CLASSIFICATION OF FUSES by IEEE

Fuses for high voltage as defined in IEEE Std C37.40-1993 refers to fuses with rating above 1000 V. It covers covers fuses used in both medium- and high-voltage systems. 

Fuses may also be classified as power fuses and distribution fuses, depending on the intended location of the fuses in the power system.

In addition, fuses may be classified for

— Outdoor application only, or

— Application indoors or in enclosures

Fuses using new technologies have been available since the early 1980s, but have not yet been addressed by standards.

POWER FUSES

According to ANSI C37.42-1996, a power fuse is identified by the following characteristics:

— Dielectric withstand [i.e., basic impulse insulation level (BIL)] strengths at power levels

— Application primarily in stations and substations

— Mechanical construction basically adapted to station and substation mountings

Power fuses have other characteristics that differentiate them from distribution fuses in that they are available in higher voltage ratings, higher continuous-current ratings, higher interrupting-current ratings, and in forms suitable for indoor and enclosure application and for all types of outdoor applications.

A power fuse consists of a fuse support (commonly called a mounting) plus a fuse unit or, alternately, a fuse holder that accepts a refill unit or fuse link.

Power fuses are rated as E or R depending on their melting characteristics. They are defined as follows:

—

E rating

.

The current-responsive element for ratings 100 A or below shall melt in 300 s at a root-mean-square (rms) current within the range of 200% to 240% of the continuous-current rating of the fuse unit, refill unit, or fuse link. The current-responsive element for ratings above 100 A shall melt in 600 s at an rms current within the range of 220% to 264% of the continuous-current rating of the fuse unit, refill unit, or fuse link.

—

R rating

The fuse shall melt in the range of 15 s to 35 s at a value of current equal to 100 times the R number. When interchanging E-rated fuses of one manufacturer with another, coordination should be carefully checked because the time-current characteristics (TCCs) may be different. The same guidance applies to R-rated fuses. E-rated fuses are available as both expulsion and current-limiting, and R-rated fuses are available only as current-limiting.

Power fuses employing new technology, such as vacuum or sulfur hexafluoride (SF6) as the interrupting medium, have recently been developed. In general, these fuses have melting and clearing characteristics similar to expulsion fuses. Other new technology fuses feature built in sensing and electronics to develop special melting characteristics. 

These fuses ordinarily carry current through a bus bar. When the built-in sensing calls for operation, current is transferred almost instantaneously to a current-limiting fuse section for interruption by physically separating the bus bar element sufficiently to prevent restrike from the system voltage and the transient impulse created during the current-limiting interruption process. Some designs can take a command from other protective systems located remotely from the fuse.

DISTRIBUTING CURRENT LIMITING FUSES

According to IEEE Std C-37.40-1993, a distribution current-limiting fuse contains a fuse

support and a current-limiting fuse unit and is identified by the following characteristics:

a) Dielectric withstand (BIL) strengths at distribution levels

b) Application primarily on distribution feeders and circuits

c) Operating voltage limits corresponding to distribution system voltages

The specification for current-limiting distribution fuses is detailed in ANSI C37.47-1981. Depending on the melting time characteristics, they may be given a C rating, which is defined as follows: The current-responsive element shall melt in 1000 s at an rms current within the range of 170% to 240% of the continuous-current rating of the fuse unit.

The C rating specifies but one point on the TCC curve. While interchanging a C-rated fuse of one manufacturer with another, coordination should be carefully checked because the TCCs may be different.

The current-limiting fuse unit may be a disconnecting type or it may fit into a set of clips. Some fuses rated up to 15.5 kV also have circuit interrupters so they can be used to disconnect a live circuit. 

The principle application is in underground distribution systems and they are used for the protection of pad-mounted transformers supplying residential areas or small commercial or industrial plants. Another application is in small, enclosed capacitor banks.

Both the clip and disconnecting styles may be used to provide an open point on loop feeds. Backup fuses and some general purpose and full range fuses are also used in overhead systems where current limitation is desired. These types are also applied as under-oil fuses in distribution transformers for the same reason. 

Because current-limiting fuses do not emit any exhaust, they are also used in enclosures or vaults. Special types are used for the protection of individual capacitors in outdoor capacitor banks.

DISTRIBUTION FUSE CUTOUTS

According to IEEE Std C37.40-1993, a distribution fuse cutout is defined by the following

characteristics:

a) Dielectric withstand (BIL) strength at distribution levels

b) Application primarily on distribution feeders and circuits

c) Mechanical construction basically adapted to pole or crossarm mounting, except for

distribution oil-fused cutouts

d) Operating voltage limits corresponding to distribution system voltages

Characteristically, a distribution fuse cutout consists of a special insulating support and a fuse holder. The fuse holder, normally a disconnecting type, engages contacts supported on the insulating support and is fitted with a simple inexpensive fuse link. This type of fuse is normally an expulsion fuse; the holder is lined with a gas-evolving material, historically bone fiber. Interruption of an overcurrent takes place within the fuse holder by the action of deionizing gases liberated when the lining is exposed to the heat of the arc established when the fuse link melts in response to an overcurrent.

Distribution fuse cutouts were developed many years ago for use in overhead distribution circuits. They are commonly applied on such circuits along with distribution transformers supplying residential areas or small commercial or industrial plants. Fuse cutouts provide protection to the distribution circuit by de-energizing and isolating a faulted transformer. They are also used for protecting pole-mounted capacitor banks used for power factor correction or voltage regulation.

ANSI C37.42-1996 details the specifications for the distribution cutouts and fuse links. Distribution fuse cutouts are available up to a continuous current of 200 A at 15 kV and up to 100 A at 38 kV. 

Reference: IEEE HIGH VOLTAGE FUSES (1000 V THROUGH 169 KV) Std 242-2001

SPACING AND CLEARANCES FOR POWER TRANSMISSION LINES

From safety considerations, power conductors along the route of the transmission line should maintain requisite clearances to ground in open country, national highways, rivers, railways, tracks, telecommunication lines, other existing power lines.

The ground clearance for different voltages, which generally applicable are:

5.66 kV 6.5 m at  +650 C conductor temperature

6.132 kV 7.0 m at  +650 C conductor temperature

7.220 kV 7.5 m at  +800 C conductor temperature

The minimum clearances of conductor over rivers, which are not navigable, shall be kept 3.05 m over maximum flood level.

