This document provides an outline for a webinar on insulation coordination fundamentals. It begins with definitions of insulation coordination and different types of studies. It then covers key parameters considered in studies like surge characteristics and equipment ratings. Examples of basic and complex substation and transmission line studies are provided. The document also defines insulation terminology like BIL and discusses surge phenomena like backflash. Resources for further information are listed.
Auto-reclosing has been applied throughout the world in order to quickly restore supply
after system faults or incidents.
This report details the information gathered by Cigre Working Group 34.01 (2000) Autoreclosing
and Local System Restoration. In order to appreciate the depth and differences
to which auto-reclose is applied throughout the world the initial chapter of the report
details current practice of auto-reclose. In order to gather information regarding current
practice a survey was conducted to determine worldwide application.
Despite the efforts of those who responded, the survey was not well supported. A request
was issued to some 73 organizations. Japan made an outstanding contribution supplying
ten of the 32 responses. Scandinavia was also well represented. The majority of the other
replies came from countries, organizations or individuals represented on the WG or
strongly active in CIGRE. So in all, just fourteen countries responded. The Working
Group had hoped for a better return of the survey, although the 32 responses did return an
excellent coverage of adverse applications of auto-reclose, the other related topics
provided far less information.
Tutorial on Distance and Over Current ProtectionSARAVANAN A
Contents
• Protection Philosophy of ERPC
• Computation of Distance Relay Setting
• System Study to Understand Distance Relay
Behaviour
• DOC and DEF for EHV system
UNIDAD I. FILOSOFÍA DE LA PROTECCIÓN DE
SISTEMAS ELÉCTRICOS.
UNIDAD II. PRINCIPIOS Y CARACTERÍSTICAS DE
FUNCIONAMIENTO DE LOS RELÉS.
UNIDAD III. PROTECCIÓN DE SOBRECORRIENTE.
UNIDAD IV. PROTECCIÓN DE DISTANCIA.
UNIDAD V. RELÉS DIFERENCIALES.
UNIDAD VI. RELÉS DE APLICACIÓN ESPECIAL.
UNIDAD VII. PROTECCIÓN POR HILO PILOTO.
UNIDAD VIII. RELÉS ELECTRÓNICOS
Cable sizing to withstand short-circuit current - ExampleLeonardo ENERGY
A short circuit causes very extreme stresses in a cable which are proportional to the square of the current:
A temperature rise in the conducting components such as conductor, screen, metal sheath, armour. Indirectly the temperature of adjoining insulation and protective covers also increases,
electro-magnetic forces between the current-carrying components.
The temperature rise is important for its effect on ageing, heat pressure characteristics etc. and should be limited to a permissible short-circuit temperature. The thermo-mechanical effects of the current shall also be considered.
For the given short-circuit condition the short-circuit capacity of a cable should be investigated with respect to all these parameters. For multi-core cables in most instances the thermal effect - related to the magnitude of fault current and clearance time - is the critical parameter, since the cable will normally have enough mechanical strength. With single-core cables however the mechanical effect - related to the magnitude of the peak short-circuit current - is of such significance that, next to the thermal, the mechanical strength of both cable and its supports should be investigated.
Also accessories must be rated with respect to thermal and mechanical short-circuit stresses.
The short circuit strength of a cable system is not quantitatively defined with regard to permissible number of repeated short circuits, degree of deformation or destruction or impairment quality. It is expected, however, that a cable installation will remain safe in operation and that any deformation remains within tolerable limits even after several short circuits.
This course provides practical overview of short circuit performance of a cable.
Introduction
Very low frequency (VLF) AC voltage testing in the
frequency range from 0.01 to 1 Hz is increasingly
being used for both high voltage (Hi-Pot) acceptance
and condition assessment of installed large
capacitance power components [IEEE standards,
IEC standard, etc.].
The main advantage of such tests is the low amount
of reactive power needed compared to testing at
power frequency. Today, equipment for VLF afterlaying
tests are becoming available at voltages up
to 400 kV. In addition, diagnostic parameters as
for example partial discharge activity and dielectric
losses, are regularly measured using VLF voltages.
Auto-reclosing has been applied throughout the world in order to quickly restore supply
after system faults or incidents.
