1. Developments in Diagnosis of High Voltage Apparatus Michael Muhr Univ
Developments in Diagnosis of High Voltage Apparatus Michael Muhr Univ.-Prof. Dipl.-Ing. Dr.techn. Dr.h.c. Institute of High Voltage Engineering and System Management University of Technology Graz

2. Recording of technical or characteristic values Monitoring
Evaluation of
these values
Analysis
Recognition of the condition and
proposal for problem-solving strategies
Diagnosis
M. Muhr

3. Technical Diagnostics - TD
Science of recognition of the condition of technical systems
Aim of TD is to identify, to check and to classify characteristics of the condition of technical systems 
to change or to influence the condition of these systems
Quality assurance of technical systems
Avoidance of an outage of technical systems
M. Muhr

4. Technical Diagnostic
+ Prevent failure
+ Increase reliability
+ Economic use of equipment
- Costs
- Effort
- System
Optimized usage of diagnostic tools
Technique / method
Time interval
Complexity
M. Muhr

5. Availability of technical systems
Condition evaluation
Risk evaluation
Repair
Maintenance
Modernization
Technical Diagnostics
M. Muhr

6. „lifetime extention" by maintenance
Life Cycle
Condition
load t
„lifetime extention" by maintenance
pollution
ageing
critical threshold
„normal“
defect
failure
Lifetime
M. Muhr

7. Stress and Ageing Models
M. Muhr

8. Lifetime Estimation of Transformers
M. Muhr

9. Technical Diagnostic Evaluation
M. Muhr

10. Original condition with ageing
Aim of TD
Original condition
- Monitoring
- Analysis
- Diagnosis
Current condition
- Ageing behaviour
- Life time
- Preventive maintenance
- Repair
Modernization
Original condition with ageing
M. Muhr

11. Monitoring of equipment Investigations at equipment and models
Tasks of TD
Monitoring of equipment
Investigations at equipment and models
Characteristic values, current, voltage etc.
Life-time behaviour
Determining of limits
Setting of continuous voltage strength
Optimization of life-time
Decision
- Continuation of operation
- Maintenance
- Renewing
M. Muhr

12. Determination of Early Failures
Bathtub Curve: from statistical analysis
Weibull Distribution:
d<1: early failure
d=1: stochastic process
d>1: ageing process
M. Muhr

13. Ageing of an electrical insulation system
Ageing stress
Thermal
Electrical
Ambient
Mechanical
Ageing mechanism
Instrinic
Exstrinic
Single stress
Multi stress
Electrical insulation system
Failure
M. Muhr

14. M. Muhr TD at equipment of electrical power engineering
Analytic and spectrometry
UV, VIS, IR - Spectrometry
Gaschromatography
Mass spectrometry
Thermal diagnostic
Thermovision
Temperature measurement
Mechanical diagnostic
Sound emission analysis
Dilatometry
Mechanical spectrometry
Analysis of mechanical quantities
Visual diagnostic
UV - Videography
Thermography
Endoscopy
X-ray graphy
Dielectric diagnostic Ue
u(t)
C(f)
tan δ(f)
Breakdown diagnostic Ud
φ (Ud)
t (Ud)
Partial discharge diagnostic Ue
Q (pd)
φ (pd)
M. Muhr

15. Maintenance Strategies - Lifetime
M. Muhr

16. Blockdiagramm of a Diagnosis System
Excitation
Measuring voltage
Measuring temperature
Reference components
Diagnosis sample
Original
Mode
Stress generation
Voltage
Temperature
Vibrations
Climate
Control
Voltage
Temperature
Data acquisition - Sensors
Assessment and control unit
Storage of quantities
Run-off control
Data processing
Input and Presentation
Further processing
Interface
M. Muhr

17. Non – Destructive TD at Power Apparatus
Cables
Solid switchgears
Capacities
Transformers
Instrument-transformers
Rotating machines
Insulators
Conventional switchgears
Circuit breaker
Gasinsulated switchgears
Dielectric diagnostic
Visual TD
Pd-diagnostic
Sound emission diagnostic
Gas analysis
TD of mechanical quantities
Leakage current diagnostic
TD of thermal and mechanical quantities
TD of thermal quantities
M. Muhr

