DRAFT OPERATING PROCEDURE OF SOUTHERN REGION 2014

CHAPTER-1

1. GENERAL

1.1 Introduction

The Southern Regional power system covers geographical areas in Andhra Pradesh, Karnataka, Kerala, Puducherry, Tamil Nadu & Telangana.

OPERATING PROCEDURES document developed by SRLDC sets out the Internal Operating Procedures to be followed by all the constituents of Southern Regional grid. This is the revision of Operating Procedures issued by SRLDC earlier in July 2015.

The revision / updation is based on the provisions of revised IEGC 2010 effective from 3rd May 2010, its amendments, Deviation Settlement Mechanism and other recent Orders/Regulations issued by Honble CERC and decisions taken various SRPC forums.

The importance of such document increased manifold as the power system operation & control in the Region has become more complex day by day not only with the rapidly rising demand growth but also with the intricate EHV transmission network. At the same time the System Operation in the Indian Power Sector has undergone a paradigm shift with narrowing down of operating frequency range, deviations allowed for inadvertent actions only, and revision of IEGC, introduction of Renewable Energy Scheduling, RGMO, PoC Methodology of Transmission loss Computation etc.,

In the present scenario, to operate the system in a desired manner, the role of each player in the grid has become more important & inter-dependent viz. Mix of Central / State Sector Generating and Transmission Utilities, Independent Power Producers, Traders, Power Exchanges, System Operators and other involved agencies.

It has thus become necessary to review and update the Internal Operating Procedures which lays down the rules and guidelines for operation and maintenance of the regional grid in an efficient, reliable and economic manner. This revision is in line with clause 5.1 (f) of IEGC 2010 and in compliance of schedule mentioned in clause 1.4 of this document.

1.2 SCOPE

This document describes the role of all agencies connected in the region in order to operate grid in an integrated manner in conformation to the desired security standards and to meet the common interests of all the agencies. The Operating Procedures are without prejudice to the SRLDC s power to give directions and exercise supervision and control as stated under Sections 28 and 29 of the Electricity Act, 2003. This document would come in force with immediate effect. It super cedes the Operating Procedure issued earlier by SRLDC in July 2015.

1.3 OBJECTIVE

The Objective of this document is to

a) Compile various provisions in the statute and regulations for guidance of the staff of the SRLDC, SLDC and regional entities in the Southern Region.

b) Clearly spell out the procedures in maintaining consistency and compliance of IEGC adopted for the integrated system operation and role of each agency and inter-relationship in the grid operation viz. RPC, NLDC, RLDC, SLDC, CTU, STU, ISGS and others.

c) Facilitating operation, maintenance and development of regional power system in the most efficient, economic, secure and reliable manner.

d) Facilitating beneficial trading opportunities in the Region.

1.4 MAINTENANCE OF OPERATING PROCEDURES

These procedures shall be maintained and reviewed for changes / modifications, if any, at regular intervals. However, in case of urgent need arising due to operating problem to any constituent, the procedures can be reviewed expeditiously. SRLDC will be the agency for updating / reviewing and issue of Operating Procedures. All modifications / reviews will be done taking the constituents of SR in to confidence. Comments and suggestions on the document may be sent to the osmail@srldc.org or srldcosmail@gmail.com

1.5 STRUCTURE OF OPERATION OF OPERATING PROCEDURES

Following is the structure of Internal Operating Procedures of Southern Region.

1. General

This chapter describes the objective, scope and structure of the Operating Procedures for Southern Region.

2. Frequency Control

This chapter describes the procedures for frequency control to ensure compliance to security standards prescribed in the CEA (Grid Standards) Regulation, 2010 and IEGC 2010 & its amendment and DSM regulation along with its amendments.

3. Voltage Control

This chapter describes the procedures for Voltage control to ensure compliance to security standards prescribed in the CEA (Grid Standards) Regulation, 2010 and IEGC 2010 & its amendment and DSM along with its amendments.

4. Planned Outage& Emergency Outage Coordination

This Chapter deals to formulate a coordinated outage programme of transmission lines and generating units for the regional grid considering all the available regional resources and taking into account transmission constraints, system operating conditions and maintaining load generation balance.

5. Switching Coordination

This chapter describes the protocol to be followed while coordinating switching operation in Regional Grid

6. Network Security and Congestion

This chapter describes the congestion management philosophy and procedure in line with the CERC (Measures to relieve congestion in real time operation) Regulations, 2009, Detailed Procedure for relieving congestion in real time operation as approved by CERC vide its order dated 22.04.2013. This Chapter also covers some of the important aspects of Network security

7. Demand Estimation and Control

This chapter deals with the procedures/ responsibilities of the SLDCs for Demand Estimation of both Active Power and Reactive Power and also the provisions to be made by SLDCs to effect a reduction of demand in the event of insufficient generating capacity and / or withdrawal of external assistance on the event of break down or operating problems (such as frequency, voltage levels of thermal overloading) on any part of the grid.

8. Short Term Open Access

This Chapter explains the procedure for reservation of transmission capacity including bidding by STOA customers for inter-State transmission System and processing of STOA applications is explained in this chapter. This procedure is in accordance with the various provisions of the Central Electricity Regulatory Commission (Open Access in inter-state Transmission) Regulations 2008 dated 25.01.2008 and Power Market Regulations 2010 and subsequent amendments thereof hereinafter referred to as the Regulations

9. Scheduling and Despatch

This chapter illustrates the procedure for scheduling with the treatment to be accorded for special situations.

10. Grid Disturbances & Revival

The objective of this chapter is to achieve restoration and re-synchronization of constituent systems effected, in case of a grid disturbance, in the shortest possible time, taking into consideration all essential requirements like traction loads, core sector industrial loads, generation capabilities and the operational constraints of Regional Transmission System. This chapter also aids the constituents to be aware of the steps to be taken during a grid disturbance.

11. Defense Mechanism in SR

This chapter explains the various defense mechanisms available in SR

12. Event Information and Reporting

This chapter explains define the incidents required to be reported and information to be submitted in order to ensure consistent approach in reporting of the events/incidents.

13. Metering and Settlement System

This chapter explains the settlement system which is an important part in implementation of Availability Based Tariff (ABT). The system involves metering, data collection and processing, energy accounting and raising of bills by the different Regional Entities. This chapter indicates the roles and responsibilities of the different Regional Entities in making the settlement system operative.

14. SCADA & Communication System

This chapter explains the ULDC Scheme & PMUs installed in Southern Region.

1.6 OPERATING MANPOWER

The control rooms of SRLDC, CPCC and all SLDCs, power plants, grid substations (above 110kV) as well as any other control centre of regional constituents shall be manned / monitored round the clock by qualified, certified and adequately trained manpower who would remain vigilant and cooperative at all the times so as to maintain the system safe, secure and operate it in the most optimum manner.

CHAPTER-2

2. FREQUENCY MANAGEMENT

2.1 Introduction

One of the main assumptions of the power system planner is that the system parameters viz. frequency, voltage, etc., remain close to nominal values. The paradigm shift in Indian Power System emphasis the system operators focus not only in maintaining the system frequency but also voltage, line loading etc., well within the prescribed limit through proper load-generation balance, demand forecast, outage co-ordination, etc., and injection / drawal close to schedule. This section lists the measures to be adopted by the system operators at SRLDC / SLDCs / ISGS / Regional Entities for frequency control.

2.2 Operating Range

In compliance to the IEGC section 5.2 (m), All Users, RLDC, SLDC STUs , CTU and NLDC shall take all possible measures to ensure that the grid frequency always remains within the 49.90 to 50.05Hz band and as amended from time to time.

The maximum and minimum values in the band are the outer limits and all the Constituents would endeavor to maintain the frequency range well within the above limits.

2.3 Frequency Violation Type / Category / Message consideration

During the real time operation, though the system frequency tends to vary continuously, all the Regional Entities will endeavour to maintain the deviation within the IEGC mandated frequency band. As frequency is one of the critical indicator that represent system state, the deviation of frequency has been classified into the following categories for the purpose of issuing messages by SRLDC and taking actions by the respective Regional Entities / SLDC / RLDC.

Violation Type

Range / Condition

Category

Frequency Violation

>50.1 Hz or (20%or 80 MW whichever is higher) or 250 MW

(whichever lower)

Emergency

Non Renewable Rich State

(12% or 48 MW) to (20% or 80 MW) whichever is higher) or

150 MW to 250 MW

(whichever lower)

Alert

Nominal Operating Range

(=1000 MW and 250 MW

Emergency

200 MW to 250 MW

Alert

Nominal Operating Range

3000MW

Deviation Violation

>300 MW

Emergency

250 MW to 300 MW

Alert

Nominal Operating Range

25 %

Emergency

>15% to 25 %

Alert

Nominal Operating Range

Thermal Loading under n-1 contingency

Emergency

= Thermal Loading under n-1 contingency

Alert

< Thermal Limit under n-1 contingency

Normal

2.7 Sudden Change

Except under an emergency, or to prevent an imminent damage to a costly equipment, no User shall suddenly reduce his generating unit output by more than one hundred (100) MW ( 20 MW in case of NER) without prior intimation to and consent of the RLDC, particularly when frequency is falling or is below 49.7 Hz.. Similarly, no User / SEB shall cause a sudden variation in its load by more than one hundred (100 MW) without prior intimation to and consent of the RLDC.