This report details the information gathered by Cigre Working Group 34.01 (2000) Autoreclosing
and Local System Restoration. In order to appreciate the depth and differences
to which auto-reclose is applied throughout the world the initial chapter of the report
details current practice of auto-reclose. In order to gather information regarding current
practice a survey was conducted to determine worldwide application.
Despite the efforts of those who responded, the survey was not well supported. A request
was issued to some 73 organizations. Japan made an outstanding contribution supplying
ten of the 32 responses. Scandinavia was also well represented. The majority of the other
replies came from countries, organizations or individuals represented on the WG or
strongly active in CIGRE. So in all, just fourteen countries responded. The Working
Group had hoped for a better return of the survey, although the 32 responses did return an
excellent coverage of adverse applications of auto-reclose, the other related topics
provided far less information.
Tutorial on Distance and Over Current ProtectionSARAVANAN A
Contents
• Protection Philosophy of ERPC
• Computation of Distance Relay Setting
• System Study to Understand Distance Relay
Behaviour
• DOC and DEF for EHV system
UNIDAD I. FILOSOFÍA DE LA PROTECCIÓN DE
SISTEMAS ELÉCTRICOS.
UNIDAD II. PRINCIPIOS Y CARACTERÍSTICAS DE
FUNCIONAMIENTO DE LOS RELÉS.
UNIDAD III. PROTECCIÓN DE SOBRECORRIENTE.
UNIDAD IV. PROTECCIÓN DE DISTANCIA.
UNIDAD V. RELÉS DIFERENCIALES.
UNIDAD VI. RELÉS DE APLICACIÓN ESPECIAL.
UNIDAD VII. PROTECCIÓN POR HILO PILOTO.
UNIDAD VIII. RELÉS ELECTRÓNICOS
Cable sizing to withstand short-circuit current - ExampleLeonardo ENERGY
A short circuit causes very extreme stresses in a cable which are proportional to the square of the current:
A temperature rise in the conducting components such as conductor, screen, metal sheath, armour. Indirectly the temperature of adjoining insulation and protective covers also increases,
electro-magnetic forces between the current-carrying components.
The temperature rise is important for its effect on ageing, heat pressure characteristics etc. and should be limited to a permissible short-circuit temperature. The thermo-mechanical effects of the current shall also be considered.
For the given short-circuit condition the short-circuit capacity of a cable should be investigated with respect to all these parameters. For multi-core cables in most instances the thermal effect - related to the magnitude of fault current and clearance time - is the critical parameter, since the cable will normally have enough mechanical strength. With single-core cables however the mechanical effect - related to the magnitude of the peak short-circuit current - is of such significance that, next to the thermal, the mechanical strength of both cable and its supports should be investigated.
Also accessories must be rated with respect to thermal and mechanical short-circuit stresses.
The short circuit strength of a cable system is not quantitatively defined with regard to permissible number of repeated short circuits, degree of deformation or destruction or impairment quality. It is expected, however, that a cable installation will remain safe in operation and that any deformation remains within tolerable limits even after several short circuits.
This course provides practical overview of short circuit performance of a cable.
Introduction
Very low frequency (VLF) AC voltage testing in the
frequency range from 0.01 to 1 Hz is increasingly
being used for both high voltage (Hi-Pot) acceptance
and condition assessment of installed large
capacitance power components [IEEE standards,
IEC standard, etc.].
The main advantage of such tests is the low amount
of reactive power needed compared to testing at
power frequency. Today, equipment for VLF afterlaying
tests are becoming available at voltages up
to 400 kV. In addition, diagnostic parameters as
for example partial discharge activity and dielectric
losses, are regularly measured using VLF voltages.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
Explore the innovative world of trenchless pipe repair with our comprehensive guide, "The Benefits and Techniques of Trenchless Pipe Repair." This document delves into the modern methods of repairing underground pipes without the need for extensive excavation, highlighting the numerous advantages and the latest techniques used in the industry.
Learn about the cost savings, reduced environmental impact, and minimal disruption associated with trenchless technology. Discover detailed explanations of popular techniques such as pipe bursting, cured-in-place pipe (CIPP) lining, and directional drilling. Understand how these methods can be applied to various types of infrastructure, from residential plumbing to large-scale municipal systems.
