IEEE Power & Energy Magazine - March/April 2016 - 61

so the converter transformers and dc reactors are provided
with acoustic shields.

Fenno-Skan Refurbishment and Upgrade
The Fenno-Skan connection, between Sweden and Finland,
consists of two HVdc links today, Fenno-Skan 1 (FS1, original name Fenno-Skan) and the newer link Fenno-Skan 2
(FS2). In 2011, the new HVdc interconnector FS2 800 MW
and 500 kV, between Finland and Sweden, was put into operation. One year later the refurbished FS1, rated at 500 MW
and 400 kV, was put into operation after refurbishment that
was carried out in conjunction with the new interconnector
FS2. This article will focus on the refurbishment of FS1. In
this case there was a combination of drivers for the solution:
1) a need for higher power transfer capacity and 2) the age of
the HVdc link, especially the control and protection system.
Since both poles were commissioned, they are now operating as a bipole for balancing the current in the sea electrode
that still is in use and can be used up to full power if one of
the poles is out of service. The FS1 scheme was originally
commissioned in 1989.
The background and reason for the FS1 refurbishment
is that the HVdc station was 23 years old at that time, and
while the primary equipment has been well maintained and
appears to have a long remaining life, the equipment causing
concern was the control and protection system. First, there
is a limited lifetime for electronics and problems finding
spare parts; second, the people with knowledge of this older
equipment are also aging and more difficult to find. Another
advantage to the refurbishment was to have the same type of
control system as implemented in FS2, which would improve
the maintenance efficiency.
For the market situation and possibilities to transfer
power, the best solution for changing the control and protection system was after a new pole was installed and in service,
making it easier to make allowance for the necessary outage
of the link. It would be easier to have the two poles in bipole
operation if they had the same type of control system.
When FS1 was upgraded to a similar control system
as FS2, it was easier to make the current balancing and to
operate the scheme from one "local" control point together.
The scope limit for the upgrade was the upper levels of the
control system, retaining the existing valve-base electronics cubicles, which is the interface toward the valve, and the
switch-yard interfaces toward the primary ac and dc sides.
This means that the mimic boards and many other cubicles
would disappear or host new equipment. The outage time
was planned not to be more than four weeks for the FS1 pole
when the control system was changed.
One challenge with the work was the market situation
as a lot of Nordic hydropower was available. The area
price in Sweden ranged 10-15 €/MWh and in Finland
30-40 €/MWh. With the minimum power transmission
test (40 MW), flow between the countries was not a problem. Since FS2 significantly increases the cross-border
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capacity, the challenges occur when the test power was
above the capacity of the existing pole (>500 MW) or
when the transmission direction was against the intrinsic
direction of the market. Almost all tests with Sweden as
rectifier were carried out in the beginning, hoping that the
price difference would go down. But in the end, the tests
required transmission direction from Finland to Sweden,
so the project had to run 800 MW against the intrinsic
transmission direction of the market. To mitigate unexpected market implications, the following remedies were
employed. First, FS1 compensated net flow by 500 MW
to 300 MW, second, on some rare occasions, transmission system operators reduced the cross-border capacity
temporarily, and finally, as a last resort, counter-trade was
applied between Finland and Sweden.
The conclusion was that waiting for the refurbishment of
FS1 until the new pole was in operation was very successful.
It saved money during the testing with a market situation that
demanded power in the opposite direction from that needed
for testing. It also kept down the price difference as the new
pole was able to transmit power during the outage. It also
seems reasonable to keep equipment that is duplicated and
can be changed during operation, such as redundant cooling
fans and pumps.

McNeill Back to Back
The first HVdc installation in Alberta, Canada, was supplied to Alberta Power Limited (now ATCO Electric Ltd.) in
1989. The McNeill converter station is a 150-MW back-toback HVdc system linking Saskatchewan and Alberta. The
site is the most northerly link between the North American
western system (Western Electricity Coordinating Council)
and the eastern interconnected system (Midwest Reliability
Organization). The historical reliability of the system has
been quite good, with the main cause of concern being the
aging control system. McNeill is the only interconnection
between Alberta and Saskatchewan utilities, so the continued reliable operation of the station will be required for the
foreseeable future. The following major life-extension activities have been undertaken at McNeill to ensure continued
safe and reliable operation:

Medium Voltage Filter Breaker Replacement
Harmonic filters and reactive power compensation use
binary switching on both sides of the converter, with capacitive and reactive elements switched in and out in coordination to achieve smaller steps in reactive power (Mvar) and
less impact to the weak ac networks. This results in a significant number of breaker operations over the years as power
dispatch and network voltages fluctuate. The 25-kV filter
breakers began exhibiting increased frequency of mechanical failures and were deemed to be at end of life after only
10-15 years of operation. ATCO Electric replaced all 16
reactive element breakers in a planned program between
2000 and 2006.
march/april 2016

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