SRLDC will issue sudden change over messages at 10 days interval in excel format through email/web group along with data 5 minutes prior and 5 minutes subsequent wrt the incident to take care of any time stamping issues. Constituents shall analyse those instances and revert back for any discrepancies and for reasons/corrective actions for avoiding in future within 3 days. The analysis would be discussed in OCCM. In the event states did not revert back on SRLDC observations, the same would be deemed to be accepted. SCADA validations with all SLDCs and ISGS station/ Regional Entities on daily basis between 10:00 hrs to 1200 hrs. All the constituents has to ensure that the concerned SCADA officer would be available for validation during the said hour as per the decision of 103rd OCCM of SRPC.

2.8 Low Frequency Control

This would be ensured by adhering to the following steps:

All constituents shall continuously observe their respective drawl / injection pattern as per schedule and to prevent low frequency operation below 49.9 Hz, shall take all necessary steps when it is anticipated that low frequency condition could arise, All Regional Entitiesare expected to suo motto curb such deviations and abide by SRLDCs instructions in this matter..

1) PRIMARY RESPONSE

All regional entities shall ensure that the generating units synchronised with the grid provides primary response through Restricted Governor Mode Operation (RGMO) or Free Governor Mode Operation (FGMO) with MI in line with sections 5.2 (f), 5.2 (g), and 5.2 (h) of IEGC, more detailed in sec 4.14 of this document. In case of difficulty for sustained operation at the increased / decreased level of generation due to RGMO / FGMO with MI performance (or) deviation of injection / drawal beyond the limits specified in the CERC (Deviation Settlement Mechanism) Regulations 2014, the unit may come back to original generation level through supplementary control / Territarycontrol.

2) SUPPLEMENTARY CONTROL & TERRITARY CONTROL

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

3) Actions from Beneficiary/Buyer

1. In line with regulation 6.4.5 of IEGC, the regional grids shall be operated as power pools with decentralized scheduling and despatch, in which the States shall have operational autonomy

2. The system of each regional entity shall be treated and operated as notional control area. The algebraic summation of scheduled drawal from ISGS and from contracts through longterm access, medium-term and shortterm open access arrangements shall provide the drawal schedule of each regional entity, and this shall be determined in advance on day-ahead basis. The regional entities shall regulate their generation and/or consumers load so as to maintain their actual drawal from the regional grid close to the above schedule such that the deviation will not be beyond 12% of schedule or 150MW whichever is less.

3. The constituents who maintains drawl from the grid as per schedule or below, shall also to the extent possible contribute to improve the frequency by increasing the generation in their partly loaded generating units. In order to meet such a requirement operating reserves are to be maintained in each constituent area.

4. To avert the system moving from Normal states (frequency/deviation/zero crossing) as defined above to Alert State/Emergency the maximum inadvertent deviation shall not exceed the limits specified in the Normal states defined above.

5. Such deviations should not cause system parameters to deteriorate beyond permissible limits and should not lead to unacceptable line loadings. To avert moving to alert / emergency states, the actions shall be taken whenever alert mode as specified above is reached for returning to normal.

6. The concerned SEB/distribution licensee/User, SLDC shall ensure that their automatic demand management scheme (ADMS) mentioned in clause 5.4.2 is in place and acts to ensure that there is no over-drawal beyond 12% of schedule or 150MW, whichever is less. Similarly, in case of instances of under drawal beyond 12% of schedule or 150MW whichever is less, there shall be reduction of generation on merit order to offset such under drawal.

7. In case of non-availability of / failure to operate ADMS for any reason, necessary demand disconnection to curtail over drawal shall be effected by manually tripping of the feeders from SLDC to restrict the net drawal from grid to within schedule and ensure all actions for early restoration of Automatic Demand Management Scheme (ADMS).

8. Load changeover, ramp-up / ramp-down of generation, purchase / sale of power through bi-lateral / collective transactions shall be co-ordinated / staggered in such a manner that there shall not be any sudden increase / decrease in load by more than 100 MW at a instance.

4) Actions from ISGS / Seller

1. The ISGS is normally expected to generate power according to the daily schedules advised to them barring any inadvertent deviations. Maximum deviation allowed during a time block shall not exceed the limits specified in the CERC (Deviation Settlement Mechanism) Regulations 2014 as amended from time to time.

2. To avert the system moving from Normal states (frequency/deviation/zero crossing) as defined above to Alert State/Emergency the maximum inadvertent deviation shall not exceed the limits specified in the Normal states defined above.

3. Such deviations should not cause system parameters to deteriorate beyond permissible limits and should not lead to unacceptable line loadings. To avert moving to alert / emergency states, the actions shall be taken whenever alert mode as specified above is reached for returning to normal.

4. Any infirm injection of power by a generating station prior to COD of a unit during testing and commissioning activities shall be exempted from the volume limit specified above for a period not exceeding 6 months or the extended time allowed by the Commission in accordance with the Connectivity Regulations. However, the generator shall furnish the tentative quantum of time block wise infirm power injection details in advance on day ahead basis facilitating SRLDC properly monitor and control system parameters & loading of transmission elements. Also, in case of system constraint, quantum of such injection of infirm power shall be reduced / limited as per the direction of SRLDC

5. All constituents including ISGS shall put all out efforts to follow the despatch guidelines in the IEGC band of frequency. If frequency falls below 49.9 Hz, all partly loaded generating units of over drawing constituents / under injecting ISGS shall pick up additional load to offset the drawal / injection deviation and combat declining system frequency.

6. There shall not be any sudden reduction in generator output by any constituent by more than one hundred (100) MW unless under an emergency condition or to prevent an imminent damage to the equipment. Sale / purchase of power, ramp-up / ramp-down and etc., shall be co-ordinated appropriately to avert sudden change in generation.

5) Inter-Regional Deviation

In the process, SRLDC may check the Inter Regional deviations from schedule and take necessary action as per network condition of integrated grid to facilitate the Southern Grid to maintain effective LGBR by

(i) Reduce / stop export of Deviation power to other regions, unless system constraints/ emergency exist in the neighboring regions.

(ii) Start / maximize import of Deviation power from other regions, if it is not overloading the transmission network of neighboring regions.

2.9 High Frequency Control

1) Generation Backing Down due to RGMO / Unstable Operation

When the system frequency is above 50.05 Hz. and in the rising trend, the RGMO / FGMO with MI shall ensure reduction in generation following the governor droop characteristic to the extent of 5% of generation. There shall not be any over injection by the generating station (irrespective of type and ownership) provided that when the frequency has risen from a previous lower level to 50.05 Hz or higher, and due to normal governor action, the MW output of a generating unit has fallen to a level requiring oil support or which results in unstable operation of the unit, then the MW output may be increased to the lowest possible level at which oil support is not required, and the unit can operate in a stable manner.

When the system frequency is above 50.05 Hz. and in the rising trend, all regional entities shall endeavor to restrict their drawal from the grid to within their drawal schedules However when the grid frequency is higher than 50.05 Hz, there shall not be any under drawal by the regional entity.

2) Inter-Regional Deviation

In the process, SRLDC may check the Inter Regional Deviation from the schedule and take necessary action as per network condition of the integrated grid and facilitate the Southern Grid to maintain LGBR effectively.

(i) Stop / minimise import of deviations power from other regions,

(ii) Start / Increase export of deviations power to other regions.

3) Staggering of Loads

All the regional entities are expected to maintain their actual drawl from the regional grid close to schedule and any inadvertent deviations from the above do not cause system parameters to deteriorate beyond permissible limits and / or do not lead to unacceptable line loadings.

To arrest steep high frequency excursions especially during the load change over periods, all constituents shall ensure all efforts to stagger their loading pattern within the state as well as with reference to other states in Southern Region as suggested by the SRPC forum in order to make the Regional load curve as flat as possible.

2.10 Decrease / Increase of Generation as per SRLDC Directions

However as per the system requirement SRLDC may direct reduction of injection / increase in drawal which shall be complied with immediate effect.

In the interest of grid security and in case of any violation, SRLDC would take such action as necessary including issue of caution / IEGC violation messages as per the prescribed formats and attached to this document at Annexure-9.

