Security- Constrained Economic Dispatch

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SECURITY CONSTRAINED
ECONOMIC DISPATCH
(SCED)
Tanzim Mokammel
Sarmad Zulfiqar
Mellitus Ezeme

Overview
•Efficiently model a security
constrained economic dispatch
problem
•Analyze Optimal point to dispatch power
without violating limits
•Demonstrate contingency ranking using
performance index
•Suggest best approach to operate
the power system

Introduction
•In North America (NA) and Europe
(EU), power systems are subject to
near limit operation due to:
•Cheaper generation in distant locations
•Easy transportation of power
•Leads to the necessity of analyzing
varying operating conditions under
multiple contingency scenarios to
ensure
•No sudden cascaded failures resulting
from overloading
•Failure from equipment malfunction or
natural disasters

Introduction (Cont’d)
•Operators always focus on
dispatching on highest profit
margin
•Efficient operation while
maintaining system security
becomes a vital need

Agenda
1. Treating Economic Dispatch
2. Security Analysis
3. Security Assessment
4. Contingency Analysis
5. Case Study

1. Economic Dispatch
•Determine quantity of
power to dispatch by
each generator to meet
demand at minimum cost
•Usually neglects line and
generator constraints, but
SCED requires it

2. Security Analysis
•Monitoring
•Use real time system measurements
to determine the operating conditions
of the system
•Check if normal, otherwise command
control to take action
•Assessment
•Check if the system is secure from
probable contingencies
•Control
•Take action to revert system to
normal operating conditions

3. Security Assessment
•Check robustness of system subject to
perturbations with the following methods:
•Direct Approach
•Use the probability of the system, given current
state and load projections
•Depends on a unit to fail to determine if the
entire system is at risk
•Indirect Approach
•Ensure there are enough reserve margins to
cope with emergencies
•Captures more constraints, increases cost
•Decision to use either method depends
on performance index
•Integrated approach is used in the case
study

4. Contingency Analysis
•A way of analyzing the power
system to determine overload and
other problems resulting from
contingencies:
•Line Outage
•Results in overloading remaining
lines
•Power flow readjustment needed
•Generator failure
•Sudden load increases

4. Contingency Analysis (Cont’d)
•Main Tradeoff:
•Increased security requires
increased costs
•Solution
•Identify lines which require
preventive action, and lines that
require post-contingency action
•Goal
•Maintain integrity of the system and
ensure no damage to transmission
equipment

5. Case Study
•IEEE Standard 5-Bus System
•Given system topology, load conditions, and ratings of
transmission and generation units:
•Determine optimal operating conditions under base case (ignore TL
limits)
•Determine line flow of each line using DC flow equation: Plines =
BΔΘ
•Check for line flow violations; if found, re-run optimal dispatch with
new limits
•Determine PI by removing one line at a time
•Rank contingency based on PI

5. Case Study (Cont’d)
1 2 3 4 5 6
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
Line Violaons under Outages
Line Limits
Line 2 Outaged
Line 4 Outaged
Line 6 Outaged
Lines
Power Flow (pu)

5. Case Study (Cont’d)
2 4 6
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
8.00
9.00
10.00
9.2532
2.4352
0.9836
Performance Index of Outaged Lines
Performance Index
Lines
Performance Index

5. Case Study (Cont’d)
1 2 3 4 5 6
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
Security Constrained Economic Dispatch
Base ($460/hr)
Preven've using Line 2 Condi'ons
($540/hr)
Line Limits
Lines
Power Flow (pu)

5. Case Study (Cont’d)
1234567
420
440
460
480
500
520
540
560
Cost Comparison
Line Dispatch at Op'mal Condi'ons w/o Line
Constraints
Line Dispatch at Op'mal Condi'ons w/ Line
Constraints
Lines
Cost ($)

Conclusion
•Efficiently modeled a SCED problem
•Suggestion
•Preventive vs Post-Contingency
•Run system in preventive conditions with increased cost to avoid
unquantifiable damages
•Reputation
•Death
•Ripple Effects

Q&A

Backup

5. Case Study (Cont’d)
Line Dispatch at Opmal Condions w/o Line Constraints
LOT
Lines Base 1 2 3 4 5 6
10.0839 0.0000 0.6000 0.0000 -0.0400 0.1200 -0.0250
2-0.5161 -0.6000 0.0000 -0.6000 -0.6400 -0.4800 -0.6250
30.0839 0.0000 0.6000 0.0000 -0.0400 0.1200 -0.0250
40.3097 0.2857 0.4571 0.2857 0.0000 0.4000 0.3750
50.0903 0.1143 -0.0571 0.1143 0.4000 0.0000 0.0250
6-0.1742 -0.1143 -0.5429 -0.1143 -0.3600 -0.1200 0.0000
Cost 460.0000 460.0000 460.0000 460.0000 460.0000 460.0000 460.0000
Line Dispatch at Opmal Condions w/ Line Constraints
LOT
Lines Base 1 2 3 4 5 6
1 0.6000 0.2000 0.0000
2 0.0000 -0.4000 -0.6000
3 0.2000 -0.2000 -0.0333
4 0.3200 0.0000 0.3667
5 0.0800 0.4000 0.0333
6 -0.2000 -0.2000 0.0000
Cost 460.0000 460.0000 540.0000 460.0000 520.0000 460.0000 465.0000