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12/22/2000 State of Art Fiber Optic 1
UTILITY APPLICATION OF FIBER OPTIC CABLES
George G. KaradyArizona State University
2000
© Arizona State University. All rights reserved.
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UTILITY APPLICATION OF FIBER OPTIC CABLES
Utilities are installing fiber optic cables on high voltage transmission lines. Three basic designs employed are: • 1) OPGW (optical ground wire)• 2) Wrap-type• 3) ADSS (all dielectric self supporting
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FIBER OPTIC CABLES
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UTILITY APPLICATION OF FIBER OPTIC CABLES
OPGW (optical ground wire) which replaces shield wires• Provides lightning protection• Provides communication• Lightning short circuit damage • Installation requires long tem outage• Expensive• Superior performance
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UTILITY APPLICATION OF FIBER OPTIC CABLES
Wrap-type which is wound around shield wires and, in some instances, around energized conductors • Hot-line installation is difficult• Cost more than ADSS, but less than OPGW• Need a shield wire• No operation problem is observed
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UTILITY APPLICATION OF FIBER OPTIC CABLES
ADSS (all dielectric self supporting) which is mounted at various locations, typically 3 to 10 meters below the phase conductors.• ADSS costs less than OPGW• Higher fiber count than Wrap type.• Can be installed on towers not designed for
shield wires.• Suitable for hot line installation
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UTILITY APPLICATION OF FIBER OPTIC CABLES
• Loose tubes around central FRP• Super absorbent tape• Inner sheath: PE• Para-aramide yarns• Cable jacket
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UTILITY APPLICATION OF FIBER OPTIC CABLES
ADSS DisadvantagesHigh electric field caused cable failure has been reported by utilities• Corona problem• Dry-band arcing in polluted area
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UTILITY APPLICATION OF FIBER OPTIC CABLES
ADSS INSTALLATIONTECHNIQUE
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UTILITY APPLICATION OF FIBER OPTIC CABLES
Corona Location Corona Location Corona Location
Corona Location
CoronaLocation
CoronaLocation
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UTILITY APPLICATION OF FIBER OPTIC CABLES
Fiber optic cableassembly
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UTILITY APPLICATION OF FIBER OPTIC CABLES
ADSS CORONA CAUSED DAMAGE
Analysis and mitigation techniques
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UTILITY APPLICATION OF FIBER OPTIC CABLES
15 kV20 kV
25 kV
Conductor
Fiber Optic Cable
Grid Size =1.2 x 1.2 m
10 kV
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UTILITY APPLICATION OF FIBER OPTIC CABLES
Table 1. Space potential and rod tip surface gradients.
StructureEvenendedrods
2.5 cmExtension
SpacePotential(2D)
Tower/Pole kV/cm kV/cm kV230 kV Wood Pole 12.8 25.9 22.60
230kVSteel lattice 10.1 20.2 25.00345 kV Wood Pole 13.8 26.6 28.70500 kV Steel delta 0.9 1.4 3.00
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UTILITY APPLICATION OF FIBER OPTIC CABLES
High Electric field generates corona dischargeThe long-term effect of this discharge is the deterioration of the cable jacket, which may result in puncture and failure.
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Corona Caused Aging of Fiber Optic Cable
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Corona Caused Aging of Fiber Optic Cable
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UTILITY APPLICATION OF FIBER OPTIC CABLES
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UTILITY APPLICATION OF FIBER OPTIC CABLES
Location SpacePotential
Rod TipGradients
PDIntensity
A 33 kV 60 kV/cm heavyB 25 kV 35 kV/cm mediumC 19 kV 25 kV/cm light
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UTILITY APPLICATION OF FIBER OPTIC CABLES
Exposure 1000 hours 5500 hoursArmor Rod Core Full Core FullA 1 2.3 14.7 24.2 84.8A 2 0 0 12.7 43.2A 3 0 95.4 33.9 163Average A 0.76 36.7 23.6 97B 1 0 0 1.9 15.2B 2 4.2 37.1 10.9 96.6B 3 9.41 51.3 18.5 195.3Average B 4.53 29.46 10.4 102.2
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UTILITY APPLICATION OF FIBER OPTIC CABLES
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UTILITY APPLICATION OF FIBER OPTIC CABLES
ADSS CORONA CAUSED DAMAGE
CABLE TESTING TECHNIQUES
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UTILITY APPLICATION OF FIBER OPTIC CABLES
Five different cables were tested The cables were energized to generate a maximum field of 48.3 kV/mmThe field was calculated by a 3D field plotting programThe test duration was 3052 hours
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UTILITY APPLICATION OF FIBER OPTIC CABLES
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UTILITY APPLICATION OF FIBER OPTIC CABLES
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UTILITY APPLICATION OF FIBER OPTIC CABLES
The discharge caused two types of deterioration:
–Surface damage: deterioration spread along the surface at a shallow depth.