18. Basis Aspects of TD Aim Technique Method Quantity
Connection between quantity and physical / chemical / technical structure of diagnostic sample
Diagnostic criterion - limit
M. Muhr

19. Meaningfulness (stress)
Technical Diagnostic
Thermal
Mechanical
Dielectrical
Partial Discharge
Breakdown
Material analytic
and Spectrometry
Non-destructive
individual testing
Quasi non-destructive
Partly individual testing
Destructive
Type approval test
Random check
Meaningfulness (stress)
M. Muhr

20. Electrical Diagnostic Methods
Dielectric
Breakdown
Partial Discharge
M. Muhr

21. Dielectric Diagnostics
Observation and evaluation of interaction of electric fields and material
Insulation Resistance
Capacity and Dissipation Factor
Isothermal Relaxation Current Analysis (IRC)
Polarisation / Depolarisation Current Analysis (PDC)
Frequency Response Analysis (FRA)
M. Muhr

22. Insulation Resistance
Guard Ring Arrangement U= I RS RO RD U= I RS RO RD
Insulations Resistance
Surface Resistance
M. Muhr

23. Capacity and Dissipation FactorCX RX CN R3 R4 HV CX RX CN PC
DSP A D
M. Muhr

24. Analyse in Time Domain M. Muhr V A PDC IRC PDC RVM
Discharge Voltage Analyse
Discharge Current Analyse
Recovery Voltage Analyse
Charging current Analyse 0%
20%
40%
60%
80%
100%
120%
PDC
IRC PDC
RVM
current
voltage V A
Schema
M. Muhr

25. Isothermal Relaxation Current Analysis (IRC)V A
Schema
M. Muhr

26. Polarisation / Depolarisation Current Analysis (PDC)
Time V A
Polarisation
Schema
Depolarisation
M. Muhr

27. Frequency Response Analysis (FRA)
U, I
U, I HV LV
M. Muhr

28. Breakdown Diagnostic
HV-AC
M. Muhr

29. Breakdown Test with Insulating Oil
M. Muhr

30. Partial Discharge (PD) Measurement
Sensitive nondestructive method
as important diagnostic tool
for evaluation of the insulation condition
PD-defect
Location and Detection
Electrical
Non electrical methods
M. Muhr

31. Partial Discharge DiagnosticHV
Optical
IEC 60270
Electrical
HF/VHF/UHF
Mechanical
Acoustic
Opto-acoustic
Chemical
M. Muhr

32. PD-Detection Methods IEC 60270
Conventional electrical measurement
Integration at frequency domain
Narrow-band
Wide-band
Integration at time domain G
ZFilter
HV-Source
Test object
Coupling capacitor
PD-System
HV measure PD
Pulse
Quadripole
Measuring impedance
M. Muhr

33. PD-Measurement Results
Phase correlated
Single impulses
Time correlated
M. Muhr

34. PDC Analyse
M. Muhr

35. Unconventional PD-DetectionRd ST CC VP W
RPA1
HST1
AMP
SYNC
ICM
LWL
Signal-
conversion
acoustic
optical
Oscilloscope
ADU
electrical
Surface
LWL fibre
Fibre in oil/board
M. Muhr

36. PD-Detection Methods Electrical measurements with high frequencies
HF / VHF method – 3 MHz to 300 MHz
UHF method – 300 MHz to 3 GHz
Acoustic measurements – 10 kHz to 300 kHz
Optical measurements – ultraviolet – visible – infrared range
Chemical measurements
- Acoustic HV
- Chemical
- Optical PD
Directional
microphone
M. Muhr

37. HF / VHF – PD-Measurement
cable
PD-signal
Rogowski coil
PD-signal
current
wire sheath
cable
inductive
PD-signal
sheath interruption
measurement
impedance
cable
measurement impedance
cable HV
source
PD-signal
galvanic
M. Muhr

