Dave Phillips

8/8/2019 Dave Phillips

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Corona Tutorial

Dave PhillipsSubmarine Operating Authority Engineering

Space and Naval Warfare Systems Center

San Diego, California

IEEE Joint Technical Committee Meeting 2007

Orlando, Florida7 January 10 January


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What Is Corona?What Is Corona?


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Corona is a luminous dischargeCorona is a luminous discharge

due to ionization of the airdue to ionization of the air

surrounding an electrode,surrounding an electrode,

caused by a voltage gradientcaused by a voltage gradient

exceeding a certain criticalexceeding a certain criticalvalue.value.


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Example of Conductor Corona


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Whats The Fuss?Whats The Fuss?


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Corona from conductors and hardwareCorona from conductors and hardware

may cause audible noise and radio noisemay cause audible noise and radio noise


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Corona from conductors and hardware

may cause audible noise and radio noise

Audible noise from conductors mayAudible noise from conductors mayviolate noise standardsviolate noise standards


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Corona from conductors and hardware

may cause audible noise and radio noise

Audible noise from conductors mayviolate noise standards

Radio noise from conductors mayRadio noise from conductors may

interfere with communications orinterfere with communications ornavigationnavigation


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Corona from conductors and hardware may

cause audible noise and radio noise

Audible noise from conductors may violatenoise standards

Radio noise from conductors may interfere

with communications or navigation

Corona loss may be significant whenCorona loss may be significant when

compared with resistive loss of conductorscompared with resistive loss of conductors


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Corona from conductors and hardware may cause

audible noise and radio noise

Audible noise from conductors may violate noise

standards

Radio noise from conductors may interfere with

communications or navigation

Corona loss may be significant when compared with

resistive loss of conductors

Corona can cause possible damage to polymericCorona can cause possible damage to polymeric

insulatorsinsulators


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Corona Discharge Currents are Impulsive

Ic(t)

t0.01 0.1 sec


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Physical Parameters of CoronaPhysical Parameters of Corona

Corona is caused by the ionization of theCorona is caused by the ionization of the

media (air) surrounding the electrodemedia (air) surrounding the electrode

(conductor)(conductor)


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Corona is caused by the ionization of the

media (air) surrounding the electrode

(conductor) Corona onset is a function of voltageCorona onset is a function of voltage


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(conductor) Corona onset is a function of voltage

Corona onset is a function of relative airCorona onset is a function of relative air

densitydensity


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(conductor) Corona onset is a function of voltage

Corona onset is a function of relative air

density

Corona onset is a function of relativeCorona onset is a function of relative

humidityhumidity


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Corona and the Electric FieldCorona and the Electric Field

Corona isCorona isNOTNOT solely a function of thesolely a function of the

Electric FieldElectric Field


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Corona is NOT solely a function of theCorona is NOT solely a function of the


Corona is a function of the electric field onCorona is a function of the electric field onthe surface of the electrode (conductor)the surface of the electrode (conductor)


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Corona is NOT solely a function of theCorona is NOT solely a function of the



Corona is also a function of the radius ofCorona is also a function of the radius of

curvature of the electrode (conductor)curvature of the electrode (conductor)


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Corona is NOT solely a function of theCorona is NOT solely a function of theElectric FieldElectric Field


Corona is also a function of the radius ofCorona is also a function of the radius ofcurvature of the electrode (conductor)curvature of the electrode (conductor)

Corona is also a function of the rate of decayCorona is also a function of the rate of decayof the electric field away from the electrodeof the electric field away from the electrode(conductor)(conductor)


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For the preceding reasons, selecting theFor the preceding reasons, selecting the

conductor with the smallest electric field atconductor with the smallest electric field at

its surface is not correct.its surface is not correct.

