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Corona Tutorial. IEEE Joint Technical Committee Meeting 2007 Orlando, Florida 7 January – 10 January. Dave Phillips Submarine Operating Authority Engineering Space and Naval Warfare Systems Center San Diego, California. What Is Corona?. What Is Corona?. What Is Corona?. What Is Corona?.

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slide1

Corona Tutorial

IEEE Joint Technical Committee Meeting 2007

Orlando, Florida

7 January – 10 January

Dave Phillips

Submarine Operating Authority Engineering

Space and Naval Warfare Systems Center

San Diego, California

what is corona5
What Is Corona?

Corona is a luminous discharge due to ionization of the air surrounding an electrode, caused by a voltage gradient exceeding a certain critical value.

what s the fuss8
What’s The Fuss?
  • Corona from conductors and hardware may cause audible noise and radio noise
what s the fuss9
What’s The Fuss?
  • Corona from conductors and hardware may cause audible noise and radio noise
  • Audible noise from conductors may violate noise standards
what s the fuss10
What’s The Fuss?
  • 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
what s the fuss11
What’s The Fuss?
  • 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
what s the fuss12
What’s The Fuss?
  • 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 polymeric insulators
physical parameters of corona
Physical Parameters of Corona
  • Corona is caused by the ionization of the media (air) surrounding the electrode (conductor)
physical parameters of corona15
Physical Parameters of Corona
  • Corona is caused by the ionization of the media (air) surrounding the electrode (conductor)
  • Corona onset is a function of voltage
physical parameters of corona16
Physical Parameters of Corona
  • Corona is caused by the ionization of the media (air) surrounding the electrode (conductor)
  • Corona onset is a function of voltage
  • Corona onset is a function of relative air density
physical parameters of corona17
Physical Parameters of Corona
  • Corona is caused by the ionization of the media (air) surrounding the electrode (conductor)
  • Corona onset is a function of voltage
  • Corona onset is a function of relative air density
  • Corona onset is a function of relative humidity
corona and the electric field
Corona and the Electric Field

Corona is NOT solely a function of the Electric Field

corona and the electric field19
Corona and the Electric Field

Corona is NOT solely a function of the Electric Field

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

corona and the electric field20
Corona and the Electric Field

Corona is NOT solely a function of the Electric Field

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

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

corona and the electric field21
Corona and the Electric Field

Corona is NOT solely a function of the Electric Field

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

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

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

corona and the electric field22
Corona and the Electric Field

For the preceding reasons, selecting the conductor with the smallest electric field at its surface is not correct.

One utility found out (the hard way) that simply choosing large diameter conductors did not work well because the electric field decayed slowly away from the surface

corona and the relative air density24
Corona and the Relative Air Density
  • Corona has an inverse relationship with air density
corona and the relative air density25
Corona and the Relative Air Density
  • Corona has an inverse relationship with air density
  • Standard line designs that perform well at sea level, may have significant corona issues if used on lines that are installed over mountainous areas
corona and the humidity27
Corona and the Humidity
  • Corona has an inverse relationship with humidity at power frequencies
corona and the humidity28
Corona and the Humidity
  • Corona has an inverse relationship with humidity at power frequencies
  • Fair weather corona is more prevalent in low humidity environments
corona is dependent surface condition of the conductors30
Corona Is Dependent Surface Condition Of The Conductors
  • Corona is enhanced by irregularities on the conductor surface
corona is dependent surface condition of the conductors31
Corona Is Dependent Surface Condition Of The Conductors
  • Corona is enhanced by irregularities on the conductor surface
  • Irregularities include: dust, insects, burrs and scratches and water drops present on new conductors
corona is dependent surface condition of the conductors32
Corona Is Dependent Surface Condition Of The Conductors
  • Corona is enhanced by irregularities on the conductor surface
  • Irregularities include: dust, insects, burrs and scratches and water drops present on new conductors
  • Corona will generally be greater on new conductors and will decrease to a steady-state value over a period of approximately one year in-service
corona is dependent surface condition of the conductors33
Corona Is Dependent Surface Condition Of The Conductors
  • Corona is enhanced by irregularities on the conductor surface
  • Irregularities include: dust, insects, burrs and scratches and water drops present on new conductors
  • Corona will generally be greater on new conductors and will decrease to a steady-state value over a period of approximately one year in-service
  • Corona is significantly increased in foul weather.
slide39

