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Failure Modes in High Voltage Systems for Automotive and Aerospace: An Overview of Partial Discharge Electronics Reliability Webinar
Dr Adam [email protected] 09/02/2021
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Bob Willis Online Webinarswww.bobwillis.co.uk
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Effect of high voltage (up to 1000V) on Dendrite Failures and Conductive Anodic Filament (CAF) Failures of Electronic CircuitsTuesday 13th April 2021
Ling ZouNP
Book webinar online at https://register.gotowebinar.com/register/7709096448651536652
Failure Modes in High Voltage Systems for Automotive and Aerospace: An Overview of Partial Discharge Electronics Reliability Webinar
Dr Adam [email protected] 09/02/2021
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Outline
Introduction to Electronic and Magnetic Materials Research at NPL
Motivation for Understanding Partial Discharge
Overview of Partial Discharge Damage Mechanisms
Review of Existing Standards
Antenna Characterisation Project and Effect of Air Pressure
Ongoing Partial Discharge Measurements at NPL
Conclusions5
INTRODUCTION TO ELECTRONIC AND MAGNETIC MATERIALS RESEARCH AT NPL
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The UK’s national standards laboratory
• Founded in 1900
• World leading National Measurement Institute
• 600+ specialists in Measurement Science
• State-of-the-art standards facilities
• 360+ laboratories
• The heart of the UK’s National MeasurementSystem to support business and society
World leadingmeasurement
science building
36,000 m2
nationallaboratory
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About NPL …
Electronics and Magnetic Materials Group
SIR and condensationtesting
CAF
PCB Reliability
PCB Delamination
TinWhiskers
Printed electronics
InterconnectReliability
Smart Textiles
Conformal Coatings
High Temp.Interconnects & Substrates
WEEE
Printed Sensors
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How we work: Bespoke 3rd party research and measurement
• Mission extension consultancy and testing• Sn whisker behaviour• Replacement alloy testing• SIR & CAF testing• Condensation performance of components
National Measurement System – to develop capability –in collaboration with industry• Metrology for high temperature electronics• Coatings for harsh environments• High voltage SIR and CAF testing• Reliability of embedded components• Power cycling in low vacuum
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How we work: Collaborative research
Multi-partner projects• Sn whisker mitigation• Condensation testing
UKRI (Innovate UK)• High temperature interconnect materials• Protective coatings to operate at elevated
temperatures• Cost effective high temperature substrates
Test services• Surface Insulation Resistance• CAF• Condensation 10
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Thermal shock• -70 °C to 300 °C, ramp rate: ~40 °C/min• programmable dwells • rates of change of temperature of ~40 °C/min• typically used for fatigue life testing of assemblies
Thermal cycling • -65 °C to 200 °C, ramp rate: ~10 °C/min• typically used for fatigue life testing of assemblies
Humidity bias testing • 5% to 98% relative humidity• -20 °C to 100 °C electrical bias up to 1000 V • typically used for electrochemical reliability testing
Condensation testing• Controlled condensation using custom platen to chill samples
below dew point of humidity chamber
Thermal ageing• up to 300 °C with in-situ monitoring
Power cycling• multi-channel switching and monitoring of power devices
using cooling platens to increase cycle time • including low vacuum capability
Mechanical shock testing • accurate control of acceleration rate and shock pulse width• hot mechanical shock testing – up to 250 °C
Shear testing of component attachments• degree of crack propagation and damage to solder joints or
die attach, strength of the joint, comparison of alloys, post thermal fatigue
• typically used for testing joint formation with new platings, fluxes or finishes
• hot shear testing – up to 300 °C
Pull testing• temperature controlled - up to 300 °C
Solder joint reliability testing• low cycle fatigue, driven by the mismatch of the coefficients
of thermal expansion, solder joint cracking, adhesive loss of glob tops and underfills, delamination in multilayer boards and modules
Reflow soldering• for sample build and simulated manufacturing conditioning
Conditioning, Ageing, Stressing
Monitoring(before, during & after)
Analysis
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Constant continuity monitoring• in-chamber monitoring of electrical continuity: up to 900 channels • simultaneous measurement for interrupts of >100 µs.