The minimum clearances between the conductors of a power line and telecommunication cable shall be:

132 kV 2.44 m
220 kV 2.74 m
400 kV         4.88 m

The minimum spacing between power lines shall be:

132 kV 2.75 m
220 kV 4.55 m
400 kV 6.00 m

The spacing of conductors is determined by considerations, which are partly electrical and partly mechanical. Usually conductors will swing synchronously (in phase) with the wind, but with long spans and small size of conductors, there is always possibility of the conductors swinging non- synchronously, and the size of the conductor and the maximum sag at the centre of the span are factors, which should be taken into account in determining the phase distance apart at which they should strung. As a rule of thumb, minimum horizontal spacing between conductors should not be less than 1% of the span length in order to minimize the risk of phases coming into contact with each other during swing.

There are number of empirical formula in use, deduced from spacing, which have successfully operated in practice:

NESC, USA formula
Horizontal spacing in cm,

Where A = 0.762 cm per kV line voltage
S = Sag in cm, and
L = Length of insulator string in cm
Swedish formula
Horizontal spacing in cm,

Where S = Sag in cm and
E = Line voltage in kV
French formula
Horizontal spacing in cm,

Where S = Sag in cm
L = Length of insulator string in cm
E = Line voltage in kV

Tower top clearance

Tower top clearance is the vertical clearance between earthwire and top conductor, which is governed by the angle of shielding. The shield angle varies from about 250 to 300,depending on the configuration of conductors. Tower top clearance shall be taken 1.5 and 2.25 m for 132 kV and 220 kV respectively for 00 swing.

CONDUCTOR STRINGING METHODS OF TRANSMISSION AND DISTRIBUTION LINES

Conductor stringing systems currently employed in the power industry are almost as numerous as the organizations that string conductors. Below is an outline of the basic methods currently in use, but they are invariably modified to accommodate equipment readily available and the ideas and philosophies of the responsible supervisors. 

In addition to a description of the various methods being used are comments relative to application and a listing of equipment applicable to each method. 

Slack or layout method

Using this method, the conductor is dragged along the ground by means of a pulling vehicle, or the reel is carried along the line on a vehicle and the conductor is deposited on the ground. The conductor reels are positioned on reel stands or jack either placed on the ground or mounted on a transporting vehicle. 

These stands are designed to support the reel on an arbor, thus permitting it to turn as the conductor is pulled out. Usually, a braking device is provided to prevent overrunning and backlash. When the conductor is dragged past a supporting structure, pulling is stopped and the conductor is placed in travelers attached to the structure before proceeding to the next structure.

This method is chiefly applicable to the construction of new lines in cases in which maintenance of conductor surface condition is not critical and where terrain is easily accessible to a pulling vehicle. The method is not usually economically applicable in urban locations where hazards exist from traffic or where there is danger of contact with energized circuits, nor is it practical in mountainous regions inaccessible to pulling vehicles.

Major equipment required to perform slack stringing includes reel stands, pulling vehicle(s), and a splicing cart.

Tension method

Using this method, the conductor is kept under tension during the stringing process. Normally, this method is used to keep the conductor clear of the ground and obstacles, which might cause conductor surface damage, and clear of energized circuits. 

It requires the pulling of a light pilot line into the travelers, which in turn is used to pull in a heavier pulling line. The pulling line is then used to pull in the conductors from the reel stands using specially designed tensioners and pullers. 

For lighter conductors, a lightweight pulling line may be used in place of the pilot line to directly pull in the conductor. A helicopter or ground vehicle can be used to pull or lay out a pilot line or pulling line. 

The tension method of stringing is applicable where it is desired to keep the conductor off the ground to minimize surface damage or in areas where frequent crossings are encountered. The amount of right-of-way travel by heavy equipment is also reduced. 

Usually, this method provides the most economical means of stringing conductor. The helicopter use is particularly advantageous in rugged or poorly accessible terrain.

Major equipment required for tension stringing includes reel stands, tensioner, puller, reel winder, pilot line winder, splicing cart, and helicopter or pulling vehicle.

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FIBER OPTICS TECHNICIAN'S MANUAL, 4E is the ideal practical guide for designers, installers, and troubleshooters of fiber optic cable plants and networks. It reflects recent changes in fiber optic technology, marketing, and applications, including wider usage of Fiber To The Home (FTTH) applications and Local Area Networks (LANs). This book begins with a brief history of the development of fiber optics and progresses from the basics of this technology and its components, to installation and testing. FIBER OPTICS TECHNICIAN'S MANUAL, 4E will provide readers with a comprehensive overview of all aspects of fiber optics as used in communications systems, including telephone, CATV, and computers.


About the Author
Jim Hayes is a founder and President of The Fiber Optic Association, the professional society for fiber optics. He is also a partner in VDV Works, a company that provides tech support to the voice-data-video industry in the form of marketing, training and technical content for websites, literature or newsletters and other technical assistance services. Originally educated as a physicist and astronomer at Vanderbilt University and The University of California at Santa Cruz, Jim has been involved with the electronics and test instrumentation industry since 1968. For the last 25 years, he has been involved with fiber optics and communications. Jim was founder and President of Fotec, Inc., the Boston-based fiber optic test equipment company which was sold to Fluke Networks in 2001. He started the Fiber U and Cable U training conferences. Jim is a frequent lecturer on communications, writes monthly columns for Electrical Contractor and TED (The Electrical Distributor) and is the author of two VDV books, The Fiber Optic Technicians Manual and Data, Voice and Video Cabling and numerous articles on fiber optics and cabling. --This text refers to an out of print or unavailable edition of this title.

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Fiber optics is the hottest topic in communications and this book from the world's leading experts clearly lays out all the details of optical communications engineering

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* Clear explanations and answers to tough challenges for WDM, DWDM, amplifiers, solitons, and other key technologies

OPTICAL COMMUNICATIONS ENGINEERING -- FROM THE LEADING EXPERTS IN THE FIELD
With their proven ability to provide both enormous speed and capacity, fiber optic networks have become the hands-down technology favorite for capacity-intensive broadband access applications. Business Week estimates the current fiber-optic networking market at an incredible $16.1 billion. Understanding fiber optical communications engineering has become must know information for engineers, engineering managers, researchers, and students. This authoritative reference, culled from the pages of the OSA's renowned Handbook of Optics, offers the combined expertise of a team of international experts to give you the answers you need to ride the fiber optics wave to success.

Prepared under the auspices of the Optical Society of America, Fiber Optics Handbook includes detailed, expert coverage of every essential topic in what has become the hottest field in telecom:

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* Solitrons
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* Tapered-Fiber Couplers, MUX, and deMUX
* Optical Time-Division Multiplexed Communications Networks
* Infrared Fibers
* Optical Fiber Sensors
* Fiber-Optic Communications Standards
* Sources, Modulators, and Detectors
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This book provides you with the knowledge to analyse, specify and debug SCADA systems in the instrumentation and control environment.

