Florida International University Department of Electrical

1-1

Florida International University

Department of Electrical & Computer Engineering

EEL-5270 Electrical Transients in Power Systems

Lecture Notes

Set No. 1

Professor Osama A. Mohammed

Miami, Florida

Fall 2020

EEL-5270 Electrical Transients in Power Systems, Prof. Mohammed, Copyright All rights reserved, 2008-2020

1-2EEL-5270 Electrical Transients in Power Systems, Prof. Mohammed, Copyright All rights reserved, 2008-2020

FLORIDA INTERNATIONAL UNIVERSITY DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING

EEL-5270 Electrical Transients in Power Systems Fall Semester, 2020

INFORMATION SHEET AND COURSE TOPICS

COURSE INSTRUCTOR:

Professor Osama A. Mohammed, Ph.D., Fellow IEEE Distinguished ProEnergy Systems Research Laboratory

Department of Electrical & Computer Engineering Room EC-2441

Florida International University Miami, Florida 33174 USA

Tel: +1 (305) 348-3040 (Office), Tel: +1 (305) 348-6194 (ESRL Lab) Fax: +1 (305) 348-3707 (Office)

E-mail: [email protected] Zoom link: https://fiu.zoom.us/j/9610584022 (Please Use during office hours only or by Appointment)

Class Time/Room: Thursdays: 5:00-7:40 pm, Remote with zoom OFFICE: EC-2441 Office hours Thursdays 4:00-4:00 pm PHONE: (305) 348-3040/4591/2807 (office/staff) PREREQUISITE: EEL-4213 or permission of instructor. CREDIT HOURS: 3 Hours TEXT_BOOK AND NOTES: 1. Electrical Transients In Power Systems by Allan Greenwood, Wiley, 1994. 2. Selected lecture notes by Professor Mohammed and other demonstration material and examples will be made

available at the above Web site and in class. Who Should Take This Course? FIU Electrical and Computer Engineering Students who took EEL4213 (power I) and Graduate Students. Students at other Universities in Florida or out of State with the course's prerequisites. Engineers and technical personnel in Industry preparing for Engineering License Engineers and technical staff who want to keep current and reach a deep understanding of energy

conversion concepts.


Objectives:

1. Introducing Electrical Transients in power systems 2. Cover the concepts of traveling waves and propagation 3. Modeling of transmission lines as distributed parameter systems. 4. Discuss issues related to insulation coordination, grounding and limiting of surge effects 5. Develop techniques related to reflections at transition points in lines and cables 6. Multi conductor transients and distributed parameter modeling for components and shielding issues. 7. Involve students in practical experience through the term project.

Course topics: Introduction to Electrical Transients in Power Systems (Circuit opening and closing transients, Recovery

transients. Traveling waves on Transmission Systems (Propagation of Surges) Modeling of Transmission Lines by Distributed Parameter Concepts (Lossless cases, loss cases,

distortion-less cases, Lines with small losses) Distortion due to Corona Energy in Traveling Waves Characteristics of Traveling Waves (wave shapes, standards, impulse, and switching surges, lightning,

Basic Impulse Insulation Level (BIL), Flashover surge generators) Analytical approximation of Surge Wave Shapes Transition Points (Lines, Cables, Voltage Buildup, various types of Transition points, terminations) Lumped Series and Shunt Impedance Transition Points (Junctions at Cables, Substations Dissimilar Voltage and Current Surges Surge Arresters (Linear and Nonlinear Characteristics. Successive Reflections on Transmission Systems Grounding Insulation Coordination Multi-Conductor, Multi-velocity Systems Transient Performance of Distributed parameter Systems for Transformer, Generator and Motor

Windings Shielding Practical Examples, projects References: Appropriate lists and copies of technical papers will be distributed or listed for your collection. A list of recent text-books and other technical records will be suggested to you. However, you are also required to research and obtained other pertinent materials related to the topics covered. ASSISTANCE: Please try to see Dr. Mohammed during his listed office hours or through the communicationforum on the web page. If this proves impossible, a personal appointment should be arranged by calling my directphone number or the ECE department secretary at extension (305-348-2807). ABSENCE: Class attendance (physical or virtual) is very important and is considered in your overallperformance in the course. Students are responsible for all material covered in that class.