1) Manual/Automatic Load Shedding

The Constituents shall restrict their net drawl from the grid to with in their respective drawl schedule. All the constituents (especially who are overdrawing) shall initiate load shedding (manual / automatic) measures at system frequency of 49.95 Hz itself to prevent further fall in frequency.

Further, incase of certain contingencies and / or threat to system security, the SRLDC may direct SLDCs to decrease its drawl by a certain quantum. Such directions shall immediately be acted upon.

Each Regional Constituent shall make arrangements that will enable manual demand disconnection to take place, as instructed by the SRLDC / SLDC under normal and / or contingent conditions.

The measures taken to reduce the constituents drawl from the grid shall not be withdrawn as long as the frequency / voltage remain at a low level unless specially permitted by SRLDC.

2) Desirable self-healing measures by constituents:

SRLDC may issue violation message as per clause 6.4.7 of IEGC, If automatic / manual demand disconnection does not take place even after instructed by SRLDC. The quantum of the demand to be put on such manual / automatic demand disconnection may be finalised in the SRPC forum

The details of desirable self-healing measures to be taken by constituents during low and high frequency conditions are as stated below.

2.11 SUMMARY

The following specific action shall be taken in the event of frequency going high / low

1) Under low frequency conditions

All constituents are expected to maintain the frequency within IEGC band and to the extent possible take appropriate corrective actions, to combat declining system frequency, like

a) Take all the necessary demand side control management measures

b) Recall any surrendered power from ISGS following merit order, if felt prudent considering the LG Balance applicable at 4th time block

c) Despatch of all available generation to the full extent possible

d) The constituent particularly who is overdrawing from the grid may take further necessary actions to improve the system frequency to above 49.9 Hz or as amended from time to time. including the following:

1) Maximise generation in all their operating machines.

2) Explore additional import through STOA/Px from other States/constituents, if available.

3) Start manual load shedding / curtailment of load, if there is no other possibility to reduce over drawal for maintaining system frequency above 49.9 Hz.

4) Avail URS Power if any, from other Regions or same Region ISGS, if available.

2) Under high frequency conditions

All constituents are expected to maintain the frequency within IEGC band and to the extent possible take appropriate corrective actions, to combat frequency rising above 50 Hz, like

Operate available hydro units on pump mode.

a) Surrender relatively high cost entitled power from ISGS.

b) ISGS at their discretion may back down the generation without waiting for an advise from SRLDC to restrict the frequency raise subject to the limit specified by DSM Regulation

c) Follow merit order and conserve fuel by reducing or shutting down high cost generators by all constituents in all their generating stations including IPPs / high cost generating stations.

d) The constituent who is under drawing may take the following actions to contain the system frequency to below 50.05 Hz. and avoid further rise.

1) Minimise generation in all their operating machines.

2) Explore additional export through STOA/Px to other states / constituents, if available.

3) When frequency is above 50.2 Hz, and after all possible measures if high frequency persists, the run of river hydro generating units / Wind Power Generating Units may be stopped until the freq comeback to 50.2 Hz or below.

e) Except under an emergency, or to prevent an imminent damage to a costly equipment, no constituent shall suddenly increase his generating unit output by more than one hundred (100) MW ) without prior intimation to and consent of the RLDC

f) In case of persistent high frequency, all constituents may resort to shutting down of generators in the event of threat to system security as per directions of SRLDC

2.12 Inter-Regional Exchanges

In consultation with NLDC, SRLDC shall endeavor to exchange power with the neighboring regions on opportunity basis in addition to the interregional bilateral agreements (STOA) and Px already in vogue based on the criteria of flow of power from surplus to deficit region. While effecting such Inter Regional Exchange quantum of more than 100MW at any instance, SRLDC will inform the over drawing / under drawing constituents as the case may be for their suitable corrective action to maintain the system frequency with in the IEGC mandated range. However during the process of transfer of STOA/Px or deviation power from / to other regions at times, for short intervals there could be a possibility of negative deviation i.e., deviation power flowing from lower frequency region to higher frequency region in situations like

(a) Ramping up / down of HVDC stations.

(b) Load change over period of either of the regions

(c) Network contingent conditions in either of the regions.

(d) Wheeling of other regions power during contingencies.

(e) Testing/ Maintenance of important elements.

(f) Providing power assistance during emergencies in either of the regions.

However the prime consideration for such exchange would be the improvement in grid parameters and system security followed by economy. Any direction by NLDC for achieving Grid Security, Reliability, maximum efficiency and economy in the operation of National Grid Shall be binding.

2.13 Special requirements for Solar/ wind generators

System operator (SLDC/ RLDC) shall make all efforts to evacuate the entire available solar and wind power. However, System operator may instruct the solar /wind generator to back down generation on consideration of grid security or safety of any equipment or personnel is endangered and Solar/ wind generator shall comply with the same.

For this, Data Acquisition System facility shall be provided for transfer of information to concerned SLDC and RLDC

2.14 FRC Calculations

In line with CERC order on petition no 52/MP/2012, FRC will be computed for all events involving a sudden 1000MW or more load/generation loss or a step change in frequency by 0.5Hz. FRC shall be worked out by NLDC,RLDCs and SLDCs to compute each interconnection/region/control areas FRC The detailed procedure & relevant formats are enclosed at Annexure 15

2.15 Restricted Governor Mode of Operation (RGMO) /FGMO

1) IEGC Requirement

1) Constituents would ensure that all thermal generating units of capacity 200MW and above hydro generating units of capacity 10MW and above (except those upto three hours pondage) generating units synchronised with the grid are operated on restricted governor mode of operation and with necessary primary and secondary control in line with sections 5.2 (f ), 5.2 (g), 5.2 (h) and 5.2(i) of IEGC, its First & Second Ammendment 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

2) RGMO Analysis

1) Any Events which requiresRGMO analysis will be intimated by SRLDC thru web group within 2 days.

2) Thegenerating stationsshall send the data / RGMO Performance for the events mentioned above & those mentioned in the agenda in the web group.

3) SLDC/SRLDC will prepare the analysis for the generators in the respective control areas& post the same in web group & shall be discussedin every OCCM/Spl Meetings on RGMO & MVAR.

4) The generators who are not reconciling the observation made by SLDC/SRLDC will be treated as remarks of SLDC/SRLDC as accepted

5) SRLDC may also consider the df/dtalong with dip/rise in frequency while selecting the Event for analysis

3) Understanding of IEGC for Analysis of RGMO / FGMO with MI Performance in SR

All SLDC/RLDC/Generators shall observe the RGMO response of generating units in their control area based on the following requirement

System Frequency Level

Direction & Rate of Change of Frequency

RGMO / FGMO with MI Contribution expected as per IEGC

When System Frequency Below 50.05Hz

When rate of rise / fall in frequency is less than 0.03Hz per sec

No Response of RGMO or FGMO with MI is expected

Rate of rise of Frequency is more than0.03Hz per sec

No reduction in generation

Rate of fall in Frequency is more than0.03Hz per sec

Generation shall increase along the droop to a value correspondence to total fall in frequency limited to 5% of the current generation subject to 105% of MCR and then unit can go on hold mode. After a couple of minutes, if it is not sustainable, the generator ramp down to original value at a rate of 1% per minute

When System Frequency Above 50.05Hz

When rate of rise / fall in frequency is less than 0.03Hz per sec

No Response of RGMO or FGMO with MI is expected

Rate of rise of Frequency is more than0.03Hz per sec

Generation shall decrease along the droop to a value correspondence to total rise in frequency limited to 5% of generation or MCR whichever is less and then unit can go on hold mode. After a couple of minutes, if it is not sustainable, the generator ramp up to original value at a rate of 1% per minute

Rate of fall in Frequency is more than0.03Hz per sec

No increase in generation

4) Categorisation of RGMO/FGMO Response

All SLDC/RLDC/Generators shall classify the response based on the following categorisation and criteria

Descriptions Used ( Expected Response is taken as 5% of Generation)

Sl No

Response Code

Description

Explanation

1

R

Responded

Response Greater than 70% of Expected response is achieved

2

PR

Partially Responding

Response 30 to 70 % of Expected response is achieved

3

IR

Insufficient Response

Response less than 30% of Expected response is achieved

4

NR

No Response

No Change in Generation

5

RR

Reverse Response

Generator acts against the RGMO/FGMO feature. i.e when frequency dips , generation also reduces & vice versa

5) RGMO Analysis

1) Data validation was thus needed to be carried out between state generators and the respective SLDCs and the ISGS generators and SRLDC.

2) DC declaration by generators could be made appropriately to ensure RGMO response. State Load Despatch Centers could also schedule appropriately so as to ensure the response.

3) STOAs should not be transacted/permitted by SLDC beyond MCR to ensure that response is available for purpose of grid security.

