# Research on a Partial Discharge Expert System for the Diagnosis of Damaged Transformation Equipment
## 1 Introduction  
The majority of damages to substation transmission and transformation equipment are due to insulation degradation, which is usually an aging phenomenon caused by electrical stress, thermal stress, or mechanical stress. These aging phenomena are further accelerated by partial discharge (PD), leading to serious accidents. To prevent major accidents, it is essential to have real-time knowledge of the equipment's condition. In the operation of the power system, the high-voltage power equipment is responsible for the supply, transmission, and distribution of electricity [1, 2, 3, 4]. Given the increasing complexity of the power system and the demand for power going up, insulation defects of high-voltage power equipment will cause serious power outages, equipment damage, economic loss, and inconvenience to the industry, and even equipment failure and human casualties. To prevent such incidents from happening, the prediction and preventive measurement of insulation defects have become the main subject of research. PD measurement has been identified as a reliable insulation evaluation diagnostic tool for high-voltage equipment, as voids, cracks, and gaps are significant defects in dielectric materials, whether in solid, liquid, or gas form. When electrical equipment is subjected to high-pressure stress that will cause physical and chemical degradation of the insulation interface, PD measurement is significant for the characterization of its insulation state [5, 6]. PD measurement methods include pulse current, ultrasonic, and ultra-high frequency methods [7, 8]. Although numerous studies have used the amount of PD charge integrated from the PD pulse current, few studies have measured the high-speed nanosecond PD pulse current itself, which is easilyburied in noise [9]. To satisfy the requirements, one may use a high-speed A/D-acquisition card or oscilloscope [10]. For example, a high-speed data acquisition unit is used to obtain complete discharge waveform information in a power frequency cycle. PD in this study is a tiny signal that occurs due to an insulation defect of the power supply equipment that is usually accompanied by physical phenomena such as light, sound, and heat; we aimed to develop a self-made portable partial discharge analyzer for its detection. PD inspection is an effective technology to evaluate the condition of the insulation components of power equipment. It can replace defective insulation components in advance to ensure a stable power supply [11; 12; 13]. Under the influence of a strong electric field, some of the defects in the internal insulation of the equipment, such as bubble gaps, impurities, and spikes or points all cause uneven electric field distribution inside the equipment insulation [14]. The PD, which is the electric field intensity of the defective component, increases, which can easily cause discharge and does not penetrate the overall insulation [15]. On the other hand, PD inside the insulation of high-voltage electrical equipment will affect the service life of the insulation. These PD phenomena include needle plate discharge, creeping discharge, air-gap discharge, and metal-particle discharge [16]. PD occurs in degraded high-voltage insulation. The specification of IEC60270 defines partial discharge as only the partially bridging the insulation between conductors and states that it may or may not happen near the conductor. PD is usually the result of a local electric stress concentration in or on the surface of an insulator. Usually, this discharge is a pulse lasting much less than one microsecond. These discharges will cause the resistance to decrease and ultimately lead to malfunction. Each discharge represents a current pulse. The monitoring of these pulses is a mature technology for evaluating the insulation status of high-voltage equipment [17]. Traditional techniques for detecting PD current pulses include high-frequency current sensors (HFCT), transient ground voltage sensors (TEV), and UHF sensors [18].