IMPORTANT RULE: Students are encouraged to discuss the course topics with the professor and with eachother. Any work submitted (Homework, Tests, projects, etc.) should be pledged and signed as the students' work, and that there is no unauthorized help was obtained. Violators will be subject to academic misconduct, whichmight lead to dismissal from the university. GRADING POLICY: Homework will be assigned regularly, collected, and graded. Efforts in homework indicate that you are studyingand caring about the course and, therefore, can have an impact on your final Grade. Time for the mid-term will be announced one week in advance. Any work submitted must be neat and detailed for a partial mark. YourGrade will be calculated as follows:

Homework and Class Projects 20% Mid Term 25% Term Project/Research Paper 20% Final Exam 35% _______ Total 100%

TERM PROJECT: The project will involve one or more of the topics of this course. The final presentation (oral and written) ofthe overall project results will be required. Software available for this class can be utilized for the projects.

1-5

The Electromagnetic Pulse (EMP) Effect


1-6

The Influence of a Charged Cloud


1-7

I. HOW LIGHTNING IS FORMED

AVERAGE THUNDERCLOUD USUALLY BOTTOMS AROUND 2 MILES (10,000・) AND TOPS OUT AROUND 8 MILES (50,000feet) IN ELEVATION.

TEMPERATURE IS ABOUT 40oF AT BASE T0 -65 o AT THE TOP.

WARM MOIST AIR ON LEADING EDGE ASCENDS RAPIDLY FROM 40oF TO -65oF FORMING ICE CRYSTALS AND WATER DROPLETS.

IT IS THIS RAPID ASCENT AND SWIRLING MOTION THAT FORMS THE ELECTRIC CHARGE.


1-8

THIS CREATES A HIGHLY POSITIVE CHARGE IN THE TOP OF THE CLOUD (6 MILES AT-65ºF), A HIGHLY NEGATIVE CHARGE IN THE LOWER CENTRAL PART (3 MILES AT 0ºF) AND A SMALL POSITIVE CHARGE AT THE BASE (2 MILES AT 40ºF). THE DIFFERENCES IN POTENTIAL RESULTS IN THE LIGHTNING STROKE.


1-9

TYPICAL STROKE TO EARTH IS AROUND 125 MILLION VOLTS, 20,000 AMPS, WITH TEMPERATURE AROUND 50,000oF.


1-10

POINTS OF INTEREST

YOU CAN TELL HOW NEAR THE STORM IS BY COUNTING THE SECONDS BETWEEN LIGHNING AND THUNDER. DIVIDE THE NUMBER OF SECONDS BY 5.

THUNDERSTORMS ARE RESPONSIBLE FOR MAINTAINING EARTH’S NEGATIVE CHARGE.

LIGHTNING PRODUCES NITROGEN COMPOUNDS THAT ARE ESSENTIAL FOR MOST PLANTS.

LIGHTNING KILLS MORE PEOPLE IN THE U.S. EVERY YEAR THAN TORNADOES, HURRICANES, OR FLOODS.



1-12

AVERAGE THUNDERSTORM DAYS PER YEAR IN U.S.


EEL-5270 Electrical Transients in Power Systems, Prof. Mohammed, Copyright All rights reserved, 2008-20201-13

ELECTROMAGNETIC COUPLING

ELECTROMAGNETIC COUPLING IS THE MOST COMMON WAY LIGHNING GETS INTO THE SYSTEM.

AS A CHARGED CLOUD MOVES INTO THE AREA (OR BUILDS UP IN THE AREA), THE LINE BECOMES IMMERSED IN THE ELECTROSTATIC FIELD.

WHEN LIGHTNING STIKES IN THE VICINITY (WITHIN A FEW HUNDRED FEET), IT MAY RESULT IN A COUPLING EFFECT BETWEEN THE FIELD AROUND THE STROKE AND THE LINE SIMILAR TO THE WAY THE COILS OF A TRANSFORMER OPERATE.

THIS RESULTS IN OVERVOLTAGES (SURGES) ON THE LINE WHICH TRAVEL UNTIL IT FINDS A PATH TO GROUND. THIS POINTS OUT THE NEED FOR MAINTAINING A GOOD GROUNDING SYSTEM.


