This paper proposes to survey a good part of the research work accomplished to date on the atmospheric icing of conductors and insulators in the presence of high voltage, with emphasis laid on the studies carried out at the University of Quebec in Chicoutimi. The review covers laboratory testing and mathematical modelling. The role of several electrical parameters, such as electric field strength and polarity, corona discharge, water droplet charge and ionic wind velocity, on the structure and amount of ice accretion on high–voltage conductors, is discussed. Concerning the icing of insulators, the initiation of electrical discharge on the ice surface, the formation of local arcs along the air gaps and their development to a flashover arc along the insulators are discussed. Basic experiments on the role of several major parameters relating to ice accretion, insulator characteristics and voltage type and polarity, on the maximum withstand voltage of short insulators, are also discussed. Finally, several measures for improving the withstand voltage of insulators are briefly recalled.

Ice accretions on high–voltage conductors and insulators and related phenomena

Status review on partial discharge measurement techniques in gas-insulated switchgear/lines

Online transformer condition monitoring techniques based on transfer function methods, such as transmission-line diagnostics and swept frequency-response analysis, require the injection of a known test signal into the transformer On larger power transformers, a practical method is to use the available bushing tap connection In this paper, we will discuss a custom high-power signal generator that injects high-frequency signals on the bushing tap of the transformer under investigation, as well as a circuit to replace the bushing tap short and allow online operation of the system Finally, the system is demonstrated on a 650 kV transformer

Apparatus for Online Power Transformer Winding Monitoring Using Bushing Tap Injection

A system for measuring charge distribution on an insulating spacer is developed. An electrostatic probe is set close to the spacer, and it moves along its surface maintaining a small gap. The accumulated charge is inversely calculated from the measured data by utilizing the relationship that is obtained through the numerical electric field computation. Using this system, the surface charge distribution on a truncated cone spacer of 80 mm diameter and 15 mm height is measured. The number of measured points is 3402, and the spatial resolution is 3.9 mm. After the application of DC 10 kV for 19 hours, the spacer surface is charged with a spotted pattern. The charge density reaches 60 pC/mm/sup 2/ at its maximum. In addition, the residual charge distribution of partial discharge from metallic particles on the spacer is observed.

Charge distribution measurement on a truncated cone spacer under DC voltage

Power utilities are struggling to reduce power failure incidents in substations and their components to operate more reliably and economically [1]. Many power failures are produced directly or indirectly because of the insulation system of utility components [2], [3]. The selection of the insulation should ensure power plant operational continuity along with completely resolving or significantly limiting the actual power system's failures [4]. Gas insulated substations (GIS) have the best insulation performance which ensures achieving minimum failure incidents, although at high installation cost. The most common insulating gas used in GIS is Sulfur hexafluoride (SF 6 ) gas, which is widely used as an effective electrical insulation as well as an arc-quenching medium [5]. Basic GIS and gas insulated transmission lines (GITL or GIL) consist of a conductor supported by solid insulators inside an enclosure filled with SF 6 gas or its mixture [6].

Partial discharge detection and diagnosis in gas insulated switchgear: State of the art

In compressed GIS (gas insulated switchgear), the control of wire particle contamination by dielectric coating of enclosure is demonstrated in this paper. Assuming that a particle acquires free charge through a partial discharge, the modeling of particle movement when the inside surface of a horizontal section of GIS/GITL (gas insulated transmission line) enclosure is coated is described. Under an applied 60 Hz ac voltage, the maximum height reached above the enclosure by a particle is much lower for a coated than for an uncoated enclosure. When the applied ac voltage varies, the maximum height reached depends on the magnitude of the applied voltage, phase and velocity at which the particle hits the enclosure. Typical results show that by coating the enclosure, the maximum height reached by a wire particle in a coaxial system can be reduced, thus inhibiting particle movement and minimizing the possibility of insulation breakdown.

Movement of particles in compressed SF/sub 6/ GIS with dielectric coated enclosure

Insulation integrity of GIS/GITL systems and management of particle contamination

A simplified computational algorithm has been developed to study the behavior of metallic particles in gas insulated transmission line (GITL) systems. The model provides an estimate of the effectiveness of particle trapping for a particular trap design at a given commissioning voltage. Results of measured breakdown probabilities of particle contaminated SF/sub 6/ show fair agreement with calculated values. A computational model was developed to calculate the corona inception voltage due to conducting particle motion in GITL systems. The computed results for various parameters were in fair agreement with the measured values. A corona pulse pattern is computed and plotted using the same algorithm. Oscillographic records of the transient corona show that particle discharge is larger for long particles, and its magnitude increases with voltage level. Corona patterns obtained in the laboratory indicate that conducting particles can be detected in GITL systems and that the particle size can be determined through partial discharge measurements with AC voltage at different gas pressures. >

Metallic particle movement, corona, and breakdown in compressed gas insulated transmission line systems

Results of an investigation to clarify the process of surface flashover in gases are reported. Two hemispherical capped rods of 12 mm diameter, separated by a half-cylindrical spacer of 50 mm diameter, formed the samples. The spacer materials were polytetrafluoroethylene, acrylic and nylon. High-speed streak photographs of impulse flashover indicate that the presence of a spacer not only lowers the impulse breakdown voltage but also reduces the breakdown time. The discharge on spacers may be initiated anywhere between the electrodes and develops rapidly into a flashover in /spl sim/5 ns for an 18 mm gap. >

http://ieeexplore.ieee.org/iel4/94/8444/00368686.pdf

Nanosecond streak photography of discharges on spacer surface in gases

The authors discuss corona and breakdown in compressed sulfur hexafluoride (SF/sub 6/) gas-insulated transmission line (GITL) equipment due to free conducting particles. For particle-contaminated conditions, dynamic models of particle movement and particle-initiated corona and breakdown have been developed. Moreover, a method is proposed to utilize externally measured quantities (for example, time to first corona, corona magnitude, and repetition frequency) during testing and commissioning for identifying the size of contaminating particles. >

K.D. Srivastava

Papers

Movement of particles in compressed SF/sub 6/ GIS with dielectric coated enclosure

Insulation integrity of GIS/GITL systems and management of particle contamination

Metallic particle movement, corona, and breakdown in compressed gas insulated transmission line systems

Nanosecond streak photography of discharges on spacer surface in gases

Particle-initiated corona and breakdown in GITL systems