4) Generators to appropriately take up the issue regarding uprating/installed capacity of their units.

5) Reasons for nonperformance needed to be qualified with proper technical justification by the generators.

6) All technical issues needed to be taken up with OEM and concrete action plan to be ensured within two months.

7) All the stations should have data logging facility (up to six months) for fruitful analysis/deliberation.

8) RGMO should always be in service including at technical minimum.

9) Generators to initiate steps to ensure visibility of RGMO status in the SCADA.

10) Parameters needed to be maintained so as to ensure that RGMO response is available at all instances.

11) SLDCs to take proactive role for RGMO implementation/monitoring.

12) GENCOs/SLDCs take up the issue with their Irrigation Department for allowing RGMO to be put in service.

13) Individual GENCOs needed to approach through petition to Honble CERC for obtaining any exemption/extension of RGMO/FGMO compliance.

14) Generators shall take permission of SRLDC directly by Regional Generators & thru SLDC in case of embedded generators for putting RGMO out of service for technical reasons. However Generators shall take approval of Honble Commission whenever the expected duration of outage of RGMO feature exceeds more than a week due to technical/operational limits.

6) Compliance of CERC directions in Petition No 302/MP/2013

a. Units should not be scheduled by SRLDC/SLDC beyond 100%/MCR rating.

b. SRLDC to restrict the schedule to the minimum of Normative DC taking care of the Units on bar and DC declared by the station.

c. SRLDC while restricting the schedule to follow the below mentioned rationale /logic

i. Case 1: When all the constituents are requesting as per their entitlement and the sum of requisitions exceeds the Normative DC, then drawal schedule of beneficiary will be reduced on prorata.

ii. Case 2: When some of the constituents are requesting reduced requirement and some constituents has requested URS, the sum of requisition may/ may not exceed the Normative DC, if it exceeds then first URS will be cut to the extent required and if after cutting URS, still if it is excess, then the drawal schedule of beneficiary will be reduced prorata to the extent of excess.

d. The generators should ensure that the units are not operated with valve wide open condition even at part loads ensuring primary governor response at all stages.

e. SLDCs/SRLDC to keep watch on the response of generators during major frequency excursions and submit report on quarterly basis to SERCs and POSOCO.While furnishing the quarterly report to CERC, SRLDC to additionally furnish quantum of restriction (DC Restricted Schedule of SRLDC) for ISGS stations in the report to Honble CERC

f. The requests for outage of RGMO/FGMO with MI based on valid technical reasons shall be dealt at SLDC/RLDC level. In case of any dispute/difficulty, the matter should be resolved at RPC level at first instance.

7) Ancillary Services

6.11 The objective of the ancillary regulations is to restore the frequency at desired level and to relieve the congestion in the transmission network. The detailed procedure along with regulations is available at NLDC website http://nldc.in/AncillaryServices.aspx. A virtual regional entity called SR_VAE to be created for SR. Power Number for Southern Region

The Computation of Power Number for the year 2015-16 is as per annexure 31

CHAPTER-3

3. VOLTAGE MANAGEMENT

3.1 Introduction

One of the main assumptions of the power system planner is that the system parameters viz. voltage remains close to nominal values. This section lists the measures to be adopted by the system operators at SRLDC / SLDCs / ISGS / substations for voltage control measures in order to maintain the voltage close to nominal.

3.2 Operating Range

In compliance to the IEGC section 5.2 (s) , All Users, RLDC, SLDC STUs , CTU and NLDC shall take all possible measures to ensure that the grid voltage always remains within the following operating range.

Normal

Nominal

Maximum

Minimum

765

800

728

400

420

380

220

245

198

132

145

120

110

121

99

66

72

60

33

36

30

The maximum and minimum values in the above table are the outer limits and all the Constituents would endeavor to maintain the voltage level well within the above limits.

3.3 Voltage Violation Type / Category / Message consideration

During the real time operation voltage tends to deviate and may violate the voltage band. The violation of voltage has been classified into the following violation types and category for the purpose of issuing messages by SRLDC and taking actions by the respective constituents/SLDC/RLDC. SRLDC may also consider the reactive drawals by the constituentsgreater than zero for minimum voltage condition and reactive injection by the constituents greater than zero for maximum voltage condition along with the voltage for issuing messages; however constituents shall endeavour to improve the voltage profile.

Description

Range / Condition

Category

Voltage Violation

> 425 kV or 390 kV to 0 and Voltage is below 380kV.This interim measure of physical regulation may be implemented till installation of sufficient capacitors / UV relays.The messages will be issued by SRLDC as per Annexure 9 under low voltage conditions and the constituents shall take all possible measures to ensure that the grid voltage always remains within the range specified in IEGC. The list of nodes for under voltage relays are as per Annexure 11. Switching-off of 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, prevailing grid conditions, geography of the network, etc., can be switched off in order to improve the system voltage. The details of such reactors in SR are included in the list of reactors shown at Annexure 2 of this document. The switching off of such line reactors and reviving them back would be carried out as per the instructions issued by SRLDC.

3.9 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 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 SRLDC in real time and as per the standing instructions issued from time to time. While taking such action, SRLDC would duly consider that to the extent possible the same does not result in affecting ISGS generationas well as the system security & reliability is not affected. Line Opening would be the Last Resort by SRLDC after receipt of message from the constituents. Details of measures taken needed to be communicated in the line opening request message by the regional entity/ SLDC when the voltage rises above IEGC specified upper limit. The request for line opening should be as per format enclosed at Annexure 12

3.10 SUMMARY

The following specific action at Grid Substations / Generating Stations shall be taken in the event of voltage going high / low.

3.10.1 High voltage

On observing the High voltage at sub-stations(e.g., 400kV bus voltages going above 410kV), the following specific steps would be taken by the respective grid substations / generating station at their own, unless specifically mentioned by SRLDC otherwise;

a) The bus reactors be switched in

b) The manually switchable capacitor banks be taken out

c) The switchable line/ tertiary reactors are taken in.

d) Optimize the filter banks at HVDC terminal. ***

e) All the generating units connected on bar shall absorb reactive power within capability limits of the respective generating units.

f) Operate synchronous condensers wherever available, for VAR absorption.

g) Operate hydro generators / gas turbines as synchronous condenser for VAR absorption wherever such facility is available.

h) Re-route the power flows between HVDC links to control voltage rise.

i) Open one of the lightly loaded double circuit and single circuit lines in consultation with SRLDC, keeping in view the security of the balance network. Line Opening would be the Last Resort by SRLDC after receipt of message from the constituents. Details of measures taken needed to be communicated in the line opening request message. The request for line opening should be as per format enclosed at Annexure 12

3.10.2 Low voltage

On observing low voltage (e.g., 400kV bus voltages going down below 390kV), the following specific steps would be taken by the respective grid substations / generating station at their own, unless specifically mentioned by SRLDC otherwise;

a) Close the lines which were opened to control high voltage, in consultation with SRLDC

b) The bus reactors be switched out

c) The capacitor banks be switched in

d) The switch able line / tertiary reactors are taken out.

e) Optimize filter banks at HVDC terminal. ***

f) All the generating units shall generate reactive power within capability limits of the respective generating units

g) Operate synchronous condensers wherever available, for VAR generation

h) Operate hydro generators / gas turbines as synchronous condenser for VAR generation, wherever such facility is available.

i) Re-route the power flows between HVDC links to improve voltages.

*** The details of filter bank availability with their runback schemes at HVDC terminals are furnished atAnnexure 6of this document.

3.11 Solar/ wind generators

SLDC/RLDC may direct a wind farm to curtail its VAr drawl/injection in case the security of grid or safety of any equipment or personnel is endangered.

During the wind generator start-up, the wind generator shall ensure that the reactive power drawl (inrush currents incase of induction generators) shall not affect the grid performance.

3.12 Additional Reactive Compensation and Healthiness Monitoring

The person already connected to the grid shall also provide additional reactive compensation as per the quantum and time frame decided by respective RPC in consultation with RLDC. The Users and STUs shall provide information to RPC and RLDC regarding the installation and healthiness of the reactive compensation equipment on or before 5th of every month for deliberation in OCCM. RPC shall regularly monitor the status in this regard

3.13 Defence Plan for Voltage Control

The details may be referred in Chapter on Defence Mechanism for Southern Region

3.14 MVAR Injection/Absorption / Generator & ICT Tap Analysis

a) Thegenerating stationsshall submit the MVAR Injection/Absorption along with tap details in the prescribed format ( Annexure 16)in the sr_voltage@googlegroups.com web group on monthly basis / as per requirement.

b) SLDC/SRLDC will prepare the analysis for the generators in the respective control areas& post the same in web group & shall be discussedin every OCCM/Spl Meetings on RGMO & MVAR.

c) The generators who are not reconciling the observation made by SLDC/SRLDC will be treated as remarks of SLDC/SRLDC as accepted

3.15 MVAR Capability Testing

In addition to proper demand side management, Tap Optimisation & switching operation of Reactors, optimisation of MVARabsorption / Injection by the generators plays a vital role in maintaining the voltage profile within the IEGC mandated range. Although the Manufacturer supplied Capability curves give a fair idea on the extent to which the generators MVAR Capability can be utilised, the influence of operating parameters as well as operator are significant in deciding absorption / injection of MVAR quantum in real time grid operation. To facilitate the operators real time decision making process effectively, an endeavour is made to ascertain the MVAR absorption / injection of each generating unit in SR within the safe practical limits. Hence Capability testing gains importance & series of testing has been planned in Southern Region.

