PSERC

PSerc Summer WorkshopLake Tahoe, CAAugust 4, 2008

Smart GridPanel Presentation

Robert J. ThomasCornell University

PSERCSmart Grid Values

(Why are we doing this?)

Some reasons

• A more reliable grid - power where and when users need it with a quality they value

• A more secure grid - able to withstand natural and manmade attacks w/o blacking out or exorbitant recovery costs

• A more economic grid - a grid that supports fair market design that results in fairprices and adequate supply

• A more efficient grid - promotes investment, reduces electrical losses, promotesefficient power production and power usage, and improved asset utilization

• An environmentally friendly grid - reduced environmental impact thoroughimproved and/or adoption of new generation, transmission, distribution, storage, and consumption

PSERC

Smart Grid Characteristics

• Enable active participation by consumers by giving consumersnew information, control, and by giving operators willing consumersas a resource.

•Accommodate all generation and storage options by seamlesslyintegrating all option types and sizes through “plug and play”

• Enable new products, services and markets by linking buyersand sellers and supporting new electricity markets from home energymanagement to market operations across regions

• Provide power quality for the digital economy at various levelsand at different pricing

• Optimize asset utilization and operate efficiently to deliver thedesired functionality at minimum cost

• Anticipate and respond to system disturbances by continuousmonitoring, self-assessment, and automatic reconfiguration formaximum resiliency in the fact of uncertain disturbances either naturalor manmade

PSERC

The Underlying Enablermonitoring and communication

Currently the communication system is SCADA with little or no two-way communication with consumers possible

PSERC• Basic elements are sensors which

measure the desired quantities• Current Transformers CTs –

measure currents and PotentialTransformers PTs- measurevoltages.

• Today there is a whole new breed ofIntelligent electronic devices (IEDs)

• These data are fed to a remoteterminal unit (RTU)

• The master computer or unit residesat the control center EMS

SCADA - Architecture

PSERCControl Communication Architecture

From a presentation by D. Whitehead, “Communication and Control in Power Systems”, tcip summer school, June, 2008

PSERC

A large amount of serial communication • EIA-232, EIA-422/485

Media Type • Copper and Fiber Optics

Various Data Rates •As slow as 300 bits/sec and as fast as 115k bits/sec

Legacy Intra Substations Communications

Ethernet Media Type

•Copper and Fiber Optics Various Data Rates

•10/100 MB, 1GB

Modern Intra Substations Communications

8

Vision: End-to-End Trust Provisioning for PowerGrid Monitoring and Control

SubstationLevel

ControlCenterLevel

Sensor/Actuator Level

ISO

Private IP-BasedNetwork(Secure, Real-time,Monitored)

Private IP-BasedNetwork(Secure, Real-time,Monitored)

Data “Smart” Gateway/Hub

Ethernet / IP-Network(Secure, Real-time,Monitored)

IED IED IED

Local HMI

IED

DFR

IED IED IED

“Smart” Gateway/Hub

Ethernet / IP-Network(Secure, Real-time,Monitored)

Private IP-BasedNetwork(Secure, Real-time,Monitored)

BackupEthernet / IP-Network(Secure, Real-time, Monitored)

NetworkLevel

Metering andLoad Control

CoordinatorLevel

From a presentation by Klara Nahrstedt, “TCIP Trusted Networked Cyber-Infrastructure”, June, 2008

PSERCSmart Grid

PSERC

Markets, reliability and the smart grid

What can markets do with a ubiquitous communication system?

PSERC

• Used by both purchasing and selling entities, including utility generation, toarrange for interchange transactions by buying and/or selling energy and capacityand recording the transaction by transmitting the information required in theInterchange Transaction Request template (generally referred to as the “tag”) tothe appropriate control areas• Control areas assess and “approve” or “deny” interchange transactions based onreliability criteria and adequacy of interconnected operations services andtransmission services• The TIS supports scheduling of interchange at multiple time standards and tracksindividual interchange schedules so that during a ramp the actual ramped MWlevel of the schedule is known•Transaction modifications - Purchasing-selling entities that reallocate (aggregateor split) an interchange transaction submit new interchange transaction(s) todisplace modified transaction(s). If modified while in progress, the transaction isterminated and a new transaction entered for the remainder of the transactionperiod

Transaction Management –Transaction Information System (TIS)Non-SCADA information

PSERC

One problem

• The data from the TIS is used by the ISO’s to “clear the market (I.e.,determine generation dispatch and the prices generators will be paidand the amount loads will pay). A DC OPF with proxy limits is usuallyused with a sequential AC power flow analysis checking scheme toensure reliably operation.

• Some of the dispatches that result from a linearized (DC) OPF mightnot be feasible due to violation of constraints that were not considered

• No science-based method to choose the best set of proxy limits• The choice of proxy limits can result in a large deviation from the

solution obtained from an AC OPF - especially the price part of thesolution.

PSERC

Example: Voltage Stability

P,Q

V<θ

P

VNote that V and P are related. Placing a limit on V automatically places a limit on P

In this simple case, P is an exact proxyfor V

P

PSERC

An example of limits and pricing

Case 1:Cutset flow limit

Case 2:Cutset flow limit

$50$10

Case 4:Voltage+ Q limit

Case 3:Individualflow limit

1

2

3

4

Example from Alvarado “Converting System Limits to Market Signals” IEEE PES, May 2003 w/ mods by Thomas

Line reactance's areall 0.1pu

200MW

Voltageproblem

PSERC

Some Proxy Limit Options

1) Declare bus 4 to be a load pocket and limit the imports into bus 4 bylimiting the total flow across the 2/4 and 3/4 interface;

2) Limit the imports into bus 4 by controlling the flows across the 1/2 and1/3 interface;

3) Limit the imports into bus 4 by limiting any one line, such as limitingthe flow on line 1 (from 1 to 2);

4) Directly impose a limit on the voltage at bus 4 along with a limit on thereactive power that can be supplied by bus 4.

PSERC

Locational Prices and Dispatch

50202010Case4

50307010Case3

50505010Case2

50101010Case1

4321

LMP’s for each case Dispatch for each case

**Case4

50150Case3

50150Case2

50150Case1

41

Note: The dispatch remains the same but what a load pays (in this example) is vastly different depending on what limit is chosen.

PSERCPhasor Measurementsand

Locational Marginal Pricing

!

min p,"

C(p)

st p - pd - f(") = 0

"n = 0

!

pd i

!

Vip "

i

!

pi

!

f (")

PSERC

!

But

L(p,") = C(p) +#T (p $ pd $ f ("))+ #0"n

and

%L

%p=%C

%p+ #T = 0

!

We know that the LMP at bus i is given by :

"i =#C(p(pd ))

#pdi

(the system cost to deliver one more MW

to bus i)

So, knowing v and theta means we know p and if we know C we can compute LMP directly for the current operating point