Types of Conductors

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Types of Conductors:

There is no unique process by which all transmission and/or distribution lines are

designed. It is clear, however, that all major cost components of line design depend

upon the conductor electrical and mechanical parameters.

There are four major types of overhead conductors used for electrical transmission and

distribution.

AAC - All Aluminum Conductor

AAAC - All Aluminum Alloy Conductor

ACSR - Aluminum Conductor Steel Reinforced

ACAR - Aluminum Conductor Aluminum-Alloy Reinforced

The various combinations and modifications of these conductor types provide a wide

variety of possible conductor designs. AAC - All Aluminum Conductor, sometimes referred to as ASC,Aluminum Stranded

Conductor, is made up of one or more strands of 1350 Alloy Aluminum in the hard

drawn H19 temper. 1350 Aluminum Alloy, previously known as EC grade or electrical

conductor grade aluminum, has a minimum conductivity of 61.2% IACS. Because of its

relatively poor strength-to-weight ratio, AAC has had limited use in transmission lines

and rural distribution because of the long spans utilized. However, AAC has seen

extensive use in urban areas where spans are usually short but high conductivity is

required. The excellent corrosion resistance of aluminum has made AAC a conductor of

choice in coastal areas.

ACSR - Aluminum Conductor Steel Reinforced, a standard of the electrical utility industry

since the early 1900's, consists of a solid or s tranded steel core surrounded by one or

more layers of strands of 1350 aluminum. Historically, the amount of steel used to

obtain higher strength soon increased to a substantial portion of the cross-section of the

ACSR, but more recently, as conductors have become larger, the trend has been to less


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steel content. To meet varying requirements, ACSR is available in a wide range of steel

content - from 7% by weight for the 36/1 stranding to 40% for the 30/7 stranding. Early

designs of ACSR such as 6/1, 30/7, 30/19, 54/19 and 54/7 strandings featured high

steel content, 26% to 40%, with emphasis on strength perhaps due to fears of vibration

fatigue problems. Today, for larger-than-AWG sizes, the most used strandings are 18/1,

45/7, 72/7, and 84/19, comprising a range of steel content from 11% to 18%. For the

moderately higher strength 54/19, 54/7, and 26/7 strandings, the steel content is 26%,

26% and 31%, respectively. The high-strength ACSR 8/1, 12/7 and 16/19 strandi

are used mostly for overhead ground wires, extra long spans, river crossings, etc.

The inner-core wires of ACSR may be of zinc coated (galvanized) steel, available in

standard weight Class A coating or heavier coatings of Class B or Class C. Class B

coatings are about twice the thickness of Class A, and Class C coatings about three

times as thick as Class A. The inner cores may also be of aluminum coated (aluminized)

steel or aluminum clad steel. The latter produces a conductor designated as ACSR/AW in

which the aluminum cladding comprises 25% of the area of the wire, with a minimum

coating thickness of 10% of the overall radius. The reinforcing wires may be in a central

core or distributed throughout the cable. Galvanized or aluminized coats are thin, and

are applied to reduce corrosion of the steel wires. The conductivity of these thin coated

core wires is about 8% IACS. The apparent conductivity of ACSR/AW reinforcement wire

is 20.3% IACS.


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String affieancyH.V insulation provides isolation paths in T&D networks. The first aerial transmission line was designed in 1880 with

50 and 66 kV maximum operation voltage. Population growth as well as daily development of industrynecessitates power transmission reliability. In the other hand, strategic situation of power industry and necessity of reliable networks with minimum outage as vital demand of today's societies, stimulate extended activities in design,develop and operation of H.V insulators. Insulators hold conductors in transmission lines. As well, they isolate highvoltage lines from pole body (i.e. ground). Forced outages by insulation fault form high percentage of whole networkoutages. Operation under excessive voltages, more than insulator breaking voltage, is cause of most outages. Thissituation can be result of network design deficiency, insulator manufacturing process problems, inappropriateinsulator choice considering regional climatic conditions, insulator damage by human or natural accidents andunscheduled maintenance application.High voltage insulators are exposed to various climates. Severe environmental conditions and pollution degree havea strong influence on insulator performance and affect the reliability of T&D networks. Flashovers on high voltageinsulators due to natural pollution cause problems in the performance and reliability of overhead lines in pollutedareas. Deposited Pollution on insulator surface combined with humidity provides a conductive electrolyte and aconductive layer for leakage current. Daily development of T&D networks and necessity of power systems reliabilityto provide minimum outage in addition to pollution effects made pollution determination important. Types and degree