3.15.1 Procedure

The MVAR Capability testing of Generators in Southern Region are to be conducted in line with the approved procedure as per Annexure 21a. A sample filled in data for Thermal & Hydel Power plant is attached at Annexure 21b. Any deviation due to field conditions is to be recorded.

3.15.2 Frequency of Test

The MVAR Capability test is to be carried out whenever the following conditions are met

a) If MVAR Capability testing is yet to be done after COD or

b) R & M works has been carried out or

c) Major Overhauling of Generators / Field winding / Exciter / Excitation system has been carried out or

d) 4 years has been elapsed after MVAR Capability testing or

e) Recommendations of the MVAR Capability Testing Committee has been Implemented

3.15.3 Participation of SLDC/RLDC

The MVAR Capability Testing committee constituted by SRPC may test at different stations on selected units for the sharing of experience. However SLDC/RLDC shall participate as part of the committee formed by SRPC as well as take initiative and ensure that tests are being carried out as per the frequency mentioned above for the generating units in their control area.

3.15.4 General recommendations of the committee to be implemented by all generators in SR

a) The Generator shall come out with specific difficulties with supporting documents and mere apprehension shall not be the reason for not utilising the capability curve. Wherever the OEM advice / consultation is required, efforts shall be put to get the same within a months time.

b) Wherever any important monitoring / protection system is not available / repair like Field voltage / Current monitoring system is not available / under repair, the same may be kept in place at the earliest.

c) The Capability curves / GT details / ICT details shall be updated to SLDC / RLDC, whenever there is change

d) The constraints already encountered during the testing at Simhadri, Karnataka & Andhra Pradesh may be reviewed at all generating stations of Southern Region and Protection settings in general may be reviewed w.r.t standard practices.

e) All the meters are to be calibrated as per standard industrial practice.

f) The data between SLDC SCADA & Generator may be validated after meter is calibrated optimum utilisation of capability curve.

g) The generator shall consider the Mvar capability curve with AVR in service.

h) The confirmation with report in this regard may be sent to SRLDC & SRPC.

i) Similarly the Tap position , whenever there is change, the same has to conveyed to SLDC /RLDC

j) RGMO of the unit under test may be kept out of service during the period of testing.

k) Similar tests may be carried out in all units whenever system conditions are permissible for maximum absorption/injection.

CHAPTER-4

4. OUTAGE MANAGEMENT

To formulate a coordinated outage programme of transmission lines and generating units for the regional grid considering all the available regional resources and taking into account transmission constraints, system operating conditions and maintaining load generation balance

4.1 Introduction

The earlier chapters have dwelt on the network security, reliability and demand estimation. The next logical step is outage planning of generating units, transmission lines and ICTs subject to the above constraints. This would have to be done in line with section 5.7 of the IEGC. As already mentioned earlier, the list of important elements of the Southern Regional Grid and the list of important generating stations is enclosed at Annexure 1. Outage planning would be done centrally only in respect of these lines, ICTs and generating units, allowing sufficient discretion to the SLDCs / STUs in respect of other lines and units, unless otherwise decided by SRPC Secretariat. Outages in the system have an effect on the network security and have to be planned carefully. Power system studies would have to be done by the SRPC and SRLDC for the outage planning (up to monthly review) and for day-to-day operations respectively, to assess the effect of outages on the grid security. Further, as the outage plan finalised would also have commercial implications for each SEB / STU / ISGS, the same would have to be done meticulously.

4.2 OUTAGE PLANNING PROCESS

4.2.1 Annual Outage Planning

The following calendar shall be followed in respect of annual outage planning for the ensuing financial year:

a) Constituents will forward to SRPC Secretariat the required data of outage planning for the next financial year, by 31st October.

b) SRPC Secretariat will issue the draft outage programme to all the regional constituents and SRLDC by 30th November.

c) The mutually agreed final outage plan shall be intimated by SRPC Secretariat to all regional constituents, SRLDC and NLDC for implementation, latest by 31st December.

4.2.2 Quarterly and Monthly Reviews

The annual outage plans formulated as above shall be reviewed on quarterly and monthly basis as per following programme:

a) The above outage plan would be reviewed on Quarterly and Monthly basis in joint meetings to be attended by all regional constituents and SRLDC as coordinated by SRPC secretariat. The Quarterly meetings would be held in the months of March, June, September & December. The revisions / changes if any in the outage plan the same may be incorporated and communicated by SRPC within a week of the review meeting.

b) Monthly review of the outage plan for the current month and the consecutive month would be done in the Operation Co-ordination Committee (OCC) of SRPC meeting. SRPC Secretariat would issue the outage plan so frozen in this meeting, to all constituents and SRLDC within next two working days.

c) All the Regional Entities shall discuss and finalise the outage plan for the ISTS elements as well as the state owned critical elements during the Operation Co-ordination Committee (OCC) of SRPC meetings and ensure all possible efforts to avoid un-planned outages.

d) Outage plans of the Inter Regional links shall be coordinated through NLDC after due deliberation in the OCC forumof involved regions.

e) The Detailed outage procedure will be as per NLDC Procedure for Transmission Elements Outage Coordination as amended from time to time enclosed at Annexure 20

4.2.3 Unforeseen outages and re-scheduling of outages after freezing of Monthly schedules

i) In the event of any requirement to re-schedule any planned shutdown or to avail an emergency / unforeseen shutdown not anticipated earlier, the concerned constituent shall forward such request to SRLDC indicating the nature of emergency or the reason for deferment. SRLDC would approve such unforeseen outages / re-scheduling of an already planned outage based on the exigency of the case vis--vis system conditions. In case, any spill over beyond the next month OCC meeting occurs on account of the deferment, the same would have to be brought to the notice of the Operation Coordination Committee of SRPC by the concerned constituent and SRLDC.

ii) In order to facilitate changes in the dates of construction outages, critical shut downs etc. one more set of transmission proposals would be considered through OCC Outage web group. Modifications in the dates of the constructions/critical shut downs would only be considered (not normal AMP works) provided it is supported by valid reasons. The procedure to be followed is below:

a) The construction/critical shutdown proposals would be submitted to Outage Web Group/SRPC/SRLDC in the requisite format by 20th of the month for the outages planned for next month.

b) SRPC/SRLDC would jointly review the proposal and furnish the details along with observation/ATC curtailment etc. between 21st to 25th of the month. SRLDC would coordinate with NLDC /other RLDCs for the Inter Regional / critical elements shutdown proposals. It would be posted in the OCC Outage Web Group.

c) Constituents/entities could revert back with observations between 26th to 28th of the month in the OCC Outage Web Group. In case no comments received, shut down would be treated as approved.

d) The approved outages would be posted on SRPC website before end of the month.

e) It needs to be noted that the new list of shutdown proposals would consists only the modified/additional construction/critical shutdowns. Approval would be at the discretion of SRLDC/SRPC/Constituents.