–Localized damage: deterioration evidenced by deep, localized erosion craters on the surface.
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UTILITY APPLICATION OF FIBER OPTIC CABLES
CableNumber
Max. depth ofdeterioration,
µm
Rank
A 210 3B 371 4C 132 2D 45 1E 411 5
Table 2: Maximum depth of deterioration
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UTILITY APPLICATION OF FIBER OPTIC CABLES
ADSS DRY-BAND ARCING CAUSED
DAMAGE
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UTILITY APPLICATION OF FIBER OPTIC CABLES
Dry-band arcing occurs when:• The cable is polluted and wet• The longitudinal electric field is sufficiently
large to flashover the dry-band• The current in the dry band is around 0.5-5
mA• The deterioration of the jacket is caused by
the heating of the arc root.
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UTILITY APPLICATION OF FIBER OPTIC CABLES
The high voltage conductor induces a space potential on the fiber optic cable.The voltage difference between the grounded armor rod assembly and cable
space potential generates a longitudinal field along the cable jacket.This voltage drives a surface current along the cable if the jacket is covered by a
conductive layer.Pollution and simultaneous wetting produces a conductive layer.
HV conductor
Fiber optic cable
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UTILITY APPLICATION OF FIBER OPTIC CABLES
The current is the maximum at the armor rod assembly.The current drays the wet layer on the cable and produces a small dry band near the armor rod.High voltage will appearacross the dry-band.This high voltage produces an arc, which destroys the cable.
E
Fiber Optic Cable
Thin Conductive LayerArmor Rod Assembly
E
Dry-Band Arcing
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UTILITY APPLICATION OF FIBER OPTIC CABLES
Dry-band arcing caused damage ranges from erosion to fire on the cable jacket
Fire extinguished Fire did not extinguished
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UTILITY APPLICATION OF FIBER OPTIC CABLES
ADSS DRY-BEND ARCING CAUSED
DAMAGEAnalysis and mitigation techniques
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Experimental Study of Dry-band Arcing
Test circuit
Current limitingresistor
Shunt
HV transformer
Fiber –optic cable
ElectrodeDischarge
Water spray
Two electrodes were placed on the cable. The distance between the electrodes was 150mm, the applied voltage was : 2.5-10 kV.The current was limited by a capacitor (470pF, 2000pF, 40nF) or a resistance (1.5, 5, 10 Mohm).
The cable was wetted by water, consisting of wetting agent and salt.
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Typical Experimental Results
After wetting the cable, the system was energized and the dry-band formation was monitored.
After energization a sinusoidal leakage current started to flow.
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Typical Experimental Results
Dry-band development
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Typical Experimental Results
The high voltage flashed over the dry-band, which modified the current shape. The arc current is shown below:
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Typical Experimental Results
The dry band arcs over.
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Typical Experimental Results
The arc intensity increases.
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Typical Experimental Results
The dry-band expands and the current become irregular.
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Typical Experimental Results
The further extension of the dry-band stops arcing.The current rapidly decreases to the dry cable current.The voltage increases to the open-circuit voltage.After about 300 second the current and voltage become constant.The current flows through the dry cable surface. The layer resistance increases to 5-6 Mohm/cm.
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Experimental Study of Dry-band Arcing
ConclusionDry band arcing needs a current more than 0.8-2 mA.Dry-band arcing needs a gap voltage more than 7-8kV.Capacitance and resistance together determine the character of arcing.The obtain values depend on the source impedance (resistance or capacitance).
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Spark Discharge
The cables were energized to 10 kV.
The cables were sprayed by tap water, light pollution.The water formed droplets on the hydrophobic cable surface.
Spark discharge developed at different points on the cable.The discharge contained short, bluish arcs.
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Spark Discharge
Low energy bluish spark discharge
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Artificial Dry-band
Sparking produces bluish discharge
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Artificial Dry-band
Sparking DischargeThe current contains high amplitude, fast rising short duration current pulses.The high current pulse generates sudden collapse of the voltage.The voltage and current oscillation are shown in the next slide:
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Artificial Dry-band
Sparking generated current pulse and voltage
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Artificial Dry-band
Arcing discharge• The discharge 60 Hz component appears on
the discharge current, supply voltage 8 kV.
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Artificial Dry-band
Transition from spark to arc:• Change of the color of the discharge.• Both pulses and 60Hz component appear.
• When 60 Hz current flows, the voltage decreases to the arc voltage.