specification of pollution seems to be vital for efficient operation and proper choice of insulation.Based on the dc artificial pollution tests of various types of porcelain, glass, and composite insulators, the followingconclusions have been obtained in.1. There is a nearly linear relation between the dc pollution flashover voltage and the disc-type insulator stringlength.2. Compared with the porcelain disc insulators, the glass disc insulators with the same profiles have better antipollution performances.3. The pollution flashover performances of the composite long-rod insulators are affected by their materials andshed shapes.

A self-consistent dynamic model for application to ac voltage was established in [3] in order to simulate arc behavior on the surface of ice accumulated on insulator surface. The model considers the arc as time-dependent impedanceconstituted of a resistance in series with an inductance. The arc resistance throughout the period of arc propagationis determined by using Mayrs equation. The unbridged ice layer is replaced with an equivalent resistance, where thesurface conductivity is calculated by taking the effect of melting water into account. Conditions of slight wetting(drizzle, fog, high humidity) are probably most favorable for building up concentrated stable zones. Their temperatureis higher than the ambient, and leakage current is in the range of 1 mA.Concentrated stable discharges cause the degradation of polymer insulation. The related very no uniform voltagedistribution along the leakage path can initiate the ignition of internal partial discharges inside surge arresters or other high-voltage apparatus and can also decrease the flashover voltage of external insulation.

An experiment to study the form of the discharge during its evolution at the electrolyte surface and to determine thedifference between the real dynamic features of flashover and the theoretical dynamic ones has been done in.In some recent investigations ,it is shown that with the use of an alternating diameter shed design with small shedspacing, or selective protection to the regions that are prone to dry band activity by cup shaped sheds, the insulatorsperform significantly better than the commonly used straight shed designs.Climates play significant rule in pollution procedure and resulted electrical breakage. The followings are affected byclimate:1. Pollution deposition on insulation2. Pollution distribution on insulators surface3. Durability of Pollution condition4. Pollution dispersion amount from resourceHumidity is the most effective factor on pollution, pollution layer formation, self-cleaning and natural cleaning of insulation. Humidity includes different variables like relative and absolute humidity, fog, breeze and fallings.Precipitation effect on insulators self-cleaning and result in insulation faults if less than 20 mm annually. Basically drypollution layer is ineffective on insulation strength and only in moistening periods particles solvent provide conductivelayer on insulation surface. Other environmental parameters like temperature, precipitation, wind speed and direction,numbers of dusty and stormy days are effective on degree and intensity of pollution accumulation.

Assessment of wind influence on superficial electrical discharge and pollution deposit process is very complicated.Wind, depends on speed and direction, can be cleaner or polluter; it can transfer particles from near or far pollutionresources to insulation or clean them on their surface. Contamination monitoring is required in order to determine theproper design and choice of insulation type and level. This monitoring is also important for addressing an effective


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solution against pollution flashover. Meteorological conditions vary considerably from the coastal areas to the inlandareas and play an important role in the deposition rate of pollutants and electrical behavior of insulators. The surveyproved that the insulator contamination problem is strongly environment-dependent and no generalized anti-pollutioncriteria can be offered. The determination of outdoor insulation level and design, in a new location is a difficult matter without having some information on the severity of prevailing pollution.The problem becomes more serious at higher levels of transmission voltage. It is, therefore, imperative to have areasonable and accurate assessment of site severity. Works in [7-12] have found considerable relationships between

