Monitoring & Measurement
Wind Turbine DFIG Slip Ring Fault: Case Study

Over 60% of all wind turbines are currently using the doubly fed induction generators (DFIGs). At the time of their introduction they offered higher efficiency (in sync with grid with variable wind turbine speed). And also better power factor control (import/export of reactive power).
In addition, reduced converter cost (only 25-30% of power passes through the convertor) compared to the previous generation of generators. This is possible by connecting the rotor windings to the grid via a multi-phase slip ring unit and a voltage converter. The slip ring unit consists of a set of spring-loaded brushes. They ride on slip rings mounted on the rotor, for each phase.
A number of generator faults are detectable by accelerometers in the load zone of the generator bearings, including faults with the slip ring assembly. This case study shows how early detection of slip ring defects could result in a fast, inexpensive repair. If, on the other hand the slip ring fault is not corrected at an early stage of development, this could lead to a catastrophic failure where the generator is destroyed.
MACHINE/INDUSTRY/PROCESS
A multi-MW wind turbine in a wind park was operating at full production. At that time, Brüel & Kjær Vibro condition monitoring system temporarily disconnected for approximately two months. Shortly after, when the condition monitoring system went back online, the customer notified the Brüel & Kjær Vibro Surveillance and Diagnostics Service Centre. And, requested the initial data analysis.
OBSERVATION/DIAGNOSIS
Then, Brüel & Kjær Diagnostics Group analysed the data using a detailed time waveform and frequency spectrum, as shown in Figures 1-2. Increased vibration indicated a potential problem with generator slip ring unit.

Figure 1: The time waveform showing amplitude modulation of a little less than 2.5 Hz.
OBSERVATION/DIAGNOSIS (Cont.)

Figure 2: Increased vibration amplitude for several harmonics as measured by the accelerometer located on the non-driven end generator bearing.
They issued an alarm report by phone conversation with the customer explaining the problem, in the following step. And, below is an extract from the recommendation section of the report:
• In addition, generator inspection within 1-2 weeks is a recommendation.
• Another recommendation is to perform an up-tower generator test run with particular focus on the slip ring unit. Check the height of the slip ring brushes to be within the acceptable limits. Then, inspect the condition of the cooling groves, insulation ring and the current clamps.
RESULTS/FEEDBACK
A site inspection was done one day after the report was issued.

Figure 3: Slip ring shown with worn out cooling groves (left), and worn out brushes (right).
RESULTS/FEEDBACK (Cont.)
Aftermath, the slip ring unit and brushes were replaced. In this way, the wind turbine returned to production with lower vibrations measured on the generator bearings.

Figure 4: Vibration amplitudes returned to normal (6x harmonic shown), as measurement by the accelerometer on the non-driven end generator bearing.
BENEFITS/COST SAVINGS ESTIMATION
There are clear benefits in detecting a slip ring fault early. The cost and downtime in replacing the slip ring unit is small in relation to the maintenance and downtime with a catastrophic failure of the generator.
• Slip ring unit replacement: Approximately, 4000 € plus a few hours downtime (500-1000 €) • Generator replacement: With approximation, 100 000 € (includes crane) plus downtime (four weeks at 2000 € per day), with a total of 156 000 €
Hence, this gives a savings of 151 000 €, which does not include labor.
Monitoring & Measurement
ZX Measurement Services Supports Noise Monitoring at Proposed North Logiealmond Wind Farm

As part of the campaign, ZX Measurement Services deployed a ZX 300 wind Lidar to provide precise wind data for correlation with acoustic measurements, enabling a more detailed and accurate noise impact assessment. Noise monitoring is a critical tool for risk management, planning, and community engagement, ensuring wind farms are developed responsibly, sustainably, and in compliance with all applicable standards.
At the heart of the campaign is the ZX 300 wind Lidar, renowned for its industry- leading accuracy in wind measurement. By capturing data at hub height,the ZX300 helps improve the precision and efficiency of environmental impact assessments for proposed wind farms.
All Lidar data is accessible via the ZX Data Portal, a secure cloud-based platform offering near-real-time access to wind data. The portal gives Muirhall Energy a unified view of all their measurement data, empowering their team to make informed decisions. Available insights include system uptime, data availability, wind speed, wind direction, wind roses, wind speed profiles and distribution, turbulence, and environmental conditions.
“With our integrated approach — combining the latest Lidar technology with instant data access via our portal — clients like Muirhall Energy can gain actionable insights efficiently and reliably.” said Joanna Cadman-Goodwin, Commercial Manager at ZX Measurement Services. “This deployment showcases our integrated approach to supporting renewable energy development across Europe.”
Monitoring & Measurement
TWRE and Nordex Acciona’s Second Wind Turbine Training has been completed

