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.