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RGMO POSOco

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  • JULY-2013 REV 0

  • TABLE OF CONTENTS

    .

    Page No

    1. General:01

    2. Network Security and System Operation.:05

    3. Demand Monitoring & Control Procedure..:16

    4. Outage Planning.:20

    5. Defence Mechanisms .................:24

    6. Collective Transaction Procedures...:27

    7. Scheduling & Despatch Procedures..:30

    8. Grid Disturbances & Revival Procedure..:34

    9. Event Information & Reporting Procedure.....:37

    10. Switching Coordination.:39

  • ANNEXURES

    Page No

    I. Frequency Linked Despatch Guidelines..:42

    II. FRC-CERC Approved Procedure and Formats:44

    III. Surge Impedance Loading(SIL) of Transmission Lines....:73

    IV. Thermal loading-As per CEA Planning Criteria.:74

    V. NLDC Advisory on High capacity 765kV corridors...:76

    VI. Congestion Formats..:84

    VII. UI Price Vector..:91

    VIII. List of important Grid Elements...:94

    IX. Procedure for Outage Planning - Proposed....:115

    X. UFR & df/dt Load Shedding.:129

    XI. System Protection Schemes-All India Level:136

    XII. Islanding Schemes..:168

    XIII. Multiple Element Outage Circular ..:178

    XIV. Regional Power Maps....:179

    XV. Glossary and Definitions...:192

  • ACRONYMS

    CERC - Central Electricity Regulatory Commission

    SERC - State Electricity Regulatory Commission

    IEGC - Indian Electricity Grid Code

    NLDC - National Load Despatch Centre

    RLDC - Regional Load Despatch Centre

    SLDC - State Load Despatch Centre

    TTC - Total Transfer Capability

    ATC - Available Transfer Capability

    TRM - Transmission Reliability Margin

    ISGS - Inter State Generating Stations

    ISTS - Inter State Transmission System

    CEA - Central Electricity Authority

    STU - State Transmission Utilities

    CTU - Central Transmission Utility

    RPC - Regional Power Committee

    STOA - Short-term Open Access

    MTOA - Medium-term Open Access

    OCC - Operation Coordination Committee

    IPP - Independent Power Producer

    DR - Disturbance Recorder

    AVR - Automatic Voltage Regulator

    SVC - Static VAR Compensator

    UI - Unscheduled Interchange

    NER - North Eastern Region

    RGMO - Restricted Governor Mode of Operation

    FGMO - Free Governor Mode of Operation

    HVDC - High Voltage Direct Current

    MCR - Maximum Continuous Rating (MCR)

    UFR - Under Frequency Relay

    FRC - Frequency Response Characteristic

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    1. General

    1.1 Objective:-

    1.1.1 Operating Procedures of National Load Despatch Centre (NLDC) document has been developed

    by NLDC as per Cl. 5.1(e) of Indian Electricity Grid Code (IEGC) in consultation with the

    RLDCs for the guidance of the staff of NLDC. This document is brought out in line with IEGC,

    2010. After that Honble CERC issued amendment to IEGC principal regulation (2010) on 05/03/12.

    The revision/updation of this procedure is based on amendment in various regulations, recent

    Orders/Regulations issued by Honble Central Electricity Regulatory Commission (CERC) and recent changes in the power sector. CERC amended IEGC, UI Regulations, Grant of Connectivity,

    LTA & MTOA in ISTS and related matters Regulations, Terms & Conditions of Tariff

    Regulations, Procedure, Terms and Conditions for Grant of Trading Licence and other related

    matters Regulations. Also the procedure for relieving congestion in real time operation has also

    been revised by NLDC and approved by CERC vide its order dated 22.04.2013, Procedure for

    assessment of Frequency Response Characteristic (FRC) of Control Areas was approved by

    CERC and Manual on Transmission Planning Criteria was revised by CEA in Jan 2013. CERC

    has approved the detailed "Procedure for the Implementation of the Mechanism of Renewable

    Regulatory Fund" under Regulation 6.1 (d) of Central Electricity Regulatory Commission (Indian

    Electricity Grid Code), Regulations 2010 vide its order dt 09-07-13.

    This procedure supersedes the earlier procedure issued by NLDC in June, 2012.

    1.1.2 The real time operation of National Grid is one of the important functions of NLDC. As more and

    more inter regional links are coming up and more number of 765kV lines are coming, demand

    rising rapidly, the task of real time grid operation is becoming more and more complex. The

    Indian Grid has interconnections with neighbouring countries like Bhutan and Nepal also. In

    India, two power exchanges are in operation as per the regulations of CERC for collective

    transactions and the approved procedure prepared by NLDC. The need was felt to develop the

    written document for the guidance of real time operator of National Grid and to develop the

    reference manual for day to day operation.

    1.1.3 Objective of this document is to clearly spell out the procedures adopted for the integrated system operation and roles of each agency and their responsibilities in grid operation in compliance of

    IEGC. This document aims at operation and development of national power system in the most

    efficient, economic, secure and reliable manner. This document also aims to facilitate beneficial

    trading opportunities to harness bottled up power.

    These procedures are to be read in conjunction with the Central Electricity Regulatory

    Commission (Indian Electricity Grid Code) Regulations, 2010 IEGC and its first amendment-

    2012, CEA (Grid Standards) regulation, 2010 and respective RLDCs Operating Procedures. If any

    ambiguity arises in interpretation of this operating procedure, the meaning, intent and the purpose

    of clauses as provided in IEGC and CEA (Grid Standards) shall prevail.

    1.2 Role of NLDC:- 1.2.1 National Load Despatch Centre (NLDC) has been constituted as per Ministry of Power (MOP)

    notification, Government of India, under section 26(2) of the Act, dated 2nd March 2005 and is

    the apex body to ensure integrated operation of the national power system.

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    1.2.2 The main functions assigned to NLDC as per the above notification are: a) Supervision over the Regional Load Despatch Centres.

    b) Scheduling and despatch of electricity over inter-regional links in accordance with grid standards specified by the Authority and Grid Code specified by Central Commission in

    coordination with Regional Load Despatch Centres.

    c) Coordination with Regional Load Despatch Centres for achieving maximum economy and efficiency in the operation of National Grid.

    d) Monitoring of operations and grid security of the National Grid.

    e) Supervision and control over the inter-regional links as shall be required for ensuring stability of the power system under its control.

    f) Coordination with Regional Power Committees for regional outage schedule in the national perspective to ensure optimal utilization of power resources.

    g) Coordination with Regional Load Despatch Centres for the energy accounting of inter- regional exchange of power.

    h) Coordination for restoration of synchronous operation of national grid with Regional Load Despatch Centres.

    i) Coordination for trans-national exchange of power.

    j) Providing operational feedback for national grid planning to the Authority and Central Transmission Utility.

    k) Levy and collection of such fee and charges from the generating companies or licensees involved in the power system, as may be specified by the Central Commission.

    l) Dissemination of information relating to operations of transmission system in accordance with directions or regulations issued by Central Government from time to time.

    1.2.3 NLDC shall also carry out the following functions as per directions issued from time to time.

    a) NLDC is the nodal agency for collective transactions as per CL.5 of CERC (Open Access in Inter-State Transmission) Regulations, 2008.

    b) NLDC is the implementing agency for (Sharing of Inter-State Transmission Charges and Losses) Regulations as per Cl 18.1 of the above regulation.

    c) NLDC is the Central Agency for Renewable Energy Certificate(REC) mechanism vide CERC Order dated 29.01.2010.

    d) NLDC would act as the Central control room in case of natural & man made Emergency/disaster where it affects the power system operation vide MOP letter dt 27-05-

    2009.

    e) Any other function as may be assigned by the Commission by order or regulations from time to time.