38. HF / VHF – PD-Measurement
Rogowski coil
Rogowski coil
PD Analyser
Measuring for HF – PD-detection on machines, VHF – PD-coupler,
Split ring Rogowski coil
M. Muhr

39. HF / VHF – PD-Measurement2 1 3
direct. coupling
A B
C D
impulse source / - No.
signal at coupling output A B C D
joint /1 – X
left cable / 2
right cable / 3
Principle of the coupler sensor
M. Muhr

40. UHF – PD-Measurement M. Muhr Wide band Narrow band
low-pass
filter
Peak detector
PD measuring
instrument
PRPD
pattern
Wide band
Narrow band
Spectrum
analyser
amplifiers
UHF – PD-measurement
M. Muhr

41. Field grading electrodes
UHF – PD-Sensors
Conductor
Cage
Detector
Dectector
Conductor
Cage
- Mobile
UHF-window
sensor
Conventional
UHF-sensors
Disc sensor
Cone sensor
Field grading electrodes
M. Muhr

42. UHF – PD-Fault Location
Schematic arrangement
Sensor 1
Pre amplifier
Measuring
instrument L2
Sensor 2
1 ... Sensor 1
2 ... Sensor 2
Time delay
Zeit
Amplitude 1 2
Defect
M. Muhr

43. Acoustic – PD-Measurement
Acoustic Partial Discharge Detection
Acoustic signal as a result of the pressure wave produced by PD
Frequency spectrum 10 Hz up to 300 kHz
SF6
Box
AE Sensor
Air
Principle schematic to the acoustic PD-detection
M. Muhr

44. Acoustic – PD-Sensors
- Piezo-electric (sound emission) - Condenser microphones
Structure-born sound-resonance - Accelerometer
Opto-acoustic-sensor HV
Time delay
Sensor PD
Time
Signal
Directional
microphone PD HV
M. Muhr

45. Acoustic – PD-Measurement
PD-Detector
AE Sensor
Oscilloscope
amplifier
Filter
A/D Converter
Acoustic – PD-detection system
M. Muhr

46. Opto-Acoustic – PD-Measurement
Laser
Reference optical fibre coil
Sensing optical
fibre coil
Oil tank
High
Voltage
PD-source
Detector
Beam
Splitter
Experimental setup of the optical interferometric detection of PD
M. Muhr

47. PD – Optical Detection M. Muhr Measuring circuit after IEC 60270
Optical fibre with lens
Optical fibre
Lens
Peak
Medium oil
Observation area Rd PC
LWL M ST CC VP PR W
IEC 270
optical system
Oscilloscope,
ADU
Signal-
conversion
Voltage supply
Fluorescent optical fibre
conventional
opt. fibre
Peak
fluorescent
Plate
Measuring circuit after IEC 60270
and optical measuring system
M. Muhr

48. Optical – PD-Detection in GIS
SF6
Photomultiplier
Conv.
PD Detector
ADU
I/U
Oscilloscope
Emission spectrum of
corona discharges in SF6
Test arrangement for optical PD-measurement
M. Muhr

49. Optical – PD-Measurement
Operation diagram camera DayCor IITM
and application
M. Muhr

50. Electrical PD – Application Optical Acoustic Chemical HF / VHF UHF
GIS
Overhead lines
Acoustic
- High voltage
cables
GIS
Transformers
Overhead lines
Chemical
GIS
Transformer
Machines
PD – Application
Electrical
Transformers
GIS
Machines
Overhead lines
...
HF / VHF
- High voltage
cables
- Transformers
UHF
- GIS
- GIL
- Transformer
monitoring
M. Muhr

51. Monitoring, Data Processing, Announcement
Data input
and
monitoring unit
Report
Display
Data archiving
Real time
announcement
Alarm
Data transfer
Trend analysis
Modem
Telephone lines
PC station
M. Muhr

52. Example for signal processing
Pattern Recognition
Signal processing
Report
Display
Data store
Data transfer
Trend analysis
Example for signal processing
M. Muhr

