The charge accumulation and its mechanisms are studied based on the experiments of post and conical epoxy spacers subjected to high dc voltages in compressed SF 6 gas. The charge measurement is performed using electrostatic probe and dust figure techniques. The charge accumulation is strongly influenced by the surface condition of epoxy spacer. Heterocharge deposits locally on the surface of untreated spacer. The flashover voltage of highly charged spacer decreases considerably at the time of polarity reversal. In the case of epoxy surface treated with horning, only a small quantity of charge is deposited uniformly on the surface of spacer. The mechanism of inhomogeneous surface conduction is suggested by the local surface charging on the untreated spacer. Field emission is also found as the other charging mechanism on the conical spacer set in rough finish electrode system.

Surface Charging on Epoxy Spacer at DC Stress in Compressed SF 6 Gas

Compressed-gas insulated transmission lines or cables have been in service since 1968, with over 13 km (circuit length) in operation worldwide at voltages from 145 to 550 kV. The design philosophy and development are reviewed for the "rigid", flexible, and semi-flexible isolated phase lines, the three-conductor lines and the prototype dc gas-insulated cable system. The various designs of insulators, conductors, enclosures, particle traps, and terminations are described, together with the techniques for grounding and corrosion protection, factory and site testing, fault diagnostics, and calculation of current ratings.

Gas-Insulated Cables

Microelectrodes for use in stimulating and detecting activity in neurons of living organisms, and a method of manufacturing such microelectrodes. An electrically conductive electrode core member is sharpened and coated with a thin layer of a dielectric material. An extremely small area of the core at the sharpened point is exposed by ablating the dielectric material by the use of ultraviolet laser beam scanned over the material. Multiconductor microelectrodes include multiple fine wires which may be arranged in helical strands, optionally supported by a central core member of stiffer material. Multiple conductors may also be supported within a tubular support such as a hollow needle whose distal end is cut at a slant to expose the conductors, or in flat ribbon configuration with openings in dielectric material defining active electrode sites. Multiple active electrode sites may be defined on a microelectrode accompanied by an integrated circuit after connection of the integrated circuit to a multiconductor cable.

Method of making implantable microelectrode

A capacitive probe measurement that can be used to quantify the charge density on solid insulators is introduced. Studies performed in the development of a +or-125 kV high-voltage DC (HVDC) gas-insulated converter station and +or- 500 kV HVDC switchgear (HVDC-GIS) are reviewed. The properties and mechanisms of surface charging, the optimum design of the spacer and its breakdown characteristics are summarized. Problems associated with capacitive probe measurement of surface charge and a practical solution to obtain the charge distribution on the spacer are presented. >

Charge accumulation on insulating spacers for HVDC GIS

The measurement of surface charging on a spacer in a +or-500-kV HVDC gas-insulated switchgear (GIS) is performed by a capacitive probe set inside the gas tank. The various factors that cause measurement errors are examined using a simple model. An analytical method to correct the measurement errors and transform the probe output into the charge distribution on the surface of the spacer is developed. The method is an extension of a numerical method for 3-D surface charge calculation. It is shown that the charge distributions from the probe measurement agree fairly well with dust figures. >

Analytical method for evaluating surface charge distribution on a dielectric from capacitive probe measurement-application to a cone-type spacer in +or-500 kV DC-GIS

An electrical cable having an improved graded insulation which minimizes uneven electrical stresses caused therein by a lack of a symmetrical cable structure, and a method of overcoming disproportionate electrical stresses at interfaces intermediate the sections of a graded insulation for electrical cable.

Graded insulation cable construction, and method of overcoming stresses therein

The objective of this paper is to report on studies made on a fullscale model of the coolant system for a gas insulated, fluorocarbon liquid cooled HVDC thyristor valve. Confidence in the selection of the coolant system and its associated dielectric containment structure stemmed from the parametric study of the coolant, and the more than adequate dielectric strength of the coolant even when it was in the cavitated state. An explanation is proposed on the apparent anomoly of the exceptional dielectric strength of the system, even when bubble nucleation is induced by the injection of a dielectrically weak (nitrogen) gas into the flowing coolant.

Dielectric Behavior of the Coolant for a Gas Insulated HVDC Thyristor Valve

Câble dans lequel on a reduit les effets nuisibles des contraintes electriques irregulieres ou disproportionnees aux interfaces entre les couches d'isolant. Il comprend un conducteur electrique metallique de forme allongee 12, enferme dans une masse composite d'isolant qui l'entoure et qui comprend au moins deux couches contigues distinctes d'isolant polymere ayant des permittivites differentes placees autour du conducteur electrique de facon a ce que la couche 16 situee le plus a l'interieur de la masse composite d'isolant ait la permittivite la plus elevee et que les couches exterieures successives 18 de la masse composite d'isolant aient des permittivites decroissant graduellement, la permittivite de la couche situee le plus a l'interieur et celle de la couche contigue qui lui est adjacente dans la masse composite d'isolant etant dans un rapport inferieur a 1,4. Application aux câbles haute tension.

Cable electrique isole

Results of work undertaken to evaluate solid dielectric materials containing inorganic fillers with respect to voltage endurance are reported. The results obtained are associated with degradation caused by the growth of dendrites within the solid dielectric when under voltage stress.

Nirmal Singh

Papers

Graded insulation cable construction, and method of overcoming stresses therein

Dielectric Behavior of the Coolant for a Gas Insulated HVDC Thyristor Valve

Cable electrique isole

Influence of Inorganic Fillers on the Voltage Endurance of Solid Dielectric Power Cables