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    1.3 Role of RLDC:-

    According to Sections 28 and 29 of Electricity Act, 2003, the functions of RLDCs are

    as follows:

    a) The Regional Load Despatch Centre shall be the apex body to ensure integrated operation of the power system in the concerned region.

    b) The Regional Load Despatch Centre shall comply with such principles, guidelines and methodologies in respect of wheeling and optimum scheduling and despatch of electricity as

    may be specified in the Grid Code.

    c) The Regional Load Despatch Centre shall a. be responsible for optimum scheduling and despatch of electricity within the

    region, in accordance with the contracts entered into with the licensees or the generating

    companies operating in the region;

    b. monitor grid operations;

    c. keep accounts of quantity of electricity transmitted through the regional grid;

    d. exercise supervision and control over the Inter State Transmission System ; and

    e. be responsible for carrying out real time operations for grid control and

    despatch of electricity within the region through secure and economic

    operation of the regional grid in accordance with the Grid Standards and the Grid Code.

    d) The Regional Load Despatch Centre may give such directions and exercise such supervision and control as may be required for ensuring stability of grid operations and for achieving the

    maximum economy and efficiency in the operation of the power system in the region under its

    control.

    e) Every licensee, generating company, generating station, sub-station and any other person connected with the operation of the power system shall comply with the directions

    issued by the Regional Load Despatch Centers.

    f) All directions issued by the Regional Load Despatch Centers to any transmission licensee of state transmission lines or any other licensee of the state or generating company (other than

    those connected to interstate transmission system) or substation in the state shall be issued

    through the State Load Despatch Centre and the State Load Despatch Centers shall ensure that

    such directions are duly complied with by the licensee or generating company or sub-station.

    g) If any dispute arises with reference to the quality of electricity or safe, secure and integrated operation of the regional grid or in relation to any direction given by the Regional Load

    Despatch Centre, it shall be referred to Central Commission for decision. However, pending

    the decision of the Central Commission, the directions of the Regional Load Despatch Centre

    shall be complied with by the State Load Despatch Centre or the licensee or the generating

    company, as the case may be.

    The following are contemplated as exclusive functions of RLDCs

    1) System operation and control including interstate transfer of power, covering contingency analysis and operational planning on real time basis;

    2) Scheduling / re-scheduling of generation; 3) System restoration following grid disturbances; 4) Meter Data Processing; 5) Compiling and furnishing data pertaining to system operation; 6) Operation of regional UI pool account, regional reactive energy account and Congestion

    Charge Account, provided that such functions will be undertaken by any entity(ies) other than

    RLDCs if the Commission so directs.

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    7) Operation of ancillary services

    In cases of Short Term Open access bilateral transaction in Inter State Transmission, the Regional

    Load Despatch Centre of the region where point of drawal of electricity is situated, shall be the

    nodal agency for the short-term open access. The procedure and modalities in regard to short-term

    Open Access shall be in accordance with the Central Electricity Regulatory Commission (Open

    Access in Inter State Transmission)\Regulations, 2008, as amended from time to time.

    1.4 Role of SLDC:-

    In accordance with section 32 of Electricity Act, 2003, the State Load Despatch Centre

    a) The State Load Despatch Centre shall be the apex body to ensure integrated operation of the power system in a State.

    b) The State Load Despatch Centre shall - a. be responsible for optimum scheduling and despatch of electricity within a State, in

    accordance with the contracts entered into with the licensees or the generating companies

    operating in that State;

    b. monitor grid operations;

    c. keep accounts of the quantity of electricity transmitted through the State grid;

    d. exercise supervision and control over the intra-State transmission system; and

    e. be responsible for carrying out real time operations for grid control and despatch of electricity within the State through secure and economic operation of the State grid in accordance with

    the Grid Standards and the State Grid Code.

    In accordance with section 33 of the Electricity Act 2003, the State Load Despatch Centre in a

    State may give such directions and exercise such supervision and control as may be required for

    ensuring the integrated grid operations and for achieving the maximum economy and efficiency in

    the operation of power system in that State. Every licensee, generating company, generating

    station, sub-station and any other person connected with the operation of the power system shall

    comply with the directions issued by the State Load Depatch Centre under subsection (1) of

    Section 33 of the Electricity Act,2003. The State Load Despatch Centre shall comply with the

    directions of the Regional Load Despatch Centre.

    In case of inter-state bilateral and collective short-term open access transactions having a state

    utility or an intra-state entity as a buyer or a seller, SLDC shall accord concurrence or no

    objection or a prior standing clearance, as the case may be, in accordance with the Central

    Electricity Regulatory Commission (Open Access in Inter-State Transmission) Regulations, 2008,

    amended from time to time.

    1.5 Maintenance of Operating Procedures:-

    These procedures shall be maintained and reviewed periodically. However, in case of urgent need

    arising due to operating problems, the procedures can be reviewed / revised expeditiously. NLDC

    will be the coordinating agency for updating/review of Operating Procedures.

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    2. Network Security and System Operation

    2.1 Introduction:

    This chapter highlights the actions required to be undertaken by system operators to keep the

    network secured at all times against contingencies arising in the grid due to outage of critical

    lines, bus, generating units or other important elements of the grid. It also describes the actions

    required to maintain system parameters close to nominal values in day-to-day operation.

    2.2 Network Security

    2.2.1 Background

    i) At present, the Indian power system has two asynchronous grids i.e., NEW grid comprising

    Northern, Eastern, North-Eastern & Western regions and SR (Southern region) grid. The NEW

    grid and SR Grid together caters about 120 GW of demand with a peak shortage in the range of

    6000 to 10000 MW with about 2700 MU energy consumption. The NEW grid has already yielded

    various benefits by taking advantage of diversity of time, surplus/deficit management due to

    demand forecast errors/ weather variations, increased economic transactions, improvement in

    overall system security and efficiency due to increase in stability margin and a stiffness of about

    3500 MW/Hz. The stiffness of SR grid is of the order of 2000 MW/Hz.

    ii) However, synchronisation of regional grids has also resulted in evolution of different contingencies

    of critical nature in the grid, which has a potential to snowball in to credible contingency in the

    grid In addition, system may operate at times beyond the assumptions of the planner in line with

    various transmission security standards and associated criteria mentioned in section 3.5 of IEGC

    due to following reasons:

    a. Planned maintenance programme of the generators and transmission lines/elements. It is

    imperative to ensure that such maintenance programmes are properly coordinated and do not

    result in reduced redundancy not envisaged during planning.

    b. The events beyond the control of operators such as extreme weather conditions affecting the

    reliability of transmission system, uneven demand growth or delay in commissioning of

    generators/transmission elements.

    2.2.2 Measures to ensure Network Security and Reliability

    For safe and secure grid operation, it is imperative that system parameters i.e. frequency, voltage

    etc., remain close to nominal values. This section highlights the measures to be adopted by the

    System Operators at NLDC/ RLDCs / State Load Despatch Centres (SLDCs) / Inter State

    Generating Stations (ISGS) / substations for frequency and voltage control.

    2.2.3 Frequency Control

    2.2.3.1 Frequency Band:-All the regions would make all possible efforts to ensure the maintenance of grid frequency within the normal IEGC band that is 49.7 Hz to 50.2 Hz currently as per IEGC

    Clause. 5.2(m) and as specified by the IEGC from time to time. The nominal frequency of

    operation in Indian grid is 50.0 Hz.

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    This would be ensured by implementing following measures:

    i) Each RLDC shall regulate the load / generation under its control so that the region may not draw more than its schedule whenever the system frequency is below 49.8 Hz and less than its

    schedule drawl whenever frequency is above 50.1 Hz and has rising trend.

    ii) Each regional entity shall maintain generation under its control such that it may not generate more than its schedule whenever the system frequency is above 50.1 Hz and has rising trend

    and less than its schedule whenever frequency is below 49.8 Hz.

    iii) In no case, entities in a region would resort to over drawl at a frequency of 49.7 Hz and below. Similarly, entities in the region should not under draw / generate more than schedule at

    frequency above 50.2 Hz.

    iv) PRIMARY RESPONSE :- All regional entities shall ensure that the generating units synchronised with the grid provide primary response in line with sections 5.2 (f), 5.2 (g), and

    5.2 (h) of IEGC.

    v) SUPPLEMENTARY CONTROL:- All regional entities shall provide supplementary control in line with regulation 5.2 (i) of IEGC. Whenever frequency falls below 49.8 Hz, all partly

    loaded generating units, particularly of overdrawing regional entities shall pick up additional

    generation to control declining system frequency. The Frequency Linked Despatch Guidelines

    is attached as Annexure I.

    vi) Sudden reduction in generator output by any entity by more than 100 MW (20 MW in case of North Eastern Region (NER)) shall be avoided particularly when frequency is falling or is

    below 49.7 Hz unless, under an emergency condition or, to prevent an imminent damage to the

    equipment.

    vii) Sudden increase/decrease in load by any regional entity by more than 100 MW shall be avoided to minimize frequency fluctuation. Sudden increase in load by more than 100 MW by

    any regional entity, particularly when frequency is falling below 49.7 Hz. and reduction in load

    by such quantum when frequency is rising above 50.2 Hz. shall be avoided.

