| dc.description.abstract | Mechanically switched capacitor with damping network (MSCDN) is used as reactive
power compensation unit in the modern power systems. MSCDN stabilizes the voltage
and increases the transmission capacity to ensure the availability of reactive power for
feeding in the injection of reactive power at short notice. The transient overvoltage
phenomenon often occurs in MSCDN due to the lightning surge, switching surge, fault,
resonance, circuit breaker operation, etc. These transients impose great stresses to the
MSCDN and its components and could lead to insulation breakdown, discharge,
flashover, explosion, and so on. For this reason, studying the overvoltage of power
system is of extreme importance. In this thesis, the studied MSCDN consists of a main
capacitor (4.54 μF) supplying the desired amount of reactive power (225 MVar) at a
nominal voltage of 400 kV, connected to damping network providing sufficient
damping of switching processes. The damping network consists of an auxiliary
capacitor (35.81μF), damping resistor (474.07 Ω) and a filter reactor (282.94 mH). The
main aim of this study is to determine transient voltages and currents for single and
three phase’s system and find the ideal switching condition that gives the lowest
overvoltage magnitude at each MSCDN components. In this work, the transient stresses
of MSCDN components were determined by varying the closing and opening times of
the circuit breaker for both single and three-phase connections. Variations in the circuit
breaker times simulate the synchronous switching conditions of the MSCDN. For the
single-phase analysis, analytical calculation using Laplace transform was used to
calculate the transient currents and voltages, and the results obtained were compared
with ATP simulation for validation. Alternative Transient Program (ATP-EMTP) was
employed to reproduce the switching operation of MSCDN, as ATP gives solution in
time domain and very useful for comparisons with analytical method conducted in this
work. For single phase, it was found that the ideal switching cases were obtained when
switching at 0 and 5 ms respectively. Furthermore, for three-phase MSCDN, the
energisation and de-energisation of MSCDN were simulated to identify the transient
voltages and currents for synchronous switching. Based on the results obtained, the
ideal synchronous closing time of all phases was 5 ms. For MSCDN de-energisation
studies, the simulation results obtained showed that there are no visible transients
produced by synchronous de-energisation of MSCDN. This is the advantage of
MSCDN circuit as compared to regular capacitor banks. | en_US |
