Smart Grid Application of
Optimal Transmission Switching
By,
Kory W. Hedman, et al.*
University of California, Berkeley
INFORMS Annual Meeting
Washington, DC October 15, 2008
*Dr. Richard P. O’Neill (Chief Economic Advisor, FERC), Emily B. Fisher
(Ph.D. Student, Johns Hopkins University), and Dr. Shmuel S. Oren
(Professor, UC Berkeley)
Motivation
  Co-optimize
transmission topology and
generation dispatch
  Efficiency
improvements with no reliability
degradation
  Smart
grid application by flexible
reconfiguration
  Proof
of concept: ISONE 5000, IEEE 118,
and IEEE 73 (RTS 96) bus model
2
Overview
  Introduction
  Optimal
transmission switching and
transmission planning
  Transmission switching DCOPF and N-1
DCOPF formulations
  Results
  Practical implications – revenue adequacy
  Current and future work
  Conclusions
  References
3
Introduction
  Control
of transmission assets not fully
utilized today
Transmission assets are seen as static in the short
term
  Currently operators change transmission assets’
states on ad-hoc basis


Personal communication with Andy Ott, VP, PJM
  Network
redundancies
Required for reliability but not required for every
market realization
  Redundancies may cause dispatch inefficiency
4

Introduction continued
  Smart
grid application of co-optimizing
transmission and generation

With appropriate switching technology, backup
transmission can be kept offline (just in time
transmission)


DCOPF Optimal Transmission Switching Model
If not, enforce N-1 standards with transmission
switching

N-1 DCOPF Optimal Transmission Switching Model
  FERC
order 890 calls for economic
transmission - makes transmission switching
relevant
5
Introduction continued
  Electric
Transmission Network Flow Problem
  Optimal
Power Flow (OPF)
  Alternating
(ACOPF)

Current Optimal Power Flow
With contingency constraints: N-1 ACOPF
  Direct
Current Optimal Power Flow (DCOPF)
Linear Approximation of the ACOPF
  With contingency constraints: N-1 DCOPF

6
Introduction continued
  Example:
7
Optimal Transmission Switching and
Transmission Planning
  Transmission
planning
Long run problem
  A line need not be beneficial for every hour
  A line may not be necessary to meet reliability
standards for every hour
  Long investment cycle leaves room for efficiency
improvements by topology reconfiguration

  Optimal
transmission switching
Short run problem
  Does not necessarily indicate inefficient
transmission planning

8
Traditional DCOPF Formulation
  Minimize:
Total generation cost
Constraints:
  Bus angle constraints
  Generator min & max operating constraints
  Node balance constraints
  Line flow constraints
  Line min/max thermal constraints
  No generation unit commitment
  We do not use PTDFs rather:

9
Optimal Transmission Switching
DCOPF Formulation
  Zk:

Binary variable
State of transmission line (0 open, 1 closed)
  Update
line min/max thermal constraints:

Original:

New:
  Update
line flow constraints:

Original:

New:
10
Optimal Transmission Switching
DCOPF Formulation continued
11
Results – DCOPF
  IEEE

118 bus model
25% savings found by Fisher et al.
  ISONE
5000 bus model (includes NEPOOL,
NYISO, NB, NS – costs for NEPOOL only)

5% to 13% savings of $600,000 total cost
for NEPOOL for one hour (feasible solutions)
  Does
not include reliability constraints
12
Optimal Transmission Switching N-1
DCOPF Formulation
  N-1

standards:
Demand must be satisfied even if any single
element (transmission line or generator) is lost
due to a contingency
  Optimal
transmission switching N-1 DCOPF
formulation
Repeat OPF constraints for each contingency
  Create binary parameters representing the
state of each element in the system
  Optimal topology and generation dispatch
solution must satisfy steady-state constraints
and all N-1 contingency constraints

13
Results – N-1 DCOPF
  Savings
while including reliability
constraints
  IEEE

Up to 16% savings with N-1 DCOPF
transmission switching (feasible solutions)
  IEEE

118 Bus Model
73 (RTS 96) Bus Model
Up to 8% savings with N-1 DCOPF
transmission switching (feasible solutions)
14
Practical Implications – Revenue
Adequacy
  Revenue
adequacy not guaranteed with
transmission switching
  Social
welfare will not decrease
  There
may be wealth transfer issues due
to Financial Transmission Right (FTR)
settlements
15
Current Optimal Transmission
Switching Research
  Generation unit commitment
  Speed up B&B by introducing valid inequalities
that exploit the problem structure
  Explore heuristic techniques, separation
techniques, etc.
  Benders’
decomposition
Analyze various sub-problem formats
  Research local branching approach

16
Future Optimal Transmission
Switching Research
  ACOPF
  MINLP very difficult
  Research heuristic techniques
  Revenue
adequacy & FTR settlement
Can revenue adequacy be maintained with
transmission switching?
  Do we need a compensation scheme to offset
the impact on FTR settlements?

17
Conclusions
  DCOPF
for ISONE networks ranged from
5% to 13% savings (without N-1)
  N-1 DCOPF for IEEE 118 & RST 96 system
showed savings from 1% to 16%
  Substantial results for off-peak and peak
  Increases social welfare
  Transmission switching can be beneficial
even with well planned networks and adds
another level of control
18
References
[1] E. B. Fisher, R. P. O’Neill, and M. C. Ferris,
“Optimal transmission switching,” IEEE Trans.
Power Syst., vol. 23, no. 3, pp. 1346-1355, Aug.
2008.
[2] K. W. Hedman, R. P. O’Neill, E. B. Fisher, and S.
S. Oren, “Optimal transmission switching –
sensitivity analysis and extensions,” IEEE Trans.
Power Syst., vol. 23, no. 3, pp. 1469-1479, Aug.
2008.
[3] K. W. Hedman, R. P. O’Neill, E. B. Fisher, and S.
S. Oren, “Optimal transmission switching with
contingency analysis,” IEEE Trans. Power Syst., to
be published.
19
References continued
[4] K. W. Hedman, R. P. O’Neill, and S. S. Oren,
“Analyzing valid inequalities of the generation unit
commitment problem,” PSCE 2009, to be published.
[5] K. W. Hedman, R. P. O’Neill, E. B. Fisher, and S.
S. Oren, “Optimal transmission switching applied to
ISO networks,” working paper.
[6] K. W. Hedman, M. C. Ferris, R. P. O’Neill, E. B.
Fisher, and S. S. Oren, “Optimal multi-period
generation unit commitment and transmission
switching with N-1 reliability,” working paper.
[7] K. W. Hedman, R. P. O’Neill, and S. S. Oren,
“Optimal transmission switching using Benders’
20
decomposition,” working paper.