    2.2.3.2. NLDC shall exchange the power between the NEW and SR grid to minimise the frequency

    differential between the grids in consultation with the concerned Regional Load Despatch Centre

    (RLDC) on opportunity basis in real-time in addition to the Inter-regional scheduled power.

    2.2.3.3 Measures during high frequency conditions

    Based on the scheduled load shedding programme, hydro pick up, change in STOA schedules and

    load ramp ups, NLDC shall anticipate possible frequency rises at the beginning of each hour and

    initiate advance actions.

    When the system frequency is above 50.1 Hz and in the rising trend:-

    i) NLDC will co-ordinate with WR, ER to export the power to SR region in case the NEW grid

    frequency is above 50.1 Hz and margin is available in the inter regional links and associated

    lines of the regions & vice versa in case the SR grid frequency is above 50.1Hz.

    ii) NLDC will coordinate with all the regions to maximize the load in case of under drawl and

    minimise the generation based on merit order after ensuring that all pumped storage schemes

    are in operation in pumping mode.

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    iii) Advise all RLDCs to endeavour to restrict their actual net injection to within their scheduled

    dispatch. All regions shall follow frequency linked dispatch guidelines.

    iv) All the regions shall endeavour to ensure that their drawl from the grid is not less than their

    schedule by following actions:-

    a. Instruct SLDCs to Phase out scheduled load shedding

    b. Advise constituents to surrender relatively high cost entitled power from ISGS through

    revision of schedules.

    c. Follow merit order and conserve fuel by reducing or shutting down high cost generators

    including IPPs.

    d. Explore additional export through Short-term Open Access (STOA).

    v) All regions shall stagger their rostering pattern in a manner so as to arrest stiff high frequency

    excursions during load changeover period.

    vi) In case of persistent (based on merit order) high frequency, all regions may resort to shutting

    down/ backing down of generators in the event of threat to grid security as per directions of

    NLDC.

    2.2.3.4 Measures during low frequency conditions

    All regions shall carry out day ahead operational planning by balancing availability from all

    sources and expected demand.

    When the system frequency is below 49.8 Hz and in the decaying trend:

    i) All regions shall endeavour to ensure the actual net injection of ISGS generation as per their

    scheduled dispatch.

    ii) All the regions shall ensure that their drawl from the grid is not more than their schedule by

    maximizing generation in line with frequency linked dispatch guidelines.

    iii) NLDC would advise RLDCs for further instructing to SLDC to restrict the over drawl at 49.8 Hz, within its schedule as per the Clause 5.4.2(a) IEGC-2010.

    iv) If frequency further deteriorates and goes below 49.7 Hz and the over drawl of the region

    continues then NLDC shall advise the RLDCs to make arrangements that will enable manual

    demand disconnection to take place as instructed by RLDC/ SLDCs.

    v) The measures undertaken to reduce the drawl from the grid shall not be withdrawn as long as

    the frequency / voltage remain at a low level unless specifically permitted by NLDC/RLDC.

    vi) In case of certain contingencies and / or threat to system security, NLDC may direct RLDCs

    to ensure reduction of drawl by particular regional entity by a certain quantum. Such

    directions shall immediately be acted upon.

    vii) NLDC will co-ordinate with WR, ER to import the power from SR region in case the NEW

    grid frequency is below 49.8 Hz and margin is available in the inter regional links and

    associated lines of the regions & vice versa in case the SR grid frequency is below 49.8Hz.

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    2.2.3.5 Governor Operation

    a) In accordance to the Clause 5.2(f), 5.2(g), 5.2(h), 5.2(i) of IEGC, all thermal generating units of

    200 MW and above and all hydro units of 10 MW and above (except those with upto three hours

    pondage), which are synchronized with the grid, irrespective of their ownership, shall have

    restricted governor mode of operation (RGMO) with effect from 01.08.2010.

    b) The restricted governor mode of operation shall essentially have the following features.

    i There should not be any reduction in generation in case of improvement in grid frequency below 50.2 Hz. ( for example if grid frequency changes from 49.3 to 49.4 Hz. then there

    shall not be any reduction in generation). Whereas for any fall in grid frequency, generation

    from the unit should increase by 5% limited to 105 % of the Maximum Continuous Rating

    (MCR) of the unit subject to machine capability.

    ii Ripple filter of +/- 0.03 Hz. shall be provided so that small changes in frequency are ignored for load correction, in order to prevent governor hunting.

    iii If any of these generating units is required to be operated without its governor in operation as specified above, the RLDC shall be immediately advised about the reason and duration of such

    operation. All governors shall have a droop setting of between 3% and 6%.

    iv Provided that if a generating unit cannot be operated under restricted governor mode operation, then it shall be operated in free governor mode operation with manual intervention to operate

    in the manner required under restricted governor mode operation.

    v All thermal generating units of 200 MW and above and all hydro units of 10 MW and above operating at or up to 100% of their Maximum Continuous Rating (MCR) shall normally be

    capable of (and shall not in any way be prevented from) instantaneously picking up to 105%

    and 110% of their MCR, respectively, when frequency falls suddenly. After an increase in

    generation as above, a generating unit may ramp back to the original level at a rate of about

    one percent (1%) per minute, in case continued operation at the increased level is not

    sustainable. Any generating unit not complying with the above requirements, shall be kept in

    operation (synchronized with the Regional grid) only after obtaining the permission of

    RLDC.

    vi The recommended rate for changing the governor setting, i.e., supplementary control for increasing or decreasing the output (generation level) for all generating units, irrespective of

    their type and size, would be one (1.0) per cent per minute or as per manufacturers limits. However, if frequency falls below 49.7Hz, all partly loaded generating units shall pick up

    additional load at a faster rate, according to their capability.

    c) If any of the generating units are required to be operated without its governor in operation as

    specified above, the RLDC shall be immediately advised about the reason and duration of such

    operation.

    d) Procedure to monitor primary response through Frequency Response Characteristic (FRC) from

    different control areas was submitted by NLDC and it is approved by the Honble CERC through its order dt.03-05-2013. The detailed procedure is attached as Annexure II

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    2.2.4 Voltage Control

    2.2.4.1 Operating Range

    As defined in the IEGC Section 5.2(s), the operating range of the voltages at various voltage levels

    of the grid is as follows:

    Voltage (kV-rms)

    Nominal Minimum Maximum

    765 728 800

    400 380 420

    220 198 245

    132 122 145

    110 99 121

    66 60 72

    33 30 36

    The maximum and minimum values in the above table are the outer limits and all the regions shall

    endeavour to maintain the voltage level within the above limits. NLDC operators should monitor

    the above voltage limits across all inter regional links& important nodes and should interact with

    RLDCs for keeping the system voltage within the above specified limit.

    As defined in the IEGC Section 5.2(J), all users and SEBs shall ensure that temporary over voltage

    due to sudden load rejection and the maximum permissible values of voltage unbalance

    shallremain within limits specified under Central Electricity Authority (Grid Standards)

    Regulations, 2010.

    Reactive Power manual of NLDC may be referred for detailed Reactive power management and

    voltage control procedures.

    2.2.4.2 AVRs of Generators

    Generating units of all the region shall keep their Automatic Voltage Regulators (AVRs) in

    operation and power system stabilizers (PSS) in AVRs shall be tuned in line with clause 5.2(k) of

    IEGC.

    2.2.4.3 VAR Exchange by regional constituents for Voltage and Reactive Control

    Each constituent shall provide for the supply of its reactive requirements including appropriate

    reactive reserves, and its share of the reactive requirements to support safe and secure power

    transfer on interconnecting transmission circuits. The RLDC and constituent states shall take

    action in regard to VAR exchange with the grid looking at the topology and voltage profile of the

    exchange point. In general, the beneficiaries shall endeavour to minimize the VAR drawl at

    interchange point when the voltage at that point is below the nominal value and shall not inject

    VARs when the voltage is above the nominal value. In fact, the beneficiaries are expected to

    provide local VAR compensation so that they do not draw any VARs from the grid during low

    voltage conditions and do not inject any VARs to the grid during high voltage conditions.

    2.2.4.4 VAR generation / absorption by generating units

    In order to improve the overall voltage profile, the generators shall run in a manner so as to have

    counter balancing action corresponding to low/high backbone grid voltage and to bring it towards the

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    nominal value. In order to achieve the same, all generators shall generate reactive power during low

    voltage conditions and absorb reactive power during high voltage conditions as per the capability limit

    of the respecting generating units. The online tap changers (OLTC) on the generator transformer

    wherever possible should also be used to achieve this. Off load tap changes should be used to take care

    of the seasonal variations in the voltage profile.

