IV. REACTIVE POWER COMPENSATION STUDY
The subsea cable length affects the amount of reactive
power to be compensated, the capacitive component of the
cable increases with the length of the cable [10]- [11]. Under
no-load conditions, the cable mainly carries the reactive current
for charging the cable capacitance. The cable charging current
increases with the system frequency, cable capacitance, and
the cable length. Longer the subsea cable, the higher is the
charging current. In addition to the active power required by
the loads, a large amount of reactive power needs to be sup-
plied leading to large and expensive cables and power losses.
This also leads to more expensive umbilicals with a higher cost
of installation and retrieval. This issue is especially severe for
longer step-out distances. Without proper compensation, the
reactive current through the line may reach the rated current
of the cable, which may not allow the cable to transfer any
active power. The characteristics of the subsea cable used for
the reactive power compensation study are provided in Table II.
Since the study only focuses on the cable performance during
the steady state condition, a simple -model is considered.
TABLE II. PARAMETERS OF THE CABLE
Rated Voltage (kV) 150
Rated Current (A) 1088
Inductance (mH/km) 0.352
Resistance (
/km) 0.0311
Capacitance (μF/km) 0.233
For subsea cables the following three reactive power com-
pensation cases are considered, (a): Without compensation; (b):
Fixed compensation at both ends; and (c): Variable compensa-
tion at both ends. The capacitive reactive power generated in
a specific cable (specific capacitive component) is determined
by the applied voltage; due to this component is a shunt
impedance. However, the inductive reactive power generated
by the cable depends on the amount of active current flowing
through the cable (transmitted active power). The philosophy
of the reactive power management is the minimization of the
total current flowing through the cable by reducing the reactive
current flowing through the cable as much as possible. How-
ever, considering the total capacitive reactive current generated
by the cable, this variation is quite little. So, the use of big
inductances to perform the reactive power compensation is an
economic option.