Development of PD catch monitor for substation maintenance

Partial discharge diagnostic device that can be remotely monitored 24 hours a day, 365 days a year

Komiya:If the insulation inside a transformer, which is one of the pieces of equipment in a substation, deteriorates, a ground fault occurs in which current flows to the ground, causing power outages, fires, and electric shocks. Therefore regular inspection is necessary. In the past, this insulator deterioration diagnosis was performed by a professional engineer who brought a measuring instrument to the site and performed an inspection about once every six months. At this time, a device called an "AE sensor" that captures and diagnoses ultrasonic waves is used for inspection. However, this device is expensive and requires an amplifier to amplify the ultrasonic waves, adding more cost. Therefore, a sensor called a "surface current sensor" was adopted for this inspection device.

Miyazaki:Problems with the insulator of transformers cause localized discharges called partial discharges. When a discharge occurs, an electromagnetic wave is generated on the surface of the transformer. A surface current sensor has a function to convert this magnetic wave into an electrical signal. Surface current sensors are cheaper than AE sensors because they have a simpler structure. In addition, since they do not require an amplifier, the cost of the device itself is significantly lower. We have experimented many times. The detectivity is good, and the result is equivalent to or better than that with an AE sensor used.

Fujino:The PD Catch Monitor constantly monitors the electric signal obtained from the surface current sensor. The waveform of this electrical signal can be analyzed to issue an alarm when partial discharge is detected. Alarms can be issued even when the sensor is disconnected, the power supply is disconnected, or the device itself is in an error. Therefore, it is possible to respond quickly to these errors.

Takano:Since the device has a USB port, it is possible to acquire logs before and after the occurrence of an abnormality on site, analyze the abnormality in detail, and change various setting values. In addition, since the device's LED lamps can also indicate abnormalities, the specialized skills previously required for inspections are no longer required, leading to labor savings.

Groping development
Steady progress was made step by step.

Tell us about the division of roles.

Takano:I was in charge of designing the software for operating devices and processing information.

Fujino・Miyazaki:We designed hardware such as circuits and housings for devices.

Komiya:While designing the hardware, I managed the team as a leader.

Komiya:Our company did not have a product using a surface current sensor, so the development started from a state of lack of knowledge. Using an actual surface current sensor, we conducted a test called an electric charging test in which partial discharge is generated by applying a voltage to a simulated tank filled with insulating oil, and collected data at substations that are actually in operation to investigate what type of waveform can be obtained when partial discharge occurs. These investigations were difficult because working with my hand at the site was indispensable in the investigations, but the data obtained here became a big foothold for development.

Fujino:Even in designing hardware, we also had to understand the electrical-specifications, such as the frequency-characteristics and sensor-sensitivity of the surface current sensor. Since it was the first time to develop the system, many of the operating principles are unclear, so when testing to understand the characteristics, we designed and manufactured special jigs by ourselves, referring to papers and other materials. With the cooperation of universities involved in the development of surface current sensors, we were able to determine the configuration of the design.

Miyazaki:When the team was formed and development started, I was in my second year at the company. The design of the analog circuit I was in charge of was different from the field I have learned so far, and I was also worried at first because there was little contact with the team members. I had never read analog circuits before, so I had a lot of difficulty in understanding the flow of signal processing and the waveform. In the field survey using the surface current sensor, I was in charge of confirming the acquired waveform data with the oscilloscope. However, I felt the difficulty of development due to some failures, e.g., the appropriate sampling rate and input voltage range were not known in advance, and data was not obtained successfully after analysis.

Fujino:I often saw how you understood the customer's needs while communicating with other departments, and you were proactively working to incorporate those needs into the product.

Miyazaki:The team was actively communicating, and there were many occasions for discussions and information-sharing outside the regular meetings.. At first, I participated in the meeting without knowing anything, but I was able to learn a lot while actually working with my hand in an environment where I can freely ask questions and propose ideas, and I was able to work on development.

Development continues for a safe and secure future

Miyazaki:Currently, the number of EV (Electric Vehicle) is increasing and the use of ICT infrastructures is becoming more active, and demand for electric power is expected to increase more and more. On the other hand, we believe that there is a shortage of personnel to manage it, so it is necessary to save labor in the monitoring of equipment as much as possible. Under these circumstances, the number of digital substations that can save labor in operation is increasing, and we would like to develop inspection and diagnostic systems that respond to such a new age environment and support safety and security.

Fujino:PD Catch Monitor is being installed at substations and will be put into trial operation in stages, but the development is not yet complete. We believe that the data obtained during the trial operation will contribute to future improvements. It is considered to be important to reflect the data obtained here in the design.

Komiya:This product is specialized for oil-insulated substation equipment, but we would like to support other insulation methods in the future. We also plan to focus on the development of new products for digital substations that are capable of more detailed remote monitoring.

Conclusion - Sincere Efforts to Support Important Social Infrastructure-

Demand for electrical energy is increasing as environmental problems become more serious and a transition to a carbon-neutral era is required. Even today, the four engineers of TAKAOKA TOKO are making sincere efforts to support the stable supply of electricity, an important social infrastructure, so that our daily lives will not change