Ideal for homeowners, contractors, engineers, and anyone interested in modern plumbing solutions, this guide provides valuable insights into why trenchless pipe repair is becoming the preferred choice for pipe rehabilitation. Stay informed about the latest advancements and best practices in the field.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
Immunizing Image Classifiers Against Localized Adversary Attacksgerogepatton
This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
(CNN)s, to adversarial attacks and presents a proactive training technique designed to counter them. We
introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
When combined with 3D convolution and deep curriculum learning optimization (CLO), itsignificantly improves
the immunity of models against localized universal attacks by up to 40%. We evaluate our proposed approach
using contemporary CNN architectures and the modified Canadian Institute for Advanced Research (CIFAR-10
and CIFAR-100) and ImageNet Large Scale Visual Recognition Challenge (ILSVRC12) datasets, showcasing
accuracy improvements over previous techniques. The results indicate that the combination of the volumetric
input and curriculum learning holds significant promise for mitigating adversarial attacks without necessitating
adversary training.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
2. Webinar Outline
Initial basics of Insulation Coordination Studies
Definitions , Types, Parameters, Purposes
Examples of an Insulation Coordination Study
Basic Substation , Complex Substation, Transmission Line
BIL,BSL
The Backflash
Traveling Wave Phenomena
Arrester Fundamentals
Margin of Protection
Ground Flash Density
The Report
3. Resources for this Webinar
1. Book: “Insulation Coordination of Power
Systems” by Andrew (Bob) Hileman, 1999.
2. AR Hileman Software
3. ATP and ATP Draw, XY Plot
4. IEC 60071-1,2,3,4
5. IEEE C62.82.1 and .2 Formerly 1313.1 and .2
(Insulation Coordination Standards)
6. IEEE C62.11 Arrester Test Standards
7. IEEE C62.22 Arrester Application Guide
8. IEEE 1410 and 1243 Improving Lightning
Performance of lines
4. Definition of Insulation Coordination
Simple Definition
Insulation coordination is the selection of the insulation
strength of a system. (Hileman)
Better One
Insulation coordination is the process where the insulation
characteristics of all components of the power system are
determined, specified and coordinated to avoid failure due
to expected internal and externally occurring surges.
(Hileman)
Arrester
Insulator
5. Types of Insulation Coordination Studies
Transformer Protection
Substation Protection Open Air and GIS
Line Protection
Distribution and Transmission
Breaker Protection
Generator Protection
Determine clearances
Determine Separation Distances
Determine Arrester Energy and Voltage Ratings.
And on and on and on
6. Types of Insulation Coordination Studies
Deterministic
This is the conventional method where the minimum strength of
the insulation is equal or greater than the maximum surge stresses.
.
Transformer insulation is not
statistical in nature. It has one
lightning withstand value and
one switching withstand value.
Therefore a deterministic
analysis is all that we can do.
7. Types of Insulation Coordination Studies
Probabilistic
This type of analysis consists of selecting the insulation level and
clearances based on specific reliability criterion. Since the insulation
strength of air is statistical in nature, we can only determine its
probability of Flashover for a given surge.
Studies of transmission line performance is based on a flashover
rate per year per 100km, and because the flashover parameter is
statistical, resulting levels are probabilistic.
Studies of substation performance is also probabilistic for the
same reason. For this type of study we base the performance on
MTBF (Mean Time Between Flashover). More later on this.
8. Types of Insulation Coordination Studies
Lightning Surge Studies
This type of study deals strictly with lightning surges and backflash over
surges. Is completed for all system voltage levels.
Switching Surge Studies
This type of study is usually for systems above 240kV since it is this type
of system that can produce switching surges of relevance.
If a lower voltage system has large cap banks, then a switching study is
justified.