4.2.4 Outages Day to Day Request and Monitoring

i) All Constituents to submit the data/ request through web based outage coordination system for requisitioning the OCC approved outages on D-3 basis which is available at RLDC website http://scheduling.srldc.org:8080/OCS/Account/Login.aspx

a) The web base system is meant only for OCC approved outages.

b) Any deferred outage / change in dates will be treated as fresh outage. Any deferred outage should be sent again through mail for entry by the administrator.

c) Emergency shut downs could be applied to SRLDC with proper remarks/reasons/justification.

d) Shutdown list for D-3 day will be available in the website for requisition. In addition, D-4 & D-5 shutdown list also will be available.

ii) All SLDCs and RTAMC to monitor the D-3/5 outages and ensure that outages are taken as per approved schedule.

iii) SRLDC would post the approved outages availed and non-availed by 3rd of every month for the previous month.Subsequently constituents should revert back with the reasons for non-availing the shut down by 6th of every month

4.3 AVAILING OF SHUTDOWNS

a) SRLDC would review on daily basis the outage schedule for the next two days and in case of any contingency or conditions described in Sec.5.7.4 (g) of the IEGC, defer any planned outage as deemed fit clearly stating the reasons thereof. The revised dates in such cases would be finalised in consultation with the concerned constituent/s if it falls within the next OCC meeting. Such revised dates would be communicated to OCC of SRPC by the respective constituent.

b) For a transmission element the outage of which shall affect more than one constituent, the information about the approval or deferment shall be communicated by SRLDC to all such constituents so that they may remain informed about the said outage.

c) In respect of important elements of the grid, a code would have to be obtained from SRLDC before taking the said element for maintenance. All preparatory works for maintenance must be done well in advance before availing the code so as to keep the outage time to minimum. Similarly, a code would have to be obtained from SRLDC before reviving the element after shut down. The switching operation of element shall be done within a reasonable time say 15minutes from the time of availing code from SRLDC. Due to any practical difficulties if the switching operation could not be completed within 15 minutes, the same needs to be appraised to SRLDC immediately and get consent / revised code from SRLDC.

d) The code issued by SRLDC for opening / revival of the circuit signifies such approval only from the system point of view notwithstanding anything contained in respect of safety measures and other switching operations to be carried out locally. The related line / substation personnel would be responsible for ensuring all safety precautions to be followed while opening / closing of any element to avoid any threat to operating personnel and equipment.

e) During the period of shutdown, all efforts shall be made by the constituents to ensure timely return of shutdowns. Delays if any shall immediately be reported to SRLDC along with the reasons and likely time of return of shut down. On assessing the grid condition and the status of the shutdown work, SRLDC may concur for extension of shutdown duration or advise for rescheduling the shutdown in consultation with the concerned agencies. The details shall be informed by SRLDC to all concerned as detailed in clause 4.2.4 b of this document.

f) Where it is foreseen that return of Permit To Work (PTW) could be delayed due to physical distance involved in case of a transmission line, mobile / satellite phones would be used for communication with the substation to minimise the outage period.

g) Any maintenance work on opportunity basis proposed to be carried out by related agencies during a line / ICT shutdown would be carried out, only in consultation with and consent of SRLDC. Any Regional Entityplanned to avail opportunity shutdown shall also discuss the details in the OCC forum while clearing the intended Shutdown for the outages cleared in the OCC forum.

h) NLDC/SRLDC may defer the planned outage in case of any of the following, taking into account the statutory requirements:

1. Grid disturbances

2. System Isolation

3. Partial Black out in a state

4. Any other event in the system that may have adverse impact on the system security by the proposed outage.

i) Maintenance / Replacement works on elements kept out on System constraint.

j) No maintenance or replacement work on any element that were kept out on system constraint shall be carried out without written consent / code of SRLDC as the element may be required to restore at any point of time as per system requirement. Incase of elements that were kept out in prolonged manner, for carryingout any works the same procedure of applying outage request and getting approval after deliberation in OCC shall be followed.

CHAPTER-5

5. Switching Coordination

5.1 Introduction

Coordination of switching operations in the grid is important for ensuring safety of personnel and equipment as well as for ensuring adequacy and security of the grid. Before any operation of important elements of the Southern Regional Grid is carried out on a User/STU system, the Users, SLDC, STU, CTU, licensee shall inform SRLDC, in case the Southern Regional grid may, or will experience an operational effect.

5.2 Switching Diagram:

One copy of the latest updated switching diagram of all generating stations, 400KV, and important 230 KV / 220 KV / 132 KV / 110KV substations along with the details of FSCs / Reactors / ICT Tap position etc., shall be kept at concerned SLDCs, SRLDC, CPCC, SCC and SRPC Secretariat to enable the system operation, outages, system restoration and operational analysis in a coordinated manner. A copy of the State level / Regional level grid maps and single line diagrams shall also be maintained at these places. In case of any changes / updating in any such diagrams, the same shall be communicated to SRLDC & SRPC by the concerned on immediate basis.

5.3 Switching Coordination

5.3.1 Switching of System Elements for first time

In line with Regulation 6 (1) of the Central Electricity Authority (Grid Standards) regulations 2010, no entity shall introduce an element in the ISTS of Southern Grid without the concurrence of SRLDC in the form of an operation code. In case a new power system element in Southern Regional grid is likely to be connected with the Inter-State Transmission System or is to be energized for the first time, from the ISTS, the applicant User/STU/CTU/licensee/generator shall send a separate request in advance along (at least one week) with the confirmation of the following:

a) Any New Element / Modification in the existing Transmission elements like LILO should submit the details in the NLDC prescribed format Annexure 24a prescribed along with supporting documents at Annexure 24a &and shall also submit the additional details in the SRLDC format prescribed format Annexure 24b along with supporting documents at Annexure 24b

b) In case of commissioning of new generating units/ Transmission projects, approval for metering schemes are required to be obtained from SRPC at least 1 year prior and the concerned Regional Entity shall also ensure the availability of SEM data to SRLDC well ahead of synchronization of the unit. Also login id and password and abbreviated station name to upload weekly SEM data to be obtained from MO department of SRLDC.

c) The New Units/ upgrading shall submit the details as per annexure 25a along with supporting documents Prior to Synchronisation of New Generating Unit

d) The New Units / upgrading of unit capacity prior to synchronization to the grid shall submit the compliance report as per annexure 25balong with supporting documents prior to Declaration of COD

e) The Procedure for availing Start up power from the Grid by the Generating Stations under commissioning phase through Deviation Settlement Mechanism is enclosed at Annexure 23

f) LVRT requirement for WTGs:

i. LVRT should be implemented for all wind turbines (>& = 500 kW) commissioned before 15.4.2014 and connected to voltage level of 66 kV and above except for Stall Type WTGs, which are not technically feasible to be retrofitted with LVRT.

ii. In case of wind turbines of less than 500 kW and installed before 15.04.2014(except stall types), may be decided after CEA study regarding technical feasibility of installation LVRT

iii. After the issue of necessary regulations/clarification by CEA with regard to the voltage level above which LVRT would be mandatory, the same requirement shall be applicable even in case of WTGs installed prior to 15.4.2014 keeping in view the safety and security of the grid.

iv. WTGs, whose useful life is going to expire in the next 5 years (By 04.01.2021), shall be exempted from installation of LVRT.

v. LVRT should be implemented for all wind turbines commissioned after 15.4.2014 and connected to voltage level of 66 kV and above

g) Solar: SLDC/STU/RLDC/CTU as the case may be shall ensure that the provision of LVRT is available for all solar generators connected at the voltage level of 11 kV and above. The solar generators whose bidding process has not yet commenced i.e. NIT has not yet been issued on 04.01.2016 shall take necessary steps to implement LVRT in their generating stations.

h) SLDC/RLDC as the case may be shall ensure that LVRT is installed even before commencement of trial operation

5.3.2 Trial run of Generating units

All New Generating unitsentities shall intending to demonstrate 72 hrs trial operation, shall keeping in view the public holidays, weekends etc. Since demand is likely to be low on those days, in case of extreme circumstances, Generators may be asked to back down their injection based upon real time system condition. In such cases, Generators need to carry out the same for another 72 hrs to meet the requirements in line with Terms and conditions of tariff 2014-19 Regulations and sIEGC 4th amendments regulations and also in line with the decision of 28th CCM of SRPC. During trial run, the unit shall demonstrate, after taking a begin/end code from SRLDC, instantaneous picking up of generation to 105% of the MCR. After the demonstration, the generation may be brought down at the rate of 1%/min.

The new units before declaring COD shall follow the guidelines/ submit necessary documents as envisaged in IEGC 6.3A .The formats to be submitted before Commercial operation of Central generating stations and inter-State Generating Stations is attached as Annexure 25c

5.3.1 Switching of Important Elements

a) All Users, CTU and STUs shall endeavor to operate their respective power systems and power stations in an integrated manner at all times

b) No part of the grid shall be deliberately isolated from the rest of the National/Regional grid, except (i) under an emergency, and conditions in which such isolation would prevent a total grid collapse and/or would enable early restoration of power supply(ii) for safety of human life (iii) when serious damage to a costly equipment is imminent and such isolation would prevent it, (iv) when such isolation is specifically instructed by RLDC. Complete synchronization of grid shall be restored as soon as the conditions again permit it. The restoration process shall be supervised by SRLDC, in co-ordination with NLDC /SLDC in accordance with operating procedures separately formulated NLDC/SRLDC.

c) In order to maintain the security of the regional power system on a day-to-day basis, it is important that the planned outage of generation & transmission system is properly coordinated.

d) No important element of the National/Regional grid shall be deliberately opened or removed from service at any time, except when specifically instructed by SRLDC or with specific and prior clearance of SRLDC. Any opening of the important elements, have to be carried out only after prior clearance of SRLDC. Important elements of the Southern Regional Grid, which have a bearing on the network security, are enclosed at Annexure-1 of this document.

e) The regional entities, users, STU, CTU, licensee shall obtain operation code from SRLDC before carrying out any switching operation on any of the important elements of the Southern Regional grid. Shut down of any 400 kV bus at substation needs approval of SRLDC.

f) In case of opening/removal of any important element of the grid under an emergency situation, the same shall be communicated to SRLDC within ten minutes after the event. Likewise, tripping of any of these important elements should also be informed to SRLDC within ten minutes time indicating preliminary details like the reason(to the extent determined), likely time of restoration if assessable etc. In case,Likely time of restoration cannot be assessed at the time of FIR, same shall be submitted within one hour. In addition to the above, it is necessary that special attention be paid for maintaining the reliability of the system.

g) RLDC shall inform the opening/removal of the important elements of the regional grid, to NLDC, and to the concerned Regional Entities (whose grid would be affected by it) as specified in the detailed operating procedure by NLDC.

