Propagation characteristics of partial discharge signals in medium voltage branched cable joints using HFCT sensors

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Muhammad SHAFIQ (1), Guillermo ROBLES (2), Kimmo KAUHANIEMI (2), Brian STEWART (3), Matti Lehtonen (4). Propagation characteristics of partial discharge signals in medium voltage branched cable joints using HFCT sensors. 3 – 6 June 2019, 25th international conference and exhibition on electricity distribution (CIRED 2019). Madrid – Spain

(1) University of Vaasa – Finland

(2) Carlos III University of Madrid – Spain

(3) University of Strathclyde – UK

(4) Aalto University – Finland

Abstract—Rapid proliferation of underground cables in today’s distribution networks need improved fault monitoring and diagnostic capabilities. Dielectric insulation is the most critical element of underground cables and exposed to various stresses. Cable joints and terminations are always needed and are the most vulnerable locations for insulation defects within the cable feeder. Partial discharge (PD) signals emerging during the progression of insulation faults, travel along the lines and split into connected branches at the T/Y splices. This makes the use of conventional diagnostics solution inappropriate as compared to straight cable section. This paper presents a study on the propagation behaviour of PD signals in a branched joint configuration. Experimental investigations are presented to study the PD propagation across the T/Y-splices. The presented study provides interesting outcomes that can be used for development of an efficient PD monitoring system to watchdog the cable feeder.

Keywords— Power cables, Partial discharges, Signal Propagation, Transmission lines.


Insulation design of low voltage electrical motors fed by PWM inverters

L. Lusuardi, A. Cavallini, M. G. de la Calle, J. M. Martínez-Tarifa and G. Robles, “Insulation design of low voltage electrical motors fed by PWM inverters,” in IEEE Electrical Insulation Magazine, vol. 35, no. 3, pp. 7-15, May-June 2019.

doi: 10.1109/MEI.2019.8689431

Abstract— This paper proposes a model to determine the partial discharge inception voltage of magnet wires, including the effect of elevated temperatures, and shows its applicability to the complete range of wire geometries considered in IEC Standard 60317-13.

For long, the insulation of magnet wires used in low voltage motors was mostly stressed by temperature and vibrations. In addition, moisture sometimes hastened thermo-mechanical stress by hydrolyzing the insulation leading to crack formation. The ultimate breakdown mechanism was an excessive leakage current throughout cracks and pinholes in the insulation. Within this framework, the thickness of the insulation was dictated mostly by mechanical considerations, to prevent crack formation during manufacturing and operation. Electrical stress did not play a key role in the aging process.
Power electronics changed this picture…

Keywords— inverter-fed machine, partial discharges, insulation design.