Figure 20. Response on HV cable energization for a DFIG based
hybrid system.
From above, it is possible to energize a HV cable if there is proper
compensation. In this case there is sufficient capability from the SC
and for 80% compensation, it is driven to underexcitation and negative
excitation. Negative forcing excitation capability is possible in static
excitation systems if excess short-term reactive power absorption
capabilities are required. However, this prompted the UEL to increase
the AVR voltage reference thus the increase in the RMS voltage to 1.1pu
for the DFIG and 1.15pu for the SCIG which is the higher limit of the
range of voltage at MV level. One of the major challenges associated
with simultaneous energization of compensated transmission lines is the
missing zero phenomenon. This occurs when the current through a breaker
does not cross the zero mark for a few cycles. This is dangerous if
there is a fault that needs to be cleared during the few cycles leading
to circuit breaker (CB) damage when trying to open. In investigating the
missing zero phenomenon on the compensated lines, Figs. 21 and 22 show
the stator current response on cable energization at different
compensation levels.