The role of sensors in wind turbine O&M

Sensors can greatly improve wind turbine operations and maintenance. Provided the sensors themselves do not break down, of course.

Ft Technolgies' FT702LT-V22 is s fitted with a thermostatically controlled ‘all-body’ heating system. The sensor maintains its temperature at a user specified heater set point of between 0⁰C and 55⁰C. Three software controlled heaters are used...

Anyone wondering about the value of sensor technology in the wind industry might want to talk to First Wind in the US. In December 2013 the company started using Lidar to correct yaw alignment after a field test showed a 1.8% improvement in annual energy production.

Renewable NRG Systems, one of the partners in Avent Lidar Technology, the company commercialising the Wind Iris Lidar used by First Wind, estimates the improvement could translate to more than USD$155,000 a year across 20 2MW turbines.

That’s not a bad for a piece of kit that can fitted onto a nacelle in half a day. But it is only one example of how sensor technology is helping to improve wind farm profitability.

It is almost safe to say that modern turbines could not achieve a fraction of their cost-effectiveness without a host of sensors. Some, like the Wind Iris, are aimed at improving turbine operations. Many others help to reduce unscheduled downtime.

Farnell, a UK industrial electronics reseller, has an extensive list of turbine sensor and related devices on its web site, including accelerometers, encoders, particle counters, and temperature, oil level, voltage, current and humidity sensors.

This mass of sensors feeds into a processing system, usually via a wireless technology such as ZigBee, which allows the wind farm operator to monitor the condition of each turbine in real time.

Planning ahead

The information gleaned from sensors helps wind farm operators to plan ahead, providing an insight into parts and components that might be operating under stress and therefore likely to fail.

These parts can then be replaced ahead of time within routine maintenance schedules, reducing the likelihood of unforeseen failures and unplanned downtime. Equipping a turbine with a host of electronic sensors is not cheap, of course.

But the consequent reduction in operations and maintenance (O&M) costs more than justifies the investment, particularly for instance on offshore wind farms where a turbine failure could take days or weeks to solve because of adverse meteorological conditions.

And as sensor technology has become more commonplace in the largest and most expensive turbines, its value is starting to be appreciated even by the manufacturers of small-to-medium-sized turbine models.

The Spanish turbine maker Norvento, which sells 100kW machines and offers a round-the-clock monitoring service, is aiming to stand out in the UK market precisely thanks to its use of sensor technology for improved O&M.

“The Norvento machine is fully electrical,” says Ivo Arnús Montsalvatge, Norvento UK business development director. “There are no hydraulic systems. That has facilitated the addition of sensors in most of its components, sensors which can be controlled or monitored remotely.”

Turbine failure

For Norvento, the main benefit of this is that when there is a turbine failure the sensor data can tell engineers what has gone wrong before they set out to carry out repairs, so there is no danger of turning up on site without a critical tool or component.

“Instead of a black box, we know what is wrong,” Arnús says. “That’s how you improve costs, by avoiding needless trips and long calls with the owner of the machine.”

For scheduled maintenance, meanwhile, Arnús says: “You can go to the turbine with your homework done, if I can put it like that.”

A further benefit is that distributors can make a margin on O&M, which gives them an incentive to sell Norvento machines.

This is all well and good, but it is also true that sensor technology itself adds an extra level of complexity to the turbine design. Sensors can, and do, go wrong. So a challenge for sensor makers is to ensure their products are more reliable than the processes being monitored.

Fred Squire, director of business development at FT Technologies, which makes wind sensors, says: “Different manufacturers have different standards, but generally the wind-sensing system has to be able to give data continuously or the turbine has to shut down for safety reasons.”

Wind sensors

Wind sensors are usually mounted on top of the nacelle, where they may be subject to high winds, rain or lightning.

To counter the chances of the sensor failing, says Squire, many turbine manufacturers will use at least two sensors per nacelle, sometimes even mixing ultrasonic and mechanical designs. In any case, says Squire: “Our sensors last for a number of years.”

Wind sensor O&M can be reduced by using ultrasonic models, which do not need recalibration. FT Technologies recommends an annual check on its ultrasonic sensors, but maintenance “is fairly low key,” Squire says.

Mechanical wind sensors, on the other hand, would need recalibrating on a regular basis, and might need replacing as frequently as every nine months in very dusty or sandy environments.

Compared to the potential benefits the technology can deliver, though, the chances are that even this worst-case performance will be worth the investment.