Partial discharge (PD) is a common and detrimental phenomenon that can cause damage and potential breakdown in insulation systems. According to the air breakdown voltage behaviors shown by Paschen's curve, from sea level to high altitude, the partial discharge inception voltage (PDIV) of the air is expected to decrease with decreasing pressure. So far, there has not been a widely accepted PD testing method for aviation wires in low pressure environments with pulse width modulated (PWM) voltage excitations. There have been studies of the PD behaviors of aviation wires with conventional triangular impulses, ac voltages, and PWM pulses with relatively low $\text{dv}/\text{dt}$ . But existing test methods and study results cannot be directly utilized to test and predict PDIV of aviation wires when high $\text{dv}/\text{dt}$ PWM excitation is applied with wide-bandgap (WBG) power devices, such as Silicon Carbide (SiC) Metal Oxide Semiconductor Field Effect Transistors (MOSFETs). Thus, this paper aims to provide more insights on PD behaviors of aviation wires under high $\text{dv}/\text{dt}$ PWM excitations and possible ways to improve the existing PD test methods. A test setup including an ultra-high $\text{dv}/\text{dt}$ PWM generator, a test sample fixture, and associated PD sensors including a photomultiplier tube (PMT), a high frequency current transducer (HFCT), and an ultra-high-frequency (UHF) antenna will be introduced. Experimental results and associated analysis for aviation wire test samples at various pressures under high $\text{dv}/\text{dt}$ PWM excitations will be presented. The effect of the rise time of the PWM will be discussed in detail. Suggestions on how to improve test methods and test standards will be provided.
In modular multilevel converters (MMCs) of HVDC system, the metallized film capacitors (MFCs) suffer from complex electrical stresses. The aging of MFC is related to the accumulation of self-healing processes, which threatens the safety and reliability of the power system. In this study, a test platform was built for applying DC voltage as well as DC superimposed AC voltage to MFCs. On this platform, the ultrasonic method and ultra high frequency (UHF) method were investigated so as to detect the self-healing discharge signals of operating MFCs. The differences of ultrasonic signals and UHF signals were compared between DC voltage and DC superimposed AC voltage, and the feasibility of MFC monitoring methods based on the detection of ultrasonic and UHF signals was demonstrated.
An electric power system (EPS) with high-power-delivery and low-system-mass is required for wide body all electric aircraft (AEA). Cables are an essential component of this future EPS. At the cruising height of a wide-body aircraft the pressure is about 16.8 kPa. At that pressure, heat transfer to the ambient air by convection is strongly limited, so the distribution of temperature field across the aircraft cables is expected to be different from atmospheric pressure. The temperature field across the cable depends on the velocity field of the ambient air, which depends on the pressure and temperature. Also, to obtain the electric field of DC cables in the electric aircraft power system, the conductivity of the insulation, a function of temperature and electric field, should be calculated. In this paper, a 5 kV DC cable is studied at 16.8 kPa pressure to compare the cable's electric field and temperature field at low pressure to the atmospheric pressure. In our earlier research, we suggested novel EPS topologies for wide body AEA, and 5 kV DC is the voltage level that was taken into consideration. Moreover, the maximum permissible flowing current of the cable is investigated at the pressure of 16.8 kPa regarding the thermal limits of the cable. It is shown that at low pressures the temperature of the cable is highly increased compared to atmospheric pressure, so permissible current is lower than rated current.
A popular technique for arc detection in aircraft electrical power systems is current signature analysis, which relies upon predictable current/voltage characteristics of electrical breakdown of a gaseous gap. Measurements were made of electrical characteristics of arcs in air at various humidity levels at pressures corresponding to sea level and 60,000-Ft (18.3-km) flight altitude. Variations in humidity introduced by uncontrolled laboratory air, even when water-vapor levels are well above those expected at temperatures $< 0 \ \mathrm{C}$, were shown to have insignificant effects while employing the current signature analysis technique.
Drift Step Recovery Diodes - DSRDs - are known since 1960s. All this time silicon DSRDs were made by basically the same technology: deep diffusion - cut into dies - stacking dies - side passivation. As technology did not change, DSRD pulse performance did not improve significantly. We suggest and experimentally validate new process flow: epitaxy - side passivation – stacking wafers - cut into stacked dies. Advantages of the new process over traditional one is described. Pulsed performance of final devices to be described in a separate paper.
