Wind Turbine Testing For Safety,
Efficiency, and Fault Identification
Solutions from Megger
Questions?
• Dr Ahmed El-Rasheed
• Industry Director - Renewables
• Ahmed.El-Rasheed@megger.com
Introductions
• Agenda:
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Why test turbines?
What are the most common faults?
What are the most costly faults?
What testing is recommended?
• Generally
• Electrically
• Generator
• Control
• Protection
• Transformer
• Cables
• How to get the most from testing?
• Where to go for additional info?
• Questions
Dr Ahmed El-Rasheed
Industry Director - Renewables
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PhD in Electrical Engineering from the University of
Liverpool, UK
Worked at Megger for over 8 years
Based in Toronto, Canada
Over 14 years in test instrument product development
Published several papers on Insulation Testing, Earth/Ground
Testing, & using Artificial Intelligence for asset maintenance
Sits on several Standards Committees including IEC, SCC,
BSi, and IEEE
The Rise of Wind Energy and Renewable Energy
• Solar & wind energy are the
lowest cost and quickest to
build sources of electricity
• Globally, both solar & wind
have experienced exponential
growth.
• There are already thousands
of gigawatts installed.
• The International Energy
Agency forecasts that the
install base of Solar & Wind
will double by 2028
Protect your investment.
From the very beginning.
And throughout its life.
The 360° solution for power applications
For a complete
health assessment
of your
asset
Efficiency & high Return on Investment needs low failure rates
• Good commissioning practice will reduce Early
“Infant Mortality” failures
• Good diagnostic test practice will reduce the
Constant Failure Rate
• Fast fault-finding practice will reduce downtime
• Good O&M practice will extend the lifespan of the
installation
• EPRI survey shows average O&M Costs per
Turbine(WTG) for a 200MW Wind project (using Dec
2009 US$)
• The survey shows that each turbine experiences an
average of 1 major outage (6hrs+) every 2 years
Survey of type and severity of faults on wind turbines: EPRI
• The Electrical System has the
most frequent faults, and each
fault takes 1.6 days to resolve
• Gearbox faults are the most
severe, causing 6.2 days of
lost generation. However, they
are less frequent
• Based on this survey, the
electrical system should be a
high priority in Operation &
Maintenance procedures
O&M General Recommendations
Frequency
Maintenance Activity
Check for abnormal operating temperatures
Daily
Check for abnormal vibration or noise
Check for fluid leaks (oil, hydraulic, etc..)
Check power flow & quality (e.g., THD)
Check operation of alarms
Monthly
Check for oil contamination: gearbox & transformer
Analysis of power quality
Check of protection & control equipment
Analysis of oil samples: gearbox & transformer
Quarterly
Electrical System health check: cables, generator, transformer, etc..
Check lightning protection
Annually
Mechanical System health check: bearings, gearbox, drivetrain etc..
Site health check
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Use Toolbox Philosophy – the right tool for the problem in front of you
Electrical System Maintenance: Generator
• Recommended tests include:
• Insulation Resistance testers
• Finds faults to ground
• Polarization Index test or Dielectric Absorption test
• Diagnostic measure of the ground wall insulation
• Coil winding resistance test
• Indicates health of the conductor(s) in a winding
• Inductance of windings
• Changes indicated degradation
• Step Voltage Test
• Tests the ground wall by approximating starting and stopping
• Hi-Pot or Withstand test
• Demonstrates the ground wall insultation strength
• Surge test
• Finding winding turn-to-turn faults and weaknesses
• Diode test
• Partial Discharge Detection and Monitoring
Insulation Life Curve
BREAKDOWN
VOLTAGE
Max voltage
before damage
Insulation Degradation
Optimum test voltage range
Operating
Voltage
TIME (Years)
Insulation
Failure
Electrical System Maintenance: Frequency Converters & Power Quality
• The frequency and general quality of the
electrical energy from Wind Turbines must
meet set requirements in order to
seamlessly integrate with the wider grid
• Turbine generator energy is converted to
DC and then back to AC at the power
frequency (50Hz or 60Hz) with the correct
phase angle and voltage level
• At this stage, harmonics can be introduced,
and general power quality needs to be
controlled and maintained
Wind Turbine Lightning Protection
n Wind turbines are at an
increased risk of being
struck by lightning
n Statistically, most common
cause of damage
n Protection must built in to
minimise the damage when
hit by lightning.
n Otherwise…
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Lightning Damage to Wind Turbines
This
happens!
