Corona Tutorial Dave Phillips Submarine Operating Authority Engineering Space and Naval Warfare...
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Transcript of Corona Tutorial Dave Phillips Submarine Operating Authority Engineering Space and Naval Warfare...
Corona Tutorial
Dave PhillipsSubmarine Operating Authority Engineering
Space and Naval Warfare Systems CenterSan Diego, California
IEEE Joint Technical Committee Meeting 2007 Orlando, Florida
7 January – 10 January
What Is Corona?What Is Corona?
What Is Corona?What Is Corona?
What Is Corona?What Is Corona?
What Is Corona?What Is Corona?
Corona is a luminous discharge Corona is a luminous discharge due to ionization of the air due to ionization of the air surrounding an electrode, surrounding an electrode, caused by a voltage gradient caused by a voltage gradient exceeding a certain critical exceeding a certain critical value.value.
Example of Conductor Corona
What’s The Fuss?What’s The Fuss?
What’s The Fuss?What’s The Fuss?
Corona from conductors and hardware Corona from conductors and hardware may cause audible noise and radio noisemay cause audible noise and radio noise
What’s The Fuss?What’s The Fuss?
Corona from conductors and hardware may cause audible noise and radio noise
Audible noise from conductors may Audible noise from conductors may violate noise standardsviolate noise standards
What’s The Fuss?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 Radio noise from conductors may interfere with communications or interfere with communications or navigationnavigation
What’s The Fuss?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 Corona loss may be significant when compared with resistive loss of conductorscompared with resistive loss of conductors
What’s The Fuss?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 Corona can cause possible damage to polymeric insulatorsinsulators
Corona Discharge Currents are Impulsive
Ic(t)
t0.01 – 0.1 μsec
Physical Parameters of CoronaPhysical Parameters of Corona
Corona is caused by the ionization of the Corona is caused by the ionization of the media (air) surrounding the electrode media (air) surrounding the electrode (conductor)(conductor)
Physical Parameters of CoronaPhysical Parameters of Corona
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
Physical Parameters of CoronaPhysical 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 Corona onset is a function of relative air
densitydensity
Physical Parameters of CoronaPhysical 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 Corona onset is a function of relative
humidityhumidity
Corona and the Electric FieldCorona and the Electric Field
Corona is Corona is NOTNOT solely a function of the solely a function of the Electric FieldElectric Field
Corona and the Electric FieldCorona and the Electric Field
Corona is NOT solely a function of the Corona is NOT solely a function of the Electric FieldElectric Field
Corona is a function of the electric field on Corona is a function of the electric field on the surface of the electrode (conductor)the surface of the electrode (conductor)
Corona and the Electric FieldCorona and the Electric Field
Corona is NOT solely a function of the Corona is NOT solely a function of the Electric FieldElectric Field
Corona is a function of the electric field on Corona is a function of the electric field on the surface of the electrode (conductor)the surface of the electrode (conductor)
Corona is also a function of the radius of Corona is also a function of the radius of curvature of the electrode (conductor)curvature of the electrode (conductor)
Corona and the Electric FieldCorona and the Electric Field
Corona is NOT solely a function of the Corona is NOT solely a function of the Electric FieldElectric Field
Corona is a function of the electric field on Corona is a function of the electric field on the surface of the electrode (conductor)the surface of the electrode (conductor)
Corona is also a function of the radius of Corona is also a function of the radius of curvature of the electrode (conductor)curvature of the electrode (conductor)
Corona is also a function of the rate of decay Corona is also a function of the rate of decay of the electric field away from the electrode of the electric field away from the electrode (conductor)(conductor)
Corona and the Electric FieldCorona and the Electric Field
For the preceding reasons, selecting the For the preceding reasons, selecting the conductor with the smallest electric field at conductor with the smallest electric field at its surface is not correct.its surface is not correct.