the contamination severity in terms of Equivalent Salt Deposit Density (ESDD) and flashover with respect to themeteorological parameters. An attempt has been done in [13] and [14] to relate most of the meteorologicalparameters respectively with ESDD and leakage current to develop a new mathematical model using multipleregression analysis technique.So far, the researchers have studied the effect of the meteorological parameters on ESDD or flashover in piecemealmanner. Reference [7, 8] described that the contamination layer and leakage current depends upon the wind speedand the distance between the seashore and insulator; a mathematical relationship has been developed betweenthese factors. Sometime non-uniform contamination due to wind direction can be found on the surfaces of highvoltage insulators as described in [9].High temperature is responsible for lower humidity which leads to lower flashover voltages; the relationship isdescribed in [10, 11]. As regards the air pressure it has been found that the flashover voltages of polluted insulatorsdecrease as the pressure deceases [12, 13].Insulation design in transmission lines and substations depend to over voltage and regional pollution. Each factor iscritical for insulation design. Two kind of pollution can result in insulation electrical breakage in power frequencyvoltage:

a) Pre-deposit pollution.b) Instant pollution.Pre-deposit pollution can be one of the followings: high dissolvable salts (NaSo4MgCl2 and NaCl) those define asESDD. Low dissolvable salts (gypsum, suspension ash) or non-solvable materials (clay, Kaolin, soot and oil) thosedefine as NSDD and acids and SO2). Instant pollution includes conductive fog and birds' pollution (NoX, SO3(residue).

Although composite insulators with polymeric housings have been used around the world in outdoor high voltageapplications for over 30 years, there still exists a lack of adequate pollution testing procedures that would allow for evaluation and comparison of their properties. This is mainly caused by a fact that the majority of compositeinsulators , because of the variable hydrophobicity of their external surfaces, represent dynamic (time variable)properties [7].Suspension insulators are very popular due to their less expensive price, flexibility to work in various voltage levelsand low maintenance cost.Insulator string can be applied in various voltage levels by changing insulators units. Non-homogenous voltage

distribution on these insulators is considered as a defect; therefore, various tests are defined and performed todetermine stability voltage of the insulators. Test approaches are very important cases to determine insulation leveladequacy. Also, insulator must have suitable mechanical strength in load conditions.The Electrical strength must be high enough to resist in normal and excessive voltages, but should break atexcessive harmful voltage for the equipment [8], [9].In this paper, it is offered to change the insulators unit's dimensions to make voltage distribution more uniform in thestring. This paper managed in 5 sections. Section 2, describes pollution and its effect on insulators. In part 3 we talkabout inhomogeneous voltage across an insulator string and explain a simple method, using KVL, KCL equations tocalculate exposed voltage at each unit of string. At next section we introduced our novel design. Part 5 showssimulation result by using two different dimension insulators. Simulations showed increment in insulator stringefficiency factor by varying units' dimensions.


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3rd rail to overhead wire transition zone on the Skokie Swift

[edit ]Construction

Linemen on a maintenance of way vehicle repairing overhead lines

To achieve good high-speed current collection, it is necessary to keep the contact wire geometry

within defined limits. This is usually achieved by supporting the contact wire from above by a


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second wire known as the messenger wire (US & Canada) or catenary (UK). This wire

approximates the natural path of a wire strung between two points, a catenary curve , thus the use

of catenary to describe this wire or sometimes the whole system. This wire is attached to the

contact wire at regular intervals by vertical wires known as droppers or drop wires. The

messenger wire is supported regularly at structures, by a pulley , link, or clamp . The whole system

is then subjected to a mechanical tension .

As the contact wire makes contact with the pantograph, the carbon insert on top of the

pantograph is worn down. Going around a curve, the "straight" wire between supports will cause

the contact wire to cross over the whole surface of the pantograph as the train travels around the

curve, causing uniform wear and avoiding any notches. On straight track, the contact wire

is zigzagged slightly to the left and right of centre at each successive support so that the

pantograph wears evenly.

The zigzagging of the overhead line is not required for trams using trolley poles or for

trolleybuses.

Depot areas tend to have only a single wire and are known as simple equipment. When overhead

line systems were first conceived, good current collection was possible only at low speeds, using

a single wire. To enable higher speeds, two additional types of equipment were developed:

Stitched equipment uses an additional wire at each support structure, terminated on either

side of the messenger wire.