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Electrical Maintenance: Lightning Protection & Earthing/Grounding System
• Vestas’ procedures specify these pass limits for
the lightning system:
• 23m blades: 15mW
• 25m blades: 15mW
• 32m blades: 20mW
• 39m blades: 25mW
• 44m blades: 30mW
• Earthing/Grounding system needs to be below
1Ohm for each turbine, and some manufacturers
specify 900mOhm limit
Case Study
Ø
Recommended by Vestas for turbine lightning
protection system
Electrical System Maintenance: Transformer
• Transformer commissioning and diagnostic
tests include:
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Insulation Resistance
Turns Ratio test
Excitation Current test
Winding Resistance test
Short Circuit Impedance test
Power Factor (tip-up) test
Partial Discharge detection
Swept Frequency Response Analysis
Transformer oil
• Withstand/Breakdown test
• Power Factor (Tan-Delta) test
• DGA detection
Electrical System Maintenance: Protection Relays
• Each Wind Turbine has electrical protection
systems that can include relays
• Protection Relay tests include:
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Under/Over voltage test
Under/Over frequency test
Vector shift test
Rate of Change of Frequency (ROCOF) test
Testing protection functions
• Some installations use self-powered relays
(SPRs), and they have unique challenges for
testing and verification
Electrical System Maintenance: Circuit Breakers
• Circuit breakers are the key disconnection devices that
must operate quickly in the event of a fault
• Tests of circuit breakers (depending on type) include:
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Timing and Travel
Motion
Coil current
Static Contact Resistance Measurement (SRM)
Dynamic Contact Resistance Measurements (DRM)
Vibration
Motor current
Minimum pick-up (minimum voltage to operate)
Supply voltage (battery voltage)
Power factor/dissipation factor/tan delta
Vacuum bottle test for vacuum circuit breakers
Electrical System Maintenance: Batteries
• The protection devices, like relays, usually
operate from battery power.
• This makes the supply batteries critical to
the electrical safety system
• These are essential safety devices and
must be tested at commissioning and
during regular maintenance work
• Battery tests include:
• Battery impedance measurement
• Battery discharge/capacity test
• Ground fault location, in the event of a
fault
Electrical System Maintenance: Cables
AC Cable
DC Cable
Electrical System Maintenance: Cables
• Cable commissioning
and diagnostic testing
includes:
• VLF tests for medium
voltage
• Mega Ohm test for
low voltage
• Sheath test
• Partial Discharge
detection
• Fault finding tests
include:
• TDR (Radar)
• Thumping
• High-voltage bridge
Testing Cables with TDR Technology
§A
reflectometer (TDR) works on the principle
of a radar device and was therefore also called
cable radar in the past.
§The pulse sent into the cable is partially
reflected at every change in impedance and
thus returns to the reflectometer. The size of
the change in impedance determines the level
of reflection. Total reflection occurs at an open
end or a short circuit.
§The distance can be determined from the time
t and the propagation speed v / 2: L = v / 2 * t
Wind power and transmission grid
Ensuring highest network availability
Interconnectors Offshore / Onshore
High-voltage onshore and offshore
cable fault location container solutions,
tailored to very long HV AC and DX
underground and submarine cables,
rated up to 525 kV and interconnector
lengths of up to 900 km
Rotor and generator testing
in the wind turbine
Substations
Transform power into appropriate voltage level
Offshore HVDC converter platform
Converts AC to DC for feeding into
the power grid
Grid
conector
AC
cable connection at sea
20-72 kV
Converter station
(converts DC to AC)
DC
export cable connection at sea
DC cable
connection
on land
AC voltage (AC cable)
Converter station
Transforms AC to DC voltage
for low-loss power transmission
via HVDC cables, and reserves
this from DC to AC back to the
distribution grid for households,
commerce and industry
Transforming voltages and
feed-in into the electrical grid
Commissioning according to international standards, e.g., IEC, IEEE, and Cenelec
Cable fault location, cable diagnostics, earth resistance testing, partial discharge, and dielectric loss diagnostics
Cable section station
Improves fault location
and optimises its
availability: main
conductor and cable
shield access
HV AC/DC transmission lines
Maintenance Database and Certification
• It is necessary to have robust
maintenance programs with historical data
in order to ensure reliable and efficient
electrical power
• A testing database is necessary to be able
to trend data as well as comply with
regulations
• Each test must be well planned before,
conducted under all safety guidelines, and
the results provides using certification
documentation
Questions?
Technical Support
Contact Information
APACtsg@megger.com
Presenter
Dr Ahmed El-Rasheed
Industry Director - Renewables
Ahmed.El-Rasheed@megger.com
Marketing
meggerhongkong@megger.com