Centre for Power Systems r esearch (CPS r )

In 2014, the CPSR conducted research on HVDC and UHVDC transmission systems, efficiency in networks under distorted waveform conditions, effectiveness and impact of harmonic filter types on efficiency, utility theory for making a mitigation decision on harmonic resonance, and the installation and commissioning process for open rack MV harmonic filters.

The centre further specialises in the evaluation, application and comparison of modern industrial grade frequency and time-domain software packages to produce graduates with modelling, design and analysis skills. The objective is to develop manpower with advanced skill in the technological aspects of the real world environment of power systems.

Some of the specific topics researched and published in 2014 include:

1. optimisation of loss reduction through a converted HVaC transmission line into HVDC model in digsilent software

Losses are an important parameter when considering the enhancement of the Transfer Capability of Power Systems. This work investigates the loss reduction for parallel operation of HVAC and HVDC transmission lines.

2. Performance of passive aC/DC filters and DC smoothing reactors in UHVDC power systems

The propagation of generated harmonics by power thyristor converters in HVDC transmission systems causes detrimental effects. Appropriate AC/DC filters and DC smoothing reactors application are essential in order to achieve desired performance criteria. In this work, appropriate passive AC/DC filter types and configurations have been carefully selected and designed to mitigate DC harmonic voltages and AC distortion levels of a 4000 mW, 1500 km, ±800 kV bipolar UHVDC power system.

3. The use of DIgSIL e NT Power f actory software for power system efficiency calculations under distorted conditions

There is an increase in electrical energy demand in the Southern African region, thus saving energy has become a vital aspect for economic growth. One cause of high demand is that the power system equipment operates at low efficiency; thus power losses increase. This prompted a need to evaluate efficiency in networks under distorted conditions to determine the impact of harmonics on efficiency. This study presents the use of DIgSILENT PowerFactory software, for efficiency calculation under distorted conditions.

4. New overall efficiency formula for analysing power systems containing multiple harmonic sources

This research looks at developing a new formula and method for investigating and analysing overall efficiency of a power system containing multiple harmonic sources. Traditionally, the power generated and consumed due to harmonics is ignored in overall efficiency studies. However, in the modern world, systems contain levels of harmonics which can no longer be ignored. In this study, five case studies that increase the number of harmonic sources (ASDs) from one to five are being conducted. A computerbased simulation methodology is being developed for overall efficiency analysis using the DIgSILENT software package. An example of the application of the new formula and the results of the case studies analysed are also included as outputs. The developed formula and methodology was found to be effective and its use is recommended.

5. Utility theory process for making a mitigation decision on harmonic resonance

A unique utility theory process for making a mitigation decision on harmonic resonance in an interconnected power system containing upstream capacitance has been developed. A user-friendly template has been developed, focusing on the application of utility theory for making decisions and applied to a case study wherein the process identifies the need for a filter, which has been designed and shown to be effective.

6. e valuation of grid code power quality requirements for wind generators in distribution networks

This work evaluates the power quality parameters that wind turbine generators must adhere to when connecting to distribution and transmission networks in South Africa. This is being investigated by means of DIgSILENT software simulation case studies for the comparison of asynchronous and doubly fed induction generators (DFIG). The two chosen wind generators have been established globally with a proven track record within the wind industry. Wind generator simulations, modelled for a variety of network scenarios are essential in order to predict and evaluate the impact that wind power will have when integrating to the national grid.

There are a number of students studying in this centre. During the year, three international, four national and five local papers were presented at conferences.

The CPSR has links with UCT, Electrotek Concepts (USA), DigSilenSA, the HVDC Research Centre (Manitoba, Winnepeg, Canada), Eskom, and local municipalities and factories in the Western Cape.