Electrical monitoring• in-chamber monitoring using programmable multichannel switching systems for resistance and capacitance
Surface insulation resistance (SIR) testing• in-chamber leakage current detection (~pA), resistance (up to 1013 Ohm)• continuous monitoring over extended test periods (1500+ hours)
Conductive anodic filament (CAF) testing• in-chamber monitoring of printed circuit boards for leakage current due to conductive salts forming
Solvent extract conductivity• using isopropanol and water to remove soluble contaminants• provide a measure of the ionic contamination
Solderability testing• performed on solder pads or component terminations
Tin whisker propensity• electrical monitoring of tin whisker growth• measuring wetting force and time
Adhesion testing• coating adhesion measurement using pneumatic or customised pull testing
Conditioning, Ageing, Stressing
Monitoring(before, during & after)
Analysis
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Micro-sectioning• high-quality polished micrographs for various investigations,
including crack detection and grain structure analysis
Optical microscopy and image analysis• a variety of high resolution optical imaging and measurements
systems
Scanning electron microscopy and focussed ion beam
• for analysis of surfaces with complex topography with a magnification of over x100,000
• used to locate tin whiskers, examine intermetallic layers, investigate crack failure modes and general failure analysis
Scanning acoustic microscopy• uses ultrasonic waves reflecting or transmitting at material
interfaces to study buried solid interfaces of dissimilar materials and non-destructive detection of features such as bonded interfaces, delaminated interface, voids and cracks
X-ray florescence• used to determine the atomic content of material, screening
for ROHS compliance, thickness measurements and validation of solder content
Energy dispersive X-ray spectra• electron microscopes for image and elemental analysis
X-ray radiography• nano-focus X-ray inspection
Fourier-transform infrared spectroscopy with microscope capability
• used to identify organic and polymeric materials, using infrared light to scan test samples and observe chemical properties
Electrochemical impedance spectroscopy• used for the characterisation of electrochemical systems and
to investigate mechanisms in electro-deposition, electro-dissolution, corrosion studies and the study of biosensors
Surface profiling• 3D micro coordinate and surface roughness using contact
and non-contact methods
Surface energy• drop shape analyser for measuring surface free energy
Electrokinetic analyser• automated surface zeta potential analysis of solids
Thermal analysis• differential scanning calorimetry (DSC) - rapid technique that
measures the heat flow associated with material transitions as a function of temp. and time
• dynamic mechanical analysis (DMA) - a versatile technique used for characterising time, temp. and frequency dependent mechanical behaviour
• thermo mechanical analysis (TMA) - used for measuring dimensional changes in a material as a function of time, temperature and the applied force
Conditioning, Ageing, Stressing
Monitoring(before, during & after)
Analysis
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Motivation for Understanding Partial Discharge
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The Push for Higher Voltages
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Push for Higher Voltages
Environmental push: Reducing CO2emissions, clean air, green energy
Industry/consumer pull: e.g. automotive, aerospace, …
Infrastructure:• Charging stations
Technologies:• Power electronics, compound
semiconductors (SiC, GaN, …)• Battery technology
Electric Vehicles in the News
16https://www.theguardian.com/environment/2021/jan/19/electric-car-batteries-race-ahead-with-five-minute-charging-timeshttps://www.bbc.co.uk/news/business-55728337https://www.theguardian.com/environment/2021/jan/22/electric-vehicles-close-to-tipping-point-of-mass-adoptionhttps://www.ft.com/content/8e69d4da-00d2-4ada-96f0-b5dc5c7ca40a
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OVERVIEW OF PARTIAL DISCHARGE DAMAGE MECHANISMS
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What is a Full Electrical Discharge?
Flow of electrical current requires charge carriers
All materials made up of charged particles• Conductors: high concentration of charge carriers• Insulators: negative charges (orbital electrons) tightly bound to atomic
nuclei
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MetalConduction Electrons
Plasma | ElectrolytesIons
ElectricalBreakdown
DielectricBreakdown
DielectricStrength
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What is a Full Electrical Discharge?
In solids electrical breakdown occurs when a strong electric field pulls outer valence electrons from their atoms, thereby making them mobile.
Breakdown field strength• Air ~3 MV m-1*
• PTFE ~30 MV m-1*
19Conductor –
Air
Conductor +
Conductor –PTFE
Conductor +
Example:300 V
Min. distance, d:Air: 100 µmPTFE: 10 µm
*Note: these are typical values used to illustrate an example
d d
Electrical Discharge Damage
Arcs are high temperature – this can damage solid insulation materials• Short burst of current• Creation of hollow channels
• Break through insulation layer
• Charring of organic dielectrics
Dielectric breakdown strength testing• Raise the voltage across a sample until
breakdown occurs
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What is Partial Discharge?