    2.2.4.5 Transformer Taps

    In line with IEGC clause 6.6.5 & 6.6.4,

    the transformer tap positions on

    different 765kV, 400kV, 220kV &

    132kV class ICTs shall be changed as

    per requirements in order to improve the

    grid voltage. RLDCs shall coordinate

    and advise the settings of different tap

    position and any change in their

    positions shall be carried out after

    consultation with RLDC. The modified

    tap position shall be informed to NLDC

    by RLDCs. The tap settings shall be

    reviewed and changed before the start

    of monsoon and winter and based on

    system requirement.

    NLDC shall review and advise RLDCs

    on the tap position of 765/400kV ICTs

    periodically.

    Fig:- Typical Transformer

    2.2.4.6 Control of Voltage at grid substations/generating stations

    Following corrective measures shall be taken in the event of voltage going high / low:-

    i) In the event of high voltage (when the bus voltage going above 410 kV), following specific

    steps would be taken by the respective grid substation/generating station at their own, unless

    specifically mentioned by NLDC/RLDC/SLDCs.

    a. The bus reactor be switched in

    b. The manually switchable capacitor banks be taken out

    c. The switchable line/tertiary reactor are taken in

    d. Optimize the filter banks at HVDC terminal

    e. All the generating units on bar shall absorb reactive power within the capability curve

    f. Operate synchronous condensers wherever available for VAR absorption

    g. Operate hydro generator / gas turbine as synchronous condenser for VAR absorption

    wherever such facilities are available

    h. Bring down power flow on HVDC terminals so that loading on parallel EHV network goes

    up resulting in drop in voltage.

    i. Open lightly loaded lines in consultation with RLDC/SLDC for ensuring security of the

    balanced network.

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    ii) In the event of low voltage (when the bus voltage going down below 390kV), following

    specific steps would be taken by the respective grid substation/generating station at their

    own, unless specifically mentioned by NLDC/RLDC/SLDCs.

    a.Close the lines which were opened to control high voltage in consultation with

    RLDC/SLDC.

    b. The bus reactor be switched out

    c. The manually switchable capacitor banks are switched in.

    d. The switchable line/tertiary reactor are taken out

    e. Optimize the filter banks at HVDC terminal

    f. All the generating units on bar shall generate reactive power within capability curve.

    g. Operate synchronous condenser for VAR generation

    h. Operate hydro generator / gas turbine as synchronous condenser for VAR generation

    wherever such facilities are available

    i. Increase power flow on HVDC terminals so that loading on parallel Extra High Voltage

    (EHV) network goes down resulting in rise in voltage.

    2.2.4.7 Load Management for controlling the Voltage

    All the regions shall identify the radial feeders in their areas in consultation with SLDCs which

    have significant reactive drawls and which can be disconnected in order to improve the voltage

    conditions in the event of voltage dropping to low levels.

    The details of all such feeders shall be kept ready in the respective control rooms of

    RLDC/SLDC and standing instruction would be given to the operating personnel to ensure the

    relief in the hour of crisis by disconnecting such feeders. Automatic under voltage load

    shedding shall commence at 380kV.

    2.2.4.8 Switching off the line reactors in case of low voltage

    In the event of persistent low voltage conditions, some of the line reactors are to be selected on

    the basis of line length, grid conditions, network topology etc. by each region which can be

    switched off in order to improve the system voltage profile. The switching off of such line

    reactors and reviving them back would be carried out as per the instructions issued by

    RLDCs/SLDCs.

    2.2.4.9 Switching off of the lines in case of high voltage

    In the event of persistent high voltage conditions when all other reactive control measures as

    mentioned earlier including opening of redundant HT lines with in the state system by the

    concerned SLDCs have been exhausted, selected 765 / 400 / 230 / 220 / 132 / 110 KV lines shall

    be opened for voltage control measures. The opening of lines and reviving them back in such an

    event would be carried out as per the instructions issued by RLDC/NLDC in real time and as per

    the standing instructions issued from time to time. While taking such action, RLDC/NLDC

    would duly consider that to the extent possible the same does not result in affecting ISGS

    generation as well as the system security & reliability is not affected.

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    2.2.5 Line loading

    In addition to frequency & voltage control measures outlined above, each system operator

    would also have before him the thermal loading limits, surge impedance loading and the loading

    permitted from stability considerations for each line listed under important elements. RLDC

    would endeavour to keep the line/ ICT loadings within limits and inform NLDC in case of

    overloading of any element. Special emphasis would be paid by each system operator in

    identifying credible system contingencies & continuously evaluating the system under his

    control against these contingencies.

    In addition to monitoring the loading of critical individual elements, the power flow across the

    identified flow gates shall also to be monitored and controlled with in the value specified based

    on the study results. All the regions hence would extend the necessary cooperation in

    maintaining network reliability and security.

    Surge Impedance Loading of the transmission lines is given in Annexure III.

    Thermal Loading limits of different conductors is given in Manual on Transmission Planning

    Criteria- Jan 2013. It is attached as Annexure IV. The advisory issued by NLDC for secure operation of the grid consequent to commissioning of

    the high capacity 765 kV corridors in the NEW grid is enclosed as Annexure V

    2.2.6 System Protection Scheme

    As per IEGC, System Protection schemes are required to take care of some special

    contingencies like tripping of important corridor/flow gates etc to avoid the voltage collapse,

    cascade tripping, load generation mismatch and finally blackouts in the system.

    It will have pre identified load shedding, generation backing down/tripping of generators and

    inter tripping features. To ensure the healthiness of SPS, necessary checking / testing will be

    done by RPC secretariat periodically.

    Several SPS schemes have been implemented in different regions and several schemes are being

    planned. It is explained in Chapter on Defense Mechanisms.

    2.2.7 Islanding Scheme

    In order to isolate the healthy subsystems following a large-scale disturbance, islanding schemes

    have been implemented by few generating stations/Users and State Utilities. This is a system

    requirement under contingency conditions according to which the power network may be split

    into healthy and self-sustaining zones so that cascade tripping of all generating stations in the

    entire region is avoided. It is explained in Chapter on Defense Mechanisms.

    .

    2.2.8 Security of Grid In line with Central Electricity Authority (Technical Standards for Connectivity to Grid)

    Regulations 2007, the utilities shall make arrangements for integration of the controls and

    telemetering features of their system in to the automatic generation control, automatic load

    shedding, system protection scheme, energy management system and supervisory control & data

    Acquisition System of the respective State or the region.

    2.2.9 Congestion Management in real time operation

    Congestion management in real time operation is tackled as per CERC Regulation dated 22nd

    December 2009 on Measures to relieve congestion in real time operation. The revised

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    procedure (Detailed Procedure for Relieving Congestion in Real Time Operation) has been

    prepared by NLDC and approved by CERC vide its order dated 22.04.2013 may be referred for

    further details.

    2.2.9.1 Transfer Capability

    i) Total Transfer Capability (TTC) means the amount of electric power that can be transferred

    reliably over the inter-control area transmission system under a given set of operating conditions

    considering the effect of occurrence of the worst credible contingency.

    ii) Transmission Reliability Margin (TRM) means the amount of margin kept in the total transfer

    capability necessary to ensure that the interconnected transmission network is secure under a

    reasonable range of uncertainties in system conditions.

    iii) Available Transfer Capability (ATC) means the transfer capability of the inter-control area

    transmission system available for scheduling commercial transaction (through long term access,

    medium term open access and short term open access) in a specific direction, taking into account

    the network security. Mathematically ATC is the Total Transfer Capability less Transmission

    Reliability Margin

    The updated ATC, TRM & ATC of all inter regional corridors and Intra Regional corridors shall

    be available to NLDC operator for facilitating optimum utilization.

    Sample format for declaration of TTC/TRM/ATC is enclosed as Format-I is given in Annexure VI

    .

    2.2.9.2 Declaration of congestion in real-time

    a) SLDCs/ RLDCs/ NLDC shall have a display available in their web-sites showing TTC, TRM,

    ATC declared in advance. Real time power flow in the corridor for which TTC has been declared

    shall be displayed alongside for comparison. The voltage of the important nodes in the grid

    downstream/ upstream of the corridor shall also be displayed. The display is available in the

    NLDC SCADA system. The same is attached as Format II in Annexure VI

    A corridor shall be considered congested under the following circumstances:

    i) Grid voltage in the important nodes downstream/ upstream of the corridor is beyond the operating range specified in the IEGC and/or

    ii) The real time power flow along a corridor is such that n-1 criteria may not be satisfied.

    iii) One or more transmission lines in the corridor are loaded beyond the normal limit specified in CEA Manual on Transmission Planning Criteria.

