the Power Grid

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Nov 15, 2013 (3 years and 8 months ago)

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RJT
WORKSHOP: The Past, Present and Future of
the Power
Grid

Cornell University

August 8, 2012

James Thorp



In

1976
-
77

a

few

years

after

Bob

came

to

Cornell

I

took

a

sabbatical

leave

at

AEP

in

NY
.

I

worked

on

a

digital

relaying

project

aimed

at

replacing

analog

relays

with

new

microprocessor

based

digital

relays
.


Thanks

to

Moore’s

law

it

turned

out

to

be

a

good

decision

on

my

part
.



Ed

Schweitzer

was

a

professor

at

Washington

State

who

formed

a

company

(SEL)
.

He

claims

to

have

sold

400
,
000

digital

relays
.

He

has

his

own

jet
.

Prof

Yang

at

NCEPU

formed

a

company

in

China

to

make

PMUs
.

He

is

a

billionaire
.


In

1983

we

published

a

paper

[
1
]

that

introduced

the

terms

PMU

and

Synchrophasor
.

Google

Scholar

has

33
,
620

total

citations

with

20
,
400

in

the

last

4

years
.

ISI

reports

the

majority

of

citations

to

PMUs

in

last

5

years
.

The

majority

of

citations

to

my

work

have

been

since

I

turned

70


The

DOE

Smart

Grid

Investment

Grant

(SGIG)

is

investing

in

~

850

PMUs

Phasor (
Steinmetz 1897)

Phaser (Star
Trek 1966)

2012

2007

1992

2002

1997

Citations by year


Synchrophasors

u
se

GPS

time

synchronized

sampling

to

get

phasors

on

a

common

reference
.

The

phase

angle

between

Maine

and

Florida

can

be

measured,

for

example
.


Used

for

monitoring



S
tate

estimation


Reconstruction

of

events



Bob

put

me

on

the

Data

A
dequacy

W
orking

G
roup

for

the

2003

blackout


San

Diego

Blackout

vs
.

2003


Control

WAMS

(wide

area

measurement

systems)


Almost

all

control

was

local



Load

frequency

an

exception


(frequency

is

universal)


Control

of

Inter
-
area

oscillations

is

popular

today


Protection


Reduce

relay

involvement

in

cascading

events


B
ack

up

projection

is

the

typical

culprit


(three

primary,

a

backup,

and

a

backup

to

the

backup)


In the digital substation it was obvious that all
sampling of voltages and currents should be
synchronous. Could share current samples between
transformer, bus, and line protection processors for
backup. A sampling pulse was distributed in the
substation.


It was also clear that there was an advantage to
sampling synchronously at the other end of the line.


Attempts at Ping
-
Pong to determine delays, use of
GOES satellite signals. None successful. GPS was the
answer.


Digital relaying depended on sampling voltages and
currents at a nominal rate of n times a 60Hz cycle



Introduction to phasors
-

Steinmetz

q

R
eal

Imaginary



The starting time defines the phase angle of the phasor
.



This is arbitrary
.



However, differences between phase angles are


independent of the starting time.

q

t=0

Samples



Motivation for synchronization

By synchronizing the sampling processes for

different signals
-

which may be hundreds of miles

apart, it is possible to put their phasors on the same

phasor diagram. Angle differences are correct

Substation A

Substation B

At different locations


“In

1893
,

Charles

Proteus

Steinmetz

presented

a

paper

on

simplified

mathematical

description

of

the

waveforms

of

alternating

electricity
.

Steinmetz

called

his

representation

a

phasor
.

With

the

invention

of

phasor

measurement

units

(PMU)

in

1988

by

Dr
.

Arun

G
.

Phadke

and

Dr
.

James

S
.

Thorp

at

Virginia

Tech,

Steinmetz’s

technique

of

phasor

calculation

evolved

into

the

calculation

of

real

time

phasor

measurements

that

are

synchronized

to

an

absolute

time

reference

provided

by

the

Global

Positioning

System
.

Early

prototypes

of

the

PMU

were

built

at

Virginia

Tech
,

and

Macrodyne

built

the

first

PMU

(model

1690
)

in

1992
.



It

is

argued

[
2
]

that

the

investment

in

improving

monitoring

of

the

high

voltage

transmission

network

represents

the

most

cost
-
effective

category

of

smart

grid

investment
.


Jim

McIntosh

Director

of

Grid

Operations,

CAISO

said

in

a

JASONS

Workshop

in

2010

in

La

Jolla

that

the

stimulus

PMUs

being

installed

in

California

would

save

California

from

$
200
M

to

$
300
M

a

year
.

