HVDC Bushings Research Articles

Conductivity and Breakdown Properties of Epoxy Resin for HVDC Bushing by Multifunctional Modifier

Conductivity and Breakdown Properties of Epoxy Resin for HVDC Bushing by Multifunctional Modifier

A Promising De-Ionized Water Cooling Based ERIP Bushing-II: Cooling Mechanism and Effect of Parameters

Overheating has become a key factor that threatens the safe operation of the epoxy resin impregnated paper (ERIP) HVDC bushing and restricts its engineering application. The de-ionized water cooling based ERIP (DIWC-ERIP) bushing utilizes diffusion and convective heat transport to achieve low temperature distribution in the DIWC-ERIP bushing. In this manuscript, the temperature, heat flux density and the heat flux distribution of the DIWC-ERIP bushing are analyzed and the cooling mechanism is discussed. The heat flux density in the current carrying conductor (CCC) is mainly in axial direction. In the ERIP it is mainly in negative radial direction in oil tank side, and in positive radial direction in flange area and air box side of the bushing. The effect of the flow rate and temperature at inlet of de-ionized water on the temperature distribution of the bushing is studied by experiments and simulations, and the simulation results are very close to the measured results. The parameters of the thermal resistance per unit length of the thermal thin layer and the radii of water tubes have little effect on the temperature distribution of the bushing. The temperature distribution of the bushing can be controlled by the temperature of water at the inlet. Due to the strong heat dissipation capacity of de-ionized water, as the flow rate is 2 L/min, the maximum temperature of the ERIP doesn't exceed 120 ℃.

Advances in HVdc Bushing Using Nonlinear Materials: Theory, Materials, Structure, and Realization

Bushings are the key equipment in a high-voltage dc (HVdc) project. HVdc bushings not only provide the insulating medium between the HV conductor and the ground electrode but also physically fix the HV conductor in the transformer or in the feedthrough assembly. In operation, HVdc bushings always experience high electric field and load current. When a fault occurs, the bushing will inevitably face instantaneous overvoltage and overcurrent conditions. This harsh operating condition poses a serious threat to the long-term performance and reliability of HVdc bushings. However, the construction of extra-HVdc projects, ultra-HVdc projects, and flexible dc transmission projects is in full swing. The market demand for HVdc bushings is growing rapidly. Take China, for example: from 2013 to 2020, about 2,600 transformer bushings for ultra-HVdc converter transformers and 400 wall bushings for valve halls were needed. The annual demand for HVdc bushings is about 375, and the cost is more than 1.7 billion CNY per year. Considering the construction of extra-HVdc and flexible dc projects, the market scale of an HVdc bushing will increase in the future.

Long-term DC voltage test method of HVDC wall bushing with resin impregnated paper capacitor core considering electro-thermal coupling coefficient

HVDC wall bushing connects the valve hall and the DC field in the converter station, which is the core equipment in HVDC transmission system. The resin impregnated paper capacitor core inside the bushing withstands long-term full DC voltage and full load DC current during operation. Thus, 2 hours long-term DC voltage test and temperature rise test are required to verify its insulation and thermal performance. However, internal discharge faults caused by overheating of current carrying structure still occur frequently in recent years, which means the insulation and thermal defects of the bushing under long-term electrothermal coupling stress can not be completely inspected only IEC standard test. In this paper, the influence of temperature on internal partial discharge measurement and electrical field calculation of resin impregnated paper capacitor core of HVDC bushing are carried out, and the electro-thermal coupling coefficient is given. Finally, a new long-term DC voltage test method during manufacturing process is proposed. This new method has important theoretical significance and engineering application value for internal defect evaluation, discharge or thermal fault diagnosis, as well as estimation of the reliability of both insulation and thermal performance in the life cycle of bushing.

Improved electrical resistivity-temperature characteristics of insulating epoxy composites filled with polydopamine-coated ceramic particles with positive temperature coefficient

Incorporating positive temperature coefficient (PTC) ceramic particles into polymer matrices provides a promising solution to suppress the distortion of DC electric field within polymeric insulation caused by the negative temperature coefficient (NTC) of electrical resistivity. However, along with the suppressed NTC effect comes the decrease of dielectric strength due to the agglomeration of PTC particles. Here, we addressed this issue in the epoxy resin system by coating polydopamine onto PTC particles to improve the compatibility with matrix, thus achieving a maintained DC breakdown strength. The improved evenness of PTC particles dispersion also provided sufficient interface to generate interface charge traps, which contributed to the increase of electrical resistivity at elevated temperature. Combined with temperature dependent charge carrier amount affected by PTC filler, NTC effect of epoxy composites was further mitigated and the maximum DC electric field was reduced by 49% within insulation assessed by the simulation of HVDC bushing. The method proposed in this paper is crucially important for the reliable and economic application of composite dielectrics under harsh conditions.