II. HOW LIGHTNING GETS INTO THE SYSTEM

DIRECT HIT


ELECTROMAGNETIC COUPLING - UNDERGROUND

A DIRECT STRIKE TO EARTH IN THE VICINITY OF BURIED CABLE OR SPILL OVER FROM THE OH THROUGH THE RISER CAN CAUSE AN OVERVOLTAGE ON THE CONCENTRIC CABLE.

WHEN THESE HIGHER VOLTAGES ARE PRESENT, THE DIFFERENCE IN POTENTIAL BETWEEN THE PHASE CONDUCTOR AND CONCENTRIC NEUTRAL CAN RESULT IN TREEING AND DAMAGED EQUIPMENT.


PRE-DISCHARGE BUILD UP - B Ø

WHEN SURGE IS PRESENT ON LINE, ALL 3 PHASES ARE AFFECTED.

ARRESTERS, ON ALL PHASES, WHICH ARE COMMONLY GROUNDED LIMIT THE SURGE OVER VOLTAGES BETWEEN PHASES.

IF THE GROUND RESISTANCE IS NOT LOW WNOUGH THE SURGE REMAINS ON THE LINE LONGER, POSSIBLY RESULTING IN DAMAGE TO THE ARRESTERS AS WELL AS OTHER EQUIPMENT.


MULTI-GROUNDED WYE CIRCUITS

MULTI-GROUNDED WYE CIRCUITS DEPEND ON INTERMEDIATE LOW RESISTANCE GROUND STATIONS FOR THE SYSTEM TO OPERATE PROPERLY UNDER ABNORMAL CONDITIONS. BECAUSE OF HIGH SURGE IMPEDENCE IN THE NEUTRAL CONDUCTOR, IT SHOULD NOT BE COUNTED ON TO DISSIPATE THE SURGE & OVERVOLTAGES OR TO CARRY THE SURGES TO THE SUBSTATION FOR DISSIPATION.






Comparison of various distribution line protective measures.


B.I.L. - BASIC IMPULSE INSULATION LEVEL

THE ABILITY OF ANY MATERIAL OR DEVICE TO WITHSTAND A PRE-DETERMINED IMPULSE LEVEL.

EXAMPLES:

PIN INSULATOR - 100 KV

35 KV INSULATOR (POST) - 180 KV

ANY POLE IN SALT SPRAY AREA - 0 KV

CONCRETE POLE - 0 KV

WOOD POLE

WET - 75 KV/FT

DRY - 100 KV/FT

WOOD X-ARM

WET - 75 KV

DRY - 100 KV/FT

AIR - 186 KV/FT

13 KV TRANSFORMER - 95 KV

23 KV TRANSFORMER - 125 KV



BIL OF 35 KV SKIRTED INSULATOR IS 180 KV -WHEN BOLT EXTENDS OUT TO COVER 2 - 3 SKIRTS, BIL IS REDUCED.

EXAMPLE: BOLTS EXTENDS OVER 3 SKIRTS

180 KV - 90 KV = 90 KV

AIR GAP BETWEEN BOLT & INSULATOR = 1 +

INSULATIONS VALUE OF AIR = 15 KV PER 1

THEREFORE BIL IS APPROXIMATELY 105 KV



CONCRETE POLE

35 KV INSULATOR - 180 KV

CONCRETE POLE - _ 0___

TOTAL BIL 180 KV

WOOD POLE

35 KV INSULATOR - 180 KV

WOOD POLE (WET) - 75 KV/FT

75 KV 180 KV

x_ 3_ 225 KV

225 KV TOTAL BIL 405 KV


INSTALLATION OF GROUND RODS

-----PREFERRED METHOD-----

RODS DRIVEN VERTICALLY IN TANDEM

DOUBLING ROD LENGTH REDUCES

OHM READING BY ABOUT 40%

EXAMPLE:

20 FT DEEP ROD - 30 OHMS

40 FT DEEP ROD - 18 OHMS


INSTALLATION OF GROUND RODS

ALTERNATIVE TO DEEP DRIVEN ROD

CLUSTERED RODS - MULTIPLE RODS DRIVEN IN PARALLEL AND CONNECTED TOGETHER

- WHEN -

ONLY WHEN INITIAL ROD(S) ARE DRIVEN TO REFUSAL BEFORE SPECIFIED RESISTANCE IS REACHED


ALTERNATIVE TO DEEP DRIVEN ROD

INSTALL GROUND ROD AT ANGLE

RECOMMENDED ONLY FOR AREAS WHERE HARD ROCK PROHIBITS DRIVING RODS VERTICALLY DEEP ENOUGH TO ACHIEVE SPECIFIED OHMS.