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.

slide40

Practical Consequences

1. Larger conductors better – to a point

2. Use conductor bundles to reduce corona

3. Corona phenomena much worse in

foul weather, high altitude

4. Compact lines more susceptible

5. New conductors can lead to poor

corona performance for a while

cautions regarding radio noise42
Cautions Regarding Radio Noise
  • Radio noise from corona should not be confused with radio noise generated by spark discharge
cautions regarding radio noise43
Cautions Regarding Radio Noise
  • Radio noise from corona should not be confused with radio noise generated by spark discharge
  • High frequency complaints are almost always due to sparks
cautions regarding radio noise44
Cautions Regarding Radio Noise
  • Radio noise from corona should not be confused with radio noise generated by spark discharge
  • High frequency complaints are almost always due to sparks
  • Causes of spark discharges can be located and repaired
cautions regarding radio noise45
Cautions Regarding Radio Noise
  • Radio noise from corona should not be confused with radio noise generated by spark discharge
  • High frequency complaints are almost always due to sparks
  • Causes of spark discharges can be located and repaired
  • Corona is a DESIGN ISSUE
cautions regarding radio noise46
Cautions Regarding Radio Noise
  • Radio noise caused by corona cannot be reduced by changing the line configuration near where the noise problem is occuring. The source of the problem can be several miles away
slide47

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 Overhead

Transmission Lines

audible noise
Audible Noise
  • May be present as “120 Hz Hum” or broadband noise
  • Can be affected by load
audible noise50
Audible Noise
  • May be present as “120 Hz Hum” or broadband noise
audible noise51
Audible Noise
  • May be present as “120 Hz Hum” or broadband noise
  • Can be affected by load
slide52

Audible Noise in Context

65

Numerous

complaints

Audible

Noise dBA

30 meters

from

centerline

60

Moderate

complaints

55

No

complaints

50

Common design limit – 53 dBA

Source: BPA study

slide53

EPA Regulations

Effect

Level

Area

Residential areas

and farms where

.. quiet is a basis

for use

Outdoor

activity

Ldn < 55 dBA

Areas where

people spend

limited time

Leq(24) < 55 dBA

Residential

Ldn < 45 dBA

Indoor

activity

Leq(24) < 45 dBA

Other

Ldn (has a -10 dB adder nightime) Leq(24) (24 hour average)

slide54

Tradeoff: Magnetic Field vs. Audible Noise

Effect of Changing Conductor Phasing

500 kV Double Circuit Line

y

A

A or C

B

B

C

C or A

White – ABC – ABC Super Bundle

Red – ABC – CBA Low Reactance

x

slide55

Magnetic Field is Reduced

ABC – ABC Super Bundle

ABC – CBA Low Reactance

slide56

Audible Noise is Increased

ABC – CBA (Low Reactance)

ABC – ABC (Super Bundle)

slide57

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 energy

between 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.

a word on corona losses59
A Word On Corona Losses
  • 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
a word on corona losses60
A Word On Corona Losses
  • 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
  • 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
slide61

Example Losses (sea level)

Corona Loss (kW/km)

Bundle

n x 2a

Load

MVA

I2R Loss

kW/km

Line

Voltage (kV)

Average

Maximum

26

2

400

41

362

2 x 3.16

550

3 x 3.3

78

4

900

52

4 x 3.3

800

2000

208

8

93

slide62

Corona On Hardware

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.

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.

corona on hardware64
Corona On Hardware
  • 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
corona on hardware65
Corona On Hardware
  • 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
  • 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