    Whenever actual flow on inter/ intra regional link/ corridor exceeds ATC and security criteria as

    mentioned above are violated NLDC, RLDC may issue a warning notice. In case SLDC

    observes congestion within the intra State grid it shall inform the respective RLDC which in turn

    shall inform the NLDC. The notice for congestion shall be communicated to all the Regional

    entities telephonically or through fax/ voice message/ e-mail and through postings on website and

    making the same available on the common screen at NLDC/ RLDCs/ SLDCs. The format III of

    the notice is enclosed in Annexure VI

    b) If the power flow on the corridor is as per the schedule, but the congestion has been caused by

    forced outages of a transmission line in the corridor, which occurs after the drawal schedule has

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    been fixed, then open access transactions shall be curtailed in the priority given in the Central

    Electricity Regulatory Commission (Grant of Connectivity, Long-term Access and Medium-term

    Open Access in inter-State Transmission and related matters) Regulations, 2009(as indicated

    below) followed by revision of TTC, TRM and ATC.

    c) If the power flow on the corridor is as per the schedule and the corridor is congested due to either

    of the circumstances mentioned in clauses 2.2.9.2 (a) i & iii, then TTC, TRM and ATC shall be

    revised accordingly.

    d) If violation of TTC limits persists for 2 time-blocks not counting the time-block in which warning

    notice was issued by RLDC and no affirmative action by the defaulting agency is taken, NLDC/

    RLDC(s) shall issue a notice for application of congestion charge. This notice shall be

    communicated to all the concerned Regional entities telephonically or through fax message and

    through postings on website and making available the same at the common screen at NLDC/

    RLDCs/ SLDCs. The format IV is enclosed as Annexure VI

    2.2.9.3 Applicability of Congestion Charge

    a) Congestion Charge shall be applicable to Regional entities as per the CERC (Measures to relieve

    congestion in real time operation) Regulations and orders on rate of congestion charge as

    applicable from time to time.

    b) At Congestion charge would be levied for

    a) over drawal or under-injection in the importing control area and

    b) under drawal or over-injection in the exporting control area.

    c) Congestion charges may also become applicable for an intra-regional corridor of one region, if the

    congestion is attributable to other regional entities of other region. Congestion charge shall be

    applicable only after two time blocks from the time of issuing the notice, not counting the time

    block in which notice is issued.

    c) Congestion charge shall be withdrawn after the power flow on the affected transmission link/ corridor has come down to the ATC and remains at this level for one time block. NLDC/ RLDC

    shall communicate to all concerned Regional entities telephonically or through fax message/ e-

    mail and through postings on website and making available the same on the common screen

    available at NLDC/ RLDCs/ SLDCs for lifting of congestion charge. The format V of the notice

    is enclosed as Annexure VI. The various formats may be referred in the Detailed procedure for relieving congestion in real time operation also.

    e) As per CERC notification, the congestion charge is currently at Rs.5.45 per kwh which will be

    applicable to all regions. The Commission may, from time to time, by order specify the rate of

    congestion charge applicable to whole or a part of the region.

    2.2.10 Inter-regional Exchanges

    NLDC shall endeavour to exchange power between the regions on opportunity basis in real-time

    in addition to the Inter-regional scheduled power. NLDC shall exchange power with the

    neighboring region on Unscheduled Interchange (UI) basis for the following.

    i) In case of Grid disturbance / Grid Incidents

    ii) Network contingent conditions in either of NEW and SR regions

    iii) Wheeling of other regions power during contingencies

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    iv) Testing / maintenance of important elements

    v) Providing power assistance during emergency

    vi) Load changeover period in either of NEW grid and SR regions

    2.2.11 Contingency Evaluation

    In addition to frequency and voltage control measures outlined above, each system operator at

    NLDC/RLDCs/ SLDCs would continuously run the Real Time Contingency Analysis (RTCA)

    application to identify credible contingencies, evaluate the system under his control against

    these contingencies and ensure immediate remedial measures for revival. All the constituents of

    each region should implement network applications under EMS at the earliest to facilitate the

    contingency evaluation. Pre-requisite for this is however the updation of network of models

    alongwith availability of real-time data from all the sub-stations / generating stations. Intense

    efforts are required from all SLDCs/RLDCs/NLDC in this direction.

    2.2.12 Requirements for Solar & Wind generator

    System operator(RLDC/SLDC) shall make all efforts to evacuate the available power from

    solar and wind and treat as a must run station. SLDC/RLDC may direct solar/wind generator to

    back down its generation for system security purpose or safety of personnel/equipments.

    SLDC/RLDC may direct a wind farm to curtail its VAr drawal/Injection on consideration of

    system security or safety of personnel/equipments.

    2.2.13 HVDC SET points

    NLDC shall inform to all RLDCs the optimum setting of the HVDC set points of all inter-

    regional HVDC system.

    Ramping up/down of all intra-regional Bipole and Back-Back HVDC has to be done with prior

    intimation of NLDC/RLDCs. .

    2.2.14 Operating Manpower

    The Control Rooms of NLDC, RLDCs, SLDCs, Power plants, Grid Substations shall be manned

    / monitored round the clock by qualified and adequately trained manpower who would remain

    vigilant and cooperative at all the times so as to maintain safe and secure grid operation.

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    3. Demand Monitoring & Control Procedures

    3.1 Objective

    This chapter describes the procedures / responsibilities of the SLDCs for all India demand

    monitoring and also the steps to be taken by SLDCs for reduction of demand in the event of

    inadequate generating capacity and in the event of breakdown or operating problems (such as

    frequency, voltage levels or network elements overloading) on any part of the grid.

    3.2 Overview

    Demand monitoring plays a very important role in grid operation. Long term demand data (five

    years and beyond) is an important input for generation / transmission planning. Medium term

    demand data (one year and below) constitutes an important input for outage planning of

    generating units and transmission lines. The short term demand forecast (spanning from one

    week to next time block) facilitates an important input for generation scheduling. Variation in

    demand in real time operation from the estimated values should be within +-2% limits to ensure

    that the grid is not affected adversely.

    Demand estimation and control is essentially the responsibility of SLDCs and RLDC/NLDC

    would generally not have a major role in this area except for integrating the demand value from

    the regions and projecting the same as national demand. NLDC however, would give instructions

    to RLDCs on demand control whenever the same has a bearing on the security of the national

    grid and such instructions would have to be complied by the SLDCs through their respective RLDCs.

    3.3 Demand estimation

    3.3.1 The SLDCs would forecast demand on an annual, quarterly, monthly, weekly and ultimately on

    daily basis which would be used in the day ahead scheduling.

    3.3.2 In line with the clause 5.3(c & d) of IEGC-2010, each SLDC shall maintain a historical database

    and develop methodologies / mechanism for demand estimation. The data for the estimation shall

    also include load shedding, power cuts etc. Similar database should be available at RLDCs and

    NLDC level.

    3.3.3 Each State / SLDCs shall utilize the forecasting modules suitable for their system and compatible

    for transfer of forecasted data in the form required by RLDCs.

    3.3.4 The historical database to be maintained by SLDCs/RLDCs shall also include major events vis-

    -vis effect of weather forecast on the actual demand, grid disturbances and loss of major

    generation. Effect of weekends and other basis of historical data.

    3.3.5 The annual, quarterly and monthly demand forecast would be finalized in the respective sub-

    committee meetings of RPCs and used in the outage plan prepared by respective RPC

    Secretariats in consultation with all the constituents.

    3.3.6 Attention would also be paid by SLDCs in demand forecasting for special days such as important

    festival and national holidays having different crest and troughs in the daily load curve as

    compared to normal days.

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    3.3.7 The load forecast utility based on Similar Day Forecast (SDF) technique is available at all the

    SLDCs and RLDC as a part of the EMS function. SDF can take two approaches for demand

    forecast i.e., Profile Based Forecast (PBF) and Weather Based Forecast (WBF).

    3.3.8 In the PBF technique, historical demand profile contains hourly demand data for 96 profiles

    consisting of recent past seven days of every calendar month and 12 special days (holidays like

    15th August, 26th January etc.). In the WBF technique, a composite weather parameter

    representing temperature, atmospheric pressure, wind speed, wind direction, rainfall and relative

    humidity and corresponding demand data are stored on hourly basis in history as profile.

