Partial discharge (PD) detection is a fundamental tool for the design and diagnosis of insulation systems, particularly organic materials that must operate throughout their life without PD. While the methods for PD measurements under sinusoidal supply voltage are well established, the same does not hold under repetitive-pulse voltage waveforms, such as those provided by inverters. Electromagnetic noise generated by electronic switch commutation in inverters can overlap with PD pulses, making it difficult to measure, separate from noise and identify PD. This is particularly more cumbersome when fast rise-time switches are employed. To address these issues, this work investigates methods to detect PD pulses on enameled wires under repetitive impulsive voltages with different rise-times of 60 ns, 500 ns and 1000 ns, proposing techniques which allows separation of PD from noise even when they overlap in time and frequency domain. This work employs a time-domain approach using standard deviation curve acquired from a set of measurements to discriminate PD from repetitive commutation disturbance. These techniques can be implemented to achieve unsupervised noise rejection, which would be an important goal for both off-line and on-line PD testing. The proposed approach is validated successfully through tests carried out on a low-voltage motor.

The development of more electrical transportation systems requires rotating machines having higher efficiency and specific power. To date, this is achieved by feeding them with rising supply voltages with higher frequencies. This generalized strategy is introducing several challenges in the correct design of the insulation that is necessary for a reliable system. A major issue to be dealt with are partial discharges (PDs), an aging mechanism that can bring insulation to failure in short times. A solution often proposed by manufacturers involves the use of the so-called corona resistant (CR) materials, which supposedly can withstand PD activity. This article investigates the possibility of using CR magnet wires for electrical machines operating at reduced pressures, such as the actuators for primary control surfaces in more electric aircraft. The results show that CR insulations are characterized by an improved behavior at ground level but are not a viable option at reduced pressures.

With an impetuous growth of DC links and future grids that will be often hybrid, providing AC and DC supply to nearby or the same customer, an important element is often neglected, that is, electrical insulation. There are no doubts that overhead lines will step back compared to insulated cables, for known reasons of environmental impact, right of way and reliability, especially in an urban or harsh environment. On the other hand, while AC insulation systems have been investigated and used for decades, there is no analogue experience for DC polymeric insulation, nor for insulation systems subjected to power electronics supply. This study aims at enhancing the attention on this topic, focusing on insulation ageing mechanisms and models of relevance for hybrid AC/DC assets and grids. Ageing and life models for AC, DC and power electronics supply are discussed and compared to experimental data, focusing on partial discharge and space charge. It is shown how these two phenomena affect lifetime for different AC, DC and transient operating conditions. The main drivers for insulation design and material selection are discussed, showing that insulation reliability can be achieved only if operating stresses, ageing mechanisms and life models are known and accounted for properly by insulation designers.

The attention given to high voltage direct current (HVDC) cables appears to be at an all-time high. In the July/August 2017 issue of IEEE Electrical Insulation Magazine, the focus was on different aspects of the design and testing of HVDC cable systems. There are several reasons for this, one of the most important probably being the worldwide attention on harvesting renewable energy at a scale never seen before. The prices of building large offshore windfarms in Europe as reflected in a recent normalized cost of electricity have unexpectedly dropped in the last year, as illustrated in Figure 1, which will further accelerate the development of HVDC cables to link offshore and onshore substations. The winning bid in 2016 for the Borssele II, 700-MW windfarm in the Netherlands was as low as 54.5€ ($61)/MWh [1].