Figure 22. SC Stator Current on HV cable energization (100%
compensated, 80% compensation) in a DFIG based hybrid system.
At the recommended 100% compensation level (from the voltage response
of Figs. 21 and 22), there is an increased chance of missing zero
phenomenon which is more pronounced on the DFIG based system as compared
to the SCIG based system. The more capacitive the system at the time of
energization the less the missing zero phenomenon effect. For the SCIG
based system, there are connected capacitor banks (required for normal
operation) which makes the system net capacitive as compared to DFIG
based system that does not require external capacitive elements as it
does its reactive power management internally through the RSC or GSC.
3.5. Overhead Line Energization
Assuming that there is a non-blackstart unit located more than 50km away
from the windfarm, the 132kV overhead lines between the windfarm and the
non-blackstart unit will need to be energized. Figs. 23 and 24 show
results obtained on overhead line energization by both a SCIG and DFIG
based hybrid system. Energization of 100km and 200km lines required some
form of compensation: 0.6 and 0.8MVAr respectively.