A SCADA system gathers information, such as where a leak on a pipeline has occurred, transfers the information back to a central site, alerting the home station that the leak has occurred, carrying out necessary analysis and control, such as determining if the leak is critical, and displaying the information in a logical and organized fashion. SCADA systems can be relatively simple, such as one that monitors environmental conditions of a small office building, or incredibly complex, such as a system that monitors all the activity in a nuclear power plant or the activity of a municipal water system.

An engineer's introduction to Supervisory Control and Data Acquisition (SCADA) systems and their application in monitoring and controlling equipment and industrial plant

Essential reading for data acquisition and control professionals in plant engineering, manufacturing, telecommunications, water and waste control, energy, oil and gas refining and transportation

Provides the knowledge to analyse, specify and debug SCADA systems, covering the fundamentals of hardware, software and the communications systems that connect SCADA operator stations



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Bestselling author Ron Krutz once again demonstrates his ability to make difficult security topics approachable with this first in-depth look at SCADA (Supervisory Control And Data Acquisition) systems, Krutz discusses the harsh reality that natural gas pipelines, nuclear plants, water systems, oil refineries, and other industrial facilities are vulnerable to a terrorist or disgruntled employee causing lethal accidents and millions of dollars of damage-and what can be done to prevent this from happening

Examines SCADA system threats and vulnerabilities, the emergence of protocol standards, and how security controls can be applied to ensure the safety and security of our national infrastructure assets

How to secure systems that weren't built for security
Worldwide, critical economic and governmental infrastructures have evolved into complex networks that facilitate communication, cost reduction, and efficiency. But the very features that create such benefits make these supervisory control and data acquisition, or SCADA, systems a security nightmare.

In the first guidebook to specifically address this vital problem, a veteran systems security expert shows you how SCADA systems have developed and how to understand their components and architecture, recognize risks and vulnerabilities, and learn to use appropriate protocols and countermeasures to protect vital information from cyber-terrorism.

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SCADA (Supervisory Control and Data Acquisition) systems are at the heart of the modern industrial enterprise ranging from mining plants, water and electrical utility installations to oil and gas plants. In a market that is crowded with high-level monographs and reference guides, more practical information for professional engineers is required. This book covers the essentials of SCADA communication systems focussing on DNP3, the IEC 60870.5 standard and other new developments in this area.

It commences with a brief review of the fundamentals of SCADA systems' hardware, software and the communications systems (such as RS-232, RS-485, Ethernet and TCP/IP) that connect the SCADA Modules together. A solid review is then done on the DNP3 and IEC 60870.5 protocols where its features, message structure, practical benefits and applications are discussed. This book provides you with the knowledge to design your next SCADA system more effectively with a focus on using the latest communications technologies available.

* Covers the essentials of SCADA communication systems and other new developments in this area
* Covers a wide range of specialist networking topics and other topics ideal for practicing engineers and technicians looking to further and develop their knowledge of the subject
* Extremely timely subject as the industry has made a strong movement towards standard protocols in modern SCADA communications systems.


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This is a free ebook about basics of Programmable Logic Controller (PLC).

A programmable logic controller, also called a PLC or programmable controller, is a computer-type device used to control equipment in an industrial facility. The kinds of equipment that PLCs can control are as varied as industrial facilities themselves.

Conveyor systems, food processing machinery, auto assembly lines…you name it and there’s probably a PLC out there controlling it. In a traditional industrial control system, all control devices are wired directly to each other according to how the system is supposed to operate. In a PLC system, however, the PLC replaces the wiring between the devices. Thus, instead of being wired directly to each other, all equipment is wired to the PLC.

Then, the control program inside the PLC provides the “wiring” connection between the devices. The control program is the computer program stored in the PLC’s memory that tells the PLC what’s supposed to be going on in the system. The use of a PLC to provide the wiring connections between system devices is called softwiring.

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TRANSPOSITION Of TRANSMISSION LINES TUTORIALS AND PDF LINKS

Transposition in transmission line is a technique use to restore some sore of “electrical voltage drop” and current balance of the transmission line system. It is only applicable though in three phase system. It us done by literally, and physically exchanging the conductor position along the line.

When the conductors of a three phase line are not spaced equilaterally, which is case often, the flux linkage and inductance of each phase are not the same. This difference in each phase results in an unbalanced circuit.

Balance of these phases can be restored by exchanging the positions of the conductors at regular intervals along the line so that each conductors occupies the original position of every other conductor over an equal distance.

A complete transposition cycle is shown below:

Transposition results in each conductor having the same average inductance over the whole cycle.

Modern power lines are usually not transposed at regular intervals, although interchange in the positions of the conductors may be made at switching stations, in order to balance the phases more closely.

More transposition tutorial and pdf download links below:

TRANSMISSION LINE TRANSPOSITION

According to existing concept the transposition of transmission line phases is intended for reducing the unbalance of current and voltage in normal operation mode of electric system and for limiting the obstructive influence of transmission lines to low-frequency transmission channel. Read more...

RESONANCE EFFECT DUE TO CONDUCTOR TRANSPOSITION IN THREE PHASE POWER LINES

This paper is concerned with the effects produced by conductor transposition in long overhead three phase power lines. Consideration of these resonance phenomena is of major importance and should be taken into account in a variety of situations. Read more...

HOW TO DESIGN TRANMISSION LINES – Engineering Basics

Once the route and length of a transmission or distribution line has been decided upon and the correct conductor size and type selected to carry the system load safely and economically, there are still several mechanical considerations which will have an effect on installation practices and may influence the final choice of conductor.

The line designer must consider such factors as tower and pole locations and heights, span lengths, conductor tension and sags, ground clearances, etc. Technically, this means that he must have detailed knowledge of conductor sag-tension characteristics as a function of span length, temperature, and weight loading. Much of this information is applied by wire and cable manufacturers in the form of tables and graphs that are to be used by the line designer.

Supplementing these, the line designer prepares other graphs, tables, templates, etc., that are related to a specific installation. Thus, there are two distinct types of study: 

(1) That which is ordinarily performed by the engineers of the wire and cable manufacturers, and 

(2) that which is performed by the line-design engineer to utilize the manufacturer supplied information to best advantage.

An overhead conductor suspended between insulator supports assumes the shape of a catenary curve provided the conductor is of uniform weight per ft. Usually it is convenient, without significant error, to regard the curve as a parabola.? A family of such curves exists for a given conductor and span.

The mid-point sag depends on tension in the conductor; the greater the tension the less the sag. To distinguish between span length and conductor length, the latter is usually designated arc length.

Anything that increases arc length after initial stringing increases the sag. Factors that may bring this about are ( 1 ) thermal expansion of the conductor because of increase of temperature above that during stringing, (2) increase of conductor apparent weight because of wind and/ or ice load, (3) creep gradually lengthening the conductor wires as a result of tension being applied over a period of many years, (4) stressing of wires beyond their elastic limits.