One utility found out (the hard way) thatOne utility found out (the hard way) that

simply choosing large diameter conductorssimply choosing large diameter conductors

did not work well because the electric fielddid not work well because the electric field

decayed slowly away from the surfacedecayed slowly away from the surface


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Corona and the Relative Air DensityCorona and the Relative Air Density


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Corona has an inverse relationship with airCorona has an inverse relationship with air

densitydensity


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Corona has an inverse relationship with airCorona has an inverse relationship with air

densitydensity

Standard line designs that perform well atStandard line designs that perform well atsea level, may have significant coronasea level, may have significant corona

issues if used on lines that are installed overissues if used on lines that are installed over

mountainous areasmountainous areas


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Corona and the HumidityCorona and the Humidity


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Corona has an inverse relationship withCorona has an inverse relationship with

humidity at power frequencieshumidity at power frequencies


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Corona has an inverse relationship withCorona has an inverse relationship with

humidity at power frequencieshumidity at power frequencies

Fair weather corona is more prevalent inFair weather corona is more prevalent inlow humidity environmentslow humidity environments


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Corona Is Dependent SurfaceCorona Is Dependent Surface

Condition Of The ConductorsCondition Of The Conductors


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Corona is enhanced by irregularities on theCorona is enhanced by irregularities on the

conductor surfaceconductor surface


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Corona is enhanced by irregularities on theCorona is enhanced by irregularities on theconductor surfaceconductor surface

Irregularities include: dust, insects, burrsIrregularities include: dust, insects, burrsand scratches and water drops present onand scratches and water drops present onnew conductorsnew conductors

Corona will generally be greater on newCorona will generally be greater on new

conductors and will decrease to a steadyconductors and will decrease to a steady--state value over a period of approximatelystate value over a period of approximatelyone year inone year in--serviceservice


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Corona is enhanced by irregularities on theCorona is enhanced by irregularities on theconductor surfaceconductor surface

Irregularities include: dust, insects, burrs andIrregularities include: dust, insects, burrs and

scratches and water drops present on newscratches and water drops present on newconductorsconductors

Corona will generally be greater on newCorona will generally be greater on newconductors and will decrease to a steadyconductors and will decrease to a steady--statestate

value over a period of approximately one year invalue over a period of approximately one year in--serviceservice

Corona is significantly increased in foul weather.Corona is significantly increased in foul weather.


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Corona Is Dependent On LocalCorona Is Dependent On Local

Electrode GeometryElectrode Geometry


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on-Critical ur aces

on-Critical ur ace

Critical ur acesumber o Elements =210

Critical ection


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r

Ground lane V = 0

phere V = V0


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0 0 . 5 1 1 . 5 2 2 . 5 3 3 . 5 4 4 . 50

5 0 0

1 0 0 0

1 5 0 0

2 0 0 0

2 5 0 0

3 0 0 0A c t u a l E l e c t r ic F i e l d vs . D i s t a n c e

D i s t an c e ( c m )

E

lectric

Field

(V

/cm

)

1 c m

2 c m

3 c m

4 c m

5 c m

6 c m7 c m

8 c m

9 c m


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Why is it a special problem for

voltage upgrades?

If the voltage of a transmission line is increased

without changing the line design, the electric field

at the surface of the line conductors (and hardware)will increase. This increase will cause additional

corona

The same can be said for compact transmission

lines.


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Practical Consequences

1. Larger conductors better to a point

2. Use conductor bundles to reduce corona

3. Corona phenomena much worse infoul weather, high altitude

4. Compact lines more susceptible

5. New conductors can lead to poor

corona performance for a while


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Cautions Regarding Radio NoiseCautions Regarding Radio Noise


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Radio noise from corona should not beRadio noise from corona should not be

confused with radio noise generated byconfused with radio noise generated by

spark dischargespark discharge


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High frequency complaints areHigh frequency complaints are almostalmost

always due to sparksalways due to sparks


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Causes of spark discharges can be locatedCauses of spark discharges can be located

and repairedand repaired


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Causes of spark discharges can be locatedCauses of spark discharges can be located

and repairedand repaired

Corona is a DESIGN ISSUECorona is a DESIGN ISSUE


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Radio noise caused by corona cannot beRadio noise caused by corona cannot be

reduced by changing the line configurationreduced by changing the line configuration

near where the noise problem is occuring.near where the noise problem is occuring.

