NTT West Subsidiary Finds Burning Junction Box by Drone-based Inspection (1)
AI used to improve analysis efficiency
Nippon Telegraph and Telephone West Corp (NTT West) established "Japan Infra Waymark KK," a new company that inspects infrastructures using drones (unmanned compact aircraft), in Chuo-ku, Tokyo, and started the operation in April 2019. The capital of the company is 400 million yen (approx US$3.71 million) and was fully financed by NTT West.
The new company offers a series of services from planning and consulting on infrastructure inspections to aerial shooting by drones, diagnosis using artificial intelligence (AI) based on inspection results and preparation of reports. The company is also engaged in the sale, rental and maintenance of drones, as well as education/training and insurance brokerage.
The company handles inspection of various structures including solar panels, windmills, transmission lines, telecommunication towers, bridges and slopes. It aims to digitalize the inspections, starting from the use of drones for inspection of general social infrastructure, and, as "Waymark" in the company name suggests, aspires to become the waymark of domestic infrastructure inspections.
The company uses drones manufactured by Autonomous Control Systems Laboratory Ltd of Chiba City for the services it offers (Fig. 1)
The company placed priority on the performance and reliability required for inspections conforming to the in-house standard, information protection and security in introducing the drones. In drone operations, software is updated to improve the control performance, and the data is frequently transmitted and received between drones and the manufacturer, like general IT systems. The company emphasizes its policy to minimize the risk of outflow of information on social infrastructures in Japan to foreign countries via drones used for inspections.
Japan Infra Waymark also offers drones that function in the environment where radio waves from GPS (global positioning system) satellites cannot be received, assuming their use under bridges, and so forth.
The NTT group began to use drones after the Great East Japan Earthquake in March 2011. Telecommunication equipment of Nippon Telegraph and Telephone East Corp (NTT East) was significantly damaged by the earthquake.
The damage was serious in telecommunication lines (trunk lines) installed on bridges in particular. In many places, communication was disrupted in the entire areas ahead divided by the collapsed bridges.
To restore telecommunication lines installed on bridges in a speedy manner, helicopters were generally used. However, there were a number of issues regarding costs and technologies. Because of such situations, the NTT group decided to actively use drones. Drones were a more realistic approach than helicopters, in terms of both costs and technologies. NTT East and NTT West introduced and came to use about 300 drones, respectively.
Bodies of drones that were widely used in those days were similar to aircraft, and the shape was different from bodies of current drones. They are sometimes called unmanned aerial vehicles (UAVs) and are larger than current drones.
The knowhow on operation of UAVs was accumulated through operations for recovery of communication equipment of the group. NTT West thought of offering the services for the equipment of other companies as a business, not limiting the services to the equipment of its own group. The company considered that inspection services are promising, as long-term needs are expected.
However, at that time, there was little need for inspections by aerial shooting. Solar panels at mega (large-scale) solar power plants seemed to be the only targets for the services. The company also thought that the policy to place priority on maintenance and inspection after start of operation following the revision of the feed-in tariff (FIT) scheme was favorable for its new business.
NTT Facilities, which is part of the NTT group, has top shares in the development and operation, EPC (engineering, procurement and construction) and O&M (operation and maintenance) of solar power plants in Japan.
In starting the business of offering services using aerial shooting intended for solar power plants, NTT West developed technologies and repeated validations needed for commercialization, with cooperation by NTT Facilities. The company repeated flying drones, aerial shooting by drones, analysis of thermal distribution images shot by drones and validation of the accuracy in discovering solar panels with problems mainly in the Kansai region where the company is based and other regions.
The Nangoku Corporation group of Kagoshima City also cooperated with NTT West in the development of technologies and commercialization of the services, in addition to NTT Facilities.
To offer panel inspection services incorporating aerial shooting by drones to a variety of solar power plants, experience in aerial shooting of thermal distribution images, identification of defective panels and analysis of situations of solar panels of various manufacturers is desired.
Because of this reason, it was not enough to gain experience only in mega solar power plants of NTT Facilities. The majority of the solar panels at the company's solar power plants were manufactured by Wuxi Suntech Power Co Ltd of China because of the company's procurement policy.
On the other hand, the Nangoku Corporation group incorporates solar panels of various manufacturers. The company could undertake inspection of solar panels of many manufacturers by including solar power plants of the Nangoku Corporation group in the technology validation targets.
The technology development and validation included understanding dimensions and situations of overheated portions in panels, the level of impact on solar panel I-V (current-voltage) property, including the parts and ranking for submission to customers.
The company decided to classify the dimensions of heated portions into the three levels of "large," "medium" and "small" for submission to customers. In "large" and "medium" levels, it is likely that the impact on I-V property is high enough to have the solar panels replaced by the manufacturer.
Serious problems were discovered in the past. Overheating was discovered on a thermal distribution image shot from the sky by a drone. When an employee went to immediately check the solar panels, junction boxes attached on the back of the panels and wires around them were burning (Fig. 2).
Cases of junction boxes and wires burning have been reported from domestic solar power plants. In the majority of the cases, "charred junction boxes and wires" were discovered.
However, at this mega solar plant, they were in the process of burning. The same situation was discovered at four locations in a solar power plant with about 5MW output. The power producer immediately stopped power generation by operating the breaker because the situation was hazardous.