A new approach to the statistical enlargement law for comparing the breakdown performances of power cables - Part 2: application

A new theoretical approach to the application of the Enlargement Law for assessing the breakdown performances of shielded power cables was illustrated in the companion paper (Part 1) of this series. In the present paper, practical case-studies of the proposed theory are presented. The so-called crossing quantities of two cable lines, i.e. crossing length, crossing dielectric strength and crossing breakdown voltage, are analyzed on the basis of the results of dielectric strength tests performed on cable models insulated with different commercial compounds. In particular, the application is relevant to mini-cable samples realized with two Ethylene-Propylene Rubber (EPR) compounds, and with two cross-Linked Polyethylene (XLPE) compounds, all subjected to standard lightning impulse dielectric strength tests. The estimation of the crossing quantities, performed for various power cable voltage ratings, shows that the crossing length – if any - is a strong function of the cable size and voltage rating. Thus the choice of the best compound should be based on a comparison between the value of crossing length and the typical lengths of full-size cables. Furthermore, since the crossing quantities are strongly affected by the values of the Weibull parameters estimated from the dielectric strength tests, a sensitivity analysis of such quantities to the uncertainty in the estimation of the Weibull parameters is also carried out

Ultrahigh frequency study of PD pulses

Conventional partial discharge (PD) measurements are carried out with instruments of relatively limited bandwidth. There arises the question as to the temporal characteristics of the actual pulses and the significance of the results so obtained. To gain a detailed knowledge of the rise time, duration and amplitude of these pulses, a study has been undertaken using as detector a 500 MHz digitizing oscilloscope in combination with a point-plane electrode geometry. In this paper the pulse characteristics of PD in air were studied as a function of polarity under dc and ac conditions

Effect of reduced viscosity on the electrical characteristics of transformer and switchear oils

The electrical characteristics of two mineral oils of different viscosity, suitable for use in transformers and switchgears, are compared. It is found that, whereas the higher viscosity oil exhibits greater dielectric losses at more elevated temperatures, it has lower AC and impulse breakdown strength and is characterized by a lower partial discharge inception voltage

Systematic approach for the analysis of the electromagnetic environment inside a building during lightning strike

This paper defines a systematic approach considering the lightning current at the base of the channel as input function, the spatial distribution of the electromagnetic (EM) field inside the building, or the overvoltages induced at the open ends of loops as output functions. A parametric analysis of the influence of the lightning protection system on the output functions is carried out in frequency domain. The systematic approach allows one to take into account the probabilistic nature of the input function, which transforms the values of the outputs from deterministic to a distribution of probability. This is extremely useful for all electromagnetic compatibility (EMC) engineers dealing with realistic systems’ designs or maintenance problems

The effect of the definition used in measuring partial discharge inception voltages

At present several definitions of partial discharge inception voltage (PDIV) have been advanced by various interested groups. To establish the value of each of these definitions, four practical electrical insulating fluids were selected and their PDIV were determined according to three of these different specifications. The results of this study are presented and they suggest that the use of PDIV as a quality criterion generally is not warranted. The significance of these findings is discussed

A New Model for the Frequency of Failure Evaluation in Electrical and Electronic Systems due to Nearby Flashes

Paper 7-2

Hazard for electronic equipment near to transmission line struck by lightning

The paper deals with analysis of magnetic field due to lightning current flowing along the conductors of transmission line. It is shown that the boundary of high magnetic field may achieve the distance of some tens meters from the line. This effect should be taken into account in the case of neigbouring structures equipped with sensitive electronic system