An electrical discharge (or spark) which occurs within a section of the insulation between two conductors.
PD can occur at any point within the insulation where the electric-field exceeds the local dielectric breakdown strength.
PD occurs multiple times and can gradually reduce dielectric breakdown strength
Solids: it can occur within defects within the insulation or across the insulation surface.
Liquids and gases: it can occur across gas bubbles.21
Factors that Affect Partial Discharge?
22E. Sili, J. P. Cambronne, N. Naude, and R. Khazaka, ‘Polyimide lifetime under partial discharge aging: effects of temperature, pressure and humidity’, IEEE Transactions on Dielectrics and Electrical Insulation, vol. 20, no. 2, pp. 435–442, Apr. 2013, doi: 10.1109/TDEI.2013.6508745.
Temperature
Humidity
Moisture Content
Contamination
Voltage waveform
Pressure
Complex interactions between factors
Drawing independent relationship between PD and factor not simple
Typically:• Increasing temperature increases
PD damage
• Increasing dV/dt (frequency and/or amplitude) increases PD damage
• Reducing pressure increases PD damage
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Waveform
PD occurs where the rate of change of voltage is highest
Gradual damage mechanism:PD damage can build up over time, reducing insulation breakdown voltage23
Voltage Time
Regions where PD occursPush to use high frequencies, this results in higher number of opportunities for PD damage to occur
Square waves: very sharp dV/dt
Paschen’s Law
Breakdown voltage is a function of the product of gas pressure and distance between electrodes.
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��� = � � × � Conductor –
Conductor +
gap, dgas pressure, p
� × �
���
Paschen’s minimum
Low pressure few collisions high e-field required to increase
probability of ionization
High e-field high voltage
High pressure short mean free path high e-field required to reach ionisation
High e-field high voltage
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REVIEW OF EXISTING STANDARDS
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Standards
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Standards BS EN 60270:2001+A1:2016, IEC
60270:2000+A1:2015 High-voltage test techniques –partial discharge measurements
IEC 61934:2011 Electrical insulating materials and systems – electrical measurement of partial discharges (PD) under short rise time and repetitive voltage impulses
ASTM D1868-20 Test Method for Detection and Measurement of Partial Discharge (Corona) Pulses in Evaluation of Insulation Systems
IEC 60034-27 Rotating electrical machines
Samples: as manufactured (unaged)
Standards give clear guidance on the test method and important considerations• Inception voltage: minimum impulse voltage
at which PD pulses occur• Extinction voltage: maximum impulse voltage
at which PD pulses do not occur• Electrical methods: current transformers,
wide and narrow band PD instruments, oscilloscopes (coupling capacitors), and antenna systems.
• Non-electrical: acoustic, optical, chemical.
Opportunity for expanding guidance for:• Long term ageing (lifetime) tests • Evaluating effect of factors affecting PD
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ANTENNA CHARACTERISATION PROJECT AND EFFECT OF AIR PRESSURE
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SamplesCircular Monopoles
A4I Project in Collaboration with AerospaceHV
Project aim: Evaluate range of antennas for detecting PD at ambient and lower pressures.
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COTS PCB ShortLong Twisted Insulated Wire Pair
https://aerospacehv.comC. Zachariades, R. Shuttleworth, R. Giussani, and T. Loh, ‘A Wideband Spiral UHF Coupler With Tuning Nodules for Partial Discharge Detection’, IEEE Transactions on Power Delivery, vol. 34, no. 4, pp. 1300–1308, Aug. 2019, doi: 10.1109/TPWRD.2018.2883828.