Though it might appear that sag-tension problems relating to these subjects could be solved in a simple manner, there are interrelated factors that must be taken into account. For example, ACSR has components that have differing stress-strain characteristics, differing coefficients of thermal expansion, and they normally undergo differing unit tensile stresses.

Thus, it is evident that proper selection of span length and sags for a given profile and conductor in order to minimize installation and operational costs requires a high order of engineering skill. However, for many applications, the required sag-tension analysis has been made by others, and the results are available in tables and graphs supplied by wire and cable manufacturers for all commercially offered conductors. Only a moderate amount of additional work is necessary to utilize them for specific applications.

TEMPERATURE MEASUREMENT ON OVERHEAD TRANSMISSION LINES (OHTL) UTILIZING SURFACE ACOUSTIC WAVE (SAW) SENSORS

In the deregulated market of electric transmission power systems today and as the energy demand continues to increase, electric utilities are faced with the challenge of moving more power via existing lines while at the same time obtaining permission for the erection of new lines and upgrading of existing lines becomes increasingly more difficult. 

As a result, power utilities and system operators are currently looking for opportunities to increase the capacity of the existing OHTLs without increasing the risk of equipment or system failure due to higher loading and an accelerated aging of the transmission infrastructure. One approach to manage the reliable operation of these systems is to utilize modern monitoring techniques as a method to prevent unexpected system outages. 

On OHTLs the sag of the individual line is an operational and security concern, which directly relates to the conductor operating temperature. The conductor operating temperature is influenced by various conditions eg. line losses, ambient temperature, wind speed and direction, solar radiation and 

conductor material properties. 

During periods of high ambient temperatures, low wind speed and high electrical system load conditions, monitoring and analyzing regional areas of the transmission network can be essential  to evaluate the actual conductor operating temperature for the purpose of optimizing the line capacity and to prohibit potential sag problems. 

For measuring the conductor temperature of an overhead transmission line a sensor, which will have approximately the same thermal behaviour as the conductor, can be mounted on the conductor. Due to the high electrical and magnetic stresses in the area surrounding the overhead transmission line, a purely passive SAW sensor is used. The temperature of the conductor at the point of installation can be measured and 

the data transmitted wirelessly by means of a radio frequency backscatter (radar principle) to a data collection 

point. 

Along the overhead transmission line, installed passive sensors observe the temperature of critical line locations allowing continuous monitoring of the line behaviour. The measuring principles of the SAW sensor, the involved radar system components as well as current applications are presented. 

Read the rest of this technical paper on the site below:

Click on this LINK!!!

TRANSMISSION LINES NEWS - BRAZIL NEEDS TO INVEST $23 BILLION FROM NOW TO 2019

This news is written by By João Carvalho / Business News Americas
Source may be found here.

Brazil needs to invest 39bn reais (US$23.5bn) between now and 2019 in new transmission lines as part of the initiative to keep power supply stable in face of the country's economic growth, according to a study from the government-linked thinktank Ipea.

Brazil will have to implement 36,000km of new transmission lines until 2019 to link new energy projects to the national power grid and to connect different regions to the main power distribution networks.

Brazilian utility sector regulator Aneel said Brazil's basic transmission network - equal or greater than 230kV - increased by 2,524km to 95,800km last year, BNamericas previously reported.

The expansion followed completion of 24 projects, the largest of which were the 400km São João Piauí-Milagres line connecting states Piauí and Ceará, and the 367km Colinas-Ribeirão Gonçalves line in Piauí.

According to Ipea, the estimate was considered with annual GDP growth of 5% through 2019.

Heating Circuits Basic Tutorial - HVAC HOT AIR HEATING

Hot-air furnaces are self-contained and self-enclosed units. They are usually centrally located within a building or house. Their purpose is to make sure the temperature of the interior of the structure is maintained at a comfortable level throughout.

The design of the furnace is determined by the type of fuel used to fire it. Cool air enters the furnace and is heated as it comes in contact with the hot-metal heating surfaces. As the air becomes warmer, it also becomes
lighter, which causes it to rise.

The warmer, lighter air continues to rise until it is either discharged directly into a room, as in the pipeless gravity system, or is carried through a duct system to warm-air outlets located at some distance from the furnace. After the hot air loses its heat, it becomes cooler and heavier. Its increased weight causes it to fall back to the furnace, where it is reheated and repeats the cycle.

This is a very simplified description of the operating principles involved in hot-air heating and it is especially typical of those involved in gravity heating systems. The forced-air system relies on a blower to make sure the air is delivered to its intended location.

The blower also causes the return air to move back to the furnace faster than with the gravity system. With the addition of a blower to the system, there must be some way of turning the blower on when needed to move the air and to turn it off when the room has reached the desired temperature. Thus, electrical controls are needed to control the blower action.

SAFETY IN TRANSMISSION LINES – PPE FOR LINEMAN

Safety is an important issue in any industry. This is most significant in the field of electricity and electrical engineering.

The linemen, best epitomize the risk involved in the filed of transmission and distribution line engineering. They are at the forefront and front line of construction, repair, and rehabilitation  of lines.

They are at risk, both from electrical shock, mechanical hazards, and the height of the pole pose more risk for them. That is why, it is very important to focus safety on their daily tasks.

This entry is about some of the personal Protective Equipment used by our Linemen, on their tasks.

PPE or Personal Protective Equipment is defined in the Regulations as ‘all equipment (including clothing affording protection against the weather) which is intended to be worn or held by a person at work and which protects him against one or more risks to his health or safety’. In the context of transmission and distribution engineering, these PPE will refer to the following:

Safety Belts (Lineman's Belt).

For use with a body belt component secured around the waist of the user such as a utility pole lineman. The safety strap and pole belt are coupled together at their midpoints, with the pole belt having buckle means at the ends for buckling the belt relatively closely around the pole.

Hard Hat. 

Hard hat is used to protect your head and skull from falling objects from up the pole. This is a basic PPE that everyone should use.

Safety Goggles. 

Safety glasses are excellent for lineman or others that are exposed to electric arc. Safety glasses that are fully dielectric with no metal parts is a good  protection from harmful UV-A and UV-B rays and are coated to offer superior scratch-resistance.

Insulating Rubber Gloves. 

Rubber insulating gloves for electrical workers are one of the most important items for personal protection that you require. The excellent insulating factor of rubber along with the high dielectric, physical strength and flexibility has earned it the reputation of providing a superior performing rubber insulating glove.

Dielectric Over Shoe Footwear

Dielectric overshoes are worn by workers who are around electricty.  Dielectric overshoes are rubber shoes worn directly over the top of normal shoes. They are worn by people who are at risk of electric shock due to working, or contact, with live electricity like linemen.

