northern Regional Electricity Board. The responsibility of licensee for Outage Planning includes:

i.               The licensee shall provide REB Secretariat their proposed outage programme in writing in consultation with SLDC for the next financial year by 30th November of each year. These shall contain identification of each line/ICT, the preferred date for each outage & its duration and where there is flexibility, the earliest start date and latest finishing date.

ii.            Final outage plans prepared by REB will be reviewed from time to time in Regional forum and will be implemented accordingly.

iii.          Licensee shall obtain the final approval from SLDC prior to availing an outage.

6        SYSTEM STUDIES & PROTECTION

6.1   The system studies including load flow studies and Transient stability studies would be carried out as often as required but at least once a year.

6.2   The settings of the Relays in the Protection Schemes of the Transmission system would be coordinated with those of the Generators, BBMB, PGCIL and grid system of neighboring States at respective points of interconnections.

6.3   The user of the Transmission System would be intimated the computed fault level of the Transmission system at the point of interconnection so as to coordinate the equipment ratings appropriately.

7.       LOAD MANAGEMENT

7.1   The MW/MVAR loadings on each transmission line and each interconnecting transformer would be monitored on real time basis locally at each sub-station as well as at SLDC. Similarly loading on each transformer at grid sub-stations would be closely monitored during peak load hours.

7.2    If any system component is being over loaded, the same would be reduced to avoid breakdown of the equipment/system.

7.3    Load management will be carried out as per instructions of SLDC through

i.                Manual load disconnection/reconnection.

ii.        PC based system for rotational load shedding with facilities for central programming and uploading of the disconnection schedule for the day from the SLDC/sub-LDC to the substations.

7.4    During the demand control by manual disconnection of loads by staggering in different groups, the roster changeover from one group to another shall be carried out in a gradual and scientific manner so as to avoid excursions in the system parameters.

8.       VOLTAGE MANAGEMENT

8.1   The voltage levels at all EHT sub-stations of its Transmission System would be monitored on real time basis at SLDC.

8.2   Since voltage is affected both by frequency and reactive power flow, efforts would be made to maintain system voltage by taking all possible measures to regulate system frequency and reactive power flows.

8.3         All local voltage problems would be addressed by operating local transformer taps and/or switching capacitor banks etc.

8.4         In the event of system high voltage the following specific steps would be taken by the licensee’s grid substations at their own, unless specifically mentioned by SLDC otherwise;

•  The bus reactors be switched in

• he manually switchable capacitor banks be taken out

• The switchable line/tertiary reactors be taken in

• Opening of the light loaded lines in consultation with SLDC, keeping in view the security of the balance network.

• Reducing taps of 220 kV, 132 kV and 66 kV interconnecting transformers.

8.5         In the event of system low voltage the following specific steps would be taken by the licensee’s grid substations at their own, unless specifically mentioned by SLDC otherwise;

• The bus reactors be switched out

• The manually capacitor banks be switched in

• The switchable line/tertiary reactors be taken out

• Closing of the lines which were opened to control high voltage Increasing system voltage by tap changing of 220kV, 132 kV, and 66kV interconnecting transformers.

• Restoration of circuit under outage.

• Demand reduction.

8.6         At the interchange points where licensee system is connected with Regional grid, licensee shall endeavors to minimize the VAR drawal when voltage is below 95% of rated, and shall not return VAR when the voltage is above 105%.

8.7        The licensee will operate on-load and off-load taps of power transformer and interconnecting transformer at each EHT sub-station in the Transmission system as and when necessitated by system requirement.

8.8          Switching in/out of all 400 kV Bus and line reactors throughout the grid shall be carried out as per instruction of RLDC. Tap changing on all 400/220 kV ICTs shall also be done as per RLDC instructions.

9.      AUTOMATIC LOAD SHEDDING DURING UNDER FREQUENCY AND BACKING DOWN DURING HIGH FREQUENCY

9.1   Under Frequency relay load shedding scheme shall conform to that formulated and reviewed by NREB from time to time in consultation with all the constituents based on both flat frequency as well as rate of change of frequency. The scheme would ensure no overlapping between areas covered by UF relay load shedding and that included in the manual load shedding plan as part of demand control. The licensee would ensure to keep all the UF relays properly maintained and functional so that automatic relief through these relays would be available to the system under all conditions. As per directions of SLDC, under normal system operation, frequency should not fall to such low value necessitating unnecessary operations of U/F relays. Manual load shedding should be carried out as directed by SLDC to avoid such situations. The automatic load shedding operation of UF and df/dt relays is meant to take care of unforeseen contingencies and should occur only in case of sudden loss of bulk generation.