    3.3.9 Presently, the SDF technique based on PBF is in vogue in all the region which calls for each

    SLDC to upload the demand forecast data for the next day by 15 hours on daily basis. It also

    facilitates SLDCs to incorporate changes on online basis and upload.

    3.3.10 The SLDC shall take into account the wind and other renewable energy forecasting to meet

    active and reactive power requirement.

    3.3.11It is also important that, the reactive power / Mvar requirements are forecasted right from

    substation level by each SLDC. The reactive power planning exercise and program for

    installation of reactive compensation equipments should take care of these requirements also.

    3.4 Demand Control

    3.4.1 The need for demand control arises on account of following conditions:

    a) Variation in demand from the estimated value (by more than 2%) which can not be absorbed by the grid.

    b) Unforeseen generation / transmission outages resulting in reduced power availability.

    c) Heavy reactive power demand, particularly during Rabi crop season (agricultural load) / high industrial activity causing low voltages

    d) Critical loading on inter-regional corridors/flow gates

    e) Sudden variations in Wind power generation

    f) Commercial reasons such as payment default leading to regulation of power supply by generating companies

    3.4.2 In line with section 5.3.(c) of IEGC, the SLDCs would regularly carry out the necessary exercises

    to estimate short term and long term demand to facilitate planning so as to ensure that they meet

    their load without overdrawing from the grid. The deviations of drawl from the schedule have to

    be controlled by the SLDCs in the following cases:

    a) Overdrawl at frequency below 49.7 Hz

    b) Underdrawal at frequency above 50.2 Hz

    c) Over/under drawl in line with real time advice from NLDC/RLDCs during critical contingencies in inter-regional corridors / flow gates

    d) Reactive power drawls / injections causing low voltage / high voltage.

    3.4.3 The constituents shall endeavour to restrict their net drawl from the grid to within their respective

    drawl schedule whenever the system frequency is below 49.8 Hz in line with section 5.4.2(a) of

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    IEGC. However, when the frequency falls below 49.8 Hz, requisite load shedding (manual) shall

    be carried out in the concerned State to curtail the over drawl in order to avert the drop in

    frequency below 49.7 Hz.

    3.4.4. All regions shall endeavour to maintain the system frequency above 49.7 Hz and would cooperate

    for helping optimum utilization of regional hydro resources so as to ensure maximum availability

    during peak hours.

    3.4.5. All regions shall ensure the availability of the defence mechanism in place .

    3.4.6. Demand control would have to be exercised under low frequency conditions by taking the

    following actions by regions.

    a) Scheduled load shedding as decided in OCCM/Board meetings.

    b) Un-scheduled load shedding for the load generation balancing exercise which is planned for the following day. Unscheduled load shedding accounts for fluctuations in

    availability due to forced outages, transmission outages, fuel related problems,

    demand fluctuations due to weather related factors and other important events

    c) Distress load shedding due to load generation imbalance in real time leading to frequency going below 49.7 Hz. This will be carried out through already identified radial

    feeders. Loads may be shed under any System Protection Schemes, UFR and df/dt relays.

    3.4.7. During the demand control by scheduled load shedding as well as unscheduled load shedding by

    staggering in different groups, the changeover from one group to another shall be carried out in a

    gradual & scientific manner so as to ensure that the change in load at any point of time does not

    exceed 100 MW so as to avoid excursions in system parameters.

    3.4.8 In the case of low voltage pockets, RLDC/SLDCs would disconnect the preidentified radial

    feeders drawing heavy quantum of reactive power which are not feeding the important loads like

    Traction, Hospital, Defence etc. when voltage goes below 380kV.

    3.4.9 Each User/STU/SLDC shall formulate contingency procedures and make arrangements that will

    enable demand disconnection to take place, as instructed by the RLDC/SLDC, under normal

    and/or contingent conditions. These contingency procedures and arrangements shall regularly be

    / updated by User/STU and monitored by RLDC/SLDC. RLDC/SLDC may direct any User/STU

    to modify the above procedures/arrangement, if required, in the interest of grid security and the

    concerned User/STU shall abide by these directions.

    3.4.10 The SLDC through respective State Electricity Boards/Distribution Licensees shall also formulate and implement state-of-the-art demand management schemes for automatic demand

    management like rotational load shedding, demand response (which may include lower tariff for

    interruptible loads) etc. before 01.01.2011, to reduce overdrawl in order to comply para 5.4.2 (a)

    and (b) . A Report detailing the scheme and periodic reports on progress of implementation of the

    schemes shall be sent to the Central Commission by the concerned SLDC.

    3.4.11 In order to maintain the frequency within the stipulated band and maintaining the network security, the interruptible loads shall be arranged in four groups of loads, for scheduled power

    cuts/load shedding, loads for unscheduled load shedding, loads to be shed through under

    frequency relays/ df/dt relays and loads to be shed under any System Protection Scheme

    identified at the RPC level. These loads shall be grouped in such a manner , that there is no

    overlapping between different Groups of loads. In case of certain contingencies and/or threat to

    system security, the RLDC may direct any SLDC/ SEB/distribution licensee or bulk consumer

    connected to the ISTS to decrease drawal of its control area by a certain quantum. Such

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    directions shall immediately be acted upon, SLDC shall send compliance report immediately

    after compliance of these directions to RLDC.

    3.5 Operational planning on day ahead basis

    3.5.1 In line with clause 6.5 of IEGC under the head of Scheduling & Despatch Procedure,plant-wise requisitions from the States are compiled a t e a ch RL D C s to draw up scheduled for

    each ISGS. The day ahead operational planning exercise helps the state with large deficit to

    opt for un-requisitioned power in some of the ISGS plants within or outside the region.

    3.5.2 The state utilities bridge the anticipated shortfall by day-ahead Short Term Open Access

    transactions/collective transactions (PX trades).

    3.6 Day Ahead Balancing

    3.6.1 The day ahead power balance cannot be obtained without planning for load shedding in case

    of deficient power region. Out of the total deficits for the following day, the scheduled load

    shedding takes care of a major portion of the deficits and is planned and frozen atleast a

    month in advance and announced to public. The balance part of the deficit is taken care of

    through planning of unscheduled load shedding.

    3.6.2 Unscheduled load shedding accounts for fluctuations in a v a i l a b i l i t y due to forced

    outages, transmission outages, fuel related problems, demand fluctuations due to weather

    related factors and other important events

    3.7 Same Day Operational Planning

    3.7.1 On the day of operation, due to errors in demand forecast, forced outage of units, some of the

    States or Central Sector Plants, sellers/buyers of Short Term Open Access transactions (advance

    reservations and first-cum-first serve basis only) may revise their schedules one and half

    hour ahead for planned deviations and one hour ahead for unforeseen problems.

    3.7.2 The deviations from schedules in any region may require purchase/sell of balancing power from

    the other power surplus regional to power deficit regional pool at a rate determined by UI price

    vector. This price vector is given in Annexure VII.

    3.8 Load Crash

    In the event of load crash in the system due to weather disturbance or other reasons, the situation

    would be controlled by SLDCs / ISGS by the following methods:-

    a) Lifting the load restrictions, if any.

    b) Exporting the power to neighbouring regions by STOA

    c) Phasing out hydro

    d) Backing down or closing down of generating units

    Further in case of hydro generation linked with irrigation requirements, the actual backing down

    or closing down of units shall be subject to limitations on such account.

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    4. Outage Planning

    4.1 Introduction

    a) This section brings out the process for preparation of outage schedules for generators and

    transmission lines at the national level subject to network security, constraints and reliability. The

    general guidelines shall be as per section 5.7 of the IEGC. NLDC operator should be familiar with

    all important transmission lines given in Annexure VIII and generation units covering the entire

    national grid and effecting the operation of the national grid concerning its security, integrity and

    economy facilitating optimum utilization of all national resources. While planning for generation

    outages and transmission line outages due consideration shall have to be made for long term

    commitments, medium and short term commitments including transactions that are settled through

    multiple Power Exchanges.

    b) Outages effecting network security on a Pan-India scale shall have to be planned meticulously and

    Power System Studies have to be carried out for this purpose.

    c) Annual outage plan shall be prepared in advance for the financial year by the RPC Secretariat in

    consultation with NLDC and RLDC and reviewed during the year on quarterly and Monthly basis.

