VSC-HVDC based Network Reinforcement

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The involved physical constraints, static voltage sensitivity analysis and
load growth trends revealed that the VSC-HVDC model shall be of back to
back topology placed in Area 2 with PCCs at bus 2 and bus 1.
The rating of the VSC-HVDC converters, 45 MVA is found to be
sufficient to transfer the planned 40 MW, and have enough reactive power
capacity together with the AC filter banks to deal with the worst case N-1
outage voltage drops
The performance of the converter controllers under steady state and
various disturbances has been found to be in agreement with other research
works.
It is not required to model the distribution grid in Area 1 in detail, i.e. the
aggregated model of the distribution grid is valid for the purpose of the
planning studies presented in this thesis.
The steady-state and dynamics of rotor angles of the large synchronous
generators G 2/G 3 is affected only marginally due to the introduction of
VSC-HVDC. Moreover, the transmission grid power flows change only by
a relatively small proportion, 3 % because of the VSC-HVDC instigate
power flow changes.
The ability of the distribution grid to remain in synchronism with the rest
of the grid is improved by the VSC-HVDC link to some extent.
The interaction of the largest wind unit installed at line 2/line 3 with the
VSC-HVDC is not significant. This may be attributed to the low i.e. 15 %
penetration level of the wind power in the 50 kV Area 2 grid.
The maximum relative increase in short-circuit current in the 50 kV Area 2
grid due to the VSC-HVDC is found to be 13 %. For grid operators, an
increases of 13 % for short-circuit current levels in the range of 4 kA is
acceptable. Thus, there is no need to upgrade existing circuit breakers and
revise the protection scheme of the existing grid.
The response of the network to deep voltage dips in the 380 kV network is
not significantly affected by the VSC-HVDC link. The performance of the
VSC-HVDC deteriorates under such deep voltage dip. However, the
probability of occurrence of such dips is rare.
Technically the VSC-HVDC is found to be an innovative and sufficient
solution to mitigate the network constraints described in this thesis.