         Licensee shall furnish to NRLDC/SLDC a list of feeders connected for UFLS, UF settings and load relief quantum etc. and shall furnish a monthly report on availability and condition of UFRs in the system under the control of licensee.

9.2   When the system frequency is beyond 50.2 Hz, the generating units with high variable cost of generation shall be advised to back down their generation and even shut down in case the frequency continues to remain high, at the directions of NRLDC, who co-ordinate integrated grid operation.

10.    ISLANDING SCHEME

10.1     To avoid total black out of the grid, during system disturbances and for early normalization, an islanding scheme involving major generating stations and part(s) of the transmission system would be developed in consultation with NRLDC.

10.2     When an exporting group is islanded, the frequency of the islanded group would be controlled below 50.5 Hz by load pick up within the island or reduction of generator outputs and, if necessary, by generator tripping.

10.3     When an importing group is islanded and the frequency of the group is below the specified lower limit, the islanded group would improve the frequency to the security limit by increasing generator output and, if necessary, by load shedding.

11.    SAFETY COORDINATION

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

11.2 Suitable control person(s) shall be designated 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      A Safety Manual for the purpose of Safety Coordination shall be developed.

12      EVENT REPORTING

12.1  All abnormal occurrences or events affecting the operation of system requiring attention would be monitored and logged by the licensee who shall be responsible for reporting events to SLDC. Following events are to be reported:-

(i)                 System islanding/system split.

(ii)                System black out/partial system block out.

(iii)              Protection failure on any element of transmission system

(iv)              System instability

(v)               Tripping of any element.

12.2   Reporting Procedure:

(a)    Written reporting of Events by Licensee to SLDC

        In the case of an event which was initially reported by a Licensee to SLDC orally, the Licensee will give a written report to SLDC in accordance with (b)

(b)    Form of written Reports:

        A written report shall be sent by licensee to SLDC and will confirm the oral notification together with the following details of the event:

i)                    Time and date of event

ii)                Location

iii)              Plant and/or equipment directly involved

iv)            Description and cause of event

v)              Antecedent conditions

vi)             Demand interrupted and duration of interruption

vii)            Sequence of tripping with time

viii)        Details of Relay Flags

ix)            Remedial measures

13.     POST DISTURBANCE ANALYSIS

13.1  The licensee will provide all information/data and assist SLDC/NRLDC in post disturbance analysis.

13.2  Recording instruments such as disturbance recorder/Event logger/Fault locator (including time synchronisation equipment) shall be provided at all the identified major grid substations to facilitate in identifying sequence of the event etc.

14.    MAINTENANCE, STANDARDISATION, SPARES, TESTING AND INSPECTION

14.1 Maintenance schedules of lines and sub-station equipment shall be developed in conformity with I.E. Rules, relevant CBI & P manuals and manufacturer's recommendations.

14.2 A hierarchy shall be established for implementation of the maintenance standards and its monitoring.

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

14.4  For the purposes of reducing inventory, procurement time, installation time, standardised designs shall be adopted for Transmission Line Towers, Structures for sub-stations, standardise layouts for sub-stations, sub-station lighting, Control Room lighting and ventilation, sub-station earthing. Standard specifications shall also be prepared for line materials, transformers, sub-station equipment, Cables, Bus bar accessories, insulators and hardware etc.

14.5  For expeditious maintenance, repair and replacement of line equipment and sub-station equipment, recommended spare parts and equipment shall be procured and adequate inventory of long delivery spare parts shall be maintained.

14.6 Routine Testing of Relays, Meters, Current-Transformers, Potential Transformer, Condenser Bushing, and other electrical accessories used in sub-stations shall be done in the Electrical Testing Laboratories of the licensee in accordance with relevant Indian Standards and Manufactures instructions.

14.7 All 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 shall be by the testing organisations of the licensee.

14.8 All necessary equipment, tools & tackles, etc. shall be maintained in good condition for carrying out maintenance of lines and sub-stations equipment and ensure their availability at all sub-stations.

14.9  Periodical inspection of all lines and sub-stations shall be carried out 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.