TESTING OF INSULATOR SETS OF TRANSMISSION LINES

Testing of insulator sets concerns the electric characteristics. Requirements on the performance under power frequency voltage as well as lightning and switching surge voltages are verified using testing.

The design of the insulation has to guarantee that the required data corresponding to the selected insulation levels. Insulation levels on the other hand are taken from the Insulation Coordination study done on the transmission line system.

Testing of insulators might be done to verify these characteristics. But these are not mandatory, as per IEC 60 383-2.

During testing, insulators must be clean and dry. They should be stored on test laboratory ambient temperature for sufficiently long period so that temperature equalizing is reached before conducting the test. This is done to prevent condensation on the insulator surfaces.

Below are some of tests conducted on insulator sets, used in transmission lines.

Power Frequency Voltage Test

Power frequency voltage test is made under rain conditions and is foreseen only for insulators sets up to 245 kV. The power frequency withstand voltage applied is the specified value after its correction. It is applied for 1 minute and no flashover or puncture may occur.

The flashover voltage can be determined only as additional information or even as the result of the previous agreement, by means of increasing the applied 75% value of the withstand voltage by 2 steps up to the point when flashover occurs. The flashover voltage is determined as the arithmetic mean of the last five consecutive reading.

Fast Front and Slow Front Overvoltage Test

The Fast Front and Slow Front Overvoltage Test dry, simulating lightning surges, is required for every voltage level. While the Slow Front Overvoltage Test, wet simulating switching surge, is a standardized for insulators sets only for highest voltage equipment above 245 kV.

Either a standard 1, 2/50  microsecond lightning surge or a 250/2500  microsecond switching surge is applied with both positive and negative polarities. No damage may occur to the insulators, although slight traces on the surface or crumbling of cementing material may be allowed.

Radio Interference Strength Test

Radio interference  levels caused by corona at high voltage lines are important only at voltage above 245 kV. Because of this, the Radio Interference test is only an optional test.

Corona Onset or Extinction Voltage Test

As a guideline, the extinction voltage should at least 1.05 Us sqrt 3. Test are usually performed on a complete insulator sets.

AIR CON ENERGY SAVING TIPS TUTORIALS

ENERGY SAVING AIR CONDITIONING TIP
Air conditioning does more than cool the air. It truly "conditions" it by removing dust and dirt as the air is drawn through a filter. Air conditioning also lowers the humidity, making the air more comfortable at any temperature. These benefits, however, can be costly. Depending on your region of the country, air conditioning can account for anywhere from 5 to 50% of your household budget. Because an air conditioner is such a sizable investment, you can save money and energy by carefully purchasing and operating your air conditioner. Continue reading...

AIR CONDITIONING ADVICE - Energy Saving Tips
Following basic energy saving tips for your air conditioning system is important since it is one of the largest power consuming devices in your home. In fact, it can cost you up to half of your electric bill! Ensuring your air conditioner is running at peak efficiency is key. Here are some really basic energy saving tips and simple maintenance tips that will help save you money: Continue reading...

Air Conditioning Energy Saving Tips
It costs you more money and uses more energy to heat and cool your home than any other system in your home. Typically, 44% to 50% of your utility bills pays for heating and cooling your home. Regardless of the type of home comfort systems you have in your house, you can save money and increase comfort by properly maintaining and upgrading your equipment. Continue reading...

Energy Saving Air Conditioners
Get the facts on cooling efficiency before you buy
If you're like most North Americans, an energy saving air conditioner can make a big dent in your household energy budget. And with energy prices on the rise, you'll definitely want to do what you can to make better use of your current air conditioner, or find the most efficient new one you can afford. Continue reading...


Air Conditioning Energy Saving Tips - A few tips to help reduce energy use during the hot summer months
More Efficient Air Conditioning:
One of the most inexpensive and effective ways to reduce your air conditioning costs is to adjust your thermostat setting. The savings can be significant when you set your thermostat at 78 degrees Fahrenheit or higher. For each degree you raise your thermostat setting, you reduce seasonal cooling costs by 6 to 8 percent. Continue reading...

Welcome to AIRCOSAVER - the Air Conditioning Energy Saver
Energy efficiency: the smart answer to today's energy crisis!
Energy efficiency improvements of today's aircon systems are by far the quickest, most affordable and most effective way to reduce CO2 emissions and lower your energy bill. Continue reading...


AIR CON TIPS ON ENERGY SAVINGS
The energy used in the average home can be responsible for more than twice the greenhouse gas emissions of the average car. When you use less energy at home, you reduce greenhouse gas emissions from power plants and help protect our environment from the risks of global climate change. Continue reading...

Energy Efficiency & Maintenance Guide for your Home Air Conditioner
Air Conditioning works to cool or warm your home, creating a comfortable living environment by filtering the air and removing the moisture which causes humidity.
Cooling
Heating
User tips Continue reading...

SAG AND TENSION CALCULATIONS OF TRANSMISSION LINE

If a conductor is sagged with a given tensile force between two points (A and B) representing the attachments of the conductor at the supports, a curve, the sagging curve or catenary will be formed due to the balance between conductor dead loads and tensile forces.

The vertical distance of the conductor to the line connecting both attachment points A and B is called the conductor sag.

The calculation of sag and tension of transmission lines can be quite useful to the engineer. The calculations are used to select the appropriate size support strand for a given application or to determine if clearance requirements are met.

With today’s clearance requirements the only way to assure clearance requirements are met is by calculation. The calculations serve as an aid to the designers who determine the mechanical stress that the cable must be capable of withstanding or to evaluate such problems as expansion loop cracks and center conductor pullouts.

The following are links to discussion of sag and tension calculations that will be useful as tips and reference to engineers and students alike.

CONDUCTOR SAG AND TENSION CALCULATIONS

The Mechanics of Overhead Distribution Line Conductors

The behavior and movement of a suspended conductor is  the most unpredictable variable in distribution line design.  Since complex equations are used to calculate the conductor sag curve, some simplifications and approximations are used.  The approximations cause small errors.  The accuracy of the final calculated results decreases as the  curve equation is simplified. Read more...

Sag and Tension Calculations for Overhead Transmission Lines at High Temperatures— Modified Ruling Span Method

This paper presents a method to calculate sags and tensions of multi-span line segments at different temperatures based on the rotational stiffness of suspension insulator strings. A simple equation, based on the parabolic approximation, is derived to calculate changes in the span lengths and conductor sags and tensions. Read more...

Sag-Tension Calculations: Refinements and Enhancements Made by Pondera

This paper discusses the modifications and enhancements related to the input data, and explains how these changes improve transmission line planning capabilities. Calculation methods are also provided. Read more...