9. Parameters of Importance in Studies
• Purpose of Study
• The Lightning Flash
• Ground Flash Density
• Shield Failure rate if known
• Types of Insulation
• BIL and CFO
• MTBS and MTBF
• Location and Altitude of Study
• Cable and Isophase specs
• Incoming Surge Steepness
• Backflash Rate (BFR)
• Calculating BFR
• Tower Configurations
• Circuit Physical Dimensions
• The Transformer Ratings and
Capacitance
• The Arrester
• VI Curve
• Selecting the Rating
10. Purpose of Insulation Coordination Studies
Can be to design proper insulation and arrester location from scratch
Can be to validate chosen insulation levels (Very common)
Can be to determine where to locate arresters
Can be to determine cause of failure of equipment (After an incident)
Can be to determine the Width of a ROW (Switching Study)
Can be to provide assurance that equipment is protected properly
Can be to put in the file for future reference
Can be to fulfill a requirement
Can be to …………. and more……
11. Examples of Lightning Studies
Simple Substation from Chapter 12 of “Insulation
Coordination of Power Systems”.
500kV Line-Substation-Generator
69kV Line Study
15. Complex Insulation Coordination Study
Incoming
Line
Switchyard with
no
transformers
Cross over line
to Generator
Station
3 generator step
up Transformers
Three generators
19. System Fundamentals Relative to Insulation
Coordination
1. Insulation
2. Traveling Waves and
Reflections, Backflash, and
Separation Distance
3. Tower Grounds and Station
Grounds
4. Corona
5. Steepness of Surges
6. Clearances
7. Physical Dimensions
8. Ground Flash Density
9. OHGW
10. Ground Flash Density
20. External Insulation
The distance in open air or across
the surfaces of solid insulation in
contact with open air that is
subjected to dielectric stress and to
the effects of the atmosphere.
Examples are porcelain or polymer
shell of a bushing, support
insulators, and disconnecting
switches.
Self-restoring Insulation
Insulation that completely recovers
insulating properties after a
disruptive discharge (flashover)
caused by the application of a
voltage. This is generally external
insulation.
Self restoring
Insulator
Terminator with
Self-restoring
Insulation on outside
and non-self-restoring
on inside
Underground Cable with
Non-Self Restoring
Insulation
21. Internal Insulation
The internal solid, liquid, or
gaseous parts of the insulation of
equipment that are protected by
equipment enclosures from the
effects of the atmosphere.
Examples are transformer
insulation, internal insulation of
bushings, internal parts of
breakers and internal part of any
electrical equipment.
Non-self-restoring Insulation
Insulation that loses insulating
properties or does not recover
completely after a disruptive
discharge caused by the
application of voltage. Generally
internal insulation.
Self Restoring
Insulation
Non-Self Restoring
Insulation
22. Basic Lightning Impulse Insulation
Level (BIL)
The BIL level is the Dry insulation
withstand strength of insulation
expressed in kV. Is commonly used to
describe substations and distribution
system voltage withstand
characteristics.
Statistical BIL is used for insulators means there is a
10% probability of flashover and is used for self-
restoring insulation
Conventional BIL is used for Transformers and
Cable
is the voltage level where there is a 0% probability of
Flashover and is applied to non selfrestoring insulation
Insulator BIL is directly proportional to the
strike distance of an insulator
BIL ≈ 15kV x S(inches)
And is affected by Altitude
Note 1: Arresters do not have a BIL rating
since their external insulation is self protected
by the internal MOV disks. In a sense they
have an infinite BIL.
Note 2: Arresters close to an insulator give
the insulator infinite BIL.
23. Basic Switching Impulse Insulation
Level (BSL)
The BSL level is the switching surge
withstand level of the insulation in
terms of kV.
BSLs are universally tested under
Wet conditions.
Statistical BSL of Insulators
apply to self restoring insulation and represents a 10%
probability of flashover.
Conventional BSL of Transformers and solid
dielectrics
apply to non-self-restoring insulation and represents a 0%
probability of flashover
BSL is proportional to the strike
distance of an insulator
BSL= 1080e((0.46 x Strike Distance) + 1)
And is affected by Altitude
Note 1: Arresters do not have a BSL rating
since their external insulation is self
protected by the internal MOV disks. In a
sense they have an infinite BSL.
Note 2: Arresters close to an insulator give
the insulator infinite BSL.
24. Power Frequency Withstand Voltage
This is the highest power frequency
voltage an insulator can withstand under
wet conditions (low level of
contamination).
