M. G. Raoot , P. Pentayya (WRLDC) and S. A. Khaparde (Indian Institute Technology Bombay)

Operational Experience In Managing Contingencies

at Western Regional Load Despatch Center (WRLDC), India

M. G. Raoot, P. Pentayya (WRLDC) and

S. A. Khaparde (Indian Institute Technology Bombay)

IEEE Power Engineering Society General Meeting, July 2009

Presentation Outline

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Western Region Grid Overview

Overview of EMS implementation at WR

Contingency Analysis Methodology

Contingency Management Methodology

Western Region Grid – A Case Study

Indian Power Control Centers

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Total installed capacity 147 GW(Source: CEA report

http://www.cea.nic.in/power_sec_reports/Executive_Summary/index_Executive_Summary.html)

NLDC - 1

RLDC - 5

SLDC - 31

ALDC - 100+

Hierarchy of Control Centers The Unified Load Despatch and Communication

(ULDC) scheme sets up the hierarchy of control centers in India

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11

55

3131>

100>

100

11,700 MW

2,650 MW5,850 MW

4,900 MW

1,200 MW3,700 MW

SOUTHERN REGION

WESTERNREGION

NORTHERN REGION

NORTH-EASTERN REGION

EASTERN REGION

Inter-regional Transfer Capacity present - 22800MW 37,000 MW by 2012

Installed Capacity 45987 MW

Max Demand Met 31608 MW

Max Energy Met 690 MU

Demand Shortage 20%

Energy Shortage 14 %

Gujarat

Madhya Pradesh

Maharashtra

GOA

Chhatisgarh

OVERALL POWER SCENARIO OF WESTERN REGION

WESTERN REGION-31.3.09

Look-up Tables Remedial Action module is not available Alternative is to use Look up tables Look up tables provide following information

What are the expected contingencies? What is the system behavior for each contingency? Corrective actions to be taken

What actions ? Which order ? (Ranking Criteria ?) Which agency ?

Look up tables are prepared after extensive offline studies on the system using PSS/E

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Co-ordination for Contingency Management: Via Look-up Tables Multiple agencies are involved in system operation

Common real-time system model is needed for all

Studies carried out by WR for all major contingencies

Internal threats (Trippings inside WR)

External threats (Trippings outside WR)

The study cases and results are made available for all agencies for verification

Workshops conducted to disseminate look up tables

Corrective actions are agreed upon by all agencies

Permissible load angles for extremes of corridors determined through stability studies

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Objective:To make Look-up Tables (Example below)

Contin-gency

System Behaviour

RankCorrective Action required to be taken

Agency to take action

400kV Itarsi-Indore ckt. I & II

• Voltage decay (collapse at Indore)

• Critical L/L on Itarsi-Khandwa corridor

1 Export to NR via HVDC Vindhyachal to be done

WRLDC

2 MP to reduce drawl at Indore/Nagda

MPSEB

3 GEB to reduce drawal GEB

4SSP/ISP generation if possible could be brought immediately

MPSEB, GEB, and WRLDC

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Ranking of Corrective Actions is based on 1) Sensitivity / Impact of the Corrective Action2) Risk assessment based on time taken for implementation and

no. of agencies involved in co-ordination loop


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Interfaces Between EMS Subsystems

GDC

IS

SCADA

HistoricalSubsystem

PNA

COPS

SDF/ WIF

Generator, Tieline, Frequency Measurements

Generator Controls

Actual Load

Generator Schedules,Load Schedule

Generator Penalty Factors,

Security-Constrained

Economic Basepoints

Interchange Scheduling Composites

Production/Fuel Cost, AGC Performance

Interchange Schedules

Interchange Transactions

Forecasted Load

Request for Security-

Constrained Dispatch

Weather Rainfall

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EMS (the journey so far…..)

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1

2

3

EMS (the journey so far…..)

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4

5

6

Salient Features of EMS in WR

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The entire Western regional grid has been modeled as per actual.

Uniform single model in RLDCs and SLDCs.

Model Verification and SE tuning

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SE working status

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SE working satisfactorily Tele-metered and estimated data with in permissible

limits Real-time network analysis (RTNA) study run at least

twice a day Day-off peak @ 1200 hrs Evening peak @ 1900 hrs

Converged RTNA made available for studies RTNA also run in case of

Contingency Outage clearance

Corrective measures taken for security enhancement

Advantages of EMS in grid operation

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Outages can be planned better

The Contingency Analysis (CA) module of EMS helps in

better emergency handling online. It would facilitate quicker

restoration.

The State Estimator (SE) output, properly tuned, gives

proper estimate of the grid measurands which can be used

during non-availability of communication channels and grid

operation is not affected.

The SCADA system also improves due to continuous

availability, comparison and improvement in EMS output

thereby improving the decision making process in real-time.


