IEEE Power & Energy Magazine - March/April 2016 - 51

HVdc and FACTS equipment located in
the northeastern United States and Canada have reached
their life expectancy.

address a thermal design issue. the dissolved gas oil readings of the transformers after the windings replacement were
considered to be good, and an independent assessment of the
transformer condition was carried out by High energy inc.,
which did not indicate any immediate concerns. the condition was judged to be adequate for at least 15-20 years of
operation. online gas monitoring was identified as a desirable feature to better monitor the condition going forward.
there was also a minor issue with oil leakage through the
low-voltage bushings into the valve hall that was judged to
be repairable, given the luxury of a longer than normal outage during the refurbishment.

Thyristor Valves
the thyristor valves had performed very well and outwardly were in pristine condition. no issues were expected
other than the possibility of increased thyristor failures
toward their end of life. the valves were inspected by
VelCo and the original equipment manufacturer supplier,
and the consensus was that continued operation should be
possible for up to 35 years based on the observed condition.
VelCo decided that additional thyristor spares should be
purchased and also that replacement of the oil-filled damping capacitors within the valve would be desirable, as some
of the seals had started to show minor seepage and new
gas-filled capacitors would mitigate much of the concerns
over valve fires.

Controls and Protections
in 2010, VelCo experienced four computer system stalls
and one internal fault in Control system a (figure 4). in the

same year, Control system B experienced nine stalls and
three internal faults. one event created the perfect storm, in
which one system stalled, and then 30 min later, the other
system experienced an internal fault that resulted in a forced
outage in the middle of the summer.
With each system event and failure, it became increasingly
more difficult to properly diagnose the root cause of control
system failures, even with assistance from the vendor. although
the vendor commitment was exemplary, the equipment was
obsolete. Knowledge of this vintage technology had declined
due to the aging workforce and the boom in newer technology.
additionally, spare parts were beginning to become more difficult to find and were greatly increasing in price.

Cooling System
the cooling system is the lifeblood of the facility; if the cooling system isn't reliable, the system is not reliable. a study
was performed to assess the efficiency of the heat exchangers
using limited real-time monitoring data of snapshots taken
every 15 min. the analysis indicated a significant degradation in efficiency when compared with the original design
documentation.
in the original configuration (figure 5), the cooling system pumps and motors were horizontally connected and
bolted down to the skid. even though the raw water system
motors and pumps were laser aligned, they were still prone
to vibrate loose and burn up bearings approximately every
six months. this resulted in an increased need for preventative maintenance to maintain the cooling system's reliability.
However, each time the pumps were out for maintenance,
redundancy was lost to the cooling system, which increased
the odds of a forced outage. also, the prerefurbishment configuration of the cooling towers was designed without redundancy. thus, if a failure occurred within the cooling towers,
a reduction in power transfer through the converter would be
needed, at least during the summer months.
full replacement of the cooling plant was judged to be
the best option to guarantee that the rating could be achieved
even on the hottest days. With full replacement, it would be
possible to provide some measure of cooler redundancy and
at the same time allow for some deterioration in performance
with age going forward.

Visits to Other Refurbishment Projects
figure 4. Original control cabinets.
50

ieee power & energy magazine

in assessing the refurbishment and what equipment to replace,
VelCo also visited several other facilities of similar vintage
march/april 2016

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - March/April 2016