A method for calculating the required current rating of
a STATCOM, and for comparison with other compensation
devices like the SVC, is also suggested. The influence of the
system parameters on the required rating of the compensation
device has been investigated and it is shown that the
STATCOM performs better than the SVC in terms of LVRT
capability if the same rating is assumed for the devices. For the
same contingency, the required SVC rating is generally larger
than required STATCOM rating. Even if the SVC is usually
considered a cheaper and simpler solution, the difference in
required rating can result in the STATCOM as the economical
solution for specific cases. For instance, if a 50% larger SVC
than STATCOM would be required for a particular application
and the STATCOM has 30% higher costs per kVA than the SVC
as indicated in the previous section, the net cost of STATCOM
would be about 85% of the cost of SVC, or SVC would be
15% more expensive than STATCOM for the same case. If a
high transient current rating of the voltage source converter is
available for LVRT purposes, these figures could be even more
favourable for the STATCOM, and the STATCOM could be the
economical solution in more situations. On this basis, further
investigations into converter design for high short term overload
capacity will be of interest, and this can give additional benefit
to the STATCOM compared to the SVC, which has no capacity
of providing transient overload rating in capacitive operation.
In this setting, it will also be relevant to investigate and utilize
the advantages regarding controllability of a voltage source
converter as a STATCOM, in addition to providing LVRT to
induction generators within a reasonable stationary rating at a
reasonable cost.