Abstract
M.Ing.
This dissertation describes the development and characteristics of a thyristor controlled
reactive three phase network which is used for the compensation of reactive power in
a power network. The problem of distortion in power networks is illustrated and the
development of a thyristor controlled reactive three phase network is motivated. The
considerations that were taken into account in the design of the network are explained
and the experimental setup is evaluated. A computer simulation was done to verify a
single phase model of the reactive power network. The driving function in power networks is a singular harmonic voltage and distortion is defined as any deviation ofthe current from a scaled, in phase version of the voltage. Distortion is caused byloads with a non-linear nature such as arc furnaces and variable speed drives. Reactive power, which forms part of the distortion problem, is caused by loads with a phase shift between the voltage and current. Distortion has several adverse effects on a power network resulting in the degrading of the quality of the supply. At present the state of the art in technology does not permit the economic compensation of distortion with dynamic filters at MVA levels. However, by compensating the reactive power present in a network byusing variable reactive elements, the remaining distortion in the network can be compensated by using a dynamic filter. The combination ofa thyristor controlled reactive network and a dynamic filter are termed a hybrid power compensator. Results are shown where a hybrid power compensator has been implimented to compensate distortion caused by a non-linear load. The thyristor controlled reactive three phase network described in this dissertation is rated at 21 kVAr and comprises the following on a per phase basis: The series combination of a fixed capacitor bank and a filter inductance is connected via an isolation transformer to a reactor and two anti parallel thyristors. The reactive elements have been dimensioned in such a way that reactive power can only be generated and not absorbed.