fp b.2 np__acoustic inspection of transmission and subtransmission power lines (screen aspect ratio...

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. (220kV, ultrasound power level 24dB, distance 20m)

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