Fp b.2 np__acoustic inspection of transmission and subtransmission power lines (screen aspect ratio 4 to 3)

FP_B.2_NP
Acoustic
Inspection of
Transmission
and
Sub-transmission
Power Lines
Goran Stojadinovic,
Innovation & Technologies
Manager, Northpower, New
Zealand
Inshik Woo, CEO, UIT
Networks Inc., Korea
CEPSI 2016 Bangkok, Thailand — 23-27 October 2016 FORESIGHT Northpower & UIT Networks

Electricity network owners’ objectives
• Network security, reliability and performance
• Network & public safety
• Operational & cost efficiencies
This presentation presents a new technology & comparisons
with traditional inspection methods for delivering the network
owner objectives

Transmission and sub-transmission overhead lines
Problem:
• Aging power lines exposed to weather elements
• Wind – one of the most destructive forces in nature
Challenge:
• Lack of cost-efficient and accurate inspection and
defect detection methods for transmission lines
• Traditional methods fail to detect many electrical defects
until a defect is well advanced, or a fault has occurred
3

FORESIGHT/UIT acoustic inspection method
• A new inspection method for transmission and sub-
transmission power lines
• State-of-the-art acoustic inspection technology
• Comprehensive asset condition diagnostic service
customised to individual network owner needs
4

Technology
• Developed and patented by UIT Networks, Korea in 2009
for KEPCO, Korean electricity network
• Used in 10 countries on over 12 million poles/structures &
associated power lines
• Detection of ultrasonic signal caused by any electrical
discharge, including Partial Discharge and Corona
• Ultrasonic range: 20kHz to 150kHz
• Voltage range: 6kV to 220kV AC
• Early detection of electrical defects
• Pinpoint accuracy
5

6
Aeolian vibrations
• Natural winds can induce vibrations and oscillations
• Aeolian vibrations - the most frequent and damaging
• Smooth laminar winds passing across the line create
Eddy shedding (Vortex) behind the conductor
• Vortices create an alternating pressure imbalance resulting in
a high-frequency (5-120 Hz) low-amplitude conductor motion
up and down at right angles to the direction of the wind
• Fast accumulation of fatigue cycles and
high bending stresses at the fitting clamps

Damaging effects of Aeolian vibrations
The most affected components of overhead lines:
1. Conductor support clamps and sections of conductors inside
the clamps (where conductor movement is constrained)
2. Conductor along a span (conductor movement is unconstrained)
3. Preformed products: armor-rods and grips, splices, line-guards
4. Vibration Dampers, Line Spacers, and Fitting Clamps
5. Joints and Terminations
Typical damage:
• Breakdown of support hardware e.g. clamps, insulators…
• Conductor fatigue, abrasion, fretting corrosion and broken
strands, and conductor failure

8
Real-life examples:
1. Defects at conductor support clamps (cond. movement constrained)
20 dB
Fig.1a – Clamp multiple fractures due to Aeolian vibrations and material
fatigue (220kV, ultrasound power level 20dB, distance 20m)

9
Fig.1b – Heavy arcing inside the clamp. Suspected broken conductor
strands inside the clamp.
(110kV, ultrasound power level 23dB, distance 12m)
23 dB

10
Fig.1b – Multiple broken strands, corrosion, deformation and Aluminium
(cont’d) pitting. After the corrosion debris was removed it was found that
31% of conductor volume across clamp length was missing.

11
Fig.1c – Fretting corrosion (black spots) between inner layers of the new
conductor. No visual signs outside the clamp, heavy arcing inside.
24 dB

12
Fig.1d – Fretting corrosion due to a loose clamp (missing bolt).
Black spots on the conductor inside and outside of the clamp.
Conductor abrasion and suspected broken strands.
18dB
Missing
bolt
Black
spots
Black
spots

13
2. Defects along a span (conductor movement unconstrained)
Fig.2a – Fretting corrosion due to Aeolian vibrations
(ACSR, 220kV, ultrasound power level 9dB, distance 25m)
9 dB

14
Fig.2b – Broken strands due to Aeolian vibrations and material fatigue.
Signs of fretting corrosion (black spots) on the surface of the
conductor. (132kV, ultrasound power level 4dB, distance 15m)
4 dB

15
3. Preformed product defects
Fig.3a – Loose armor-rod with a gap wider than a strand. Heavy arcing
and white oxide powder indicates a conductor abrasion and
damage caused by Aeolian vibrations
(110kV, ultrasound sound power level 25dB, distance 13m)
25 dB Gap

16
Fig.3b – Incorrect installation of two splices next to each other
Gap
14 dB
Armor-rod
Splice 1
Splice 2

Fig.3b – A narrow area of unconstrained movement (a gap) between the
(cont’d) two rigidly constrained conductor sections under splices.
Heavy arcing indicates broken conductor strand(s) due to
material fatigue caused by Aeolian vibrations.
14 dB
Constrained
movement
under splices
Unconstrained
movement in the gap

