The 2050 carbon-neutral vision spawns a novel energy structure revolution, and the construction of the future energy structure is based on equipment innovation. Insulating material, as the core of electrical power equipment and electrified transportation asset, faces unprecedented challenges and opportunities. The goal of carbon neutral and the urgent need for innovation in electric power equipment and electrification assets are first discussed. The engineering challenges constrained by the insulation system in future electric power equipment/devices and electrified transportation assets are investigated. Insulating materials, including intelligent insulating material, high thermal conductivity insulating material, high energy storage density insulating material, extreme environment resistant insulating material, and environmental-friendly insulating material, are categorised with their scientific issues, opportunities and challenges under the goal of carbon neutrality being discussed. In the context of carbon neutrality, not only improves the understanding of the insulation problems from a macro level, that is, electrical power equipment and electrified transportation asset, but also offers opportunities, remaining issues and challenges from the insulating material level. It is hoped that this paper envisions the challenges regarding design and reliability of insulations in electrical equipment and electric vehicles in the context of policies towards carbon neutrality rules. The authors also hope that this paper can be helpful in future development and research of novel insulating materials, which promote the realisation of the carbon-neutral vision. 

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Insulating materials for realising carbon neutrality: Opportunities, remaining issues and challenges

In this article, the partial discharge (PD) behavior inside a cavity embedded in a dc cable, upon application of a voltage step from transient till steady-state dc, is analyzed as a function of voltage slew rate. The variation of PD characteristics, namely PD charge amplitude and repetition rate, is modeled and fitted from the beginning of the voltage transient to dc steady state, and the extent of aging associated with PD at different slew rates is evaluated through a cumulative damage concept. Two possible scenarios for the electric field transient and PD repetition rate are presented, differing for the ratio of conductivity and permittivity of dielectric and cavity medium. Having demonstrated that the proposed PD repetition rate model can predict reasonably the experimental results, it is shown that slowing down voltage rise time during, e.g., cable energization or voltage polarity inversion, could be beneficial to reduce the accelerated aging extent associated with voltage transients.

Effect of Voltage Slew Rate on Partial Discharge Phenomenology During Voltage Transient in HVDC Insulation: The Case of Polymeric Cables

An innovative approach to partial discharge measurement and analysis in DC insulation systems during voltage transient and in steady state

It is an urgent requirement to suppress surface partial discharge (PD) activities of dielectrics for modern electrical and electronic devices. Here, we introduce a method to mitigate the surface PD in a manner of tailoring insulation surface conductivity. A surface coating with a conductivity ranging from 10−13 to 10−10 S is developed to regulate the surface charge migration in the vicinity of the triple junction and to suppress effectively the surface PD activity. The excellent performance of this coating provides an approach for surface PD suppression at DC voltage, which has great application potential in the insulation design of DC electric power equipment, DC generators, power electronic devices, printed circuit board (PCB) layout, and various integrated electrostatic sensors and actuators.

Tailoring insulation surface conductivity for surface partial discharge mitigation

In Power Systems, Synchronous Generators (SGs) are mostly used for generating electricity. Their insulation system, of which epoxy resin is a core component, plays a significant role in reliable operation. Epoxy resin has high mechanical strength, a characteristic that makes it a very good material for reliable SG insulation. Partial Discharges (PDs) are a constant threat to this insulation since they cause deterioration and consequential degradation of the aforementioned material. Therefore, it is very important to detect PDs, as they are both a symptom of insulation deterioration and a means to identify possible faults. Offline and Online PDs Tests are described, and a MATLAB/Simulink model, which simulates the capacitive model of PDs, is presented in this paper. Moreover, experiments are carried out in order to examine how the flashover voltage of epoxy resin samples is affected by different humidity levels. The main purpose of this manuscript is to investigate factors, such as the applied voltage, number, and volume of water droplets and water conductivity, which affect the condition of epoxy resin, and how these are related to PDs and flashover voltages, which may appear also in electrical machines’ insulation. The aforementioned factors may affect the epoxy resin, resulting in an increase in PDs, which in turn increases the overall Electrical Rotating Machines (EMs) risk factor.