Run

the

system

closer

to

limits


Most

vendors

of

control

center

software

allow

PMU

data

to

be

integrated

with

conventional

SCADA

data


From Wikipedia

[2] Paul
L
Joskow
,
Creating a Smarter US
Electricity
Grid
MIT
Center For Energy and
Environmental Policy
Research, Oct 2011




“PMUs

could

improve

the

performance

of

energy

management

systems

by

providing

real
-
time

data

to

determine

system

state

faster

and

m
ore

accurately

than

current

estimation

tools
.

A

more

extensive

deployment

of

PMUs

is

required

to

make

this

possible”
.



“Automatic

control

action

based

on

real
-
time

data

from

a

wide
-
area

network

of

PMUs

represents

a

major

change

in

system

operations
.

Today

such

system

are

limited

in

number

and

capability
.

Significant

research

in

control

algorithms

and

improved

confidence

in

the

reliability

and

accuracy

of

PMU

data

is

needed

to

make

such

control

more

prevalent
.


Presented

at

National

P
ress

C
lub
.

The

second

question

was

whether

the

federal

government

could

regulate

the

flow

of

electricity

since

there

was

no

electricity

when

the

constitution

was

written
.



Too

few

PMUs
.

“Transmission

101


[
4
]

estimates

there

are

15
,
700

transmission

substations

in

the

US
.

A

PNNL

study

[
5
]

has

48
,
000

nodes
.

That’s

Transmission

not

EHV

but

even

1
,
000

PMUs

is

probably

below

the

threshold


We

are

interested

in

state

estimation

and

control

with

measurements

of

less

than

2
%

of

the

states


Lack

of

confidence

in

the

reliability

and

accuracy

of

PMU

by

some

(reason

for

standards)

W
ould

you

write

a

paper

with

a

fix

for

a

1985

computer

problem?


Persistent

concerns

about

PMU

locations

and

latency
.



NIST, Virginia Tech, Georgia
Tech, and Texas A&M are
testing PMUs


DOE

Demonstration

Project
:

Dynamic

State

estimation

of

Dominion

Virginia

Power

500

kV

network

at

1
/
30

sec

interval
.

Linear,

t
hree

phase,

PMU

only

measurements

communicated

by

a

Sonnet

network

to

control

center

Provide

measurements

for

control

applications

with

latency

of

<

30
ms,

i
.
e
.

appropriate

for

bandwidths

of

5

or

6

Hz
.



Emphasis

on

renewable

energy

implies

more

energy

storage
.


Energy

storage

is

a

new

potential

control

means

added

to

the

power

electronic

arsenal

Linear since only PMU
measurements of
voltage and current

Time Aug 6, 2012

“Utilities now receive
updates on
transmission lines 30
times a sec instead of
every two seconds”



Arbiter Clock
SEL
421
-
4
/
5
SEL
421
-
4
/
5
SEL
421
-
4
/
5
...
...
SEL
487
E
Substation Critical Switch
SEL
3373
or
EPG ePDC
IRIG
-
B Coax
.
GPS
Antenna
to
SOC
60
messages
per second
IEEE C
37
.
118
Concentrated Data
:
Down
-
sampled to
30
messages per second
IEEE C
37
.
118
Juniper
Firewall
Cisco
Router
Monitoring Requirements
:
1
.
PMU shall provide
voltage

measurements for every
500
kV bus
element that can be isolated
.
2
.
PMU shall provide
current

measurements for all lines and
transformers connected at
500
kV
.
3
.
PMU shall stream synchrophasors
to SEL
-
3373
at the rate of
60
messages per second
.
4
.
For every current and voltage
,
the
following synchrophasors shall be
measured
:
i
.
A
-
phase
ii
.
B
-
phase
iii
.
C
-
phase
iv
.
Positive Sequence
(
calculated
)
5
.
Where dual primary line relays
exist
,
both relays shall provide
synchrophasors
.
6
.
Synchrophasor data shall be
archived locally within the SEL
-
3373
(
substation phasor data concentrator
)
7
.
Down
-
sampled synchrophasors
shall be streamed to central data
concentrator at rate of
30
messages
per second
.
Dual
-
Use Line Relays
Stand
-
Alone PMU
Substation PMU Deployment
Strategy

PDC phasor data concentrator


take data with the same
time
-
tag make one vector with one time tag

SEL Dual
-
Use Line Relay/PMU also give time tagged
breaker status


China

has

decreed

that

there

will

be

a

PMU

in

every

high

voltage

substation
.

Much

cheaper

than

retrofitting
.

They

now

have

~
2000


China’s

growth

rate

is

such

that

fixed

frequency

PSSs

are

unworkable


The

demand

has

a

doubling

time

of

~

7
.
5

years,

they

are

commissioning

a

1000
MW

plant

a

week
.


Frequency

of

modes

change

rapidly
.


They

designed

a

WAMS

Based

Wide
-
area

Coordinated

Modulation

Control

of

Multi
-
infeed

HVDC

assuming

they

knew

the

system
.