Compound equipment uses a second support wire, known as the auxiliary, between themessenger wire and the contact wire. Droppers support the auxiliary from the messenger

wire, and additional droppers support the contact wire from the auxiliary. The auxiliary wire

can be constructed of a more conductive but less wear-resistant metal, increasing the

efficiency of power transmission.

Dropper wires traditionally only provide physical support of the contact wire, and do not join the

catenary and contact wires electrically. Contemporary systems use current-carrying droppers,

which eliminate the need for separate wires.

The present transmission system originated about 100 years ago. A simpler system was proposed

in the 1970s by the Pirelli Construction Co consisting of a single wire embedded at each support

for 2.5 metres (8 ft 2 in) of its length in a clipped extruded aluminum beam with the wire contact

face exposed. With a somewhat higher tension than used before clipping the beam yielded a

deflected profile for the wire which could be easily handled at 250 miles per hour (400 km/h) by a

pneumatic servo pantograph with only 3 G accelerations.


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For tramways there is often only a contact wire and no messenger wire.

Where there is limited clearance to accommodate wire suspensions systems such as in tunnels,

the overhead wire may be replaced by rigid overhead rail. This was done when the overhead line

was raised in the Simplon Tunnel to accommodate taller rail vehicles.

Technical advances lower running costs

The introduction of supercapacitors has promised to drop electrical running costs for trains powered by

overhead lines or third rails . Kinetic braking energy is reclaimed by storing electrical energy in

supercapacitors onboard the vehicle. This stored energy is used when accelerating the train, when high

current is needed. The supplementing supercapacitors reduce current drawn through the electrical supply

during acceleration and puts less strain on the distribution system.

Later developments locate banks of supercapacitors at track side. All trains on the system can then use

the stored energy in the supercapacitors to supplement the energy drawn through a third rail or overhead

wires. Trackside location reduces vehicle weight and creates more onboard space. However, such

locations would require additional equipment to charge the supercapacitors from the overhead line

voltage and to generate supplementary power at the voltage and frequency of the overhead line from the

stored energy.

Claimed energy reduction is around 30%. Electric railway systems can be more competitive and a real

economical alternative to automobiles.

The technology can be used equally well for diesel electric locomotives, where 25% to 40% reduction in

energy consumption is claimed, however only onboard location of supercapacitor banks is feasible. (This

technology equally applies to road vehicles that use electric motors for propulsion, such as hybrid cars

and buses.) Any electrical equipment that requires regular braking can reduce operating costs using

supercapacitors. Reduced operating costs of elevators on underground railways would be a great benefit

to operators and adding to their economic competitiveness.

An additional benefit is that emissions from generating plants and diesel-electric locomotives will be

decreased.

Since 2003, the Mannheim Stadtbahn in Germany has operated a light-rail vehicle using electric double-

layer supercapacitors to store braking energy. [3][4]

A number of companies are developing electric double-layer supercapacitor technology. Siemens AG is

developing mobile energy storage based on double-layer supercapacitors called Sibac Energy

Storage [5] Sitras SES, are developing stationary trackside version. [6] The company Cegelec is also

developing an electric double-layer capacitor-based energy storage system. [7]


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[edit ]History

In 1881 the first tram with overhead lines was presented by Werner von Siemens on the International

Electric Exposition in Paris 1881 but the installation was removed after that event. In October 1883, the

first permanent tram service with overhead lines was started on Mdling and Hinterbrhl Tram in Austria.

These trams had bipolar overhead lines, consisting of two U-pipes, in which the pantographs hung and

ran like shuttles. In April to June 1882, Siemens had tested a similar system on his Electromote , an early

percursor of the trolleybuses .

Much simpler and more functional was an overhead wire in combination with a pantograph borne by the

vehicle and pressed at the line from below. This system, for rail traffic with a unipolar line, was invented

by Frank J. Sprague in 1888. Since 1889, it was used at the Richmond Union Passenger

Railway in Richmond, Virginia . That was the onset of worldwide use of electric traction.

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Types of Conductors

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