TRANSMISSION OF ELECTRIC POWE | Power transmission and power transmission line

 

TRANSMISSION OF ELECTRIC POWE

Power transmission and power transmission line

What is power transmission line and how transmission voltage translate. There are three types of transmission lines and Types of conductor using in transmission line analysis. There are three Types of insulator used as overhead line. Also Describe all about transmission line input impedance and input impedance transmission line

 

Transmission Line

Transmission line is that the long conductor with special style (bundled) to hold bulk quantity of generated power at terribly high voltage from one station to a different as per variation of the voltage level. though it's on paper simple to extend voltage and increase current once sending so as to extend the transmission capability, it truly needs overcoming numerous problems like insulation problems, safety, and dip for high-voltage large-current transmission technology. The electrical gear mechanism is employed together with power plants, distribution systems, and sub-stations to make what's referred to as the electrical grid. The grid is meant to fulfill all of society's electricity wants, and is what gets the electric power from its starting to its finish use. Since power plants area unit most frequently placed outside of densely inhabited areas, the gear mechanism should be fairly massive. Power lines or transmission lines, like those in Figure five.1, area unit wont to transport electricity from place to position. This electricity is within the kind of alternating current and begins at increase transformers, and generally spans a distance of five hundred kilometers or less.

Figure Transmission line

 

Transmission Voltage

The power comes from power plant. In power plant the generated voltage is 11 kV. This amount of voltage is not sufficient for transmission. For this reason, the authority uses the step-up transformer for increase the voltage level.

If reduce the current and increase the voltage then the electricity transmits the long distance with minimizing the loss of power. There are different values of transmission voltage are use. Like as, 600 kV, 400 kV, 230 kV, 132 kV, 66 kV, 33 kV. But the country of Bangladesh, 600kV and 66 kV are not use for transmission. But in future 600 kV and 66 kV transmissions will establish.

 

Types of Transmission Line

In transmission cable determination of fall, transmission potency, line loss etc. square measure necessary things to style. These values square measure laid low with line parameter R, L and C of the cable. Length wise transmission lines square measure 3 sorts.

·       Short transmission line (cable)

·       Medium transmission line (cable)

·       Long transmission line (cable)

 

Short Transmission line (cable)

When the length of AN overhead cable is up to regarding fifty klick and therefore the line voltage is relatively low (<20kV), it's typically thought of as a brief cable. thanks to smaller length and lower voltage, the capacitance effects square measure little and thus are often neglected. Therefore, whereas learning the performance of a brief cable, solely resistance and inductance of the road square measure taken under consideration.

There square measure some details of short transmission line:

·       Length is regarding fifty klick

·       Voltage level is up to twenty potential unit

·       Capacitance result is negligible

Medium Transmission line (cable)

When the length of AN overhead cable is about 50-150 klick and therefore the line voltage is moderately high (>20 kV<100 kV), it's thought of as a medium cable

Due to comfortable length and voltage of the road, the capacitance effects square measure taken under consideration. For purpose of calculations, the distributed capacitance of the road is split and lumped within the sort of condenser hunted across the road at one or a lot of points. These lumped parameters of a medium length cable are often portrayed victimization 3 completely different models, namely:

·       Nominal Π illustration

·       Nominal T illustration

·       End Condenser technique

   There square measure some details of medium transmission line:

·       Length is regarding fifty klick to a hundred and fifty klicks

·       Operational voltage level is from twenty potential unit to one hundred potential unit

·       Capacitance result is gift

·       Distributed capacitance kind is employed for calculation purpose

 

Long Transmission line (cable)

When the length of AN overhead cable is more than a hundred and fifty klick and line voltage is extremely high (>100kV), it's thought of as a protracted cable. For the treatment of such a line, the road constants square measure thought of uniformly distributed over the entire length of the road and rigorous strategies square measure used for answer.

There square measure some details of long transmission line:

·       Length is quite a hundred and fifty klicks

·       Voltage level is on top of one hundred potential unit

·       Line thought of as distributed over the length of a line

Transmission line transfers the wattage in Asian nation by Overhead gear. currently this method discusses within the below:

Overhead Transmission System

An overhead power line could be a structure employed in wattage transmission and distribution to transmit current on giant distances. It consists of 1 or additional conductor (commonly multiple of three) suspended by tower or pole. Since most of the insulation is provided by air, overhead power lines area unit typically the lowest-cost methodology of power transmission for giant quantities of electrical energy.

Main Components of Overhead Transmission Lines

Main elements of Overhead Transmission Lines

An overhead line could also be accustomed transmit or distribute power. The triple-crown operation of Associate in Nursing overhead line depends to an excellent extent upon the mechanical style of the road. whereas constructing Associate in Nursing overhead line, it ought to be ensured that mechanical strength of the road is such thus on give against the foremost probable weather. In general, the most elements of Associate in Nursing overhead line are:

·       Conductors: The conductor is that the kind of metal that permits the electrical current to flow through it. The electrical conductor is usually created of metals like copper, Al and their alloys. In Associate in Nursing electrical conductor, the electrical charges move from atom to atom once the potential is applied across them.

·       Supports: this might be poles or towers and keep the conductors at a suitable level on top of the bottom.

·       Insulators: Associate in Nursing dielectric could be a material that doesn't conduct electrical current. Insulating materials embrace paper, plastic, rubber, glass and air. Vacuum is additionally Associate in Nursing dielectric, however isn't truly a cloth. Most electrical conductors are coated by insulation.

·       Cross arms: The cross arm within the conductor is employed to support the electrical device. The cross arm on the ability pole or on the sunshine pole is employed to support the dielectric by double mobilization bolt or “u BOLT”. the categories of the steel cross arms are completely different in every country.

