Sag In Transmission Line And Corona EffectGroup Members Asad Mahmood JadoonWaqarHasnain Bashir

What Is Sag In Transmission Line?Sag is defined as the difference in level between point of support and the lowest point of conductor.

Actual Picture Of Sag In a Transmission Line

General Figure Of Line Sag

Formula For Sag Calculation

Factors Affecting Sag In Transmission LineTemperatureAgingWindIce

Effect Of Temperature On Sag

Effect Of Temperature On SagAs the temperature increases, the outstretched conductor length will increase by an amount equal to: L =TSWhere = the coefficient of thermal expansion T = the temperature increase in oC S = the span length in meters

This will result in increase in sag and decrease in conductor tension

Effect Of Age On SagConductor sag over time may increasedue to the effects of strand settling in andmetallurgical creep. A higher tension may beused when the conductor is first erected toallow for settling in of conductor strandsand for subsequent metallurgical creep ofthe conductor material

Effect Of Age Of Line On Sag

Effect Of Wind & Ice On Sag A wind load on the conductor will increase the apparent weight of the conductor resulting in an in increase in tension Whereas Ice build up on the conductor will increase the apparent diameter and weight of the conductor

Calculation of Weight of Ice

Calculation of Weight of Wind

Combine Effect Of Wind And Ice

Sag Due To Different Levels Of Height

Sag Due To Different Levels Of Height

Clearance DeterminationLine Clearance

What Is Corona ?The phenomenon of violet glow, hissing sound & production of ozone gas in over head Transmission Line is known as Corona.

Effect of CoronaA Violet glow Hissing SoundProduces Ozone GasMax at Rough & Dirty surface of conductorPower Loss

Factor affecting CoronaAtmosphereConductorSpacing Between ConductorLine Voltage

Atmosphere AffectBreakdown voltage inversely proportional to Density(number of Ions) of AirEg in Stormy Weather the number of ions may be more then normal so corona occur at less voltage

ConductorAffectCorona depends on size(diameter),shape(stranded/smooth) & surface condition(dirty/clean)Corona Is Inversely proportional to DiameterStranded conductor give rise to more corona then solid conductorDirt increases irregularity and thereby Decreases breakdown voltage

Corona Is Inversely proportional to Spacing between the conductor

Line Voltage AffectLine Voltage Directly Proportional to CoronaSpacing Affect Between Conductor

Advantages Of CoronaVitual Diameter Of Conductor Increases & reduces electrostatic stressCorona reduces the effect of transients produced by surges

Disadvantages Of CoronaCorona causes power losses that affects transmission efficiencyOzone Production causes corrosion of conductor due to chemical reactionNon sinusoidal voltage drop occurs in the line cause the inductive interference with the communication line.

Corona power lossCorona has power loss which has effect on the efficiency of transmission lineThe power loss is effected both by atmospheric and line conditionIn case of fair weather

In case of fair weather

In case of stormy weather

Factor effecting corona LossEffect of conductivity of air:Effect of density of airEffect of conductor surfaceEffect of conductor radiusEffect of atmospheric conditionEffect of load conditionEffect of load currentBundling of conductors

Methods of Reducing Corona EffectCritical voltage will increase by increasing the spacing between the conductor.By using the bundle conductor corona loss is decrease.Corona loss can be decreased by increasing the diameter of the conductor.

Corona discharge images under different gaps (applied voltage: 120kV, 1kHz). The discharge length from 1020cm gaps is 6.5cm (10cm), 5cm (12cm), 4cm (14cm), 2.5cm (16cm), 2cm (18cm) and 2cm (20cm)