Where fmax represents the maximum frequency under study, l
represents the length of the cable and v represents the cable velocity.
2.7. Motors
Motor energization is an important consideration associated with either
cranking of thermal based generation or cold load pick up to show the
effects of inrush currents which are about 6 times the full load rated
current. A 4th order induction motor model [30] has been used to
represent the motors.
3. Results and discussion
All across the study, voltage and frequency measurements are taken at
the onshore substation at 33 kV level. Field current and excitation
limiter outputs measurements are related to the SC. Also Type 1 WECSs
will be referred to as SCIG based WECSs while Type 3 WECSs will be
referred to as DFIG based WECSs.
3.1. Range of Operation
Pickup and drop-off of pure resistive and inductive load was undertaken
to determine the normal operating range of the windfarm. This was done
to define the limitations on the hybrid windfarm under different
scenarios.
3.1.1. Active Power
The initial connected load was taken as 4MW. At the 40th second, 3.5 MW
of load was dropped, followed by a gradual increase in windspeed from
7m/s to 9m/s at the 60th second. The aim of this was to investigate the
worst-case scenario if there is excess generation at low loading. At the
75th second, 1.5 MW of load is picked up followed by generation decrease
caused by wind gradually decreasing from 9m/s to 7m/s, starting from the
90th second. The aim of this was to investigate the response on impact
of sequential load increase and reduction in generation. Fig. 6 shows
the response.