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Innovation Challenges

Capacitor Health Monitoring


The capacitor is one of the weakest links in terms of service life in wind turbine powertrain systems.  Condition monitoring technologies currently used in wind turbines mainly focus on mechanical rather than electrical failure. The complex operating condition of a cutting-edge offshore wind turbine makes the premature failure of capacitors notoriously difficult to predict, which makes scheduling maintenance for offshore wind turbines extremely challenging. The more unscheduled maintenance there is the greater the cost of the overall maintenance programme.


Develop a capacitor health monitoring solution that identifies premature failure signatures leading to the improved prediction of faults and maintenance planning.

The proposed solutions for this challenge must be deployable without requiring changes to existing manufacturing and design of offshore wind turbines.

Functional Requirements

Generally, the degradation parameters shall be monitored for single/multiple capacitors in a DC link. The condition monitoring (CM) technologies shall detect the key degradation parameters (e.g. ESR, Capacitance, voltage, current, etc.) for the whole capacitor bank in the form of parallel, series-parallel or parallel-series. Moreover, the technology could identify the faulty capacitor within the DC back subject to the operation and maintenance requirement. The development of the capacitor CM technologies can be evaluated in three stages as below.

  1. Offline and in-situ condition monitoring. The CM technology shall be implemented offline first within a wind turbine, and thereby the in-situ technology monitors the DC link capacitor only at specific turbine running states such as maintenance, cut off, idle speed etc.
  2. Online and real-time condition monitoring. The CM technology can monitor the capacitor condition whilst the turbine is operating, allowing for real time measurement of the capacitor degradation parameters.
  3. Integration and closed-loop monitoring. The CM technology has been well developed and integrated with the turbine control system, using the available feedback from turbine or the measurement of the installed kits. The monitored/estimated health condition of the capacitors is applied to adjust the turbine operation to optimize the reliability and availability of the turbine.

Currently, the technology lies in between the stage one and the stage two. Apart from the hardware development, efforts are also required in creating algorithms to reduce poor predictions and increase the accuracy.

Technical Characteristics

  • Temperature sensing in a harsh environment, subject to space availability and high EMI
  • AC voltage sensing with high-frequency bandwidth in a harsh environment
  • AC current sensing with high-frequency bandwidth in a harsh environment
  • Modelling and calculation of capacitance, ESR, tan(δ) etc.

Usually, the degradation parameters for the capacitor cannot be measured directly such as capacitance, ESR (equivalent series resistance). They are usually derived by measured currents and voltages.

Deployment Timescale

  • Offline and in-situ CM in 3-5 years
  • Online and real-time CM in 5-7 years
  • Integrated and closed-loop CM in 7-10 years

Operating Conditions

  • Limited space available (subject to specific turbine converter)
  • High DC link voltage (above 1000V DC)
  • High temperature (above 60°C)
  • High EMI (EMC environment, high dv/dt)

Cost Requirements

  • <£100 (hardware only, excluding the software cost

The capacitor is one of the weakest links in terms of service life in wind turbine powertrain systems.


Turbines are increasing in size, therefore, blades are getting longer and powertrain systems are increasing in capacity.

From 2010 to 2016, wind turbine power rating has grown by 60%. In 2016, the average capacity of new wind turbines installed was 4.8 MW, a significant increase from 3.0 MW in 2010, reflecting a period of continuous development.  The first 8MW turbines have been in operation since late 2016.

Market size

The blades and powertrains market has seen rapid growth following a sustained offshore wind build programme in Europe led by the UK and Germany.  Europe has 3,589 offshore turbines installed and grid-connected as of January 2017 with a total capacity of 12.631GW across 10 European countries.

Market Forecast

The 11 offshore projects under construction in Europe as of June 2017 will increase installed capacity by a further 4.8GW, equating to around 800 new powertrain systems and 2400 new blades just for offshore wind alone.  In 2016 a total of 4,948MW of new capacity reached FID and it is projected that the total European installed capacity will reach 24.6GW by 2020.

Do you have a potential solution?

Improved capacitor health monitoring can reduce unplanned maintenance.

Apply now

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