Second Wind Turbine Technical Training by TWRE and Nordex Acciona has been achieved in İzmir between 20-22 October.
TWRE, Turkish Women in Renewables and Energy, was founded in 2018, in order to create a network for women who take part in energy industry development and transition, as a platform for “Gender Equality” in the energy sector in Turkey.
TWRE, which has more than 1300 members and thousands of followers today, held the second Wind Turbine Technical Training in Izmir on 20-21-22 October 2020 together with one of the world’s biggest wind turbine manufacturers Nordex Acciona. In the program, which was initiated to train white and blue-collar women for the wind energy sector, 10 young female candidate who are graduates of vocational high schools, senior students and recent graduates of electrical, mechanical, construction, meteorology and energy system engineering of universities from İstanbul, İzmir and Ankara, had the chance to have a detailed theoretical and practical training for 3 days this year.
On the first day of the program, wind turbine types, turbine mechanical and electrical system components, SCADA system, Delta4000 turbines were explained in detail.
On the second day of the program, a visit to Nordex İzmir Office and Training Center provided a practical view of the theoretical training and system components. During the site visit held on the last day, PİTANE RES N117 Gama, YUNTADAĞI RES N90 Beta ve Gama, AKÇA RES Delta4K turbines were visited and operational observations were made.
TWRE Founder President Ms. Sedef Budak’s comments on the program were: “We are very pleased that such a valuable training has become traditional, it was very important for us that young women take part in the transition of energy and guide their careers in the field of renewables. We thank a lot to Nordex Turkey for their support.”
Nordex Training Coordinator Melike Sezginer comments on the program were:
“As Nordex Turkey, we are happy to be in collaboration to encourage young women’s to work in the renewable energy business, and also to host them in Nordex Academy Turkey, and we thank to all participants.”
This training was carried out under the coordination of Nordex Training Coordinator Melike Sezginer and İzmir Office Manager Gülçe Çalışkan, and with contributions of Nordex Technology and Development Manager Selim Türkel and Technical Trainers Ahmet Paksoy and Zafer Avcı.
Monitoring & Measurement
Temperature compensation in the NRG BP60 barometric pressure sensor

The NRG BP60 is a drop-in replacement for the BP20 Barometric Pressure Sensor. There are several improvements introduced in the BP60, but perhaps the most important is the introduction of native temperature-compensation.
The BP60 continuously measures the temperature of the air volume that is being sampled inside its housing by its barometric pressure sensing element and factors this internal temperature into the sensor’s barometric pressure output. The temperature sensing element has a very low thermal mass, which allows it to react to changes in internal temperature almost immediately.

The performance improvement can be dramatic in situations with rapid temperature swings, including diurnal cycles such as the one shown in the example below from NRG’s internal BP60 field test. At the beginning and end of the time series, the BP20 (dashed yellow) agrees with the cohort of three BP60s fairly closely (approx. ± 1 hPa). However, during the daytime, there is a pronounced divergence, with the BP20 reading approximately 5 hPa higher than the BP60s as the temperature increases about 20°C over a five-hour period, from just over 2° to 22°C (solid teal). The BP60 cohort continues to read within ± 0.5 hPa throughout the same period.
The BP60’s onboard temperature compensation improves the sensor’s overall measurement accuracy relative to the legacy BP20, enabling improved estimates of future air density and annual energy production, and more reliable forecasts on operational solar and wind farms as well as in general meteorology use cases.
Please contact sales@nrgsystems.com to learn more about this exciting new sensor.
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