• When pulse current flows, high frequency disturbance occurs on the voltage wave.
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Artificial Dry-band
The results clearly demonstrate the presence of a low type of pollution discharge:• Low energy spark discharge, which produces
short duration high current pulses and bluish discharge on a hydrophobic surface.
• Dry- band arcing produces 60 Hz current and reddish, purple, flame-like discharge close to the electrodes on a non hydrophobic surface.
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UTILITY APPLICATION OF FIBER OPTIC CABLES
ADSS DRY-BEND ARCING CAUSED
DAMAGEFailure prediction method
12/22/2000 State of Art Fiber Optic 5212/96 4EPRI_Fiberoptic
Model Development
The purpose of this study is the computer simulation of dry band arcing. The polluted and wet fiber optic cable is covered by a conducting layer. This can be simulated by resistances. The unit length resistance varies between 1-10 MΩΩΩΩ/m.The phase voltages of the high voltage conductors drive currents through the capacitors between the fiber optic cable and conductors.
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Model Development
R0j/2 R0j/2
C0g
C02 C03C01
1 2 3
•The capacitor values are calculated using the Maxwell potential coefficients.•The inversion of the potential coefficient's matrix gives the partial capacitance matrix.
•The figure shows the equivalent circuit of a unit length section.
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Model Development
R0j/2 R0j/2
C0g
C02 C03C01
1 2 3•The ground capacitance is the sum of the elements of the capacitance matrix in row 0.
•C0g = C00 + C01 + C02 + C03.
•The capacitance between the cable and the phase conductors is the positive values of C01, C02, and C03 in the capacitance matrix.
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Model Development
Rs3
Rseries
Rs1
Rseries
C0g_1C0g
C20C20_1
C10C10_1
Rs2
Rseries
C30
C30_1
C10_2C10
C20_2C20 C30_2
C30
C0g_2C0g
C10_3C10
C20_3C20 C30_3
C30
C10_4C10
C20_4C20 C30_4
C30
C10_5C10
C20_5C20 C30_5
C30
C0g_3C0g
C0g_4C0g
C0g_5C0g
V2
V3
V1
X13ph_n
Res
R1
Res
R2
Res
R3
Res
R4
Res
R5 Rend
Res
0
0 0 0 0 0
0 0
V
54321
•The circuits representing the sections are connected in series. •The number of sections used for simulations is 250.•Two feet per section.
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Model Development
The circuit was analyzed using the SPICE program.The calculation assumes:• Cable is covered by a thin conductive
pollution layer.• Fully wetted by drizzle, fog or light rain.• Pollution levels: Light, Medium or
Heavy.• Heavy rain cleans the cable, washes off
the pollution.
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Results of Computer Analyses
The voltage and current distribution was calculated.Open circuit voltage was also calculated.
The effect of span length was analyzed.
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Results of Computer Analyses
Criteria for dry-band arcing:• Wetted conductive layer on the cable
surface.
• More than 1 mA short circuit current.
• More than 8-10 kV open circuit voltage.
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Results of Computer Analyses
Voltage Distribution along Fiber Optic CableSpan = 500 Feet; Wooden Towers
0
5
10
15
20
25
30
35
40
0 100 200 300 400 500 600
Distance from Tower (ft)
Peak
Vol
tage
(kV
)
Light Medium Heavy
· Fiber optic cable on 220 kV, 3 phase line· Calculated space potential = 31.11 kV· 250 sections at approx. 2 ft per section· Light Pollution = 3.0 MΩ/m· Medium Pollution = 1.0 MΩ/m· Heavy Pollution = 0.1 MΩ/m
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Results of Computer Analyses
Current Distribution along Fiber Optic CableSpan = 500 Feet; 230 kV Wood Towers
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0 100 200 300 400 500 600
Distance from Tower (ft)
Peak
Cur
rent
(mA
)
Light Medium Heavy
· Fiber optic cable on 230 kV, 3 phase line· Calculated space potential = 31.94 kV· 250 sections at approx. 2 ft per section· Light Pollution = 3.0 MΩ/m· Medium Pollution = 1.0 MΩ/m· Heavy Pollution = 0.1 MΩ/m
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Results of Computer Analyses
Effect of Span on Voltage Distribution
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
0.00 0.20 0.40 0.60 0.80 1.00 1.20
Normalized Span
Peak
Vol
tage
(kV
)
1000 500 250 100
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Results of Computer Analyses
CONCLUSIONS:• The mathematical analyses calculates
the open circuit voltage and short circuit current
• This permit the prediction of dry band arcing.
• Based on the results the utility changes the location of the cable to eliminate arcing