·       Miscellaneous items: like part plates, danger plates, lightning restraint-climbing wires etc.

·       The continuity of operation within the overhead line depends upon the considered selection of on top of

Figure Main components of overhead lines

Conductor

Conductor may be a physical medium to hold electricity kind one place to alternative. it's a crucial part of overhead and underground electrical transmission and distribution systems. the selection of conductor depends on the price and potency. a perfect conductor has following options.

·       It has most electrical conduction.

·       It has high lastingness so it will stand up to mechanical stresses.

·       It has least relative density i.e. weight/unit volume.

·       It has least value while not sacrificing alternative factors.

 

Types of conductor exploitation in line

There ar four varieties of conductors used depend on the look of the transmission lines, such as:

·       ACSR

·       AAC

·       AAAC

·       ACAR

 

These conductors are used supported the situation (hilly space or plain area), span of the transmission lines and climate at the situation (snow fall); additionally, they're used supported the preference given by the facility Grid Company in Asian nation.

Insulator

It is obvious that if overhead power lines aren't properly insulated from their support poles/towers, this can flow towards the bottom through the poles/towers that additionally become venturous. Of course, the facility line will not even add that case! thence, overhead power lines ar continually supported on insulators mounted on their support poles/towers. Overhead line insulators ought to have the subsequent properties:

·       High mechanical strength so as to face up to the conductor load, wind load etc.

·       High resistivity so as to attenuate the escape currents

·       High relative permittivity of insulation so the insulator strength is high

·       High magnitude relation of puncture strength to discharge

Most commonly used material for overhead line insulators is ceramic ware. But glass, talc and a few alternative special materials can also be used typically.

 

Types of nonconductor used as overhead line:

·       Pin nonconductor

·       Suspension nonconductor

·       Strain nonconductor

In addition to it there ar alternative 2 varieties of electrical nonconductor accessible for low voltage application on distribution system, i.e. keep nonconductor and Shackle nonconductor.

Tower

The main supporting unit of overhead line is transmission tower. Transmission towers need to carry the serious transmission conductor at a spare safe height from ground. additionally, to it all towers need to sustain all types of natural calamities. therefore, transmission tower planning is a crucial engineering job wherever all 3 basic engineering ideas, civil, mechanical and applied science ideas ar equally applicable.

A power transmission tower consists of the subsequent parts:

·       Peak of transmission tower

·       Cross arm of transmission tower

·       Cage of transmission tower

·       Transmission tower body

·       Leg of transmission tower

·       Stub/Anchor Bolt and Base plate assembly of transmission tower

 

 

 

Design of Transmission Tower

Figure Transmission tower design

During style of transmission tower the subsequent points to be thought of in mind,

·       The minimum ground clearance of all-time low conductor purpose on top of the bottom level.

·       The length of the stuff string

·       The minimum clearance to be maintained between conductors and between conductor and tower

·       The location of ground wire with regard to outer most conductors

 

Types of transmission tower

According to totally different concerns, there square measure differing kinds of transmission towers. The cable goes as per obtainable corridors.

These square measures referred to as special sort tower:

·       River crossing tower

·       Railway/ road crossing tower

·       Transposition tower

Based on numbers of circuits carried by a transmission tower, it is often classified as-

·       Single circuit tower

·       Double circuit tower

·       Multi circuit tower

 

Cross arms

Cross Arm is one amongst the key elements of cable and it holds the facility conductor. Cross arm will vary because of the situation and power carried by the cable. range of cross arms rely on the amount of circuits consist in cable.

 

Damper

Dampers employed in transmission lines for avoid oscillations in overhead transmission lines. because of laminal wind, overhead cables are excited to vibrations and oscillations that may result in injury on the conductor of the overhead transmission line, single elements or the pole. so as to scale back these vibrations associate degreed oscillations to an uncritical dimension, damping systems can need to be put in within the overhead transmission lines.

Dampers employed in transmission lines square measure of following types:

•                  Stockbridge Damper: These dampers square measure wont to counteract vibrations excited by wind, counting on the kind of the conductor of the overhead transmission line; many damper varieties with many alternative models square measure obtainable.

•                  balance dampers: Tensional damper is that the most recent anti-galloping device obtainable nowadays that has been specially designed to be used on bundled high voltage and further high voltage 132 kV and up to more than power transmission cabals.

•                  Spacer Dampers: Spacers damper serve to determine a distance between the partial conductors of a bundle line so as to forestall the conductors from knock along and therefore avoid injury done to conductors. Spacer dampers are used if vibrations excited by wind ought to be expected. The vibration amplitudes of the conductor are often reduced to associate degree uncritical dimension.

•                  Twin Spacer Damper: Twin spacer dampers square measure wont to management vibration and conductor oscillation. Maintain conductor spacing and restore conductor spacing when a brief circuit happens.

•                  Quadruple Spacer Damper: Spacer damper put in on four conductor bundles to regulate each vibration and wake iatrogenic oscillation

Sag in Overhead cable

While construction associate degree overhead line, it's vital that conductors square measure beneath safe tension. If the conductors square measure an excessive amount of stretched between supports in an exceedingly bid to save lots of conductor material, the strain within the conductor could reach unsafe worth and ensure cases the conductor could break because of excessive tension. so as to allow safe tension within the conductors, {they square measure they're} not totally stretched however are allowed to possess a dip or sag.

 

The distinction in level between purposes of supports and therefore the lowest point on the conductor is named sag.

            SAG

Figure Sag in overhead line