EXAMPLE:

- ROD DRIVEN VERTICALLY TO 20・ DEPTH

- WHEN DRIVEN AT 45・ANGLE WILL HAVE 28・ OF ROD IN CONTACT WITH EARTH

MAY LOWER RESISTANCE BY 20% - 40% OVER RODS DRIVEN VERTICALLY


TESTING OF GROUND RODS

EQUIPMENT

FUSE TESTER

VIBOGROUNG ( M&S #590-54700-5)

MEGGER EARTH TESTER

(M&S #590-56000-1)


EARTH RESISTANCE VS. INSULATION RESISTANCE METERS

EARTH RESISTANCE METERS OPERATE ON FREQUENCIES BETWEEN 97 Hz AND 125 Hz.

INSULATION RESISTANCE METERS OPERATE ON FREQ. IN 60 Hz RANGE.

INSULATION RESISTANCE METERS ARE SUSCEPTIBLE TO STRAY GROUND CURRENTS OR D.C. CURRENTS WHICH INFLUENCE READINGS.

INSULATION RESISTANCE METERS ARE NOT TO BE USED FOR EARTH RESISTANCE TESTING.


FUSE TESTER

3 AMP ------> 25 OHMS

8 AMP ------> 10 OHMS

FUSE IS DESIGN TO BLOW AT 1 - 1/2 TIMES ITS RATED VALUE

3 AMP FUSE WILL BLOW AT 4-1/2 AMPS

8 AMP FUSE WILL BLOW AT 12 AMPS

OHMS LAW E = R X 1 R = E / 1

R = 115 / 4.5 = 25.5 OHMS

R=RESISTANCE I=CURRENT E=VOLTS


VIBROGROUND AND MEGGER EARTH TESTER

NULL BALANCE INSTRUMENTS USED FOR MEASURING EARTH RESISTANCE

METHOD FOR USE:

2 POINT METHOD

3 POINT METHOD


2 POINT (DIRECT METHOD)

MEASURE RESISTANCE BETWEEN GROUND ROD AND SURROUNDING EARTH USING THE SYSTEM NEUTRAL AS REFERENCE.


3 POINT (FALL OF POTENTIAL)

MEASURE RESISTANCE OF GROUND ROD AND SURROUNDING EARTH USING POTENTIAL AND CURRENT PROBES AS REFERENCE.


TESTING GROUNDS AT EXISTING LOCATIONS

TEST FOR 25 OHMS OR LESS

IF 25 OHMS OR LESS NOT ACHIEVED, THEN:

OPTIONS:

1. DRIVE ADDITIONAL RODS ON TOP OF EXITING RODS TO ACHIEVE 25 OHMS.

2. MOVE OVER 10・ IF POSSIBLE (6・MINIMUM) AND CLUSTER RODS 25 OHMS.

3. ABANDON EXISTING INSTALLATION AND DRIVE NEW RODS TO ACHIEVE 10 OHMS IF POSSIBLE WITH 40・ OR LESS (AS PREVIOUSLY SPECIFIED)


GOOD CONSTRUCTION PRACTICES

RELATING TO

GROUNDING

THERE ARE MANY THINGS WE CAN DO TO IMPROVE OUR GROUNDING SYSTEM AND SERVICE RELIABILITY.


INSTALLATION AND ATTACHMENT OF GROUND RODS

ALL GROUNDING CONNECTIONS ARE ELECTRICAL

WIRE BRUSH AND USE INHIBITOR

TIGHTEN COUPLINGS FOR EACH SECTION OF GROUND ROD

USE SEPARATE CLAMP OR CONNECTOR FOR EACH CONNECTION


SURGE ARRESTERS AND LEADS

MAKE ALL LEADS AS SHORT AS POSSIBLE

AVOID SHARP BENDS AND KINKS(EACH KINK INCREASES IMPEDANCE BY 20%)

DO NOT COIL WIRE

AVOID KINKS ON ANY BONDING WIRE

Documents

Florida International University Department of Electrical