R. R. van Zyl

Insulator leakage current monitoring: Challenges for high voltage direct current transmission lines

Power transmission using HVDC transmission technology has existed for several years. As part of the design specification for such schemes, transmission line and substation insulator selection is crucial to ensure good operational performance. Leakage current may occur on insulators due to contamination, ageing of insulation materials and aggressive weather conditions, amongst others. If not mitigated, these currents can lead to line faults which occur as flashover of the insulator and the degradation of the insulator material. Monitoring leakage current on alternating current transmission lines may be accomplished using current transformer devices. However, this cannot be used in direct current transmission lines due to static magnetic fields. Toughened glass insulators are generally preferred for HVDC schemes, but composite insulators are proving to be cost-effective alternatives. However, because of its relatively new application in HVDC schemes, little has been published relating to operational data on typical leakage current magnitudes, waveforms and consequential effects thereof. ESKOM currently operates and maintains the South African sections of the Cahora Bassa HVDC scheme. At present, the utility does not have an in-situ, non-intrusive solution for monitoring the leakage currents on this scheme. This paper presents an overview of leakage current and the options available for measuring it. In-situ and non-intrusive sensors have the benefit of being used for real time monitoring as well as for live line work.

Comparison of the communication time of a high gain versus a low gain monopole-like low profile antenna on a 3-unit CubeSat

This paper investigates the effect of the antenna pattern on the communication time between a ground station and a low earth orbit satellite with passive attitude control, i.e. the antenna is nadir pointing. Two low profile antennas that fit on a 3-unit CubeSat are considered, namely a high gain patch and a low gain monopole-like patch antenna. The communication system is for high speed S-band communication.

The design of an HF antenna on a 1U CubeSat

This paper presents the design, the deployment mechanism and the measurement of an HF antenna on a 1U CubeSat. An HF radio beacon on this CubeSat shall be used as a space-based signal source to contribute to the monitoring of the density and movement of the polar and high-latitude ionosphere making use of the interferometer antenna arrays at the South African Antarctic station, SANAE-IV.

Current and future small satellite projects in South Africa

South Africa has embarked on a number of small satellite projects. This paper gives an overview of the history of small satellite development in South Africa and of the current projects including programs associated with Universities and with the South African National Space Agency (SANSA). The contributions of the National Space Programme of SANSA and of industrial partners in South Africa in small satellite development are outlined.

A budget supercomputer: implementation and application

This paper presents an overview of the implementation and current application of the Peninsula Technikons first cluster-based supercomputer. The cluster consists of 18 off-the-shelf, diskless PCs and 1 controller/master high-end PC. The approach taken for implementing this budget supercomputer is discussed

Transfer function approximation of an experimental domestic power network

The paper proposes a measurement process to capture the transfer function of combined noise/degradation sources on an experimental domestic power line communication network. The discussion includes an analysis of the proposed methodology and the practical implementation. The measured results for a typical network topology are presented