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Contingency Analysis (CA)

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Contingency Analysis (CA)

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• The CA can be run based on the following modes

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Contingency Analysis Execution Modes

Execution Status of Contingency Case

CS – Contingency Selection, CA - Contingency Analysis, RA – Remedial Action

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Composite Severity Index (SI) indicator

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Ranking of contingencies based on SI SI = Weighted Sum of percentage limit excursions

Voltage Violations Contingencies

compared based on voltage degradation profile

Corresponding ranks displayed

Branch Violations Contingencies

compared based on branch loading violations

Corresponding ranks displayed

Voltage CA Branch CA


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Contingency Evaluation

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WRLDC, Mumbai27





WRLDC, Mumbai28

• Due to Concentration of generation in the Eastern part of the grid and major load centers in the Western part of the grid, there is bulk active power transmission from Eastern to Western part over long distances primarily through three critical flow gates viz;

1. 400kV Chandrapur-Parli T/C2. 400kV Koradi-Bhusawal D/C3. 400kV Itarsi-Khandwa-Dhule D/C

Case Study:Contingency Management in WR Grid

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• On 25.05.2008, Western Regional grid was running in an

integrated manner and catering a demand of about 25000

MW at 1130 hours.

• The import was around 1200 MW from ER, 1400 MW from

NR, 750 MW was exported to SR

• Due to rains in NR and ER, the frequency profile was on the

higher side in the NEW grid

• Therefore economy exchanges were transacted with SR

(Power wheeled through WR) and consumed by WR due to

low UI rates

Base Case Scenario

Flow Gates Loaded Close to Limits

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It was found that around 15 lines are operating near theirfull capacity and angle limits with reduced margins.

Following contingencies were chosen for security assessment

400kV C’pur-Parli S/C outage

400kV C’pur-Parli D/C outage

400kV C’pur-Parli T/C outage

400kV Koradi-Bhusawal S/C outage

400kV Koradi-Bhusawal D/C outage

400kV Itarsi-Khandwa S/C outage

400kV Itarsi-Khandwa D/C outage

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33

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Contingency Analysis Results

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• The contingencies of Chandrapur-Parli D/C, Chandrapur-Parli T/C and Koradi-Bhusawal D/C outage are extreme and the programme did not converge because the grid may not be able to sustain these contingencies under the same power system conditions.

• As these contingencies are fatal, the composite severity index by voltage / branch / composite does not show any value. However, they are ranked at first in the order of severity of contingencies.


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• The contingency of Itarsi-Khandwa D/C outage has been found to be harmful by CA which entails system operators to take emergency measures for restoring back the normalcy.

• The composite severity index order by voltage comes to be 4150.8 whereas the composite severity index order by branch comes to 447526.5 which is ranked as the most severe contingency after the first three most severe contingencies as explained in the above paragraph.


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Similarly, other contingencies like Koradi-Bhusawal S/C outage, Chandrapur-Parli S/C outage and Itarsi-Khandwa S/C outage have been found harmful by CA which prompts operators to take emergency action.

They are also ranked subsequently based on composite severity index order by voltage and by branch violations

The corrective actions to be taken are as per the Look-up tables shown below (as we do not have Remedial Action – RA module)

Look-up Table for Koradi-Bhusawal SC Outage

Contin-gency

System Behaviour



400kV Koradi-Bhusawal-SC

• Critical line loading on ckt.II

• Large angular separation between Koradi & Bhusawal

• Low voltage at Bhusawal

1 Open Bhusawal-Aurangabad MSEB

2 Increase Koyna generation atleast by 500 MW

MSEB

3

Maximise power flow on C’pur-Padghe HVDC bipole may be upto 1900 MW (maximum overloading capacity)

MSEB

4 Increase export to SR WRLDC

5 Koradi/Chandrapur generation to be reduced

MSEB

6 Load shedding at Kalwa & Padghe area.

MSEB

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Look-up Table for Chandrapur – Parli SC Outage

Contin-gency

System Behaviour



400kV Chandrapur – Parli SC

• Critical Loading on surviving ckts

• Critical Loading on Koradi-Bhusawal corridor

• Large angular separation between Chandrapur and Parli lines

1 Maximise power flow on C’pur-Padghe HVDC bipole

MSEB

2 Export to SR to the max. extent WRLDC

3Koyna gen. to be picked up immediately and increased to the max.level above 1000 MW

MSEB

4 MSEB drawal to be reduced MSEB

5 MSEB to take up load shedding at Parli, Lonikhand, karad etc.

MSEB

6 C’pur generation to be reduced if frequency is more than 49 Hz

MSEB

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Conclusion

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• It is evident from the above case study that CA module of PNA extends valuable inputs to the system operators in evaluating the credible contingencies so that preventive action can be planned well in advance to ensure the security of the grid.

• It is therefore important that CA is regularly run during clearing of important shut downs in the critical flow gates of Western region and for evaluating the effect of N-1 contingencies during alert grid conditions etc.

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M. G. Raoot , P. Pentayya (WRLDC) and S. A. Khaparde (Indian Institute Technology Bombay)

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