copyright © sel 2004 protection for abnormal system conditions presented at: clemson power systems...
TRANSCRIPT
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