5.3.2 Other Precautions to be taken during switching:

The following areas need careful implementation by the concerned constituents / stations:

a) In case of a two bus system at any substation it must be ensured that the segregation of feeders on the different buses is uniform. This would help in minimizing the effect on the system in case of a bus fault.

b) In 400 kV substations having one and half breaker scheme, it must be ensured that the two buses at such substation remain connected at least by two parallel paths so that any line / bus fault does not result in inadvertent multiple outages. In case any element, say a line or an ICT or a bus reactor, is expected to remain out for a prolonged period at such substation, the main & tie breakers of such elements should be closed after opening the line side isolator. This should be done after taking all suitable precautions to avert inadvertent tripping. At any point of time two breakers shall be ensured in service in one parallel path

c) The substation operators must ensure the above condition even when any lightly loaded line is opened as a last resort to control over voltage. Such opening of lines is generally superimposed over other line outages on account of faults created by adverse weather conditions resulting in reduced security of the system.

d) Single pole auto re-close facility on 400 kV lines should always be in service. SRLDCs approval would be required for taking this facility out of service. Likewise, in case any transfer breaker at any 400 kV substations having two main and transfer bus scheme is engaged, the same would be informed to SRLDC.

CHAPTER-6

6. CONGESTION MANAGEMENT AND NETWORK RELATED ASPECTS

6.1 Introduction

This chapter describes the actions required to be undertaken by system operators to maintain the security of the network at all times against any plausible contingencies /outages within the SR network as well as from any contingencies arising out due to incidences occurring in the rest of the National grid that may have an adverse effect on SR system.

6.2 Line loading

In addition to frequency & voltage control measures outlined in respective chapters, each system operator would also have before him the thermal loading limits, surge impedance loading and the loading permitted from stability considerationslisted under important grid elements. Each system operator at SLDC / substations would endeavor to keep the line / ICT loadings within limits and inform SRLDC in case of overloading of any element. In addition to monitoring the loading of critical individual elements, the power flow across the identified flow gates in SR shall also to be monitored and controlled with in the value specified by SRLDC based on the study results, Special emphasis would be laid by each system operator in identifying credible system contingencies & continuously evaluating the system under his control against these contingencies. All the constituents hence would extend the necessary cooperation in maintaining network reliability and security.

6.3 Assessment of transfer capability

Assessment of Total Transfer Capability (TTC), Transmission Reliability Margin (TRM) and Available Transfer Capability (ATC) for import and export of power within Southern region as required for reliable system operation and for facilitating non-discriminatory open access in transmission shall be carried out by SRLDC in coordination with National Load Despatch Centre and other RLDCs. The Detailed Procedure for Relieving Congestion in Real Time Operation as approved by the CERC vide order dated 22.04.2013 may be referred for further details. The assessed TTC, TRM and ATC shall be posted on SRLDC/NLDC website in the formats as enclosed in Annexure 18.

6.4 Major Corridors in SR& Transmission Network congestion management:

To ensure safe and secured grid operation by maintaining the line loading with in safe permissible limits, critical corridors forming flow gates Viz. (1) S1 S2 and (2) 400kV hiryur Nelamangala DC (3) 400kV Udumalpet Palakkad DC Minutes of SRPC meeting are identified based on the studies carried out by SRLDC and explained in OCC forum of SRPC, for continuous monitoring of power flow on real time. The flow gates will be modified based on the system studies as mentioned above from time to time depending on the system network changes

The TTC / ATC limitsfor these flow gates and N-1 limits of critical linesare finalized based on the system studies carried out by SRLDC. The details of set of lines that constitute these flow gates and the prevailing TTC / ATC are listed in Annexure 17. However, depending on the system condition like major variation in generation, loads, transmission element availability etc., the TTC / ATC will be revised on day ahead basis for Power Exchangeand same day basis for bi-lateral transactions to facilitate maximum power availability with reliable grid operation of Southern Region

6.5 Monitoring of congestion

Real time data for monitoring Congestion shall be displayed on the SRLDC website in the Formats as enclosed in Annexure 18.

6.6 Generation rescheduling

SRLDC may revise the interchange schedule as allowed by IEGC regulation 6.4.12, 6.5.5, and 6.5.16. Further details may be seen in the chapter on scheduling.

6.7 Curtailment of scheduled transactions / Deviations from Schedule /Infirm Injections

The transactions already scheduled/deviations/Infirm Injections may be curtailed by SRLDC in the event of transmission constraints; congestion in the grid, or in the interest of grid security. In line with regulations 6.4.12, 6.5.28, 6.5.30 and 6.5.31 of IEGC the transactions shall generally be curtailed in the following sequence

1. Deviations from Schedule

2. Infirm Injections

3. Unrequisitione Surplus(URS)

4. Short term bilateral transactions

5. Short term collective transactions

6. Medium term transactions

7. Long-term transactions

Amongst the customers of a particular category, curtailment shall be carried out on pro rata basis. SRLDC would curtail a transaction at the periphery of the Regional entities. SLDC (s) shall further incorporate the inter-se curtailment of intra State entities to implement the curtailment.

6.8 Network Related Aspects

6.8.1 Operational areas of importance:

a) In order to damp out the low frequency oscillations in the system, the power system stabilizers on the generating units would be tuned by the respective generating unit owner as per the programme drawn out by the Central Transmission Utility (CTU) / SRPC in line with clause 5.2 (k) of IEGC,.

b) All constituents would endeavor to operate the connected generation and reactive power management devices such as Capacitors, Reactors, Synchronous Condensers, Fixed Series Capacitors (FSCs), Static Var Compensators (SVCs) etc. in a manner to maintain the voltages with the IEGC operating range under different operating conditions.

c) All constituents would also maintain in good operating conditions of all control measures such as Defence mechanisms, SPS, U/F & U/V load shedding, AVRs, PSS, RGMO, operating reserves, emergency back-up power supplies etc., and ensure that the operational security standards are maintained for reliable and secured operation of the interconnected system

6.8.2 Protection Healthiness Declaration:

The Protection healthiness declaration as per format enclosed at Annexure 14is to be submitted to SRLDC every month in the OCC Meeting of SRPC.

6.8.3 Security of Grid

In line with Central Electricity Authority (Technical Standards for connectivity to Grid) Regulation 2007, the utilities shall make arrangements for integration of the controls and tele-metering features of his system into the Automatic Generation Control, Automatic Load Shedding, System Protection Scheme, Energy Management Systems and Supervisory control and Data Acquisition System of the respective State or Region

6.8.4 PSS Tuning

1) PSS tuning has been emphasized in the following

a) Clause 5.2(k) of IEGC Regulation

b) CEA (Technical Standards for Connectivity to the Grid) Amendment Regulations, 2013

c) By the Enquiry Committee for grid disturbances constituted by GoI (Recommendation 9.9.2).

d) Para 1.4 of Meeting held on 11.03.2014 in MoP to discuss the Task Force Report

e) Need for PSS tuning of all major generators had also been raised by SRLDC on a number of occasions in the recent past keeping in view the sustained oscillations of high mode and poor damping.

2) All new units with capacity over 50 MW must carry out PSS tuning before declaration of Date of Commercial Operation (COD). A report along with model parameters shall be submitted to CTU/SRLDC/SLDC/SRPC.

3) All generating units with capacity over 50 MW, generating company would perform Step Response Test once in every 3 years (Not exceeding three years between two tests) or at the time of major overhaul of the unit, whichever is earlier. Generating company would arrange for retuning of PSS, if Step Response Test indicates insufficient damping or oscillations.

4) All generating units to set PSS in such a way that it should come into service when the unit loading is above 50 % of installed capacity. Lower setting could also be adopted in case recommended by OEM. Subsequently it may be set at 30% loading of unit installed capacity.

5) Step Response Test for Proportional Integral Derivative (PID) of AVR or DAVR at no load was very much essential before carrying out the retuning activity. This would ensure that PID is doing its coordination work properly and this test could be carried out during unit overhaul.