It is affected by creepage distance and strike distance.
Note 2: Arresters will go into conduction if
the AC voltage across the unit reaches a 1.25
pu MCOV and above. However they cannot
sustain this condition for very long or they
will over heat and fail.
Note 3: If the housing is highly contaminated,
the housing may flashover at levels below the
turn-on voltage of the arrester.
Note 4: In highly contaminated areas, extra
creepage distance insulators are used to
overcome this potentially low flashover
voltage. The same policy should be applied
to arresters.
Note 1: Insulator withstand voltages are
often >2-3 times their operating voltage.
25. Critical Flash Over (CFO) Self Restoring insulation only
This is the voltage with a 50% probability of flashover of the
insulator. It applies to both lightning and switching. It is used to
quantify insulation used on transmission and distribution lines.
Typically CFO is 4-6% higher than Statistical BIL on an insulator.
Chopped Wave Withstand (CWW)
This is a withstand level of equipment. A standard lightning
impulse is used but the surge is chopped at 3us, which means the
stress is applied for a much shorter time than a standard lightning
impulse test and must flashover near the crest of the wave instead
of on the tail as it can in BIL tests. The value of this characteristic is
about 1.10 times BIL for power transformers and 1.15 times BIL for
bushings.
Caused by insulator flashover just past crest.
Can cause winding to winding stress in some
transformers
26. CWW
Chopped Wave Withstand
BIL
Basic Impulse Withstand Level
BSL
Basic Switching Impulse
Withstand Level
Typical Values 70-1500kVp
Another form of Lightning
withstand is CFO
Critical Flashover Voltage
27. The Backflash
When the OHGW on a
transmission line is hit by
lightning, a rapid series of events
takes place.
If the system is grounded well than
the surge is transferred to earth
and there is no effect on the phase
conductors.
But occasionally a backflash will
occur, this series of slides will show
you a close up view of the
sequence of events.
28. The Backflash
Time = 0
The first event is the strike. Of
course there was already a great
deal of activity just to connect this
line to the cloud, but that is for
another sequence.
When the strike pins to the wire, it
sets up a voltage surge that travels
in both directions down the line.
(1-50 million volts)
This is all happening at nearly the
speed of light and until the surge
actually finds ground, there is little
current flow.
29. The Backflash
Time = 1
In a few Nano-seconds, the voltage front
meets the down ground and travels toward
earth at the tower bottom. While at the
same time it is inducing a voltage on to the
phase conductors
When it reaches earth, the current begins
to flow.
The voltage along the tower increases
rapidly due to ground potential rise. This
potential rise is caused by the resistance of
the ground rod of the tower.
This tower voltage rises as the current
begins to flow.
Induced
Induced
30. The Backflash
Time = 2
The voltage at the base of the base
of the insulators and on the phase
conductors increases as the surge
increases in amplitude
If the voltage at the base of the
insulator increases at a faster rate
than the induced voltage on
phases, it can reach the CFO of the
insulator
31. The Backflash
Time = 3
The voltages continue to increase
across all components as the surge
crests.
32. The Backflash
Time = 4 (.5-2 µsec)
If the voltage across the insulator exceeds the
CFO, it can flashover from the pole down ground
to the phase.
This is the backflash……
It flashes from the base to the conductor which is
intuitively backward since the down ground
spends its entire life except for these few
microseconds at ground potential.
This is the part of the event that we are interested
in with insulation coordination studies. What
effect this surge will have the substation.
But its not over yet…..
33. The Backflash
Time = 5 (20-50 µsec)
The lightning stroke is over and
the voltages on the lines revert
back to their pre-strike levels. But
the air around the insulator is
seeping with ions and still highly
conductive.
When the AC voltage reaches a
high enough level, it now flashes
forward from the phase conductor
to the down ground.
34. The Backflash
Time = 6 (50 µsec to 200ms)
When the insulator flashes over for a
second time, power frequency current
flows to ground and a fault is now
underway on the circuit and will remain
there until a breaker interrupts the
event.
At that point the event is over assuming
no damage occurred on the insulator.
