Lightning current measuring device for wind power generation equipment

Designing devices to meet diversifying needs and standardization

Sakai:Our lightning current measuring device uses a current sensor, called a Rogowski Coil, installed at the base of the wind turbine tower to measure the peak value and charge amount of the lightning current as values. GPS satellites can also be used to obtain accurate lightning strike times. It also has a function to collect lightning data remotely and a function to notify the occurrence of lightning strikes by e-mail.

Kato:In the background of the introduction of the email notification function, there was a request from the customer to grasp the measured lightning current in real time. It is used to make immediate decisions, for example, by considering the need for maintenance and inspection.

Sakai:In order to realize the measures for preventing the recurrence of lightning damage (shutdown and quick inspection in the event of a lightning strike) for wind power generation equipment proposed by the Ministry of Economy, Trade and Industry in 2015, the lightning current measuring device has a function to output a contact signal using the lightning current measurement value as an output judgment condition when a lightning strike is detected in the wind turbine. By using the signal to automatically stop only the wind turbines that were struck by lightning, and to continue operating the turbines that were not struck by lightning, it is possible to suppress the decline in the operating rate of the wind power generation equipment.

Fujioka: In 2018, we upgraded our lightning current measuring device from a conventional device to meet the requirements for further standardization.

• By setting the lower limit of the frequency band to 0.1 Hz, it is possible to accurately measure winter lightning current in the coastal area of the Sea of Japan, which has a long duration and large energy.
• A lineup of products with the maximum measurable current of 200 kA has been developed to support the measurement of large current exceeding 100 kA.
• The trigger-level has been reduced from 2% to 1% of the maximum measured current, and smaller lightning current can also be detected (when the maximum measured current is 100 kA).
• In addition to "OR conditions," "AND conditions" have been added to the judgment conditions for lightning strike occurrence contact signal output (current peak value and amount of electric charge) to enable more diverse operations.
• A lineup of products with power supply voltage of 230 VAC has been developed to meet international standards for wind power generation equipment.

Sakai:Since improvements in measurement performance have made it possible to measure the current peak value and charge amount of various lightning currents, it is now possible to identify more accurate causes of wind turbine failure and confirm the validity of lightning-resistant designs in order to investigate the causes of lightning damage.

Fujioka:In verifying the lightning current measurement device, we struggled with measures against noises that would interfere with the measurement of lightning current. If the lightning current cannot be accurately measured due to erroneous detection, it will cause trouble for the customer. Regarding that point, we are making a careful verification. Conventionally, the lightning current waveform was recorded and verified for calculation of the peak current value and charge amount. However, verification after recording the waveform once is not allowed in the lightning current measuring device, which needs to be operated in real time Designing for noise elimination and real-time measurement was particularly difficult.

For entry into offshore wind business and further functional improvement

Kato:In the next version, we are considering the addition of a client function to connect with higher-level systems to meet customer needs.

Fujioka:In some cases where a wind turbine that had detected a lightning strike was stopped and inspected, no abnormalities were detected and there was actually no need to stop the turbine. Since it is not possible to generate electricity while it is stopped, the stoppage will lead to a decrease in the operating rate. As a solution, research is underway to determine whether or not a wind turbine is stopped by comparing and analyzing data from the system that constantly monitors the operation status of the wind turbine and lightning strike data in real time. In order to put it into practical use, it is necessary to connect our lightning current measuring device with the condition monitoring system, and we are considering it.

Sakai:Currently, wind turbines are mostly built on land, but the number of offshore wind power generation equipment is expected to increase in the future. Unlike onshore wind turbines, offshore wind turbines do not have restrictions on securing land or transportation, so they are increasing in capacity, that is, they are becoming larger. To promote the introduction of lightning current measuring device into this large offshore wind turbine, the current sensor must be reviewed. In addition, since it is difficult to access and inspect the wind turbine easily, there is a need for a maintenance technology that allows remote operation without human intervention, and we plan to investigate it in the future.

Fujioka:Since the wind turbine will basically be operated for 20 years after its construction, the lightning current measuring device, which is a part of the wind turbine, must also be maintained at all times. Therefore, the technology must be inherited within the company. I am involved in research while also placing an emphasis on nurturing the next generation.
In 2015, the Ministry of Economy, Trade and Industry announced measures to prevent the recurrence of lightning damage, and we feel more social responsibility for lightning current measuring devices.
In the future, efforts will be made to expand the system to offshore wind power generation equipment and improve the operating rate. Our goal is to reduce the number of factors that can lead to breakdowns in the design process, and to reduce customer losses caused by lightning strikes.

Sakai:Lightning current measuring devices may not be familiar to the public. However, I take pride in being a part of the important product design that prevents lightning damage to wind turbines, and I am proud of my work. I would like to keep in mind the design that will satisfy the needs of the customer.

Kato:In the future, we expect to compete with domestic and overseas manufacturers. We will leverage our top market share in Japan, including our entry into the offshore wind power business, and conduct sales activities to overcome the competition with our competitors.