Sag and Tension Calculations for Mountainous Terrain

While normal sag and tension calculations based on the 'equivalent-span' concept are satisfactory, when applied to transmission lines located in a reasonably undulating terrain, the answers obtained by this method are inaccurate for mountainous terrain. An alternative method of calculation, which is based on the analysis of the change of state equation for each span of a section in turn, is given. Read more...

Sag and Tension Calculations For Conductor/Earth Wire For River Crossing

Sag and tension calculations for conductor earth wire are done for the river crossing by following steps :

Determination of Equivalent Span :

Based on anchor spans L1 & L3 and crossing span L2, the equivalent span for river crossing portion is determined by the following formula :

Eq. Span = ÖL13 + L23 + L33 / L1   + L2   + L3 Read more...

TRANSMISSION LINE ARRESTER STANDARD GUIDELINES

Line arresters are not specifically addressed in C62.11-1999, although the arresters used in these applications are part of the standard. Most of the test requirements that apply to line arresters are based on station requirements or distribution class requirements.

When specifying line arresters, it should be noted that the following points are inherent to C62.11-1999.

1. Lightning energy handling capability can be a major factor in selecting line arresters depending on their application. The requirement of lightning related energy is typically much more significant for lines than stations. Although present standards do contain some lightning-related tests, there is not presently an accepted test to quantify the lightning energy handling capability of surge arresters. Published energy handling capability of arresters is typically based on switching-related tests.

2. Heavy-duty distribution arresters may be subjected to more severe lightning-related tests than station class or intermediate class arresters. Although it is common belief that arrester lightning energy capabilities increase from heavy-duty distribution to intermediate to station, the present standards do not necessarily prove this through testing.

3. The 100-kA test for heavy-duty distribution arresters should not be confused with an arrester surviving a 100-kA lightning stroke. First, the 100-kA test is a 4 x 10 ms wave that has much less energy than a typical 100-kA lightning stroke. Second, the 100-kA tests allow up to 5 minutes before the arrester is connected to MCOV to prove thermal stability.

4. Short-circuit tests permit polymer arresters to fall apart as long as the pieces fall within specific areas. The tests allow 2 minutes before the arrester must self-extinguish. These allowances in the present standards may not be acceptable for certain areas on a line right-of-way.

LIGHTNING FLASHOVERS ON OVERHEAD TRANSMISSION LINES

 Lightning flashovers are segregated into three main types, for stroke locations on a phase conductor, on an overhead shield wire, or to nearby ground.

SHIELDING FAILURE FLASHOVERS

Shielding failure flashovers events result from a lightning stroke terminating directly on a phase conductor. For shielded lines, these events should be very infrequent and of very low stroke current magnitude.

For unshielded lines (i.e., “static less” lines), these events will be much more common and will involve the full distribution of lightning stroke current magnitudes. Arresters can be used to address shielding failure flashovers by applying the arresters on the exposed phases.

The arresters must be installed at every tower or pole to be effective at preventing shielding failure flashovers. For unshielded line applications, arrester energy requirements must be adequately addressed since the stroke currents and durations they will be exposed to are harsher than in shielded line applications.

BACK FLASHOVERS

Back flashovers, events result from a lightning stroke terminating on the ground system (i.e., shield wires, tower tops, and pole tops) causing a potential across the insulation that causes a flashover to occur.

The surge traveling on the shield wire will cause surge voltages to be induced in the phase conductors. The magnitude of the induced voltage is a function of the current magnitude, resistance, and geometry.

Stroke currents exceeding a critical current value will develop sufficient voltage between the structure and the phase conductor to cause an insulator flashover. The phase with the poorest coupling to the shield wire will be the most highly stressed and therefore most likely to flash over. Local grounding conditions have a major impact on back flashover performance.

Arresters can be used to address these types of outages by placing them on the least coupled phases (e.g., bottom phases) or in high footing resistance areas. For applications in high footing resistance areas, it is important to apply the arresters not only in the areas of high footing resistances, but also one or two structures away from the high footing resistance areas.

INDUCED VOLTAGE FLASHOVERS

Induced voltage flashovers events result from nearby lightning strokes inducing voltages on line

conductors. Because the induced overvoltages measured on distribution lines rarely exceed 300 kV, it is common belief that this phenomenon has little effect at transmission voltage levels. However, the induced voltages tend to increase with line height.

There may be some structures used at 34.5 kV through 69 kV (sometimes referred to as “sub-transmission” voltages) that could be susceptible to induced voltage flashovers from nearby lightning strokes.

For lines that are susceptible to induced voltage flashovers, arresters at relatively wide spacing may be used to minimize the effects of these events.

CAST RESIN TRANSFORMERS TUTORIALS AND LINKS

Cast resin transformers. You've probably heard it, but not seen it. Or you might seen it but you don't know what it is called. Resin casting is a method of plastic casting where a mold is filled with a liquid synthetic resin, which then hardens. Whatever is the case, we are here to help you know more about cast resin transformers.


Cast Resin Transformer
Imefy cast resin transformers are produced according to the highest specifications environmental, climatic and fire of the international standards CENELEC HD 464 and IEC 726. These transformers are called C2 , E2, F1 and their thermal class is F (155°). The tests for the qualifications of these specifications were carried out at the CESI laboratories in Italy. The main characteristics of the specifications are: Read more...

Why Cast Resin Transformers?
The High-Security, Low-Cost Solution
• Reduced Costs: Low fire risk permits location near the load – shortens expensive LV feeders – reduces volt-drop.
• Planning Flexibility and Safety: No oil sump – no fire barriers –  no siting restrictions. Thermal  mass less than 15 % of equivalent oil transformer.  No special building work. Read more...

Home Product Electric Power Solutions Transformer Cast resin Transformer
LS CAST RESIN Transformers take pride in the ability to offer a wide variety of designs and configurations necessary to satisfy customer needs. Computer and CAD/CAM systems are used for quick and accurate design and manufacture to meet specific customer requirements. Read more...

Hyundai Wind Turbine System Cast-Resin Transformer
Hyundai cast-resin transformers are designed for easy installation and maintenance. They are also designed to withstand the highest mechanical short circuit stress that may occur in service. Having undergone strict quality control during manufacturing and an entire series of tests at our laboratories, Hyundai cast-resin transformers have been proven to be of high quality by international inspection agencies. Read more...

Cast-resin transformers excel in their fire behavior
Wherever distribution transformers are used in locations very close to people, GEAFOL cast resin transformers are the low-risk answer. Cast-resin transformers lack the limitations of oil-insulated transformers but share their desirable properties, such as operational reliability and a long service life. Read more...

