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.