During lightning impulse type testing of medium voltage switchgears up to two spark-overs are accepted. Consequently, when selecting conducting composites for use in screens and shields of such equipment it is important that their surfaces not degrade after a spark-over, as this normally will reduce...
This paper shows the result of a failure survey including the entire population of gas-insulated substations in the Norwegian power transmission system. The survey comprises the complete service experience up to now—nearly 12
A supercritical (SC) fluid is formed when both pressure and temperature of a fluid exceed the critical point, where distinct gas and liquid phases no longer exist. SC fluids demonstrate combined properties of gas and liquid, which make them interesting to investigate them as an arc extinction medium...
Partial discharge measurements have been used for studying shrinkage voids in the insulation of mass-impregnated high voltage DC subsea power cables. Three 4.5-m long cable samples were subjected to ac partial discharge measurements at different ambient temperatures, both under isothermal...
The electrical properties of a power connector – such as the resistance during its service life – depend on the number, size and quality of the tiny contact spots (“a-spots”) where the current crosses the contact interface. Contact degradation or aging are due to processes occurring in and near the...
Air is an environmentally benign and attractive alternative to SF6 as arc quenching gas in switching devices for modest current and voltage ratings. Several interruption tests with a simple air medium-voltage load break test switch have been carried out to investigate the arc and the arcing...
Changing the current loading of mass-impregnated nondraining (MIND) power cables causes the pressure in the insulation to vary over a wide range. It is generally recognized that under certain conditions—typically after a large load reduction—the pressure becomes so low that shrinkage cavities (voids...
Inexpensive superconducting wires with low AC losses would open up for a large superconductor market in AC electrical power applications. One candidate for this market is the MgB2 conductor. In the development of an AC optimized superconductor, high-quality measurements of the AC losses under...
Air is an environmentally benign alternative to SF $_6$ for use in medium-voltage load-break switches. A simple, axisymmetric test switch has been used for empirical studies of the thermal phase of current interruption in atmospheric air. The purpose is to quantify how the pressure drop across the...
This paper focuses on the arc voltage measurements of electrical arcs burning inside cylindrical tubes in nitrogen at different filling pressures from atmospheric and up to 80 bar. To investigate the effect of ablation, both nonablating ceramic tubes (alumina) and ablating...
The research and development work towards a compact SF6-free load break switch for the medium voltage range has led to several design proposals. The interruption capability of three different nozzle and gas flow concepts with atmospheric air as the interrupting medium is compared and assessed. The...
To develop cost-efficient subsea switchgear for large sea depths, the extinction of arcs under high filling pressures must be understood. In this work, arc-extinction experiments have been performed with a puffer-like contact configuration using nitrogen at different filling pressures as the...
This paper presents a flexible setup to investigate ablation-assisted interruption of load currents. The electrical test circuit is grid connected with a transformer secondary voltage from 6.9 kV to 24 kV. The applied stress to the switching device, such as load current amplitude and transient...
Gases released from polymers placed near a burning electric arc are known to influence the behavior of the arc. In switching equipment, such ablation materials can be used to improve the interrupting capability. Current interruption experiments have been carried out with the purpose of comparing the...
We report on the testing of a 1 m long and 0.5 m wide racetrack coil wound from 4.5 km of MgB2 tape-shaped superconductors with a copper strip soldered to the nickel matrix. The cross-section of the coil corresponds to what is needed for the field windings of a 10 MW direct drive wind turbine...
During temperature cycling the radial flow of oil, which is caused by differences in thermal expansion between the oil and paper, may lead to cavity formation in mass impregnated HVDC cables. Partial discharge activity in these voids is an important failure mechanism in this type of cable, but...
To realize large (>10 MW) direct-driven off-shore wind turbines, a number of steps are needed to reduce weight and cost compared to on-shore technologies. One of the major challenges is to provide drive trains which can comply with the large torque as the turbine rotor diameter is scaled up and the...
MgB2 multi-filamentary superconductors are widely considered for use in dc applications. To expand the possible application range to ac apparatuses, the development of a low ac loss wire is needed. This development involves several steps, and a solid understanding of the loss mechanisms is important...
Reducing or turning off the load of a mass-impregnated non-draining cable causes its internal pressure to drop. Under certain conditions, the pressure becomes so low that harmful shrinkage voids or cavities are created in the insulation. The pressure and pressure dynamics of mass-impregnated non...