Although the adverse effects of using power electronic conversion on the insulation systems used in different apparatuses have been investigated, they are limited to low slew rates and repetitions. These results cannot be used for next-generation wide bandgap (WBG)-based conversion systems targeted to be fast (with a dv/dt up to 100 kV/ws) and operate at a high switching frequency up to 500 kHz. Frequency and slew rate are two of the most important factors of a voltage pulse, influencing the level of degradation of the insulation systems that are exposed to such voltage pulses. The paper reviews challenges concerning insulation degradation when benefitting from WBG-based conversion systems with the mentioned dv/dt and switching frequency values and identifies technical gaps and future research needs. The paper provides a framework for future research in dielectrics and electrical insulation design for systems under fast, repetitive voltage pluses originated by WBG-based conversion systems.

Accelerated insulation aging due to fast, repetitive voltages: A review identifying challenges and future research needs

Condition monitoring of an operating apparatus is essential for lifespan assessment and maintenance planning in a power system. Electrical insulation is a critical aspect to be monitored, since it is susceptible to failure under high electrical stress. To avoid unexpected breakdowns, the level of partial discharge (PD) activity should be continuously monitored because PD occurrence can accelerate the aging process of insulation in high voltage equipment and result in catastrophic failure if the associated defects are not treated at an early stage. For on-site PD detection, the ultra-high frequency (UHF) method was employed in the field and showed its effectiveness as a detection technique. The main advantage of the UHF method is its immunity to external electromagnetic interference with a high signal-to-noise ratio, which is necessary for on-site monitoring. Considering the detection process, sensors play a critical role in capturing signals from PD sources and transmitting them onto the measurement system. In this paper, UHF sensors applied in PD detection were comprehensively reviewed. In particular, for power transformers, the effects of the physical structure on UHF signals and practical applications of UHF sensors including PD localization techniques were discussed. The aim of this review was to present state-of-the-art UHF sensors in PD detection and facilitate future improvements in the UHF method.

Application of UHF Sensors in Power System Equipment for Partial Discharge Detection: A Review

Among the different solutions which allow onsite partial discharge measurement in energized power transformers, the UHF technique is gaining general interest. In order to apply this method in existing transformers, it is considered advantageous to design a UHF sensor to be fitted inside the transformer tank. This paper describes the constraints affecting the development of such sensor and the process followed to optimize its design. During this process, different solutions for broadband UHF antennas were analysed. The selection was based on computer simulation and experimental results. Computer simulation was used to evaluate differences in radiation pattern, antenna impedance, gain and effective area. Measurements of the antenna response to different partial discharge sources in oil were performed using an oil dielectric breakdown test set in an electromagnetic shielded laboratory. A group of selected antennas were then tested in a power transformer simulating the broadband signals generated by partial discharges by injecting controlled voltage pulses in the transformer. Finally, a sensor based on a conical monopole antenna structure was built and attached to a specially designed housing to be fitted inside the transformer tank through the drain valve. This final prototype was benchmarked during a high voltage factory test of a power transformer which showed a significant partial discharge activity.

Optimisation of a sensor for onsite detection of partial discharges in power transformers by the UHF method

In this paper, the design and application of a circular microstrip antenna for partial discharge detection is presented. For this purpose, the truncated ground plane technique was applied for the bandwidth enhancement. In addition, aiming at an optimized structure, the computational simulations with several combinations of the antenna dimensional parameters were performed. In order to verify whether the developed antenna met the prerequisites (bandwidth and gain) for practical application in partial discharge detection, the optimized antenna was subjected to tests in an anechoic chamber. Finally, the antenna sensitivity was compared with the IEC 60270 standard method. For this purpose, the simultaneous tests were carried out in a partial discharge generator arrangement composed of an oil cell with point-to-plane and plane-to-plane electrode configurations. The developed antenna can detect apparent charge values higher than 30 pC and has an average gain greater than 2 dB along its bandwidth. The obtained results attested to the potential of the developed antenna for the development of UHF sensors for partial discharge detection in high-voltage equipment.

Design and Application of a Circular Printed Monopole Antenna in Partial Discharge Detection

A new, bio-inspired printed monopole antenna (PMA) model is applied to monitor partial discharge (PD) activity in high voltage insulating systems. An optimized sensor was obtained by designing a PMA in accordance with the characteristics of the electromagnetic signal produced by PD. An ultra-wideband (UWB) antenna was obtained by applying the truncated ground plane technique. The patch geometry was bio-inspired by that of the Inga Marginata leaf, resulting in a significant reduction in size. To verify the operating frequency and gain of the PMA, measurements were carried out in an anechoic chamber. The results show that the antenna operating bandwidth covers most of the frequency range of PD occurrence. Moreover, the antenna presented a good sensitivity (mean gain of 3.63 dBi). The antenna performance was evaluated through comparative results with the standard IEC 60270 method. For this purpose, simultaneous tests were carried out in a PD generator arrangement, composed by an oil cell with point-to-plane electrode configurations. The developed PMA can be classified as an optimized sensor for PD detection and suitable for substation application, since it is able to measure PD radiated signals with half the voltage levels obtained from the IEC method and is immune to corona discharges.

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Bio-inspired Printed Monopole Antenna Applied to Partial Discharge Detection

As important fundamental equipment, high voltage switchgears are widely used in electric power systems and directly relative to the power reliability and quality. Partial discharge (PD) online monitoring is one of the most effective methods used for insulation testing and diagnosis in high voltage switchgears and power systems. This paper proposes a unique ultra-wide-band (UWB) antenna with high performance for PD ultra-high-frequency (UHF) detection in high voltage switchgears. Actual PD experiments were carried out, and the designed antenna was used for PD measurements. The measured results demonstrate that the proposed antenna has wide work frequency band, good omnidirectional radiation patterns and appreciable gain, which indicate that the proposed antenna is suitable for UHF online monitoring of PDs in high voltage switchgears.

https://www.jpier.org/pierc/pierc69/11.16052102.pdf

An UWB Printed Antenna for Partial Discharge UHF Detection in High Voltage Switchgears

Aiming at the overheating problem of cable joint, a 3-D finite element model of a single-core cable joint considering the coupling of electromagnetic field and temperature field has been built. In order to consider the heat losses generated by contact resistance of cable joint, the equivalent conductivity is calculated. The validity of the model and calculation method is verified by the comparison with analytical values.

Investigation of contact resistance influence on power cable joint temperature based on 3-D coupling model

Research on the UHF microstrip antenna for partial discharge detection in high voltage switchgear

The invention discloses an ultrahigh-frequency broadband microstrip antenna for partial discharge monitoring of a switchgear, and belongs to the field of an electrical equipment insulation state online monitoring technology. The antenna structurally comprises an antenna metal radiation patch, a medium substrate, a metal ground plate, a microstrip feed line and an SMA joint. The antenna provided by the invention has the advantages of wide frequency band, small standing-wave ratio, convenient impedance matching, low manufacturing cost, convenient installation, unaffected normal operation of monitoring equipment, and the like, and can meet the requirement for ultrahigh-frequency online monitoring of partial discharge of a switch gear used for a transformer station.

Qi Yang

Papers

An UWB Printed Antenna for Partial Discharge UHF Detection in High Voltage Switchgears

Investigation of contact resistance influence on power cable joint temperature based on 3-D coupling model

Research on the UHF microstrip antenna for partial discharge detection in high voltage switchgear

Ultrahigh-frequency broadband microstrip antenna for partial discharge monitoring of switchgear

Investigation of Contact Resistance Influence on Power Cable Joint Temperature Based on 3-D Coupling Model