53. Power Transformer Diagnostics
IEC 599
IEEE C
Furane Values
Dörnenburg
Moisture
Dissolved Gas Analyses (DGA)
Rogers
Neutralization Value
Duval
Oil Analysis
Other Methods
Fibre Optics
Chemical
Loss Factor
Endoscopy
Oil Analysis
Eye
Breakdown Voltage
Optical
UHF PD-Detection
Electrical
Partial Discharges
PD-Evaluation
Acoustics
Elektrisch
DAC-PD-Measurement
Mechanical
Operating Noises
Mechanisch
PD Location
Insulation
Dynamics
Thermal
Loss Factor
Thermisch
PDC-Analysis
Transient Oil Pressure
Insulation Resistance
Operating Temperature
Signal Analysis
Oil Stream
RVM, FDS Analysis
Thermography
FRA-Analysis
Temperature Monitoring
Transfer Function
Wavelet Technique
M. Muhr

54. M. Muhr Method Information Comment Oil analysis OA
Oil ageing, insulation property
Routine
Gas-in-oil analysis
DGA
Oil and paper ageing, flashovers, PD,
hot spots
Loss factor
(Dielectric dissipation factor)
tanδ
Dielectric losses in the insulation system
Furane values FA
Ageing of the paper insulation
Condition determination
Degree of
polymerization DP
Partial discharges PD
Paper ageing, ageing of the
insulation system
Polarisation and
depolarisation
currents
PDC
Water content in the paper insulation
Infrared
measurements IR
Overload, failure of the cooling system
Condition determination and for fault location
Acoustic
 AM
PD-detection and location
For fault location
Frequency response
FRA
Mechanical condition of the windings
After short circuits
M. Muhr

55. Oil Analysis Moisture Karl-Fischer titration Capacitive sensors
Water content in oil
Water content in paper
Temperature
High
Low
Moisture
Karl-Fischer titration
Capacitive sensors
Breakdown voltage
PDC
Breakdown voltage [kV]
Water content [ppm]
dilution
emulsion
M. Muhr

56. Oil Analysis Loss Factor (tanδ) Heat losses are temperature-dependent
High loss factor – thermal breakdown
Limit: tanδ ≤ 5 % by T=100° C
Temperature dependace of tanδ for new oil (1) and oils in operation (2,3,4)
M. Muhr

57. Oil Analysis Dissolved Gas Analysis (DGA)
Key gases: hydrogen, methane, ethane, ethylene, acetylene, propane, propylene, carbon monoxide, carbon dioxide
Detectable failures: thermal and electrical failure
M. Muhr

58. Oil Analysis Duval triangel DGA - Evaluation CIGRE IEC IEEE Dörnenburg
MSS / VDE-Diagnosis
Rogers
Duval
Laborelec
KEPCO
Duval triangel
M. Muhr

59. Paper Analysis Polymerisation degree (DP)
In direct correlation with the mechanical strength
new paper DP 1000 – 1200
paper at the end of life time DP approx.200
A decrease in the DP value furane is going hand in hand with an increase of components
Furane dependence
Oil temperature
Type of oil
Neutralization factor
Type of paper
Sludge content
Moisture content of oil and paper
Ratio oil / paper
M. Muhr

60. Oil Analysis Furane Analysis
Condition of paper insulation (mechanical strength) determined by degree of polymerization
High performance liquid chromatograph (HPLC)
M. Muhr

61. Measurement in laboratory
Partial Discharges
Conventional
Acoustic
Optical
Chemical
Electrical
New Systems: electromagnetic wave detection, transfer functions, damped AC voltage (DAC)
Measurement in laboratory
conventional measurement IEC 60270
Acoustic PD - measurement
Optical PD - measurement
Chemical PD – measurement (DGA)
electrical High frequency PD - measurement
Narrow band Δf ~ 10 kHz
Broadband Δf ~ kHz
HF/UHF method f ~ kHz
Narrow band Δf < 2 MHz
Measurement on-site
UHF method f ~ 0,2 - 2 GHz
Broadband Δf > 50 MHz
M. Muhr

