Thermal, electrical and mechanical stresses age the electrical insulation systems of high voltage (HV) apparatuses until the breakdown. The monitoring of the partial discharges (PDs) effectively assesses the insulation condition. PDs are both the symptoms and the causes of insulation aging and—in the long term—can lead to a breakdown, with a burdensome economic loss. This paper proposes the convolutional neural networks (CNNs) to investigate and analyze the aging process of enameled wires, thus predicting the life status of the insulation systems. The CNNs training does not require any kind of assumption of how the factors (e.g., voltage, frequency and temperature) contribute to the life model. The experiments confirm that the proposal obtains better estimations of the life status of twisted pair specimens concerning existing solutions, which are based on strong hypotheses about the life model dependency on the factors.

The online monitoring of a high voltage apparatus is a crucial aspect for a predictive maintenance program. Partial discharges (PDs) phenomena affect the insulation system of an electrical machine and—in the long term—can lead to a breakdown, with a consequent, significant economic loss; wind turbines provide an excellent example. Embedded solutions are therefore required to monitor the insulation status. The paper presents an online system that adopts unsupervised methodologies for assessing the condition of the monitored machine in real time. The monitoring process does not rely on any prior knowledge about the apparatus; nonetheless, the method can identify the relevant drifts in the machine status. In addition, the system is specifically designed to run on low-cost embedded devices.

This work deals with the growth of electrical treeing in different EVA-layered silicate nanostructured compounds. The experimental activity evidenced that the intercalated nanocomposites have longer lifetimes than pure EVA under the same constant AC stress conditions. A monitoring of the tree growth morphology allowed to evidence very interesting features of the intercalated nanocompounds showing a barrier effect to the treeing path. A preliminary investigation on the possible arrangement of the filler particles inside the matrix was also carried out.

Partial Discharges are a major cause of electrical stress and insulation failure, but their presence is also a symptom of insulation problems. Online Partial Discharges measurement allows for continuous monitoring of the insulation system. An online Partial Discharges measurement system for air insulated switchgear has been developed, based on Transient Earth Voltage (TEV) sensors, and evaluated for morphological analysis of insulation defects. The evaluation has been conducted comparing the developed system with a conventional PD measurement system based on the IEC 60270 standard. The aim of the proposed system is to facilitate its integration with minimal retrofitting and operational disruption assuring the possibility to identify and analyze the defects. A pilot system, employing an air insulated switchgear, was designed and tested. The results from both the Partial Discharges measurement systems are presented and discussed. Furthermore, the impact of a high capacitive load connected to the switchgear is investigated and the possible effects of a capacitive load due to a MV cable is considered by simulating the realistic cable geometry.

Considering high voltage direct current (HVDC) link cables, transient overvoltage can occur during fault situations. Electrical trees can be incepted by these transient effects characterized with frequency components of several kHz. Normally, a higher voltage frequency is associated with a faster polymeric insulation materials degradation. To better investigate the relationship between applied voltage and frequency and the growth of the electrical trees, cross-linked polyethylene (XLPE) samples obtained from a commercial HVDC cable have been tested in different conditions. The partial discharge (PD) activity was monitored along the degradation of such samples. The results show that both voltage amplitude and frequency influence the tree shape and consequently the time to breakdown: the increase of the frequency does not lead to a faster degradation and to a faster breakdown of the sample.

Low voltage stator windings of electrical machines are often realized by means of wires insulated by organic enamel. This kind of enamel can be subjected to partial discharges (PD) activity that could lead to breakdown condition the electrical insulating system so that the life time could be shorter than the expected one. In this research work, twisted pair specimens insulated by non corona resistant polyamide-imide enamel have been subjected to 50 Hz sinusoidal waveforms having different amplitudes. The electrical stress has been chosen so that in all the test conditions the applied voltage was higher than the partial discharge inception voltage (PDTV) value. In this way the surface aging has been inducted by the partial discharge activity. Aging tests have been carried out into an environmental chamber in order to control the relative humidity (RH) value so to analyze the effect of this parameter on the specimen life times; the total breakdown condition was chosen as end-point criterion and the relevant life time values have been recorded. The obtained results show that the PD activity is strongly influenced by the relative humidity levels and the change of its intensity considerably affects the time to breakdown values. Furthermore, the obtained data allowed to compute the life curves relevant to the different considered RH levels evidencing the relationship between the environmental conditions and the life time values.