Copyright © SEL 2004

Protection for Abnormal System Conditions

Presented at: Clemson Power Systems Conference 2005

March 10, 2005

E. O. Schweitzer

Schweitzer Engineering Laboratories, Inc.

Overview

Voltage stability

Angle stability

Wide-area measurement

Line overload protection

Communications security

August 14, 2003

Power System Challenges

Load-generation separation

Environmental restrictions (NIMBY)

Limited network growth

Network resource optimization

Separate companies for G,T,D

-> Voltage collapse, angle instability

Voltage (Load) Stability

0 .5 10

0 .5

1

P (p u )

V (

pu)

OperatingPoint

BifurcationPoint

Margin

Slow Fault Clearing TimeInitiates Voltage Collapse

Zone2

Zone2

Zone2

51

51

R estof PowerSystem

Reverse Zone 3 Element Operated During Low Voltage Conditions

X

R

Overload

Be Careful with Zone 3!

Avoid them

Use bus protection

Breaker failure protection

Line Thermal Protection

Zone 3 is NOT Overload Protection!

Block its response to load with Load Encroachment Elements

prevent false tripping under heavy load by

blocking phasedistance elements in defined load areas

We Invented Load-Encroachment Elements to…

R

X

Model to Study Voltage Stability(Kundur, Power System Stability and Control)

11

1

10

O pen

O pen

5

2

376

8

9

Z=C onstant

P=1692 M WQ =485 M VAR

P=207 M WQ =58 M VAR

Z=C onstant

I=C onstant

P=3844 M WQ =1194 M VAR

V < 95% at Buses 8 and 9 arefor Loss of Two Lines

Definite-time elements would trip loads at both buses.

0 5 10 15 20 25 30

Vol

tage

(pu

)

Seconds

0.8

0.9

1

0.95Bus 8

Bus 9

Threshold

Inverse-Time Undervoltage Elements Shed Low-Voltage Loads First

0.2 0.4 0.6 0.8

Voltage (pu)

Sec

onds

0

5

10

15

Bus 8 Voltage recovers afterInverse Element drops Bus 9 load…

without communications!

0 5 10 15 20 25 30

Vol

tage

(pu

)

Seconds0.8

0.9

1

1.1Bus 8

Bus 9

Tap Changers and Voltage Collapse

As unregulated voltage goes down, tap changers raise regulated side.

Reactive power demand increases.

Unregulated voltage goes down some more. Tap changer reaches limit.

Unregulated voltage goes further down.

Better: return tap changers to neutral and block them when unreg voltage is low.

Voltage Phasors DetermineSystem Power Flow

BAL

BA sinX

EEP

XL

A B

AAE BBE

BBAAL

B EcosEX

EQ

P ,Q

Real Power Transfer Depends on

Accelerating PowerChanges Machine Kinetic Energy

Swing Equation

dt

dWPPP kinetic

ema

2

2

a dt

dJP

TurbineG enerator

T m

T e

J t Jg

P m P e

System Swing

V S V R

G H

Event Capture From Aug. 14, 2003

Out-of-Step Detection LogicAvoids Zone 1 Tripping

Transmission Line TrippingDuring System Oscillation in Idaho

Thermal Overload Protection

Program a Thermal Model in SEL-421

Use Multiple Alarm and Trip Set Points

Add Logic Conditions to Customize Application

Initiate Actions Based on Alarm Stage

Yes

Yes

N o

Trip line if TH E = 1

S et A LA R M = 1

A ssess h ighest phasecurrent IL

C om pute tem pera ture increm ent D TC

TC (new) = TC (o ld) + D TC

TC > TH L

TC > TLL

E nd

N o

SEL-3010 Event MessengerCalls Out for Line Overload

Line ThermalOverloadSag Risk

SEL-3010 Calls System Operator

SEL

SEL-3010 Event

Messenger

CommunicationProcessor

Receives AlertSEL

SEL-421 Alarms

SEL Comm. Processor Forwards Message Line

OverloadOn HighlandLine !!!

Trip ONE end for overload!