62. Charging and discharging measurements
Dielectric Diagnosis
Charging and discharging measurements
M. Muhr

63. Diagnostics with Transient Test Voltages
Frequency response analysis (FRA) and transfer function
Low voltage impulse response (LVI)
Wavelet analyse
DAC-PD-measurement
FRA
M. Muhr

64. Thermal and Optical Diagnostic Methods
Thermography
Temperature measurement with fibre optics
PT-100 elements
Surface acoustic wave radio transponder
Visual inspection
Endoscopy
Ocular
OKULAR
Light source
LICHTQUELLE
Flexible end
FLEXIBLES ENDE
Field of vision
BLICKBEREICH
M. Muhr

65. Mechanical Diagnostic Methods
Transient oil pressure (short circuit)
Stream analysis (oil and cooling air)
Acoustic PD-locating
Stream No
stream
M. Muhr

66. Diagnosis of Rotating Machines
Tasks
Thermal monitoring
Air cooling analysis
Monitoring of vibrations
Acoustic monitoring
Chemical-analytic monitoring
Magnetic monitoring
Electrical monitoring
M. Muhr

67. Rotating Machines Electrical Diagnosis Methods
Impulse voltage test at windings
Attenuation factor
Resonance frequency of resonating circuit
- Oscillogram of a decaying oscillation
Error –free
faulty
M. Muhr

68. Rotating Machines Dielectric Diagnosis Time domain
Insulation resistance Riso
Insulation current iiso = f (t)
Frequency domain
Capacitance
Loss factor tan d = f (w), C, U
M. Muhr

69. Rotating Machines Dielectric Diagnosis
Insulation time constant t10 as criterion for the dryness limit curve t10 = Riso (600s) x C (50Hz)
t10 = f (d)
Dry condition
Humid condition
Dryness limit curve
Cooling
Heating
Insulation time constant in dependance of the slot temperature and the insulation condition
M. Muhr

70. Rotating Machines Partial discharge (Pd) diagnosis Pd’s
In cavities of solid insulation
In the are of the end winding
At no-perfect working protect system of mica
At vibrating parts of winding
M. Muhr

71. Physical Condition of Windings
M. Muhr

72. Discharge behaviour within Machine Windings
M. Muhr

73. Thermography as Diagnostic Tool
Requirement
Increasing efficiency of power grid
Decreasing of inspection and maintenance rate
Load situation
Increasing electrical power consumption
Higher loads on equipment
Demand of ON-line diagnostic tools
E.g. Contact less temperature measurement
M. Muhr

74. Thermography as Diagnostic Tool
Material/Structure
Heat Generation
Temperature
Surface temperature
power output
Surrounding
Load current Resistor
Voltage Conductivity Dielectric losses
Temperature measurement
M. Muhr

75. Temperature Measurement
High Voltage
Object Temperature
Sensor
Coupling
Signalling
Transmission power supply
Isolated Transmission
Isolated Coupling
High Voltage
Object Temperature
Sensor
Coupling
Signalling
Transmission power supply
M. Muhr

76. Spot Temperature Measurement
29.8°C
29.7°C
29.6°C
29.9°C
29.5°C
30.0°C
30.1°C
Transformer
M. Muhr

77. Temperature Distribution
33°C
23°C
Hot
Cold
M. Muhr

78. Thermography in HV - Systems
Applications
Connections
Switches
Power transformers
Measuring transformers
Overhead lines
Cable terminations
Bushings
Fuses
Rotating Machines
M. Muhr

79. Applications of Thermography
Poor contact resistance of a joint
Poor contact resistance of a disconnector
M. Muhr

80. Applications of Thermography
Compression connector of an overhead line
Asymmetrical energy flow of a cable
M. Muhr

81. Applications of Thermography
Bearing, machines
© FLIR
Slip-ring brushes
M. Muhr

82. Thank You for Your Attention
M. Muhr