The source of the problem can be severalThe source of the problem can be several

miles awaymiles away


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Audible Noise

Can get broadband noise and hum

Load can affect audible noise

For measurement see:

ANSI/IEEE Standard 656-1992 IEEE Standard

For Measurement of Audible Noise from OverheadTransmission Lines


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Audible NoiseAudible Noise

May be present as 120 Hz Hum orMay be present as 120 Hz Hum or

broadband noisebroadband noise

Can be affected by loadCan be affected by load


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Can be affected by loadCan be affected by load


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Audible Noise in Context

50

55

60

65Audible

Noise dBA

30 meters

fromcenterline

Numerous

complaints

Moderate

complaints

No

complaints

Source: BPA study

Common design limit 53 dBA

A l i


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EPA Regulations

Effect Level Area

Outdoor

activity

Indooractivity

Ldn < 55 dBA

Residential areasand farms where

.. quiet is a basis

for use

Leq(24) < 55 dBA

Areas where

people spend

limited time

Ldn < 45 dBA

Leq(24) < 45 dBA

Residential

Other

Ldn

(has a -10 dB adder nightime) Leq(24)

(24 hour average)


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0

5

10

15

20

25

0 20 40 60 80 100 120

Distance from Center Line

MagneticField(mG)

ABC ABC Super Bundle

ABC CBA Low Reactance

Magnetic Field is Reduced


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52

54

56

58

60

62

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0 20 40 60 80 100 120

Distance from Center Line (m)

AudibleNoise(

dBA)

ABC CBA (Low Reactance)

ABC ABC (Super Bundle)

Audible Noise is Increased


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Corona Loss

What is it?

Whenever corona occurs on a transmission line, there is a

corresponding loss of energy called corona loss. This loss

is one of the reasons why the transmission of electric energybetween two points is not perfect.

When can it be a problem?

Generally, corona loss is significantly less than resistive loss.

However, at higher voltages, high altitudes and during foul

weather, corona loss can actually exceed resistive loss.


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A Word On Corona LossesA Word On Corona Losses


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Whenever corona occurs on a transmission

line, there is a corresponding loss of energy

called corona loss. This loss is one of the

reasons why the transmission of electric

energy between two points is not perfect


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Whenever corona occurs on a transmission line,

there is a corresponding loss of energy called

corona loss. This loss is one of the reasons why

the transmission of electric energy between twopoints is not perfect

Generally, corona loss is significantly less than

resistive loss. However, at higher voltages, high

altitudes and during foul weather, corona loss canactually exceed resistive loss


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Example Losses (sea level)

Line

oltage (k )

Bundle

n x 2a

Load

M A

I2R Loss

kW/km

Corona Loss (kW/km)

Average Maximum

362

550

800

2 x 3.16

3 x 3.3

4 x 3.3

400

900

2000

41

52

93

2

4

8

26

78

208


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Corona On Hardware

Transmission line hardware is usually tested in thelaboratory prior to being selected to determine whether is

corona free. This test is often done on a single phase

system in order to conserve laboratory space.

It has been found that the traditional method of energizing

the system to 110% of the rated line to

ground voltage is not sufficient, especially for lines

of more compact design. Apparently, the hardware is

exposed to higher gradients in the field than those to which

the hardware was tested.


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Corona On HardwareCorona On Hardware


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Transmission line hardware is usually tested

in the laboratory prior to being selected to

determine whether is corona free. This test

is often done on a single phase system in

order to conserve laboratory space


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Transmission line hardware is usually tested in thelaboratory prior to being selected to determinewhether is corona free. This test is often done ona single phase system in order to conservelaboratory space

It has been found that the traditional method ofenergizing the system to 110% of the rated line toground voltage is not sufficient, especially forlines of more compact design. Apparently, thehardware is exposed to higher gradients in thefield than those to which the hardware was tested

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