LARGEST POWER TRANSFORMERS IN THE POWER SYSTEM WORLD

Power transformers are naturally big, both in importance and appearance. They are the focal point of a power system. This is a collection of large and massive power transformers.


World's Largest Cast Resin Power Transformer
Siemens Builds the World’s Largest Cast-Resin Transformer. With its Geafol cast-resin transformers, Siemens Power Transmission and Distribution (PTD) is increasingly developing into a specialist for high power ratings in the medium voltage range. By the end of September 2007, the world’s largest cast-resin transformer with a rated power capacity of 40 MVA left the factory in Kirchheim/Teck, Germany. Read more...

World's Largest Amorphous Metal - Based Transformer
12 MVA Oil-Filled Amorphous Metal Distribution Transformer
Produced by Korea’s Cheryong using Metglas-Based Wound Cores Manufactured by Woojin. Read more...

World’s Largest Electric Arc Furnace Transformer Manufactured By Alstom Grid Turkey
The new transformer is to be used in the iron and steel works facilities founded in Iskenderun in partnership between MMK, a major Russian steel producer, and Atakaş Group, one of the leading steel and coal production companies in Turkey. Field assembly and commissioning are to take place by year’s end. Read more...

POWER TRANSFORMERS SPECIFICATIONS & CATALOGS SAMPLES

Power Transformer is one of the most important parts in the power system. It is relatively the most expensive power equipment there is.

Specifying a power transformer entails lot of research, hard-work, and knowledge. This blog post is a collection of readily available power transformer specifications around.

In reality though, you need to come up with a specification that would best suit your needs. These specifications therefore should only be used as guides or reference as you specify your own power transformers.


Power Transformers Specifications 1
We manufacture power transformer strictly as per ISS standards. These power transformers are available up to 5000 KVA in 11, 22 and 33 KV class. These are available under the following specifications which can however be customized as per the requirements of our clients. Read more...


POWER TRANSFORMERS Specifications 2
PTI Power Transformers are designed and manufactured to meet specific customer requirements and specifications along with the applicable CSA, ANSI, NEMA, IEEE, IEC Standards. PTI prides itself in design flexibility which allows our products to be optimized to customer needs while continuing to meet the highest standards of quality and manufacturing techniques. Read more...

Toshiba Power Transformers
To cope with the increase in electrical power demand, power transformer capacity is growing larger and larger. In particular, the capacity of generator transformers for thermal and nuclear power stations have become very large. TOSHIBA manufactured a generator transformer of 200MVA in 1958, 430MVA in 1963, 680MVA in 1967, and 1100MVA in 1973. It broke the Japanese record for the largest capacity of all time.  Read more...


Oil-Immersed Power Transformer(500kv)
The oil-immersed transformer of 500kV has the distinguished features of low loss, low partial discharge, and good capability of anti-short circuit. The company has used advanced technology and analysis of magnetic field, thus optimized the structure of the products and enhanced the insulation level and safety. Read more...

Substation Transformers up to 69 kV
Prolec GE offers a complete line of liquid-filled distribution transformers that meet current applicable ANSI® / IEEE® standards. In addition to the already existing Substation Transformers product line Prolec GE now offers its brand new transformers, with high voltages from 34.5 kv to 69 kV and ranging from 5 MVA to 12 MVA (ONAN). Read more...

IEC STANDARDS DOWNLOAD LINKS

The International Electrotechnical Commission is the leading global organization that publishes consensus-based International Standards and manages conformity assessment systems for electric and electronic products, systems and services, collectively known as electrotechnology.

IEC publications serve as a basis for national standardization and as references when drafting international tenders and contracts.

The International Electrotechnical Commission serves world markets and society through its standardization and conformity assessment work for all electrical, electronic and related technologies – collectively known as "electrotechnology".

The IEC promotes world trade and economic growth and encourages the development of products, systems and services that are safe, efficient and environmentally friendly.

You may download their Standards and Publications on links below:

IEC Website
IEC Resources Page
Standards Page

GROUND FAULT CURRENT INTERRUPTER (GFCI) TUTORIALS AND PDF LINKS

GFCI or ground fault current interrupters measure the current flowing into the outlet through black or hot wires. If the GFCI deteds any difference greater than 7 milliamps, it shuts off the current. Any difference in the current is an indication that the currents is somehow shorting or leaking. These are dangerous situations, and a GFCI will shut down faster than a standard circuit breaker or fuse.

NESC and NEC required the intallation of GFCIs in the United States. According to a statistic in the US, if a GFCI is installed in every home, 2/3 of residential electrocution could have been prevented.

Recommended areas to put in GFCI re the following:

Bathrooms
Kitchen counters
Outdoors
Garage walls
Unfinished basements and crawl spaces

Water and water pipes are common on these places, and water and water pipes are good at attracting current away from its path, to your body.

Other information related to GFCI could be found on these carefully selected links.

How does a GFCI outlet work?
A GFCI is much more subtle. When you look at a normal 120-volt outlet in the United States, there are two vertical slots and then a round hole centered below them. The left slot is slightly larger than the right. The left slot is called "neutral," the right slot is called "hot" and the hole below them is called "ground." Read more...

What is a Ground Fault Current Interrupter (VIDEO)



Ground Fault Circuit Interrupter (GFCI) - Product Information
The National Electrical Code requires GFCI protection of receptacles located outdoors and in bathrooms, garages and spa areas. This GFCI circuit breaker provides protection against overloads, short circuits and ground faults. Read more...


Product safety tips from UL - Ground fault circuit interrupters (GFCIs)
UL periodically revises requirements in its Standards for Safety to harmonize with international requirements, address code and safety issues, and accommodate new product developments as applicable. UL has adopted new and revised requirements for ground fault circuit interrupters (GFCIs) that become effective January 1, 2003.  Read more...

What is a Ground Fault Circuit Interruptor (GFCI) and How it Can Protect Your Family
As a parent, you’ve probably never heard of a ground fault circuit interrupter (GFCI), but these little devices are a major advance in preventing electrical shock in and around the home. Look at the picture to the right – you probably have a few of these already installed in the outlets around your house. Read more...

Prevent Electrocutions: Install Ground-Fault Circuit-Interrupter Protection for Pools, Spas, and Hot Tubs
This fact sheet provides information about how to prevent electrocutions in pools, spas and hot tubs by installing ground-fault circuit interrupter (GFCI) protection. The U.S. Consumer Product Safety Commission (CPSC) recommends that consumers install ground-fault circuit-interrupter protection in pools, spas and hot tubs to prevent electrical shock hazards caused by underwater lighting circuits and in electric circuits of spas and hot tubs. Read more...

