Spiral Antenna Design and Analysis As a Tool to Measure Partial Discharge in High Voltage Equipment

The high-voltage equipment often experiences disturbances caused by the age of the equipment, installation errors, partial discharge disturbances. Of these kinds of disturbances, partial discharge is one of the most common disturbances in high-voltage equipment which has a percentage level of 80% due to partial disturbance. In this study, a research related to electrical equipment that can detect partial discharge disturbances in these high-voltage equipment was done. The equipment is a spiral antenna, where the spiral antenna has several advantages in detecting partial discharge. In making the first partial discharge, a literature study will be carried out first, after that designing a spiral antenna using CST 2018 software to get the Return loss and VSWR parameters as desired, namely Return Loss less than -10 and VSWR less than 2. From the results of this study Spiral antenna is measured using VNA, the measurement results show the spiral antenna is in accordance with the parameters that have been determined, namely the return loss value = -30.8 and the VSWR value = between 1 to 1.5.


Introduction
Electricity in this era is a necessary to support human daily activities. The service of electricity must high quality. So to keep the quality of the electrical system, the quality of electricity must be very stable. The Industrial consumers want the electricity supply will continously and have quality so that industrial productivity is not disturbed.
This requires monitoring and electrical protection technology to be important aspects to maintant the system running properly. The substation is the part that distributes electricity from the power plant to the electrical load with various consumer loads. At substations, there are high voltage equipment will help distribute electricity to customers.
The high-voltage equipment are Transformers, GIS (Gas insulated switchgear) and other high-voltage equipment. It can suddenly disturb, so it must diagnose. Diagnosis is by using fault detection equipment without direct contact between technicians and high-voltage equipment, one way is to use a spiral antenna. [2] Because this type of antenna has several advantages over other types of antennas. Some of the advantages of spiral antennas are broadband (wide bandwidth) where this type of antenna can work at a frequency of 300 MHz to 3 GHz, circular polarization, small size and high efficiency, and is suitable for online partial discharge measurements in high voltage equipment [2]. ] [ In this research, a spiral antenna will made which is designed using CST software and with one-sided FR4 epoxy PCB material.

Research Method
The steps of this research show in the block diagram

Partial Discharge
That is a partial electrical discharge that event in the insulation it does not fully connected between two conductors and this discharge can occur, both near and far from the conductor, and this occurs an inhomogeneous field [2][5] [ 6].
Basically partial discharge can occur in some place for example in the solid insulating materials, the liquid insulating materials and the gas insulating materials. In general, partial discharges are caused by local electrical concentration pressure, in the insulation that occurs inside or on the surface of the insulation itself.
The discharge process can be seen in Fig.2. under. The electrons first emerge from a protrusion of the conductor plate whose electric field is raised to a certain level.

Fig.2. Mekanism of Partial Discharge[2]
There are 3 kinds of partial discharge sources, namely: Internal discharge, Surface discharge, and corona discharge.

High Voltage Equipment
Power Switchgear is equipment that is covered of metal. It design is completely enclosed all of sides using sheet metal materials, (except the ventilation openings and the inspection windows) which have the switching mains electrical circuit equipped with buses and connection equipment.
To get in to interior of the power switchgear which is covered by metal, a door of cover that can be opened flexibly has been provided to make it easier for technicians to carry out inspections and repairs [1].

Antenna
Antenna is a part of a telecommunications equipment system that can convert electromagnetic energy into electrical energy or vice versa that passes through a channel, both medium and vacuum. [3]

Spiral Antenna Design
In this study, we design a spiral antenna with several advantages such as broadband, circular polarization, minimal size and high efficiency, and is suitable for online partial discharge measurements.

Manufacturing Spiral Antenna
Spiral antenna is use to detect a partial discharge signal based on electromagnetic waves generated by the needle plate electrode. The spesification of the spiral planar antenna is inner diameter spiral antenna = 1 cm and has an outer diameter =13.8 cm. Bellow show the manufakturing the antenna using FR4 PCB.  Type of VNA used is VNA (TR1300/1), which provides basic vector network analysis for various industries and applications such as wireless communication, cable TV, automotive and others.  The method to read the bandwidth measurement results is in return loss parameters section which has a value is less than -10dB, this value is an antenna parameter which states that the power lost from the signal is <90%. The data from the bandwidth measurement results on the tested spiral antenna can be seen in Table 1.

Result of measurement spiral antenna in VSWR parameters
The results of measuring the VSWR parameters using VNA on the spiral antenna. The results of the VSWR measurement on the antenna show a VSWR value is more than 1 and the best value is less than 2. From this measurement can be know that antena can detect the signal from partial discharge.

Conclusion
This study discusses the design of a spiral antenna to detect partial discharge in high voltage equipment. The results of this research will show as follows: 1. The spiral antenna has made by FR4 PCB material. 2. The antenna designed using CST 2018 software with several parameters such as return loss, VSWR and BW(Bandwidth) values as a reference to produce an antenna according to the partial discharge frequency. 3. The results of antenna measurements using VNA show that the antenna is in accordance with the partial discharge signal measurement parameters, as evidenced by the Return Loss measurement of less than -10 and the VSWR value of less than 2.