6) SRLDC to observe and analyze the change in the grid condition based on the output of the PMUs and inform the concerned generating company if un-damped oscillations beyond agreed pre-defined limits are observed. On receipt of the information, the generating company would arrange for retuning of PSS within a time frame of 3 months.

7) In some of the generating units it may not be feasible to tune PSS. Details of such units (COD date, capacity, OEM, reasons as to why PSS cannot be tuned etc.) would be furnished by the generating company. These would be discussed in OCC/TCC/SRPC and if there is general agreement that PSS tuning was not feasible, the matter would be taken up by generating company with Honble CERC for seeking exemption for those units.

8) PSS shall be kept in service (On or energized and performing as designed by the manufacturer). PSS could be taken out under intimation to SLDC/SRLDC along with technical justification i.e. for short duration of one week. Exemption beyond one week needed to be taken up with Honble CERC/SERC.

9) Retuning of PSS could be covered in AMC/Service Contract preferably entrusted to the respective supplier.

10) In case of units with Digital AVR where the PSS was in service, Step Response Test could be carried using in-house expertise and presence of OEM may not be required. Test Reports could be submitted. Tuning to be carried out by OEM.

11) All utilities to furnish the data/information in respect of PSS as per enclosed format (Annexure-28)

12) The following to be taken care during SRT/Report preparation:

a) PSS settings would be set to dampen mode with oscillations within the range of 0.2 Hz to 2 Hz.

b) Damping Torque to be calculated for every SRT test with and without PSS.

c) Power System Stabilizer Models to be given along with the implemented settings (Final).

d) SRT to be carried out at >80% Load and at 50% loading.

e) Both Step Up and Step Down tests needs to be carried out.

f) Real (Active) Power Scale to be within 10 % of operating point in the graphs. Proper Graphs (soft copy) with visible scale to be provided.

g) Make, Type & Model of Excitation System to be provided.

h) Step up to be followed by Step down with a time gap of 20 sec, if taken up, simultaneously.

i) Station personnel to co-ordinate and be associated with the OEM/Testing Agency during the SRT test to ensure the requirements as envisaged.

j) Considering that the PSS performance of brushless exciters was not evident when compared to the PSS performance of static exciters, generatorsto take up with M/s BHEL / OEM to be address the issue for making PSS performance more effective.

6.8.5 Patrolling of Transmission lines

Each Transmission utility would furnish the annual schedule of patrolling to SRPC/SRLDC along with annual outage data by October each year. Compliance report of the patrolling/maintenance carried out during previous month with respect to schedule to be furnished to SRPC/SRLDC in the OCC Meeting. The detailed Patrolling guidelines is attached at Annexure 30 a. The list of Transmission Lines and Substations in the most vulnerable terrain, coastal and polluted areas had been categorized for monitoring to ensure that Patrolling and Maintenance is being carried out as per the Patrolling guidelines. Is attached at Annexure 30 b

CHAPTER-7

7. Demand Forecasting Demand Estimation and Control

This chapter deals with the procedures/ responsibilities of the SLDCs for Demand Estimation of both Active Power and Reactive Power and also the provisions to be made by SLDCs to effect a reduction of demand in the event of insufficient generating capacity and / or withdrawal of external assistance on the event of break down or operating problems (such as frequency, voltage levels of thermal overloading) on any part of the grid.

7.1 Introduction

Demand estimation plays a very important role in system operation. Long term demand estimation (five years and beyond) is an important input for generation planning. In the medium term, say one year, it constitutes an important input for outage planning of generating units and transmission lines. In the short term, say within one week to few months, it is an important input for generation scheduling planning for Power purchase through STOA / Px etc., Variation in demand in real time operation from the estimated values could either be absorbed by the grid or affect it adversely. Even if the estimates are accurate, the generation could vary from scheduled values adversely affecting the grid. Demand control then plays an important role in arresting these adverse effects on the grid.

Demand estimation and control is essentially the responsibility of SLDCs and SRLDC would generally not have a major role in this area. SRLDC would give instructions to SLDCs on demand control whenever the same has a bearing on the security of the regional grid & such instructions would have to be complied forthwith by all SLDCs.

7.2 DEMAND ESTIMATION

a) The SLDCs would forecast demand (MW peak & energy in MWh) on an annual, quarterly, monthly, weekly and daily (Block wise) basis, which would be used in the day-ahead scheduling. Each SLDC is expected to maintain a historical database for the purpose and be equipped with the state-of-the-art tools such as Energy Management System (EMS) for demand forecasting. Ideally, the forecasts should be on quarter hourly basis (8760, 720,168 & 96 values respectively in the annual, monthly weekly and 96 block wise daily forecasts) rather than mentioning only the peak MW and energy requirements for the period.

b) Each State / SLDCs shall utilize the Forecasting Module suitable for their system and compatible to ULDC SCADA scheme for transfer of forecasted data in the form required by SRLDC.

c) Each State / SLDCs shall furnish the demand estimate for 96 time blocks of the day ahead by 15:00hrs of the day in to the web based report system developed by SRLDC

d) Each State / SLDC shall maintain a historical data base and develop methodologies / mechanisms and the same shall be used for demand estimation on daily / weekly / monthly / quarterly basis for demand estimation. The data for the estimation shall also include load shedding, power cuts, etc.

e) The historical data base to be maintained by SLDCs shall also include major events vis--vis effect of weather forecasts on the actual demand, grid disturbances and loss of major generation. Effect of weekends and other holidays on the demand pattern shall also be evaluated on the basis of historical data.

f) The annual, quarterly and monthly demand forecasts would be finalised in the respective Sub-Committee meetings of SRPC and used in the outage plan prepared by SRPC Secretariat in consultation with all the constituents.

g) Attention would also be paid by SLDCs in demand forecasting for special days such as important festivals and National Holidays having different crests and troughs in the daily load-curve as compared to normal days.

h) The above demand estimation covers only active power. It is also important that, the reactive power / Mvar requirements are forecasted right from substation level by each SLDC. The reactive power planning exercise and programme for installation of reactive compensation equipments should take care of these requirements also.

i) The monthly estimated demand by the SLDC shall be provided to RLDC and RPC for better operation planning.

j) The SLDC shall take into account the wind and other renewable energy forecasting to meet active and reactive power requirement.

k) In order to facilitate estimation of TTC/ATC on three month ahead basis, the SLDC shall furnish estimated demand and availability data to SRLDC before 5th of every month for the four months ahead and the current month (Total for five months).

l) As per 96th OCCM held on 11.06.14, MOM No 4.4.6.14, Node wise and block wise LGB data by states should commence within a period of three months, Till such time, the states may furnish upcoming 5 months LGB data which would be discussed in OCC for validation.

m) The Nodewise, block wise LGB data is to be submitted in PSSE format.

n) The infirm power shall not be considered for calculations of ATC

7.3 DEMAND CONTROL

7.3.1 As stated earlier, primarily the need for demand control would arise on account of the following conditions.

(i) Variations in demand from the estimated or forecasted values, which cannot be absorbed by the grid.

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

(iii) Heavy reactive power demand causing low voltages.

(iv) Sudden Variations in Wind Generation

(v) Commercial reasons.

7.3.2 As mentioned in section 5.3 of the IEGC, the SLDCs would regularly carryout the necessary exercises regarding short-term Mediumterm and long-term demand estimation for their respective states to enable them to plan in advance as to how they would meet their consumers load without overdrawing from the grid

4.

5.

6.

7.

7.1

7.2

7.3

7.3.1

7.3.2

7.3.3 The constituents shall endeavor to restrict their net drawal from grid to within their respective drawal schedules and operate close to their schedule and minimise inadvertent deviations as per the provision of IEGC and CERC orders on deviation settlement

7.3.4 All constituents would endeavor to maintain the system frequency above 49.9 Hz and would co-operate for helping in optimum utilization of regional hydro resources so that the availability during peak hour period is enhanced.

7.3.5 All constituents shall ensure the availability of the defense mechanism in place as listed at Chapter 11.

7.3.6 Demand control would have to be exercised under low operating frequency conditions (as indicated earlier by the SLDCs, by taking the actions like

Grouping of interruptible Loads in to the following four category as per provisions of IEGC clause No: 5.4.2 (e) for effecting automatic load disconnection during low frequency condition.

a. Loads for scheduled power cuts / Load shedding

b. Loads for unscheduled Load Shedding

c. Loads to be shed through Under Frequency Relay operation &df/dt

d. Loads to be shed under any System Protection Schemes

Shutting off or reconnecting bulk power (HT) consumers having a special tariff structure linked to number of interruptions in the day.

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.

All the necessary demand side management control measures including Manual Demand disconnection.

7.3.7 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 e