So many academic papers quote the following fact: "A line commutated converter in steady-state operation inherently consumes reactive power of about 60% of the DC power transferred."
I do not want to see this from "generating" or "consuming" vars' view. My real question is more like this: HVDC is causing current to phase shift from the voltage, what is causing the phase shift?
commutation process itself? or the reactive elements in filters, transformers and the transmission line?
I strongly believe that alpha angle in the commutation process is NOT the answer. I think, the fundamental of reactive power is the fact that
V are out of phase. Alpha angle blocks the occurrence of current, it does not cause phase shift. blocking and phase shift are very different!
For example, imagine a simple circuit with an AC source and a resistor in series. if a diode is inserted between the AC power source and the resistor, current may be blocked for half a cycle, (strictly speaking, more than half a cycle. Since the diode will only start conducting @ 0.7-ish volt, we technically have a none zero alpha angle here as well), but the current is still in phase with the voltage, no phase shift, no Var.
I find this frustrating, as most of you just accept the conclusions "var is due to alpha angle" without truly thinking it thru. I highly suspect that, at normal load of an HVDC line, the transmission line is a huge inductance, and that's the reason for the reactive power consumption.