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Initial Antenna CharacterisationResponses in Anechoic Chamber
Anechoic chamber
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-40
-30
-20
-10
0
500 1000 1500 2000 2500
Long PEEK monopoleShort PEEK monopole
MHz
dBi
Response from Monopoles
Note: whilst the PD response is in the GHz region, the switching frequency is significantly lower
Initial Antenna CharacterisationResponses in Anechoic Chamber
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-50
-40
-30
-20
-10
0
10
500 1000 1500 2000 2500
RHCPLHCP
MHz
dBiC
-50
-40
-30
-20
-10
0
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500 1000 1500 2000 2500
RHCPLHCP
MHz
dBiC
Response from COTS Response from PCB
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Test Setup
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Sample: Twisted insulated wire pair
Primary coil voltage: 30 VRMSSecondary coil voltage: ~652 VRMSFrequency 50 Hz
Pressure: Atmospheric to 0.3 bar
All measurements made with glass lid in place
Measurement equipment:
Oscilloscope: LeCroy 6100 A Current transformer: HVPD HFCT75 to confirm PD
Example of PD WaveformsPCB Antenna – Video
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Early experimental data showed all antenna systems able to detect PD, PCB antenna give largest max, but also largest SD
PCBCOTS
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Analysing the PD Waveforms in the Frequency Domain | PCB Antenna
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0.3 bar (cruising altitude)
1 bar (sea-level)
Fast Fourier Transform (FFT) applied to PD waveforms Each graph shows responses from 200 waveforms
Analysing the PD Waveforms in the Frequency Domain | Short Monopole Antenna
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0.3 bar (cruising altitude)
1 bar (sea-level)
Fast Fourier Transform (FFT) applied to PD waveforms Each graph shows responses from 200 waveforms
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Analysing the PD Waveforms in the Frequency Domain | Long Monopole Antenna
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0.3 bar (cruising altitude)
1 bar (sea-level)
Fast Fourier Transform (FFT) applied to PD waveforms Each graph shows responses from 200 waveforms
Analysing the PD Waveforms in the Frequency Domain | COTS Antenna
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0.3 bar (cruising altitude)
1 bar (sea-level)
Fast Fourier Transform (FFT) applied to PD waveforms Each graph shows responses from 200 waveforms
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Data Analysis
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Summary of Antenna Tests
With our measurement method (a high resolution oscilloscope) we were able to detect PD with all antenna systems.
PCB antenna gave largest signal, closely followed by COTS – however the monopoles have the benefit of simplicity, size, cost and very robust.
Measurements identified regions of interest in frequency spectrum.
Data collected shows PD is occurring but the following are not know:• PD location(s),• Extent of damage.
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ONGOING PARTIAL DISCHARGE MEASUREMENTS AT NPL
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Ongoing Partial Discharge Project
Need for robust, reliable datasets
Supporting development of test methods
Designing test vehicles and methods for failure analysis
• Evaluation/comparison:• PD resistant materials• Coating systems
• Validation of design
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Partial Discharge Multichannel Testing System
HV Switching System
Measurement:(e.g. insulation
resistance)
Sample#1
Sample #2
Sample#3
Sample#4
Conditioning:HV Source
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Pressure Hum
idity
TemperatureW
avef
orm
Moi
stur
e co
nten
t Contam
ination
Development of HV switching system• Link conditioning source and measurement technique to large number
of samples• Control and monitoring of wide range of environmental and
experimental factors• Combinational testing – understanding interplay between key factors• Evaluation of detection methods for quantifying evolution of PD
damage• Comparison of PD protection/prevention methods
Machine Learning and Deep Learning for PD Classification
Correlation between nature of PD source and measured PD response
Pattern recognition can be used to evaluate measured responses
Two parts to this:1. Extracting information from noisy data2. Processing of extracted data
a) Statistical analysis (e.g. of the statistical moment)b) Principal component analysis (PCA)c) Extraction of image featuresd) Derivation of Weibull parameters
Neural networks and support vector machines are popular techniques which have been used for PD source classification
These approaches need large volume of reliable data 42
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Summary
Technical, socio-economic and policy drivers behind increasing voltage
Theory behind partial discharge, including key factors and damage mechanisms
Standard test methods and short comings
Case study A4I project: antenna characterisation and effect of air pressure on PD
On-going PD test plans at NPL
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Concluding Remarks
Increase in uptake of high voltage electronics will result in more PD damage with reduction in dielectric breakdown over lifetime
Testing high voltage electronics for aerospace at sea level air pressure not appropriate (need understanding of suitable test methods)
Need to understand effect of acceleration factors, and determination of which are suitable
Need for test methods for generating data to support understanding and development of HV solutions
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Acknowledgements
The National Physical Laboratory is operated by NPL Management Ltd, a wholly-owned company of the Department for Business, Energy and Industrial Strategy (BEIS).
Colleagues:Martin Wickham, Ling Zou, Joe Beeby and Berjaeu Officer and David Knight
External collaborators:Professor Ian Cotton and David Chambers at AerospaceHV
Funding:
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Feel free to contact me:[email protected]
Effect of high voltage (up to 1000V) on Dendrite Failures and Conductive Anodic Filament (CAF) Failures of Electronic CircuitsTuesday 13th April 2021
Ling ZouNP
Book webinar online at https://register.gotowebinar.com/register/7709096448651536652
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