When

a

mode

is

observed

the

operator

inserts

the

system

which

does

a

real
-
time

Prony

to

determine

the

frequency

of

the

wave
.

Then

the

system

adjusts

parameters

in

the

controller

to

match

the

frequency

and

the

loop

is

closed
.

The

operator

removes

the

controller

after

the

mode

is

successfully

damped

[
18
]

YN

GZ

GX

GZ

Control
signals

control
server

PMU
signal

Control Unit


Increase the damping of inter
-
area oscillation
in CSG

0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
~ 10 cycles

Control Applied

Not

continuously

adaptive

control

but

a

control

that

is

engaged

by

an

operator

like

a

SIPs

system

and

observes

and

adjusts

before

acting
.

SIPs

as

we

know

them

do

not

change

parameters

before

engaging
.

Adaptive

SIPs?

(SIPS

system

integrity

protection

system)

From

observations

of

the

actual

event

the

system

selects

parameters

of

the

control

or

even

the

controller

structure

from

a

large

predetermined

list

and

then

engages
.

At

least

one

author

has

labeled

things

like

this

as

“enumeration

based

robust

control


Perhaps

“Synchrophasor

A
ided

G
ain

Scheduling”?

900

papers

in

gain

scheduling

in

power

systems

but

many

are

for

a

power

plant

and

none

mentions

WAMs




15


Create

a

large

data

base

of

situations

(~contingencies)
.


A
ugment

with

actual

archived

PMU

data
.


Use

Data

Mining

with

lots

of

options

to

find

out

what

works,

D
one

off
-
line

(cancer

researchers

are

succeeding

in

finding

DNA

markers

for

various

cancers

with

data

bases

of

millions

of

cases)


We

have

used

simulation

to

create

a

data

base

with

more

than

15
,
000

cases

for

a

4000
+bus

model
.
[
9
]

Hydro

Quebec

has

used

60
,
000

cases


Use

data

mining

to

select

the

scheduling

variables
.

Give

CART*

the

option

of

using

many

possible

scheduling

variables
.

CART

will

select

the

best
.

There

are

solvable

technical

issues

with

complex

measurements

in

CART



*
CART Classification
A
nd
R
egression Trees. There is also a
BART which is
Bayesian Additive Regression
Trees


16


University contributions in
adding PMUs to existing
estimators


Large number of papers in
Control


Improve PSSs with a few
remote PMU measurements


Robust control applied to
reduced order models with full
state feedback.

Software used to model large,
real system > 10,000 buses does
not (cannot) find eigenvalues or A
matrices.

How do you control something
with no model? MIT finding 2




Universities have made contributions in
finding locations for PMUs (there are
never enough so you must put the few
in the best places)


Best locations for:



observability (measure local voltage
and line currents
-
learn ~4 voltages
from 1 PMU


only need PMU at ~
1/3 of the buses)


Redundancy to loss of PMUs or line
opening or topology changes…


Phased installation
-
optimum per
year


Techniques


Topological


enumerating trees,


binary integer programming,


data mining

Unfortunately the utilities ignore these
results and use their own criteria ($)

Synchrophasor

Detectives


Just as new telescopes (Hubble) or new microscopes
(STEM) have shown us thing we did not predict, wide
area
-

time synchronized
-

measurements have produced
a few surprises.


The next two slides are from Mack Grady UT Austin (with
his permission) The title comes from his second slide

Load
-

Dallas
“Central
ERCOT”

Austin UT monitor
at Austin Energy
Harris substation

Wind Country

McDonald
Observatory

400 Miles

You must become a
synchrophasor detective


On

Feb
.

26
,

2008
,

a

short

circuit

in

a

Miami

electric

power

substation

and

an

operator's

error

gave

managers

of

the

nation's

electrical

grids

a

glimpse

of

an

uneasy

future
.

The

events

triggered

a

chain

reaction

of

power

plant

and

transmission

line

outages

in

the

state,

unleashing

sharp

swings

in

voltages

and

power

frequency

that

blacked

out

power

for

nearly

1

million

customers

in

southern

and

central

Florida

for

up

to

four

hours
.



A

video

depicting

the

Florida

incident's

rippling

spread

has

been

created

by

Virginia

Polytechnic

Institute

and

State

University's

electrical

and

computer

engineering

department,

which

caught

the

disturbance

on

its

first
-
generation

grid

frequency

monitoring

network
.

Some

grid

executives

have

downloaded

the

video

on

their

laptops

as

a

kind

of

horror

flick

for

engineers

of

what

could

happen
.




What terminal?

What measurements?



Determination of triggering logic

Performance evaluation

System State
Assessment

PMU data

PMU data

Critical System
Locations

Supervisory
signals

Adjustment of Dependability
-
Security balance under
stressed system conditions.

