Assignment -
Problem 1 -
a) Consider the simplified dc system shown in Fig. 1. Only one converter is modeled, with the remote end represented by a dc source. The ac system is rated at 345 kV, with the converter transformer secondary voltage nominally set to 215 kV. Each transformer has an MVA rating of 597.77 MVA and has a leakage of 18%. Other system parameter values are indicated in the figure. The rectifier dc voltage is nominally 500 kV, and the nominal power at the rectifier end is 1000 MW. Calculate the required transformer turns ratio and inverter side voltage Vd2 so that rated dc power and voltage are maintained with a firing angle α = 15^{o}.
b) Calculate power factor and the ac current (magnitude and phase) for the rectifier operating condition.
c) Simulate the circuit using either Matlab/Simulink or PSCAD/EMTDC software. Adjust the turns ratio, ac and remote end dc voltages to the values that you calculated in (a). Report observed values of Vd1, Id, Iac (in source) and power factor and compare with expected values. Report the waveforms of Vd, Vy, Vd1, Id1, and the ac-side waveforms for only a few cycles.
d) Far various α, measure the real and reactive power of the ac source and comment on them.
Problem 2 -
a) We now carry out a similar calculation for the inverter side, Fig. 2. For each of the inverter transformers, assume the transformer rating of 230 kV / 210 kV, Xc = 18%, MVA = 585.81. Assume that at the rectifier side, Vd2 = Vdr = 500 kV, and Pdc = 1000 MW. (Note, due to losses in the line, the inverter power will be smaller). Calculate the required voltage (l-l, rms) at the inverter end that will result in the rated current assuming an extinction angle γ = 15^{o}. Also calculate μ.
b) Confirm by simulation, that if α is selected as above, μ and γ are at the expected values. You are required to show a plot from the simulation to indicate how the overlap and extinction angles were measured.