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

 Western Region Grid Overview

 Overview of EMS implementation at WR

 Contingency Analysis Methodology

 Contingency Management Methodology

 Western Region Grid – A Case Study

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Indian Power Control Centers

NLDC - 1
Total installed capacity 147 GW RLDC - 5
(Source: CEA report
http://www.cea.nic.in/power_sec_reports/Executiv SLDC - 31
e_Summary/index_Executive_Summary.html)
ALDC - 100+

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Hierarchy of Control Centers
 The Unified Load Despatch and Communication
(ULDC) scheme sets up the hierarchy of control
centers in India
1

5
31
>
100

4
 Inter-regional Transfer
Capacity present - 22800MW
37,000 MW by 2012
NORTHERN
REGION

4,900 MW 11,700 MW
NORTH-
EASTERN
REGION

5,850 MW
WESTERN 2,650 MW
REGION EASTERN
REGION

1,200 MW
3,700 MW

SOUTHERN
REGION
OVERALL POWER SCENARIO OF WESTERN REGION

Madhya
Pradesh

Gujarat Installed Capacity 45987 MW

Max Demand Met 31608 MWChhatisgarh

Max Energy Met 690 MU

Maharashtra Demand Shortage 20%

Energy Shortage 14 %

GOA
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)

Corrective Agency
Contin- System
Rank Action required to take
gency Behaviour
to be taken action
400kV Itarsi- Voltage decay Export to NR via HVDC
1
•
WRLDC
Indore ckt. I (collapse at Vindhyachal to be done
& II Indore)
MP to reduce drawl at
2 Indore/Nagda
MPSEB
• Critical L/L on
Itarsi-Khandwa 3 GEB to reduce drawal GEB
corridor
SSP/ISP generation if MPSEB,
4 possible could be GEB, and
brought immediately WRLDC

 Ranking of Corrective Actions is based on

1) Sensitivity / Impact of the Corrective Action
2) Risk assessment based on time taken for implementation and
no. of agencies involved in co-ordination loop

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Presentation Outline

 Western Region Grid Overview

 Overview of EMS implementation at WR

 Contingency Analysis Methodology

 Contingency Management Methodology

 Western Region Grid – A Case Study

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 Interfaces Between EMS Weather Rainfall

Subsystems
Generator, Tieline,
Frequency Measurements
Actual Load
SCADA GDC SDF/ WIF
Generator Controls

Production/Fuel Cost, AGC Performance Generator

Interchange Request for Penalty Factors,
Scheduling Security- Security-
Composites Constrained Constrained
Dispatch Economic
Basepoints

Historical
IS PNA
Subsystem Interchange
Schedules

Interchange
Transactions

Generator Schedules,
Load Schedule

COPS Forecasted Load

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EMS (the journey so far…..)

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EMS (the journey so far…..)

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Salient Features of EMS in WR

 The entire Western regional grid has been modeled as

per actual.
 Uniform single model in RLDCs and SLDCs.

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Model Verification and SE tuning

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SE working status
 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

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Advantages of EMS in grid operation
 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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Presentation Outline

 Western Region Grid Overview

 Overview of EMS implementation at WR

 Contingency Analysis Methodology

 Contingency Management Methodology

 Western Region Grid – A Case Study

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Contingency Analysis (CA)

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Contingency Analysis (CA)
• The CA can be run based on the following modes 

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Contingency Analysis Execution Modes

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Execution Status of Contingency Case

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

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Composite Severity Index (SI) indicator
 Ranking of contingencies based on SI
 SI = Weighted Sum of percentage limit excursions

Voltage CA Branch CA
 Voltage Violations  Branch Violations
 Contingencies  Contingencies
compared based compared based on
on voltage branch loading
degradation profile violations
 Corresponding  Corresponding
ranks displayed ranks displayed

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Presentation Outline

 Western Region Grid Overview

 Overview of EMS implementation at WR

 Contingency Analysis Methodology

 Contingency Management Methodology

 Western Region Grid – A Case Study

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Contingency Evaluation

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Presentation Outline

 Western Region Grid Overview

 Overview of EMS implementation at WR

 Contingency Management Methodology

 Western Region Grid – A Case Study

27 WRLDC, Mumbai
Case Study:
Contingency Management in WR Grid
• 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/C

2. 400kV Koradi-Bhusawal D/C
3. 400kV Itarsi-Khandwa-Dhule D/C

28 WRLDC, Mumbai
Base Case Scenario
• 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

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Flow Gates Loaded Close to Limits

It was found that around 15 lines are operating near their

full capacity and angle limits with reduced margins.

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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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Contingency Analysis Results
• 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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Contingency Analysis Results
• 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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Contingency Analysis Results
 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)

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Look-up Table for Koradi-Bhusawal SC Outage

Agency
Contin- System Corrective Action to
Rank
gency Behaviour required to be taken take
action
400kV • Critical line 1 Open Bhusawal-Aurangabad MSEB
Koradi- loading on
Bhusawal- ckt.II Increase Koyna generation
2 atleast by 500 MW
MSEB
SC • Large
angular Maximise power flow on
separation C’pur-Padghe HVDC bipole
between 3 may be upto 1900 MW MSEB
Koradi & (maximum overloading
Bhusawal capacity)
• Low voltage
4 Increase export to SR WRLDC
at Bhusawal
Koradi/Chandrapur
5 generation to be reduced
MSEB

Load shedding at Kalwa &

6 Padghe area.
MSEB
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Look-up Table for Chandrapur – Parli SC Outage

Agency
Contin- System Corrective Action to
Rank
gency Behaviour required to be taken take
action
400kV • Critical Maximise power flow on C’pur-
Chandrapur Loading on 1 Padghe HVDC bipole
MSEB
– Parli SC surviving ckts
2 Export to SR to the max. extent WRLDC
• Critical
Loading on Koyna gen. to be picked up
Koradi- 3 immediately and increased to MSEB
Bhusawal the max.level above 1000 MW
corridor
4 MSEB drawal to be reduced MSEB
• Large angular
MSEB to take up load shedding
separation 5 at Parli, Lonikhand, karad etc.
MSEB
between
Chandrapur C’pur generation to be reduced
and Parli lines 6 if frequency is more than 49 Hz
MSEB

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Conclusion
• 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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