Use it as a capacitor for voltage support.

Letting lines sag and fault on thermal overloads is dangerous.

Waiting for a fault causes both ends to trip and is much more severe on stability.

Synchronized Phasor Measurements Provide a “Snapshot” of the Power

System Using anAbsolute Time Reference

Absolute Time ReferenceAcross the Power System

Synchronized PhasorMeasurement Applications

Compare state estimator to synchrophasors Is system near stability limits? Wide Area Protection and Control Systems Verifiy polarity, ratio, and operation of

instrument transformers All event recordings are synchronized to the

microsecond, making analysis of event reports across the system easier!

Simplifies analysis of major events because all phasors are on same reference.

Faster State Estimation With Synchronized Measurements

rrore )(V, h

Q

P

V

V

State

tsMeasuremen

12

12

2

1

State

tsMeasuremen

2

1

2

1

)(V, h

V

V

10 minutes 0.1 second!

Potential SEL PMUs in US and Canada

1-50

51-100

101-200

201-300

301+

9

22

45

25

46

12

1

398

29

6

29

17 62

16

20

41

68

8

66

1

9 9

4

4

58

143

26

64

11

138

130

526

7

22

52262 63

25

528

8

5

Customer Testimonial

Satendra said. “We were very excited about using the synchrophasor technology produced by Schweitzer Engineering Laboratories Inc. (SEL) and in the process ensured that Transend became the first Australian electricity supply utility to trial the SEL technology.”

Synchronized DataCollection and Local Storage

S torage

421

451

734

W ebS erver

R ea l T im eA pplica tions

S C A D A

W A N3306

D ata

D ataS torage

G PS R C VR2407

Data Alignment in Less Than 10 ms

O utputsT im e-A ligned

P hasors

PMU 01

Sample Time (Sec)13:29:59.00

Sample Time (Sec)13:29:59.00

PMU 02

SEL-3306

T im e A ligns P hasorsO bta ined from

T im e-S tam ped S am ples

P hasorC alc

P hasorC alc

Power System Real-Time Test

Reveals Model – to –

Measurement agreement of 0.05 degree !

SCADA Security Problems

Utility Communication Systems Are Vulnerable to:

unauthorized accessintruder monitoringmalicious attack

These Vulnerabilities Can Result in:lost or manipulated dataunauthorized breaker operationequipment damage

Vulnerable SCADA System

Netw ork

Master Device

Remote DeviceModem Modem

U nsecureC hannel

Attacker

Modem

AccessAllow ed

Defining the Electronic Perimeter

latigid latigid

EMS ICCP

OperatorConsole

Internet WAN

latigid

latigid

Communications Processor

latigid

RTU

latigid

RTU

latigid

RTU

latigid

RTU

Corporate LAN

Secure LAN

Electronic Security Perimeter

Electronic Security Perimeter

Encryption

Encryption is a means of concealing information in a reversible manner.

TripBreaker

TripBreaker

Encrypt

Encryption Key Decryption Key

*4gu>galL8}2=h

TripBreaker

Defensive Tools – Serial Encryption Device

Uses Advanced Encryption Algorithm Standard (AES) with 128–bit key

Multilevel Password Authentication

Point-to-Point and Multidrop Ready Trusted Network

InterfaceInsecure NetworkInterface

SEL-3021 Security

Incorporates Strong Encryption Techniques (AES)Hides sensitive data in transit (passwords,

metering data, etc.)

Strong Session AuthenticationNeed 128-bit system key to initiate a

connection

Message Replay ProtectionPreviously transmitted messages cannot be

resent to affect the same result (ex. Encrypted breaker operate frames)

SEL-3021 Benefits

Designed for Low-Latency, Time-Critical SCADA Communication

Retrofit “Bump-in-the-wire” Solution

Federal Information Processing Standards – FIPS -140 Compliant

Developed for Harsh Substation Environment

Secured SCADA System

Network

Master Device

Remote DeviceModem Modem

UnsecureChannel

Attacker

Modem

EncryptionDevice

EncryptionDevice

AccessDenied