Photonics and Its Application in High-Voltage Engineering
Rapidly increasing growth and automation of power are given the opportunity to power engineers to incorporate new ideas in the field of online monitoring of power apparatus for reliable operation of electrical system. As a part of new innovation in power system, photonics play an important role for driving innovation toward the sensor development, optical data communication to imaging, lighting and displays. In any power apparatus, degradation of insulation occurs due to the accumulation of mechanical, thermal and electrical effects for a long period. As the insulation of high voltage (HV) power apparatus are deteriorated by partial discharges (PDs), detection and measurement of PDs are of utmost important for the quality assessment of HV power equipment. In this chapter, an attempt has been made to detect the PDs with the help of photonic technology which eliminates the electrical interference; a challenge is being faced by power engineers in recent decades.
It is understood from the several studies, PDs of HV power apparatus can be detected by electrical, chemical and acoustic methods. Electrical detection focuses on capturing the electrical impulses created by the current streamer in the void and impurities. Electrical detection method has some limitations. The primary limitation is its susceptibility to noise. The high voltage transformer (HVT) environment contains high levels of electrical noise, both narrowband and broadband. Chemical detection has also some drawbacks. Firstly, this detection method does not give any information about the location of the PD and the insulation condition. Secondly, the main problem is that chemical tests cannot be performed continuously when the HV equipment are in working operation. To explore the detection of PDs through acoustic method, acoustic phenomenon of PDs has been studied, and it is found that it leads to the propagation of acoustic waves having frequencies typically between 30 and 1000 kHz inside the transformer. The propagation of acoustic wave modulates the refractive index of the medium, which modulates the intensity of the laser beam in sympathy with the acoustic waves. Acoustic methods have many advantages over other methods in that they are immune to electromagnetic interference (EMI), which can greatly reduce the sensitivity of electrical methods and they can be applied to find failure spot and location of discharges. Optical technique is also capable to couple PDs with the optical signal.
To capture the acoustic waves, an optical method is demonstrated in this chapter for detection and localization of PD sources by using photo detector inside the HV power apparatus. In this work, a new concept such as direct optical partial discharge detection technique has been introduced, where the energy exchange mechanism of electrical to acoustic is used for online monitoring of PDs. The acoustic signals are collected directly through the photonic technology, which is free from electrical interference, and finally they are converted to electrical signals for detection of amplitude as well as location of PDs occurring inside the HV power apparatus. This is a cost-effective tool for online monitoring of PDs and can be used as a predictive maintenance tool for utilities.