One utility found out (the hard way) that One utility found out (the hard way) that simply choosing large diameter conductors simply choosing large diameter conductors did not work well because the electric field did not work well because the electric field decayed slowly away from the surfacedecayed slowly away from the surface
Corona and the Relative Air DensityCorona and the Relative Air Density
Corona and the Relative Air DensityCorona and the Relative Air Density
Corona has an inverse relationship with air Corona has an inverse relationship with air densitydensity
Corona and the Relative Air DensityCorona and the Relative Air Density
Corona has an inverse relationship with air Corona has an inverse relationship with air densitydensity
Standard line designs that perform well at Standard line designs that perform well at sea level, may have significant corona sea level, may have significant corona issues if used on lines that are installed over issues if used on lines that are installed over mountainous areasmountainous areas
Corona and the HumidityCorona and the Humidity
Corona and the HumidityCorona and the Humidity
Corona has an inverse relationship with Corona has an inverse relationship with humidity at power frequencieshumidity at power frequencies
Corona and the HumidityCorona and the Humidity
Corona has an inverse relationship with Corona has an inverse relationship with humidity at power frequencieshumidity at power frequencies
Fair weather corona is more prevalent in Fair weather corona is more prevalent in low humidity environmentslow humidity environments
Corona Is Dependent Surface Corona Is Dependent Surface Condition Of The ConductorsCondition Of The Conductors
Corona Is Dependent Surface Corona Is Dependent Surface Condition Of The ConductorsCondition Of The Conductors
Corona is enhanced by irregularities on the Corona is enhanced by irregularities on the conductor surfaceconductor surface
Corona Is Dependent Surface Corona Is Dependent Surface Condition Of The ConductorsCondition Of The Conductors
Corona is enhanced by irregularities on the Corona is enhanced by irregularities on the conductor surfaceconductor surface
Irregularities include: dust, insects, burrs Irregularities include: dust, insects, burrs and scratches and water drops present on and scratches and water drops present on new conductorsnew conductors
Corona Is Dependent Surface Corona Is Dependent Surface Condition Of The ConductorsCondition Of The Conductors
Corona is enhanced by irregularities on the Corona is enhanced by irregularities on the conductor surfaceconductor surface
Irregularities include: dust, insects, burrs Irregularities include: dust, insects, burrs and scratches and water drops present on and scratches and water drops present on new conductorsnew conductors
Corona will generally be greater on new Corona will generally be greater on new conductors and will decrease to a steady-conductors and will decrease to a steady-state value over a period of approximately state value over a period of approximately one year in-serviceone year in-service
Corona Is Dependent Surface Corona Is Dependent Surface Condition Of The ConductorsCondition Of The Conductors
Corona is enhanced by irregularities on the Corona is enhanced by irregularities on the conductor surfaceconductor surface
Irregularities include: dust, insects, burrs and Irregularities include: dust, insects, burrs and scratches and water drops present on new scratches and water drops present on new conductorsconductors
Corona will generally be greater on new Corona will generally be greater on new conductors and will decrease to a steady-state conductors and will decrease to a steady-state value over a period of approximately one year in-value over a period of approximately one year in-serviceservice
Corona is significantly increased in foul weather.Corona is significantly increased in foul weather.
Corona Is Dependent On Local Corona Is Dependent On Local Electrode GeometryElectrode Geometry
Corona Is Dependent On Local Corona Is Dependent On Local Electrode GeometryElectrode Geometry
N o n -C ritica l S u rfaces
N o n -C ritic a l S u rface
C ritic a l S u rfacesN u m b er o f E lem en ts = 2 1 0
C ritica l S ec tio n
Corona Is Dependent On Local Corona Is Dependent On Local Electrode GeometryElectrode Geometry
Corona Is Dependent On Local Corona Is Dependent On Local Electrode GeometryElectrode Geometry
r
S
G ro u n d P lan e V = 0
S p h ere V = V0
Corona Is Dependent On Local Corona Is Dependent On Local Electrode GeometryElectrode Geometry
0 0.5 1 1.5 2 2.5 3 3.5 4 4.50
500
1000
1500
2000
2500
3000Actual Electric Field vs. Distance
Distance (cm)
Ele
ctr
ic F
ield
(V
/cm
)
1 cm
2 cm3 cm
4 cm
5 cm
6 cm
7 cm8 cm
9 cm
Why is it a special problem for voltage upgrades?
If the voltage of a transmission line is increasedwithout changing the line design, the electric fieldat the surface of the line conductors (and hardware)will increase. This increase will cause additionalcorona
The same can be said for compact transmissionlines.