Relay 1

Relay 2

Relay 3

OR

VOTE

AND

Supervisory
signal

See detail
below


Adjusting balance of
security
-
dependability

One of the five DOE Demonstration projects

JST

Pacific Gas & Electric


Southern California Edison

Three parallel 500Kv lines
between Midway and Vincent
path 25

2 out of 3
is voting

Voting Scheme



Adaptive Voting Scheme with three relays.


State of the System


Stressed

Security = Vote


Safe Dependability = Don’t Vote






We are NOT changing relay settings neither during,
before or after a fault.



25

Adaptive

Voting

Scheme

JST

Data Mining: CART*

Proposed Decision Tree:


Nodes = 7.


Probability of correctly distinguishing 1 and a 0: 0.99%.



Splitting Nodes


PMU placement



Terminal Nodes Vote Decision

26

*Classification And Regression Trees

JST

Utility demand for .9999.

We studied 15000 rare events, half of which would have
caused a major disturbance. By voting we reduced the
number of major disturbances from ~7,500 to 75

PMU Placement:

27

Line Current

TESLA

LOSBANOS

LOSBANOS

MIDWAY

N.GILA

IMPRLVLY

TRACY

TESLA

LUGO

VINCENT

METCALF

MOSSLAND

LUGO

MOHAVE

MALIN

ROUND MT

PMU

ROUND MT

TESLA

VINCENT

LUGO

IMPLVLY

JST

Decision Trees
-
Location of PMUs and logic for

PMU
inputs to real
-
time, discrete
-
event control
[5]

Predicting cascading
events
[6]

voltage
security
[7
-
8]

transient stability [9
-
10]

detection
of islanding
[11]

processing
post disturbance records
[12]

security assessment [13
-
14]


adaptive
security dependability of
relays [14]

Proposed

NASPI’s Planning and Implementation Task Team (PITT) has made base
lining
of phase angle differences their highest priority
.

Set angle thresholds and operator alerts

Estimation of line flows and voltages after an outage

Correlate PMU data with GIC monitoring

VAR issues

return to Pilot Points with PMUs and CART

Equipment monitoring and asset management

At 60 times a second can monitor I
2
t in transformers due to faults


There

is

a

more

limited

history

of

data

mining

of

archived

PMU

data
.

Fifteen

months

of

PMU

data

of

54

angle

differences

has

also

been

subjected

to

statistical

analysis

to

detect

abnormal

power

system

behavior

using

software

developed

for

NASA

by

PNNL

[
15
-
17
]
.


[
16
]

presents

results

using

state

e
stimator

data

sampled

every

few

minutes
.

Part

of

[
16
]

is

to

identify

data

as

atypical

[
17
]

rather

than

typical
.


Plans

to

expand

this

by

WECC

using

OSIsoft
.

They

will

ultimately

archive

150
,
000

measurements

per

second


More PMUs


All high voltage buses>100kV
~50,000 substations


Operator alarms and
alerts


Oscillation


Angles


Voltages


More adaptive relays


Possibly universal


Coordinated SIPs


WECC has >100. One went
wrong in San Diego blackout


Control


Inter
-
area oscillations


Out of step


SIPs System Integrity Protection
Schemes

Remedial Action Schemes

Special Protection Schemes

Control actuated by protection: If one
of two parallel lines trips shed load
and reduce generation

Given

we

are

likely

to

have

to

make

due

with

the

existing

wires

and

towers

as

AC

transmission

lines

for

decades,

PMU

technology,

advances

in

computing,

and

c
ommunications

offer

the

best

hope

for

a

Smart

Transmission

Grid
.


Returning

to

the

MIT

Findings


PMUs

could

improve

the

performance

of

energy

management

systems

by

providing

real
-
time

data

to

determine

system

state

faster

and

more

accurately

than

current

estimation

tools
.


Automatic

control

action

based

on

real
-
time

data

from

a

wide
-
area

network

of

PMUs

represents

a

major

change

in

system

operations
.

Significant

research

in

control

algorithms

and

improved

confidence

in

the

reliability

and

accuracy

of

PMU

data

is

needed

to

make

such

control

more

prevalent
.


Terry

Boston,

President

and

CEO

of

PJM

is

reported

to

have

said

”running

the

nation’s

power

grid

isn’t

rocket

science
-

it’s

harder”



Thank You

[
1
]

A
.
G
.

Phadke,

J
.

S
.

Thorp

and

M
.

G
.

Adamiak,

"A

New

Measurement

Technique

for

Tracking

Voltage

Phasors,

Local

System

Frequency

and

Rate

of

Change

of

Frequency,"

IEEE

Trans

on

PAS
,

PAS

102
,

vol
.

5
,

1025
-
1038
,

May

1983
.


[
2
]

The

Future

of

the

Electric

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