    All users, CTU, STU etc shall follow these annual outage plans. If any deviation is required the

    same shall be with prior permission of concerned RPC and RLDC. The outage planning of run-of-

    the-river hydro plant, wind and solar power plant and its associated evacuation network shall be

    planned to extract maximum power from these renewable sources of energy. Outage of wind

    generator should be planned during lean wind season, outage of solar, if required during the rainy

    season and outage of run-of-the river hydro power plant in the lean water season.

    4. 2 Objective

    a) To produce a coordinated generation and transmission outage programme for the

    National/Regional grid, considering all the available resources and taking into account

    transmission constraints, as well as, irrigational requirements.

    b) To minimise surplus or deficits, if any, in the system requirement of power and energy and help

    operate system within Security Standards.

    c) To optimize the transmission outages of the elements of the National/Regional grid without

    adversely affecting the grid operation but taking into account the Generation Outage Schedule,

    outages of User/STU/CTU systems and maintaining system security standards.

    4.3 Scope

    This section is applicable to NLDC, RLDC, SLDCs, CTU, STU, RPCs and all Users

    4.4 Outage Planning Process

    a) The RPC Secretariat shall be primarily responsible for finalization of the annual outage plan for

    the following financial year by 31st January of each year.

    b) All SEBs/STUs, transmission licensees, CTU, ISGS IPPs, MPPs and other generating stations

    shall provide RPC Secretariat their proposed outage programmes in writing for the next financial

    year by 30th

    November of each year. These shall contain identification of each generating

    unit/line/ICT, the preferred date for each outage and its duration and where there is flexibility, the

    earliest start date and latest finishing date.

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    c) RPC Secretariat shall then come out with a draft outage programme for the next financial year by

    31st December of each year for the Regional grid taking into account the available resources in an

    optimal manner and to maintain security standards. This will be done after carrying out necessary

    system studies and, if necessary, the outage programmes shall be rescheduled. Adequate balance

    between generation and load requirement shall be ensured while finalising outage programmes.

    The same shall be uploaded by the RPCs on their website.

    d) The outage plan shall be finalized in consultation with NLDC, RLDCs and SLDCs. The final

    outage plan shall be intimated to NLDC, Users, STUs, CTU, other generating stations connected

    to ISTS and the RLDC for implementation by 31st January of each year.

    e) The above annual outage plan shall be reviewed by RPC Secretariat on quarterly (March, June,

    September & December) and monthly basis in coordination with all parties concerned, and

    adjustments made wherever found to be necessary. Monthly review of the outage plan for the

    current month and consecutive month would be done in the Operation Coordination Committee

    (OCC) of RPC meeting and RPC would issue the revised outage plan to all constituents and

    RLDC/NLDC/SLDC.

    f) In case of emergency in the system, viz., loss of generation, break down of transmission line

    affecting the system, grid disturbances, system isolation, RLDC may conduct studies again before

    clearance of the planned outage.

    g) The NLDC/RLDC shall be authorized to defer/ cancel any planned outage involving

    lines/elements in case of any of the following taking into account statutory requirements:

    i. Grid disturbances ii. System isolation

    iii. Partial Black out in a state iv. Any other event in the system that may have an adverse impact on the system security by the

    proposed outage.

    h) The detailed generation and transmission outage programmes shall be based on the latest annual

    outage plan (with all adjustments made to date).

    i) Each User, CTU and STU shall obtain the final approval from RLDC/NLDC prior to availing an

    outage.

    j) RPCs shall submit quarterly, half-yearly reports to the Commission indicating deviation in outages from the plan along with reasons. These reports shall also be put up on the RPC website.

    k) A Draft procedure for coordinated transmission element outage planning is proposed by NLDC to all RPCs through letter dt. 28

    th February 2013. Subsequently, a letter dt 05-07-2013 also sent to

    RPCs. It is given in Annexure IX. And after getting approval from all the RPCs, it should be

    implemented. The draft procedure aims to streamline the process of outage coordination between

    SLDCs, RLDCs, NLDC, RPCs and Indenting Agencies.

    4.5 Availing Outage

    a) NLDC/RLDC would review the outage schedule on daily basis and in case of any contingency or

    any conditions described under IEGC clause 5.7.4(g), defer any planned outage as deemed fit. The

    revised dates in such case would be finalized in consultation with the concerned constituents or

    OCC meetings.

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    b) In case of any outage affecting more than one constituent in one or more than one region, the

    information about the approval / deferment shall be communicated by RLDC to all such affected

    constituents in consultation with NLDC.

    c) Before availing any planned or unforeseen outage of any important elements as per Annexure VIII

    the indenting utility shall request for a code on real-time from NLDC through respective RLDC

    under whose supervisory area the utility remains. NLDC shall issue a common code to concerned

    RLDCs involving regional grids on either end of the line. Respective RLDCs may convey their final code to NLDC as well as their respective utilities involved on either ends of the transmission

    line/equipment. All preparatory works for availing outage must be done in advance before actually

    availing code. In the same manner code must be obtained in real-time from NLDC by concerned

    utility through its RLDC before restoration/revival of the line/element. Respective RLDCs shall convey their final code to NLDC for confirmatory exchange with other RLDCs involved. RLDC would ensure that the outage availed should come into service as per the scheduled time. Delays

    with reasons thereof if any should be immediately reported to NLDC in advance. During shutdown

    RLDC may concur for extension of such shutdown after reviewing the grid conditions and status

    of shutdown.

    d) The code issued by NLDC / RLDCs for opening / restoration of line / element is consent from operational point of view notwithstanding anything contained in respect of safety measures and

    switching operations that may be carried out locally. All safety measures related to sub-station

    and/or transmission lines shall be the responsibility of the personnel authorized to execute the

    work.

    e) During the approved shutdown of line/ICT, any other opportunity based maintenance work by the

    concerned agencies to be carried out only after getting the consent of RLDC/NLDC.

    4.6 Outage Planning Procedures for NLDC Important elements

    i) In order to maintain the security of the Integrated power system, it is important that the planned outage of generation and transmission system particularly in the important flow-gates, Important

    grid elements and inter regional transmission links are properly coordinated.

    ii) Reliable operation of the All India grid is important from the view point of Quality Of Service (QoS) to the customers and other stakeholders. Proper co-ordination of transmission outages in

    the system is one of the key aspects to ensuring reliability. Outages in the transmission network

    could either be on account of planned maintenance activities or construction related activities or

    any emergency conditions arising in the field. Since these may have an impact across two or

    more regions and hence needs to be planned by the concerned regions in consultation with

    NLDC. Proper coordination of the same is important mainly due to the following factors:

    a. Reliability of operation of the All India grid b. Certainty to the electricity markets. c. Proper crew resource mobilization at the work sites to ensure that outage time is minimized.

    iii) In order to ensure the same, the following procedures may kindly be followed by all RLDCs/NLDC.

    1) Following outages might be approved only after concurrence of NLDC. This is enclosed as Annexure VIII

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    All inter-regional links irrespective of voltage level. HVDC systems and all lines operating at 765kV, & 765kV ICTS, Reactors. All outages necessitating change in TTC and/or curtailment of transactions. Trans National Links

    2) At the RPC level, outages are finalized in the Operation Coordination sub Committee (OCC). A list of the shutdowns approved by OCC may be forwarded by each RLDC to the Reliability

    Coordinators of each RLDC and NLDC by email immediately after OCC approval.

    3) On a daily basis (say day D), by 1030 hours each RLDC would forward a list of outages planned for their respective regions for the D + 3

    rd day by email to the Reliability Coordinators of each

    RLDC/NLDC along with the study results.

    4) The NLDC Reliability Coordinators would further assess the impact of these outages on the overall reliability of the all India grid and concurrence of outages under categories listed at (1) above would

    be conveyed by NLDC within a day.

    5) All planned shutdowns on the next day would be reviewed a day in advance of the shutdown. RLDCs would try to ensure that no new element gets added to the list provided three days in

    advance at Sl. no. 3 above as far as possible, unless the outage is of an emergency nature.

    6) A list of all the outages approved for the next day would be readily available at each RLDC/NLDC control room along with simulation results, if any and the precautions required to be taken.

    7) In real time if any emergency requirement of outage occurs in real time, RLDCs would inform NLDC and actions taken accordingly in real time. RLDCs/NLDC might devise separate internal

    procedures for fast co-ordination between their respective Control Rooms and Reliability Co-

    ordinators in real time.

    8) Any deviation in the outage from the schedule can affect other planned outages as well as affect reliability and also the electricity markets. RLDCs may impress on the agencies intending for an

    outage to strictly adhere to the shutdown timings.