18
4. Defects of Vibration Dampers, Line Spacers, and Fitting Clamps
Fig.4a – Missing half of vibration damper, creating erratic oscillations under
Aeolian vibrations and causing the damper clamp to become loose.
Fretting corrosion (black spots) and abrasion under the clamp.
Black
spots
3 dB
Missing

19
5. Joint and Termination Defects
Fig.5a – Increased contact resistance due to incorrect installation of
Ampact connector and exposure to Aeolian vibrations
3 dB

20
Fig.5b – Heavy arcing at the connection of drop-conductor to the line
8 dB

21
Fig.5b (cont’d) - Increased contact resistance due to a loose contact (missing
spring-washer), possibly exacerbated by Aeolian vibrations
8 dB
8 dB
Missing
spring washer

Fig.5b (cont’d) - Example of heavy erosion due to loose contact
between a plate and termination lug

23
6. Insulator Defects
Fig.6a – Hairline cracks on glass disc insulator
7 dB

24
Fig.6b – Heavy pin corrosion and compound fractures. Glass insulator disc
has cracked as a result of rust and thermal expansion.
Compound cracks
Pin
corrosion
Glass
crack
18 dB

FORESIGHT/UIT - Inspection record and results
• The defects had not been identified by traditional inspection methods
• Most defects were considered as undetectable using other methods
• Most of the defects had a potential to adversely impact network
performance, reliability, security, safety and/or operational costs
• Many of these defects had a potential to cause bushfires (in Australia)
25
Transmission lines Sub-transmission
lines
Inspected Over 2,000
towers/structures
Over 16,000 poles
No. of
defects
158 424
Voltage 220kV 132kV 110kV 66kV 50kV 33kV
Average
defect level
7.7% 9.3% 6% 5.6% 8% 2.4%

Key benefits
• Early detection of pre-fault conditions and fault prevention
• Improved defect classification, prioritization, and tracking of
asset condition over time
• Improved network safety, reliability, security and
performance
• Ability to determine the root-cause of intermittent faults
• Feedback tool for continuous improvement of network
design & work practices
• Significant operational & cost efficiencies (e.g. savings on
inspections, maintenance & network outages)
26

Conclusion
Advantages of FORESIGHT / UIT Networks acoustic
inspection method over traditional asset inspection methods:
• Superior detection of electrical defects
• Rapid & cost-effective inspection (up to 50 transmission
structures or 300 sub-transmission poles per day,
including associated lines)
• Comprehensive risk management solution
27

Conclusion
Advantages of FORESIGHT / UIT Networks acoustic
inspection method over traditional asset inspection methods:
• Superior detection of electrical defects
• Rapid & cost-effective inspection (up to 50 transmission
structures or 300 sub-transmission poles per day,
including associated lines)
• Comprehensive risk management solution
28
Questions ?

Examples of sound waves and sound power level
1 dB 15 dB 27 dB

FORESIGHT and UIT - three years of experience with
acoustic inspections in New Zealand, Australia and Pacific
• Power companies and mining industry
• Transmission lines (110 – 220 kV)
• Sub-transmission lines (33 – 66 kV)
• Substations
• Outdoor switchyards
• Cable terminations
• Intermittent faults
• Distribution lines (11 – 22 kV, HV ABC, SWER)
30

Inspection method
• Rapid - from a vehicle at approx. 30km/h (for lines along roads)
• Remote lines - from a 4WD / on foot as required by terrain/access
• Detection range: up to 45m on 220kV
• Defect reporting supported with high-resolution photography of
defective components
• Defect classification in accordance with network standards
Failure
and
Severity
Timeframe
Fault -
Report to
Asset
Owner
immediately
Replace or
Repair
< 3
months
Repair or
Replace
< 12
months
Replace or
Repair
1-3 year
timeframe
Review at
next
inspection
Priority P1 P2 P3 P4 P5
31

32
Fig.6c – Cracks on porcelain insulator disc
1 dB

33
Limitations of traditional inspection methods
Visual inspection:
• Used only if there is a specific evidence that damages occurred
• Can’t detect strand failures in inner layers of conductor
• Can’t detect strand failures inside clamps or below armor rods
Electro-magnetic-acoustic inspection:
• Can detect strand failures and steel corrosion, however,
it is unpractical, inefficient and unreliable
Corona camera:
• Detects false signals from sharp points and hardware flaws
• Unpractical - requires time and experience to analyze which
signal represents a true defect

34
Limitations of traditional inspection methods (cont’d)
Thermographic inspection:
• Can only detect joints problems e.g. hot-spots
• Detects a hot-spot usually in an advanced stage i.e. too late
• Heat signature from a hot-spot varies with wind, rain,
ambient temperature and humidity
• Load dependent
• Can not detect strand failures
• Difficult to use on a sunny day
Radiographic inspection:
• Can detect broken strands, but it is costly, complex and unreliable

Fp b.2 np__acoustic inspection of transmission and subtransmission power lines (screen aspect ratio 4 to 3)

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