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 NoiseCautions Regarding Radio Noise
Cautions Regarding Radio NoiseCautions Regarding Radio Noise
Radio noise from corona should not be Radio noise from corona should not be confused with radio noise generated by confused with radio noise generated by spark dischargespark discharge
Cautions Regarding Radio NoiseCautions Regarding Radio Noise
Radio noise from corona should not be Radio noise from corona should not be confused with radio noise generated by confused with radio noise generated by spark dischargespark discharge
High frequency complaints are High frequency complaints are almostalmost always due to sparksalways due to sparks
Cautions Regarding Radio NoiseCautions Regarding Radio Noise
Radio noise from corona should not be Radio noise from corona should not be confused with radio noise generated by confused with radio noise generated by spark dischargespark discharge
High frequency complaints are High frequency complaints are almostalmost always due to sparksalways due to sparks
Causes of spark discharges can be located Causes of spark discharges can be located and repairedand repaired
Cautions Regarding Radio NoiseCautions Regarding Radio Noise
Radio noise from corona should not be Radio noise from corona should not be confused with radio noise generated by confused with radio noise generated by spark dischargespark discharge
High frequency complaints are High frequency complaints are almostalmost always due to sparksalways due to sparks
Causes of spark discharges can be located Causes of spark discharges can be located and repairedand repaired
Corona is a DESIGN ISSUECorona is a DESIGN ISSUE
Cautions Regarding Radio NoiseCautions Regarding Radio Noise
Radio noise caused by corona cannot be Radio noise caused by corona cannot be reduced by changing the line configuration reduced 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 several The source of the problem can be several miles away miles away
Audible Noise
Can get “broadband noise” and “hum”
Load can affect audible noise For measurement see:
ANSI/IEEE Standard 656-1992 – “IEEE StandardFor Measurement of Audible Noise from OverheadTransmission Lines
Audible NoiseAudible Noise
May be present as “120 Hz Hum” or May be present as “120 Hz Hum” or broadband noisebroadband noise
Can be affected by loadCan be affected by load
Audible NoiseAudible Noise
Audible NoiseAudible Noise
May be present as “120 Hz Hum” or May be present as “120 Hz Hum” or broadband noisebroadband noise
Audible NoiseAudible Noise
May be present as “120 Hz Hum” or May be present as “120 Hz Hum” or broadband noisebroadband noise
Can be affected by loadCan be affected by load
Audible Noise in Context
50
55
60
65AudibleNoise dBA30 metersfromcenterline
Numerouscomplaints
Moderatecomplaints
Nocomplaints
Source: BPA study
Common design limit – 53 dBA
EPA RegulationsEffect Level Area
Outdooractivity
Indooractivity
Ldn < 55 dBA
Residential areasand farms where.. quiet is a basisfor use
Leq(24) < 55 dBA
Areas wherepeople spend limited time
Ldn < 45 dBA
Leq(24) < 45 dBA
Residential
Other
Ldn (has a -10 dB adder nightime) Leq(24) (24 hour average)
x
y
Tradeoff: Magnetic Field vs. Audible NoiseEffect of Changing Conductor Phasing
A
B
C
A or C
B
C or A
White – ABC – ABC Super BundleRed – ABC – CBA Low Reactance
500 kV Double Circuit Line
0
5
10
15
20
25
0 20 40 60 80 100 120
Distance from Center Line
Mag
neti
c F
ield
(mG
)
ABC – ABC Super Bundle
ABC – CBA Low Reactance
Magnetic Field is Reduced
52
54
56
58
60
62
64
0 20 40 60 80 100 120
Distance from Center Line (m)
Aud
ible
Noi
se (d
BA
)
ABC – CBA (Low Reactance)
ABC – ABC (Super Bundle)
Audible Noise is Increased
Corona Loss
What is it?
Whenever corona occurs on a transmission line, there is acorresponding loss of energy called “corona loss.” This lossis 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 foulweather, corona loss can actually exceed resistive loss.
A Word On Corona LossesA Word On Corona Losses
A Word On Corona LossesA 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 LossesA 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
Example Losses (sea level)
LineVoltage (kV)
Bundlen x 2a
LoadMVA
I2R LosskW/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
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 linesof more compact design. Apparently, the hardware is exposed to higher gradients in the field than those to which the hardware was tested.
Corona On HardwareCorona On Hardware
Corona On HardwareCorona 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 HardwareCorona 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