# Wideband UHF Antenna for Partial Discharge Detection
## 1 Introduction  
With the significant increase in electric power consumption, power equipment is currently being developed towards large capacity, ultra-high voltage, and unmanned control. If such large capacity power equipment fails to work, in general, it takes considerable time to repair the entire system and resume electric power supply. Among many factors that cause the failure in the power equipment, partial discharge (PD), which is a localized discharge in an electrical dielectric insulation system under high-voltage (HV) field, is the major cause of power equipment failure. Power plant accidents are closely related to the dielectric breakdown in HV power equipment, and thus there has been increasing demand for real-time PD diagnostics for HV power equipment [1, 2]. There are several techniques for detecting the PD, including optical, acoustic, electrical, and electromagnetic (EM) wave detection methods [3]. Among them, the electromagnetic wave detection method is widely used due to its high detection sensitivity and robust anti-interference ability [4].  
Therefore, high frequency (HF) and ultra-high frequency (UHF) sensors have popularly been studied in PD detection systems. PD events in HV power equipment typically produce very short current pulses with a rise time of less than 1 nanosecond, which can emit EM waves in the GHz frequency band [5]. When this PD occurs, the UHF sensor detects the EM waves emitted by the PD [6], so the UHF antenna is a core part of the UHF PD detection system, and the performance of the UHF antenna can directly affect the detection performance of the system [7, 8, 9, 10, 11, 12]. There are two approaches to detect the PD in the EM wave detection method. One is to install a PD sensor on the surface of the metallic chassis of HV power equipment for directly detecting the PD inside HV power equipment. The other is to place the PD sensor near a conducting ground wire for detecting the PD current flowing through the wire. Figure 1 shows a PD detection approach using a high-frequency current transformer (HFCT), which is one of the common techniques for detecting the PD currentson the conducting ground wire. When the HFCT is applied to the PD detection system of HV power equipment, the HFCT should completely surround the conducting ground wire with various shapes and sizes, which increases the complexity and inconvenience of the experiment [13].  
In this work, a novel UHF antenna is designed to detect the PD in HV power equipment, which is placed nearby the conducting ground wire, rather than completely surrounding the conducting wire as shown in the conceptual diagram of Figure 2. Herein, the PD detection can be easily implemented since it does not need to be clamped to the conducting ground wire, different from the HFCT. In addition, the proposed UHF antenna can detect the PD signals in the conducting ground wire in the GHz frequency band that exceeds the detection range of the HFCT.  
First, various shapes of loop antennas are examined to compare their near field coupling capabilities. Through the preliminary parametric study, a novel UHF antenna is proposed based on the basic loop antenna structure, which has the best near field coupling capability. The proposed UHF antenna is then fabricated, and the PD detection performance is measured using the experimental setup that can  
Figure 1: Partial discharge (PD) detection mechanism using the high-frequency current transformer (HFCT).  
Figure 2: Conceptual diagram for the PD detection in the conducting ground wire: (**a**) HFCT and (**b**) proposed ultra-high frequency (UHF) antenna.  
imitate the conducting ground wire of the HV power equipment. Experimental results demonstrate that the proposed UHF antenna can effectively detect the PD currents.