AC Follow current
causing a Line to
Ground Fault
Until breaker
interrupts
35. The Backflash
The surge that is transferred onto the phase
conductor has entered the station within a few
µsec, even before the fault was initiated.
This is the impulse that becomes the concern of
insulation coordination in substations.
36.
37.
38.
39.
40.
41. Note the voltage at the
transformer is clamped by
the arresters.
Arresters
CCVTs
42.
43.
44. Arresters
Note the voltage at the
transformer is higher than
at the arresters. This is due
to traveling wave reflection
Red = Voltage @ Arrester
Green = Voltage @ Transformer
3 m separation
30 m separation
Separation
Distance
47. • Polymer Housing
• Metal Oxide Varistor
(MOV)
• Conductive Spacer
• Strength Member
(Fiberglass)
• Spring for Compression
• Rubber Seals
• End Vents and Diaphragms
48. VI Characteristics of an Arrester or Disk is the essence of the MOV.
The resistance of the MOV disk is a function of the voltage stress
across the terminals.
Example
50kV MCOV
Arrester
49. Typical Varistor/Arrester
V-I Characteristics
|---------------------- Breakdown Region--------------------------------|
Pre-Breakdown
Region
|--------------------------------------|
High Current Region
|---------------------------------------|
Leakage Current Region
V1ma or Reference Voltage
Region
TOV Region
Switching
Surge
Region
Lightning
Impulse
Region
Normal Operating Region
20C
200C
Physicists Terminology
Engineering Terminology
Vref or Uref
V10kA or
U10kA
MCOV or UC (peak)
Rated V or Ur peak
LPL
SPL
50. Arrester Discharge
Voltage Curve
Fast Front
Voltage
10kA Lightning
Protective Level
LPL
Switching Surge Protective Level
SPL
Faster Front Surges Slower Front Surges
51. Insulation Withstand
Curve
Arrester Discharge
Voltage Curve
Chopped Wave
Withstand CWW
Front of Wave
Voltage
FOW
BSL
BIL
10kA Lightning
Protective Level
LPL
Switching Surge Protective
Level
SPL
MP1= (CWW/FOW)-1
MP2= (BIL/LPL)-1
MP3= (BSL/SPL)-1
IEEE recommends > .15 or 15%
IEEE recommends >.15 or 15%
IEEE recommends >.20 or 20%
53. Phase to phase and phase to ground clearances
are often the purpose of a study.
They are easily calculated once the maximum
voltage on a line is determined.
With arresters, the NEC clearances can be
reduced near the arrester and along ROW if
studies are completed.
For example,
Lightning Impulse withstand
of Air at STP is a linear
function at 450kV/m
54. Clearance and Altitude/Elevation
0.600
0.650
0.700
0.750
0.800
0.850
0.900
0.950
1.000
0 2000 4000 6000 8000 10000 12000
Ratio
of
Altitude
to
Sea
Level
Elevation in Feet
Change in
Withstand voltage
'δ=e-A/26710
All external insulation is
affected by altitude.
Specifically in this case, the
clearance between lines
needs to be increased to
attain the same withstand
voltage at sea level.
56. V
V
30 0m
NC
V
25 meters
V
2 m
AFram
LineA
5 ohms
LCC
R(i)
R(i)
Sourc
V
2uh 2 meters
5 ohms
L_imp H
L_Imp
LCC
I
V
R(i)
I
230kV
200 m
NC
20 m 2 m
Ej 230/13.8
BCT
Y
Et
V
Ea
R(i)
R(i)
R(i)
I
6.3nF
3m
Eb
V
Insulation Coordination of Power Systems
by Andrew Hileman
Line Entrance
Arrester
Transformer
Arrester
Flashover of
C-Phase close
to substation
6000ft 2000 ft 2000 ft
Surges travel at ~980ft per µs on
an overhead line.
In this elongated station, It can be
seen here that the surge first
appears at the metered points at
different times based on the
distance from the initial surge.
Backflash
6000 ft out
on the line
At Station
Entrance
At
Breaker
At
Arrester
Elongated Substation
60. Ground Flash Density
Is used to calculate the
• Backflash rate on a line
• The challenge rate to a line
• The outage rate of lines
• Steepness of a surge on a line
• The MTBF of a substation
