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

Slow Fault Clearing Time Initiates Voltage Collapse

Reverse Zone 3 Element Operated During Low Voltage Conditions

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 phase distance elements in defined load areas We Invented Load-Encroachment Elements to… R X

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

V < 95% at Buses 8 and 9 are for Loss of Two Lines Definite-time elements would trip loads at both buses.

Inverse-Time Undervoltage Elements Shed Low-Voltage Loads First

Bus 8 Voltage recovers after Inverse Element drops Bus 9 load… without communications!

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 Determine System Power Flow

Real Power Transfer Depends on 

Accelerating Power Changes Machine Kinetic Energy Swing Equation

System Swing

Event Capture From Aug. 14, 2003

Out-of-Step Detection Logic Avoids Zone 1 Tripping

Transmission Line Tripping During 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

SEL-3010 Event Messenger Calls Out for Line Overload Line Thermal Overload Sag Risk SEL-3010 Calls System Operator SEL-3010 Event Messenger Communication Processor Receives Alert SEL-421 Alarms SEL Comm. Processor Forwards Message Line Overload On Highland Line !!!

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 an Absolute Time Reference

Absolute Time Reference Across the Power System

Synchronized Phasor Measurement 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 10 minutes0.1 second!

Potential SEL PMUs in US and Canada

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 Data Collection and Local Storage

Data Alignment in Less Than 10 ms

Power System Real-Time Test Reveals Model – to – Measurement agreement of 0.05 degree !

SCADA Security Problems Utility Communication Systems Are Vulnerable to:  unauthorized access  intruder monitoring  malicious attack These Vulnerabilities Can Result in:  lost or manipulated data  unauthorized breaker operation  equipment damage

Vulnerable SCADA System

Defining the Electronic Perimeter latigidlatigid EMSICCP Operator Console Internet WAN latigid Communications Processor RTU Corporate LAN Secure LAN Electronic Security Perimeter

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

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 Interface Insecure Network Interface

SEL-3021 Security Incorporates Strong Encryption Techniques (AES)  Hides sensitive data in transit (passwords, metering data, etc.) Strong Session Authentication  Need 128-bit system key to initiate a connection Message Replay Protection  Previously 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