SATNAC 2008 Conference Papers
Outside Plant & Transmission Issues
Title: Misguided Sense of
Ssecurity on Data Centre Availability when Fire Protection is not Addressed
Authors: Leonardus
Durand (
Abstract: The persistent increase for superior availability of data centres is constantly adding pressure on the selection and application methodologies for technology, applicable to both IT related and support systems. Given the proposed configuration of electrical systems to produce higher availability, as promoted through the Uptime Institute’s “tier-level” principles, research has shown that 25 percent [8] of reported down-time is still credited to failure on the part of these electrical systems. The perception that the application of “dual” electrical systems will increase availability of a data centre’s electrical reticulation is misleading and largely untrue. Upon close examination and scenario identification, it is evident that these dual electrical system architectures (tier-levels III and IV) are still inundated with hidden single points of failures. This paper describes fire protection measures to address these hidden single-points of failure. It is therefore stated that, where sufficient fire protection is not provided, the perception of limited or no single-points of failure will result in extended down-time of the entire data centre.
Title: Transmission
Probability-based Dynamic Power Control for Multi-Radio Mesh Networks
Authors: Thomas Olwal (Tshwane University of Technology), Felix Aron (Tshwane University of Technology), Ben van Wyk (Tshwane University of Technology)
Abstract: This
paper presents an analytical model for the selection of the transmission power
based on the bi-directional medium access information. Most of dynamic
transmission power control algorithms are based on the uni-directional channel
and interference state information. Such studies consider energy-constrained
networks with the need to increase the battery life and improve QoS. In this
paper we propose a distributed dynamic power control solution based on the
knowledge of the PHY and MAC layers’ local information for multiple radio
WMNs. Each radio interface/link is modelled individually in order to reduce
system complexity. The design involves the derivation of a MAC based
transmission scheduling probability (MAC-TSP). The transmission power is
dynamically adjusted in response to the MAC-TSP measurements in each time slot.
Simulation results show that average throughput performance for each radio link
can be improved significantly when sufficient MAC information is available to
the power control system.
Authors: Thapelo
Pholo (
Abstract: The development of fuel cell (FC) technology offers a novel platform for independence of telecommunication utilities from the national grid, especially for remote repeater stations that are not easily accessible for power connection. Currently, there is a huge interest in the possibility that FCs could make an important contribution to the world energy supplies for both mobile and stationery applications. This paper describes the design considerations of the single cell Phosphoric Acid Fuel Cell (PAFC). The method used for assembly, operation and experimental results together with simulated results of the mono-cell are presented. Details are given only to the experimental and simulated results and not to the design of components. Firstly the assembly is discussed followed by the operational characteristics and the results. Based on the experimental data, the characteristics are then used to simulate the bigger 100 W fuel cell that can be integrated as a backup power supply for telecommunications purposes.
Title: Full Bridge DC-DC
Converter as Input Stage for a Fuel Cell based Inverter System
Authors: Martin
Rugaju (Vaal University of Technology), Johannes
van Rensburg (Vaal
University of Technology), Christo Pienaar (Vaal University of
Technology)
Abstract: Telkom and other critical service companies use batteries as the main source of energy for their inverters and uninterruptible power supplies (UPS), in the case of grid failure. An alternative to the battery run inverter or UPS system would be the use of a fuel cell as the source of energy. Fuel cells provide the main advantage of refuelabilty over battery run systems. They can also be used in places where there is no grid connectivity, provided that fuel is available to run the fuel cell. Fuel cells though have the distinct technical drawbacks of slow start up times, drop in line voltage when the cell is loaded and slow response to transients in the load. In addition, low to medium power, fuel cells deliver lower voltage with respect to the grid voltage at high currents. Therefore a higher DC link voltage is required at the input of DC-AC converters to produce the mains level voltage of 240 V AC. Various DC-DC converter schemes can be employed to regulate the varying fuel cell voltage to a required DC-link voltage. This paper presents the development of current fed fullbridge converter prototype as the input stage to a fuel cell inverter system in the 1 – 1.5 kW range. The purpose of this power converter is to boost the 30 -50 V produced by a commercial PEM fuel cell to 100 V for conversion to 240 V 50 Hz used to run various loads. The preliminary results of the experimental measurements on the prototype are given.