DIFFERENCE BETWEEN BREAKERS AND FUSES

Circuit breakers and fuses perform the same task. They interrupt electrical power when the current demand is too high. In cases such as a high unwanted current is present, and the breaker doesn't trip or the fuses won't burn out, the wire connecting could overheat and possibly start a fire.

Fuses.

Although there is a variety of fuses, most old residential system use the glass, screw in type called plug fuses. These fuses feature a narrow metal strip, visible through the glass, that quickly melts when too much current is starting to move through the circuits. Fuses are rated by amperage and cannot be reused after they burn or blow.

A fuse is generally safe if it is used according to its design. In other words.

-Always use the correct size fuse
-Be sure that the fuse is screwed in tightly
-Don't replace a fuse with anything else that a fuse

Breakers.

Breakers trip, while fuses burn. They trip when their metallic strip heats up, bends, and forces spring loaded contacts apart. After tripping they can be reset by pushing the breaker's switch all the way off, and then back again on the on position.

When resetting a circuit breaker, be sure to:

-Find out what causes the breaker to trip and shut off
-Use only one hand and keep the other one away from the service panel

Circuit breakers are rated by amperage (just like fuses). Don't even consider installing a higher rated breaker in place of a lower one. If you are having repeated tripping, you're overloading the circuit and need to change your usage or upgrade the circuit.

HOW TO READ RESISTORS BY ITS COLOR CODES

Reading color coded resistors is easy, if you know how. When you say reading, you really mean knowing the value of a resistor, before you put it in a circuit.

Reading color coded resistor's value is a basic knowledge or skill that one should have if they are into electronics and electricity. It is one of the foundation skills needed.

How to read resistor color code VIDEO

How To Read Resistor Color Codes - TRANSMISSION LINES DESIGN HUB

In school, we were taught this code: Bad Boy Rape Young Girls But Violeta Gave Silver Gold

 That code is used to know the value of the colors.

To fully understand and a tutorial on how to read the value of a resistor through its color codes, we've selected the best sites around. Browse and enjoy.

How to read Resistor Color Codes

Resistors are color coded for easy reading. Imagine how many blind technicians there would be otherwise.

To determine the value of a given resistor look for the gold or silver tolerance band and rotate the resistor as in the photo on the left. (Tolerance band to the right-- refer to the tolerance chart below for exact values.). Look at the 1st color band and determine its color. This maybe difficult on small or oddly colored resistors. Now look at the chart and match the "1st & 2nd color band" color to the "Digit it represents". Write this number down. Read more...

Resistor, Capacitor and Inductor

For example, a resistor with bands of yellow, violet, red, and gold will have first digit 4 (yellow in table below), second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold signifies that the tolerance is ±5%, so the real resistance could lie anywhere between 4,465 and 4,935 ohms.

Resistors manufactured for military use may also include a fifth band which indicates component failure rate (reliability); refer to MIL-HDBK-199 for further details. Read more...

How to Read Resistor Color Code

Resistors can come in different sizes and shapes allowing for different voltages to go through it. However, unless the size of the resistor is large, the code is rarely written on it because it would require very tiny markings. Therefore, a system was developed to use colors to determine the resistor code. In other words, by using different colors, an average user can determine exactly what the Ohms are for the resistor. Read more...
Resistor Color Codes - How to Read a Resistor 
Most resistors are color coded with multiple bands to identify the resistance value and the tolerance. While actually measuring the resistance before using it is a good idea, it's also a good idea to know what the resistance is supposed to be. Resistors (especially carbon composition) can drift in their actual resistance. Keep a stock of fresh resistors on hand. Use the following Standard EIA color code tables to identify resistors, or you can calculate the values on your your resistors using our handy resistance calculator. Click here to calculate the value of your 4-band resistors, or here for your 5-band resistors. Read more...


Resistor Color Code Calculator 
The calculator above will display the value, the tolerance and performs a simple check to verify if the calculated resistance matches one of the EIA standard values. Select the first 3 or 4 bands for 20%, 10% or 5% resistors and all 5 bands for precision (2% or less), 5-band resistors. Hover above the tolerance for min. and max. range values. Read more...

FAULT WITHSTAND CAPABILITY OF TRANSMISSION LINE CONDUCTORS

When a line (Transmission and / or Distribution) short circuit, very large currents can flow for a short time or up until a fuse, breaker or any isolation breaks the circuit. One important aspect of protecting the line from overcurrent and fault is to ensure that the fault arc and fault currents do not cause further, possibly more permanent, damage. The two main considerations are:

Conductor Annealing.

From the substation to the fault location, all conductors in the fault current path must withstand the heat generated by the short circuit current. If the relaying of fuse does not clear the fault in time, the conductor anneals and loses strength.

During high currents from faults, conductor can withstand significant temperatures for few seconds without losing strength. For all aluminum conductors (AAC), assuming temperature of 340®C is common. ACSR conductors can withstand even higher temperatures since short duration high temperature does not affect the steel core. You may assume a limit of 645®C melting temperature for Aluminum in ACSR.

Considering the heat inputs and conductor characteristics, the conductor temperature during a fault is related to the current as:

(I/1000A)² t = K log₁₀ [(T2+ƛ)/(T1+ ƛ)]

Where:

I = fault current (A)

t = fault duration (sec)

A = cross sectional area of conductor (kcMil)

T2 = conductor temperature from the fault

T1 =conductor temperature before the fault

K = constant

ƛ = inferred temperature of zero resistance

Conductor Material	ƛ, ®C	K
Copper (97%)	234.0	0.0289
Aluminum (61.2%)	228.1	0.0126
6201 (52.5%)	228.1	0.0107
Steel	180.0	0.00327

If we set conductors to their maximum temperature and at an ambient temperature of 40® C, these will be their characteristic curves:

AAC

I²t = (67.1A)²

ACSR

I²t = (86.2A)²

Covered conductors have more limited short circuit capability due to its insulation, as they are easily damaged even at relatively lower temperature.

Polyethelene

I²t = (43A)²

XLPE

I²t = (56A)²

Conductor Burndowns.

Right at the fault location, the hot fault arc can burn the conductor. If a circuit interrupter does not clear the fault in time, the arc will melt the conductor until it breaks apart.

Fault currents can damage overhead conductors. The arc itself generates tremendous heat, and where an arc attaches to a conductor, it can weaken or burn the conductor strands. On a distribution and transmission circuit, two areas stand out:

1. Covered Conductors. Covered conductors hold an arc stationary. Arc cannot move, burndowns happen faster than bare. The covering prevents the arc from moving.
2. Small Bare Wires. Small bare wires (less than 2/0) are also susceptible to wire burndowns, especially if laterals are not fused.

Conductor damage is a function of the duration of the fault and the current magnitude. Burndown damage occurs more quickly than conductor annealing.