Discharge and Flashover Behavior in Oil-Paper

Due to special operating conditions, the valve side bushing of the converter transformer connected to the converter valve is subject to complex voltage excitation, including DC voltage, AC/DC composite voltage, lightning impulse overvoltage, or composite voltage of operating overvoltage and DC. Under the action of this complicated electric field, the oil-paper insulation of the valve-side bushing of the converter transformer is prone to electric field distortion due to charge accumulation, which causes a surface discharge, which will seriously cause the edge breakdown. At the same time, since the temperature in the converter transformer rises due to a large amount of loss during the operation of the transformer, creeping discharge is more likely to occur under the electrothermal composite field. Hence, it is significant to carry out research on the surface discharge characteristics of the oil-paper insulation on the valve side of the converter transformer under the electrothermal composite field.

Trap Property and Charge Transmission in PE

The electrical properties of the dielectric are achieved by affecting the charge transfer process. The trap characteristics have an important influence on the electrical properties of the dielectric by affecting the charge transfer process. Aggregation and trap level characteristics of nanographene on low density polyethylene (LDPE). The direct current conductivity, breakdown strength, trap level distribution, space charge distribution, and charge mobility of nanocomposites were investigated. The experimental results show that the interface region between graphene and polymer introduces many deep traps in the forbidden band of nanocomposites, which can reduce the trapping process of charge and inhibit the accumulation of space charge. This indicates that the addition of nanoscale graphene has a significant improvement in the electrical performance of high voltage DC cables, which will provide a reference for production and application.

Flashover and Surface Charge in GIL Insulator

Many works have been studies in order to improve flashover voltage in GIL insulator. Under DC, the insulator electric field is decided by the conductivity and surface charge distribution. This chapter takes cone-type insulator as research object and then finds the characteristics of flashover, surface charge accumulation, and the interface electric field regulation (IER) of epoxy (EP)-/graphene (GR)-coated insulator. Theoretical analysis demonstrates that the uniform surface charge of monopole is conducive by reduce peak field and flashover voltage. Among them, that of 0.1% EP/GR possesses the highest flashover voltage. With the SiC content and coating thickness enhancement of IER insulator, the electric field regulation of EP/SiC-coated insulator becomes notable, due to energy loss and increasing leakage current. The results show that insulator coated by EP/SiC can reach higher flashover voltage than uncoated insulator and enhanced SiC content contributes to improve the flashover voltage.

Characteristics and Suppression of Space Charge in Polyethylene

In HVDC transmission systems, the space charge accumulation of polyethylene (PE) insulation is a major problem that threatens the safe and stable operation of cables. In this chapter, nanoparticles and voltage stabilizers are used to inhibit space charge in PE, which has excellent compatibility with PE. To study the thermal, mechanical, and electrical properties of the samples, differential scanning calorimetry (DSC) testing, tensile testing, breakdown, and conductivity property were measured separately. Besides, the space charge behavior based on the PEA method was studied, and the carrier mobility was calculated by the space charge depolarization process. The experimental results indicate that PE modified by graphene oxide (GO) nanoparticles and the voltage stabilizers demonstrate the suppression of space charge accumulation in PE insulation, which has less space charge accumulation than pure PE. The results show that graphene oxide and the preferred stabilizer have broad prospects in HVDC cable applications.

Treeing Characteristics in HTV Silicone Rubber

Silicone rubber (SiR) is widely used as the main insulating material in cable accessories and faces high temperature challenges during operation. Pulse overvoltages can threaten working state of the insulation. In order to understand electrical tree degradation process at high temperature under repeated pulse voltages, stress testing was performed in this experiment. The ambient temperature (Tamb) was set to 30, 60, 90, 120, and 150 ° C, and the frequencies of the pulses were set to 5, 20, 100, 200, and 1000 Hz, respectively. During operation, it is also threatened by mechanical stress, which is caused by the spring-clamping device and the expanded bundling force of the rubber stress cone, which will affect the electrical properties of the silicone rubber in the cable accessory. In this chapter, the growth characteristics of trees under tensile stress and compressive stress were studied by using the needle plane electrode system.

Surface Charge Property of SiR/SiC Composites with Field-Dependent Conductivity

An electrical field distorted by the complicated cable accessory structure and non-uniform temperature distribution is a significant threat to high voltage direct current (HVDC) cable. Thus, the field grading material (FGM) with nonlinear conductivity can uniform local field receives attention. This chapter focuses on the surface charge property of SiR/SiC composites effected by temperature. Field strength and SiC content have a positive effect on the increase in conductivity. When the temperature increases, the threshold field decreases. At high SiC content, this phenomenon is more obvious. The influence of temperature is considered under DC voltage and impulse superimposed DC voltage.

Treeing Property In Polypropylene Under Various Temperature and Electrical Field

Polypropylene (PP) has no cross-linking process and environmentally friendly properties and is considered to be a replacement for cross-linked polyethylene (xlpe) for high voltage direct current (HVDC) cable insulation. High-voltage DC cable systems generate repetitive pulse voltages during operation and may encounter different temperature environmental challenges. This chapter discusses the effects of pulse amplitude and frequency on PP trees at different temperatures. A higher pulse frequency accelerates the propagation of the tree. Higher amplitudes accelerate tree growth and fractal dimensions. In addition, the effects of DC voltage, pulse voltage, and pulse frequency on the tree characteristics of PP at DC voltage and pulse combination voltage are also studied.

Collection of Breakdown and Discharge Research on Advanced Materials

Epoxy resins are widely used to build insulators in GIL. Epoxy/AlN nanocomposite can be produced by adding AlN nanoparticals to the epoxy resin. By studying the surface discharge behavior of the nanocomposites under different operating temperature, it is helpful to improve the creeping voltage of epoxy resin. Polypropylene is a kind of material which is usually chosen to build film capacitors. The effects of voltage form on surface charge and discharge behavior were studied. Furthermore, a modification method of a polypropylene film which can suppress surface charge accumulation is proposed. Polypropylene also has great application potential in HVDC cable insulation, provided that its toughness is to be overcome. Different mass fractions of ULDPE and graphene were added to polypropylen to improve mechanical and insulating properties, respectively. Studies on the DC conductivity, space charge behavior, trap level distribution, and breakdown strength of the new material were carried out.