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In this paper, both the STATCOM and the SVC are analyzed
from the point of view of their potential for increasing the transient
margin as reported in [14], [15] to indicate their capability
as candidate solutions for providing LVRT to wind farms with
induction generators directly connected to the electric grid. The
transient stability margin is defined as the difference between
the speed after a specified fault duration and the critical speed of
the generator. A torque-slip based analysis of transient stability
limit with a STATCOMand SVC is first presented. Estimates for
critical speed and critical clearing time (CCT) are calculated for
different compensation levels of STATCOM and compared with
the case of no compensation, ideal compensation (stiff voltage)
and compensation with SVC. Measurements under voltage sag
condition that gives 20% remaining voltage for 300 ms on a
lab set-up of 7.5 kW motor-generator set representing the wind
generation are then compared to the calculated values and evaluated
for LVRT capability assessment. Calculations and measurement
results compared show a clear increase of transient
stability margin with increased rating of the SATCOM. The calculations
also indicate the better potential of the STATCOM to
increase the LVRT capability compared to the SVC. Comparison
of critical speeds from the calculation method and detailed
simulation under the same conditions are also provided as a validation
and to discuss the effect of the neglected flux transients
in the accuracy of the proposed calculation method
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