Investigation of Factors Affecting Partial Discharges on Epoxy Resin: Simulation, Experiments, and Reference on Electrical Machines

Condition monitoring and maintenance in rotating machine are generally managed through expert evaluation of the diagnostic properties and relevant harmfulness of the underlying aging mechanisms. In order to prompt broad diffusion of condition monitoring systems, especially in large assets and in the rising field of electrification transport, however, ways to get rid of the time-consuming and expensive support of experts must be prompted. A straightforward solution is transiting towards automatic and unsupervised diagnostics and condition assessment methodologies. This paper proposes and applies algorithms for the automatic detection of partial discharges, which is the property most often associated to the fastest accelerated aging mechanisms in electrical insulation, including noise rejection, identification of the type of partial discharge sources and estimation of an health condition index in rotating machines fed by AC sinusoidal voltage. The goal is to obtain a self-assessment of the health condition by each rotating machine of an asset, which can thus interact with the asset or maintenance manager when needed, that is, when reliability is at risk.

An Unsupervised Approach to Partial Discharge Monitoring in Rotating Machines: Detection to Diagnosis With Reduced Need of Expert Support

Partial discharge measurements and life estimation in DC electrical insulation during voltage transients and steady state

Reliability of DC electrical asset components has not been investigated as broadly as for sinusoidal AC supply. On the other hand, DC assets are more and more common, and they are forecasted to grow in number, power, and voltage in the near future. This is not only in transmission grids, but also in distribution/generation (renewables), industrial application and electrification transportation. To complicate the framework, it has to be recognized that DC asset components are not only subjected to DC steady-state voltage, but also to voltage and temperature transients, as those coming from energization, voltage polarity inversion, ripple, repetitive voltage impulses and load variations. The major issue to asset component reliability can come, in these conditions, from electrical insulation. While designing insulation under AC sinusoidal voltage is a century-long practice, with many feedbacks from field installations, the same does not hold for modulated sinusoidal (i.e., power electronics) and DC supply. Electrical stresses can be different in magnitude and distribution from AC to DC, and load variations in DC can contribute to electric stress variations much more than in AC. All of this may impact significantly on aging rate and reliability of electrical insulation.This paper investigates the difference between electric field distribution, and consequent aging mechanisms and rate, from AC sinusoidal to DC supply, considering, in particular, the real DC operating conditions during which voltage and load transients can occur frequently. The contribution of partial discharges to aging rate will be also taken into account, bringing to the derivation of a probabilistic life model that can allow reliability estimations in the design of DC insulation systems to be achieved.

Reliability of HVDC and MVDC Electrical Asset: The Challenge of Insulation Design

Quality control, commissioning and operation of DC cable systems (and, in general, electrical apparatus) require PD testing and monitoring technologies that are effective in rejecting noise and identifying partial discharges and their source, both under DC and AC power supply. Such technologies are not fully available at present, so that this paper presents a contribution to make them feasible. A new algorithm is suggested that may be effective to separate partial discharges from noise both under steady-state DC and during voltage transients, through an automatic and unsupervised approach which looks very promising for laboratory and on-field testing and monitoring of partial discharges in DC cable systems.

Riddhi Ghosh

Papers

An innovative approach to partial discharge measurement and analysis in DC insulation systems during voltage transient and in steady state

An Unsupervised Approach to Partial Discharge Monitoring in Rotating Machines: Detection to Diagnosis With Reduced Need of Expert Support

Partial discharge measurements and life estimation in DC electrical insulation during voltage transients and steady state

Reliability of HVDC and MVDC Electrical Asset: The Challenge of Insulation Design

An Approach to Noise Rejection and Partial Discharge Separation in DC Cable Testing, During Steady State and Voltage Polarity Inversion Transients