IEEE Power & Energy Magazine - March/April 2016 - 74

sharing of economic energy and capacity is particularly
important during the summer and winter peak periods that
are characteristic of electric power systems. The locations
and interconnection of the nodes are shown in Figure 1.
The original Inter-Island Link HVdc was constructed in
stages for a total of two poles. The first pole (pole 1) was
constructed in 1965 using mercury-arc valves and the second pole (pole 2) in 1992 using thyristors. The HVdc link
was built for bipolar power transmission. Traditional generation like gas and coal-powered generation are located on the
north island, whereas the south island contains renewable
energy power generation in the form of a hydroelectric dam.
The refurbishment, called the HVdc Inter-Island Link
pole 3 project, took place in two stages, resulting in a capacity of 1,000 MW in 2012 and 1,200 MW in 2014. Stage 1
was the construction of a new HVdc pole, called pole 3, with
a nominal rating of 700 MW. Stage 2 was the installation of
a ±60 Mvar static var compensator (SVC) PLUS at the Haywards substation for reactive power support and voltage control. An additional third stage would further increase the power
capacity to 1,400 MW by adding submarine cable and reactive
support capacities. The configuration of the HVdc link before
the refurbishment is shown in Figure 2, with the detailed components of the refurbishment stages depicted in Figure 3.
The power capacity rating of transmission is dependent on
the direction of the flow of power. The transfer capability of
1,000 MW in 2012 and 1,200 MW in 2014 are specifically for
north flow. The HVdc link cannot be operated at these ratings
in the south flow direction due to ac system constraints in the
north island. Generation reserve constraints and insufficient
Digital Object Identifier 10.1109/MPE.2015.2501106
Date of publication: 18 February 2016

march/april 2016

reactive power support in the south island cause
these constraints in the north island. The new maximum south transfer capability after the refurbishment is between 420 MW and 950 MW, depending
on the load demand of the Haywards area. South
flow is a range because it is based on the status of the
ac system. HVdc control systems monitor the ac system status and automatically adjust the power limits
of the link to prevent voltage collapse in the north
island and ensure system security.
The goal of the refurbishment was to increase
the power capacity and energy sharing capability
of the north and south islands by constructing a
third pole (pole 3) using the latest thyristor technology. Pole 3 was constructed while poles 1 and
2 remained in operation. When pole 3 was completed, pole 1 was removed and replaced by pole 3.
The refurbished system was operated as poles 2 and
3. By removing pole 1 and connecting the new pole
3 in its place, the power transfer is increased and
the voltage increased to ±350 kVdc. The voltage
of pole 3 matches pole 2. The two poles, however,
differ by their individual power capacity. Pole 2 has a rating
for 560 MW (350 kV, 1,600 A) with a continuous overload
capacity of 700 MW. Pole 3 has a nominal continuous capacity of 700 MW (350 kV, 2,000 A), a continuous overload
capacity of 770 MW (with redundant cooling), and a 30 min
overload capacity of 1,000 MW (2,857 A, without redundant

Haywards

Benmore

figure 1. The HVdc line connecting Haywards and
Benmore (map image: Google Earth).
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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2016