    9) A record may be kept of outage overshooting the approved time of return to bring in seriousness and to avoid market distortion.

    10) It is therefore necessary to carry out operational studies in order to assess the grid security and network stability while finalizing the annual outage plan of these important elements.

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    5. Defence Mechanisms

    5.1 General

    5.1.1 Well designed and healthy defence mechanism is a pre requisite for secure operation of the

    interconnected system. Despite the utmost caution exercised during operational planning and

    implementing all the above steps for improvement of network security and reliability, the

    possibility of a contingent situation cannot be totally eliminated.

    5.1.2 It calls for suitable defence mechanism to be available in the system to take care of such

    contingencies. Following are the minimum schemes which should be operational to ensure safe

    and secure grid operation

    5.2 Unit Protection System

    5.2.1 In line with the regulation 3 (e) of the CEA (Grid Standards) regulation 2010 all regional entities

    shall provide standard protection systems having reliability, selectivity, speed and sensitivity to

    isolate the faulty equipment and protect all components from any type of faults, within the

    specified fault clearance time and shall provide protection coordination as specified by the

    Regional Power Committee.

    5.2.2 Protection audit of the substations shall be carried out by the respective utilities on a regular basis

    as advised in Protection coordination committee meetings.

    5.2.3 As per 3 (e) of CEA (Grid Standard) regulation 2010, the fault clearance time shall be within the

    time mentioned in table below:

    Table 1: Fault Clearance time

    Sl.

    No

    Nominal System

    Voltage in kV rms

    Maximum time of fault

    clearing in ms

    1 765 and 400 100

    2 220 and 132 160

    All substations of 220 kV and above shall be equipped with breaker fail protection and bus bar

    protection scheme. Non clearance of the fault by a circuit breaker within the time limit mentioned

    above, the breaker fail protection shall initiate tripping of all other breakers in the concerned bus-

    section to clear the fault in next 200 milliseconds.

    5.3 Flat Frequency and Rate of Change of Frequency Relay

    5.3.1 In line with clause 5.2(n) of IEGC, all regional entities shall provide Automatic Under Frequency

    Load Shedding in their respective system to arrest frequency decline that could result in a

    collapse / disintegration of the grid as per the scheme formulated by concerned RPC forum and

    shall ensure its effective application and functionality at all times to prevent cascade tripping of

    generating units in case of any contingency.

    5.3.2 All Entities shall set their under frequency (UF) Relays and rate of change of frequency with time

    Relays in their respective systems, in accordance with the plan made by the Regional Power

    Committee, to provide adequate load relief for grid security and ensure the operation of these

    relays at the set frequencies.

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    5.3.3 Under-frequency and rate of change of frequency (UFR & df/dt) are envisaged to take care of

    sudden contingencies arising out of outage of generation stations or separation of inter-regional

    lines. UFRs setting are for steady state operation of the grid at considerably low frequency and

    df/dt settings are for fast change in frequency due to large generation outage.

    5.3.4 SLDCs shall submit a detailed report of operation of these Relays at different frequencies to

    Regional Load Despatch Centre and Regional Power Committee on monthly basis and the

    Regional Power Committees shall carry out inspection of these Relays as and when required.

    5.3.5 In line with regulation 5.4.2 (e) of IEGC, the interruptible loads in a control area shall be arranged

    in four groups of load,

    For scheduled power cuts/load shedding, loads for unscheduled load shedding, loads to be shed through under frequency relays/(df/dt) relays and Loads to be shed under any System Protection Scheme identified at the RPC level.

    These loads shall be grouped in a manner, that there is no overlapping between different groups of

    loads. This would ensure that the automatic relief through these relays would be available to the

    system under all conditions.

    Under Frequency Relay ( UFR) Load shedding, df/dt load shedding in different regions is given in

    Annexure X. CEA has revised the UFR settings for NEW grid as per the discussion at the 2nd meeting

    of National Power Committee(NPC) held on 16th July, 2013. It is to be implemented within three

    months. It is also given in the Annexure X.

    5.4 Under Voltage Load Shedding Scheme

    As per Cl. 5.3 (t) of IEGC, all Users, CTU and STUs shall provide adequate voltage control

    measures through voltage relay as finalized by RPC, to prevent voltage

    collapse and shall ensure its effective application to prevent voltage collapse/ cascade tripping.

    5.5 System Protection Scheme

    5.5.1 The complexities in Indian electric power system operation are increasing day by day. The size of

    the grid has expanded manifold and is on a high growth phase.

    As per Cl. 5.3 (t) of IEGC, All Users, STU/SLDC, CTU/RLDC and NLDC, shall also facilitate

    identification, installation and commissioning of System Protection Schemes (SPS) (including

    inter-tripping and run-back) in the power system to operate the transmission system closer to their

    limits and to protect against situations such as voltage collapse and cascade tripping, tripping of

    important corridors/flow-gates etc. Such schemes would be finalized by the concerned RPC

    forum, and shall always be kept in service. If any SPS is to be taken out of service, permission of

    RLDC shall be obtained indicating reason and duration of anticipated outage from service

    5.5.2 As per Indian Electricity Grid Code(IEGC), interstate transmission system(ISTS) shall be capable

    of withstanding and be secured against the certain outages without necessitating load shedding or

    rescheduling of generation during steady state operation. These include outage of a 132 kV D/C

    line or Outage of a 220 kV D/C line or Outage of a 400 kV S/C line or Outage of a single ICT or

    Outage of one pole of HVDC bipole or Outage of 765 kV S/C line.

    5.5.3 The aforesaid contingencies would be superimposed over a planned outage of another 220kV D/C

    line or 400 kV S/C line in another corridor and not emanating from the same substation. ISTS

    shall be capable of withstanding the loss of most severe single system infeed without loss of

    stability. It has also been stated that any one of the aforesaid events shall not cause loss of supply,

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    abnormal Disturbances cause discomfort to the people as well as results into huge economic

    loss. Therefore, in addition to conventional unit protection system few System Protection

    Schemes (SPS) are also desirable for safe and reliable operation of the power system.

    The main objective of SPS is to preserve the integrity of the electric system by using automatic

    measures that are simple, reliable and safe for the system as a whole and to provide the most

    extensive coverage against all possible extreme credible contingencies. frequency on sustained

    basis, unacceptable high or low voltage, system instability, unacceptable overloading of ISTS

    elements.

    5.5.4 As per the IEGC or transmission planning criteria, the system is not designed for 400 kV double

    circuit line or outage of HVDC bipole. In practice it has been observed that there are some

    contingencies happening in the system resulting in outage of multiple elements for which

    system is not designed.

    5.5.5 Outage of a large capacity link between two distant nodes in a synchronously interconnected

    system may result into excessive loading on parallel AC lines, severe drop in voltage profile,

    power oscillations and finally leading to a major blackout or brown out in the system, in case

    instantaneous corrective actions are not in place. On the other hand similar outage in an

    asynchronously connected system may result into load generation imbalance on either side of the link.

    5.5.6 Disturbances like loss of load, loss of generation or loss of transmission line in large grid may

    cause wide variations in frequency, voltage & load angles. Originating causes of grid failure may

    be due to equipment failure (including those of protective systems), human error and cascade

    tripping or large scale disturbances due to weather and/or natural calamities.

    In view of the above System Protection Schemes have been designed and implemented. These

    involve predefined generation backing down as well as load shedding under selected

    contingencies.

    The details of SPS schemes have been described in detail in Annexure XI.

    5.6 Islanding Scheme

    5.6.1 In order to isolate the healthy subsystems following a large-scale disturbance, few generating

    stations/Users and State Utilities have implemented islanding schemes. To avoid total black out of

    the grid during system disturbances and for early normalisation, the procedure for islanding of

    systems and major generating stations with associated loads need to be developed constituent

    wise/system wise.

    5.6.2 As per CEA grid standards, the Regional Power Committees shall prepare Islanding schemes for

    separation of systems with a view to save healthy system from total collapse in case of grid

    disturbance.

    5.6.3 As per CEA grid standards, Islanding Scheme means a scheme for the separation of the Grid into two or more independent systems as a last resort, with a view to save healthy portion of the Grid

    at the time of grid disturbance.

    Users/utilities intending to implement any islanding schemes for their station may do so in

    consultation with RLDC and RPCs secretariat.

    The details of islanding schemes have been described in detail in Annexure XII.

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    6. Collective Transaction Procedures

    6.1.0 Introduction

    6.1.1 With the implementation of Honble CE