Surface and interface charge accumulation and decay of oil-paper insulation under DC voltage

Oil-paper insulation system is an extraordinarily essential system of converter transformer as well as HVDC bushing. This paper studies the interface charge accumulation and dissipation characteristics of oil-paper insulation system under DC voltage. In this paper, an induced electrification was used to charge the oil-paper samples. The amplitudes of the DC voltage varied from 1 to 4 kV and the paper was 0.13 mm in thickness. From the research of different voltage amplitudes and charging times of the paper, conclusions can be drawn that the decay is fast initially, and then becomes slower with the lapse of time. At last the dissipation trend tends to be flat. With the increase of the voltage amplitudes, the surface potential rises more rapidly, and higher voltage would also cause the charge to dissipate more quickly. Longer charging times would cause the charge to dissipate a bit more slowly. The decay rate of the negative voltage is a little smaller than that of the positive charge. Moreover, when it comes to the effect on the interface charge of the paper layers, the surface potential is more proportional to the increase of paper layers. When the amplitude of the voltage applied in the test is small or the charging time is short enough, the interface charge can be hardly accumulated on the bottom layer. In addition, the tdV/dt and the decay time curves under the positive voltage usually have two peak values, while there is only one peak value in most of the curves under the negative condition.

Dynamic behavior of surface charge on double-layer oil-paper insulation under pulse voltage

Oil-paper insulation system is an extraordinarily essential system of converter transformers as well as HVDC bushings. When the system changes its state, such as switching the thyristors, operating over-voltage appears, and the charge will deform the dielectric internal electric field, thus easily leading to the occurrence of discharge or insulation failure, so charge accumulation and dissipation on oil-paper insulation under pulse voltage need more investigation. This paper studies the surface charge behavior on double-layer oil-paper insulation under pulse voltage and inducing electrification was used to charge the oil-paper composite. Studies of various voltage amplitudes, pulse frequencies, numbers and polarities showed that the decay is fast initially, and then becomes slower with the time. Eventually the dissipation of charge behaviors tends to be flat. With the increase of voltage amplitudes, the surface potential rises, and less positive charges are accumulated on the surface than negative charges. The increase of the pulse frequency causes the initial values of surface potential a little smaller and the charge to dissipate more quickly. Also, with the increase of pulse numbers, the initial value gets bigger and the surface charge would be slowly dissipated. From the tdV/dt and decay time curves, the figures of positive voltage usually have two peaks, while there is only one peak in most of the curves under the negative one. With the increase of voltage amplitudes, the charge will dissipate more quickly. Additionally, the peak value and the characteristic time increase with the reduction of pulse frequency and the addition of numbers.

Characteristics of space charge distribution in epoxy-paper composite insulation system

The HVDC dry-type bushing, with its main insulating medium being epoxyimpregnated- paper composite, is a key device in the ultra-high voltage direct current power transmission system. The HVDC bushing is under the combined effect of electricity, heat, and mechanical stress when it is in operation, in which case the electric field strength in the core of bushing is high, the temperature in the central conductor is high, and the interfacial effect between the epoxy layer and insulating paper is strong. Consequently, space charge will accumulate in the epoxy-paper composite insulation. Previous studies mainly focuses on the characteristics of space charge distribution in polymer-micro-nano filler, whereas the studies on that in epoxy-insulating-paper composite are quite limited. This paper, based on the HVDC bushing made up of epoxy-insulating-paper composite, establishes and a space charge measuring system which is suitable for the pulse electro-acoustic (PEA) method at high temperature (⩽110 °C). A modified PEA method which is applicable to the measurement of space charge in the multi-dielectric-layer composite with different acoustic impedance is put forward. By controlling the thicknesses of dielectric layers in the composite sample, the effect of sound wave reflection on the measuring system can be eliminated. An in-depth study is conducted on the effects of temperature and field strength on the characteristics of space charge distribution in epoxy-paper composite.

Clean fog and live washing performance of vertical HVDC bushings

An alternative bushing design for HVDC systems is investigated. The bushing is vertical in orientation and intended for roof installation. Methods of maintaining reliable operation of the bushing in a severe marine contamination environment are explored by means of a fixed washing system designed to provide sufficient cleaning to avoid contamination flashover. Results of both clean fog and washing system tests are reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>