# Advanced Progress of Optical Wireless Technologies for Power Industry: An Overview
## 2 Classification and Progress of Power Industry Optical Wireless Communications
### Wireless Optical Sensor Monitoring of Power Lines
Researchers in Brazil introduced wireless optical technology into the wireless transmission of sensor signals on high-voltage power lines and carried out a series of work [77; 78; 79]. Optical fiber sensors include two types: distributed sensors or punctual sensors. The latter could be connected in a signal fiber, or they could be used in lots of different fibers which are connected in a single detection point one by one, for instance using a distributor [80]. Specifically, the current sensor transmits the sensor signal to the remote unit fixed on the high-voltage line. According to [77], the experiment applies a distributed feedback laser wavelength of 1530 nm. Aerial cables are used to connect the remote room to the optical power phase conductor (OPPC), which also use single-mode (SM) fibers. Then multi-mode (MM) fibers are used to link to the collimator A and collimator B respectively. The FSO device is connected to the far end of the OPPC cable. Then the optical signal is transmitted from collimator A to the low-potential collimator B via FSO device. The optical signal is measured with a power meter, and data acquisition (DAQ) board collects data recorded by the computer. The block diagram of the optical wireless outfield monitoring device system is shown in Figure 20. Next, the optical signal carries the sensing information to the control unit through the MM fiber. Considering that there is a huge potential difference between the aligners, and the typical value can be as high as 138 kV, the researchers introduced the wire post insulator and suspended it vertically from the high voltage line in the air. Meanwhile, the two collimators were fixed on the upper and lower ends of the insulator respectively to achieve insulation protection. In addition, the scheme also introduced that high power laser light power technology sent 830 nm light signals by multimode fiber collimator, through the wireless optical link sent to the collimator and then sent to the remote unit, and through the internal rechargeable power supply unit for the remote unit power. Refer to Figure 20 for the specific device implementation block diagram, and the monitoring device and its main components are given in Figure 21. The scheme uses wireless optical signals to transmit high-voltage sensing signals, avoiding the huge safety risks caused by wired schemes directly guiding signals from high potential to low potential, as well as the complexity of introducing customized hollow insulators to reduce risks. In the electrical system, it is necessary to measure the current, voltage, and temperature of the high voltage overhead transmission line, which requires the special monitoring device to be completely isolated from the ground potential. Power over fiber (PoF) includes the transmission of light energy, electronics, or electrical equipment for remote power supply. PoF has the following advantages when used in high pressure environment: no spark, lightning, electromagnetic pulse durability, can be used in extreme temperature, humidity, and other harsh environments. The PoF/OWC system and its components are shown in Figure 22. In addition, PoF can be used to replace metal cables and battery power in remote areas to improve system reliability and safety. One of the major advantages of using PoF technology in substations is that conductive copper wire does not need to be inserted in high ground areas. Figure 20: Block diagram of field test of the optical wireless monitoring device [77]. Aiming at the above power line wireless optical monitoring system solution, the researchers conducted a prototype implementation and carried out field tests for 8 months, as shown in Figure 23. The researchers found that rainwater residing in collimator packages can significantly affect the wireless optical loss, especially the coupling loss. In addition, the experimental results show that when optical sensing technology does not use amplitude variations, but frequency or planned variations, power oscillations introduced by thermal variations will not be a critical factor.