POWER April 2017 - 55

OPERATIONS & MAINTENANCE
2. Signs of a problem. The isolated
phase bus shown here was contaminated
with oil-inside and out-from a generator
leak. Courtesy: SE Energy
lated phase bus will help to ensure that your
bus runs efficiently (Figure 3).
Assessing and Planning
3. Inspections are important. These
flexible braids were in need of replacement
due to degraded contact surfaces. Courtesy:
SE Energy
The inspection and planning for maintenance
on a power plant's isolated phase bus should
take place months before a major outage, if
at all possible, so that proper work and upgrades
can be performed during this extended
period of time. During a smaller outage, it is
important to do an assessment of what critical
components need to be fixed or replaced.
During the assessment, there are several
areas of the isolated phase bus that can and
should be checked and conditions documented.
A thorough inspection by a qualified and
knowledgeable isolated phase bus specialist
should provide a well-documented report of
your system's status, areas where repairs are
needed, and as-found and as-left conditions,
including any repairs or material replacements
that were performed in conjunction
with the inspection.
everything was operating smoothly. However,
recently many plants have decided
to extend the time between major planned
outages. Many now have smaller outages
once a year, during which planning is done
for work that needs to be completed during
a major outage. Often, those major outages
are only being conducted every three
years or even less often. In order to make
sure that the isolated phase bus is properly
maintained during a big outage, planning on
the work that needs to be done should take
place during a smaller outage about a year
prior.
Isolated phase bus system failure can
come in many different forms. Additionally,
the conditions that often cause the failures
are ones that can be particularly difficult to
work under, such as localized overheating.
Other causes can include condensation, dirt,
improper grounding, cracked weld joints,
poor insulation, and water intrusion (see " Facilitating
Predictive Maintenance of Electrical
Assets with Pervasive Sensing Strategies "
in this issue of POWER for more on condition-based
monitoring of electrical systems).
Conducting a thorough inspection of the isoApril
2017 | POWER
Bolted joints should be checked to ensure
that the correct hardware is present and properly
torqued. The contact surface integrity
should be looked at, and the plating condition
and the flexible connectors checked. During
this time, the insulators can be inspected
for dirt build-up and any damage that may
have occurred, including cracks or chips.
Additionally, the seal-off bushings should
be checked to ensure a proper seal is active.
Hardware covers should be removed and areas
checked for water entry, air leaks, and hot
spots. Gaskets should be verified for proper
functionality.
During the assessment and planning
phase, ground cables and connections should
be observed to ensure proper grounding is
being achieved. The filter drains should be
assessed in the isolated phase bus for water
build-up and clogs. Temperatures of the
enclosure/conductor and the support steel
should be monitored. Excessive heating of
the support steel can lead to an impending
catastrophic failure. Finally, elements of the
force-cooled system should be inspected.
These elements include the fan, fan motor
drive, dampers, cooling coils, water connections,
deionizers, drains, instruments, and the
disconnect switch.
During the minor outage, certain preventative
maintenance tasks should be performed
to ensure the isolated phase bus is in
optimal condition. The bolted covers should
be removed to gain access at the termination
enclosures. All of the insulators should be
hand cleaned, and the enclosure should have
the debris vacuumed from it.
After assessing which elements of the isolated
phase bus need attention, it is important
to plan out everything that needs to be
www.powermag.com
4. Experts can recognize problems.
The laminates shown here were in
need of replacement, which was identified
during a thorough inspection. Courtesy: SE
Energy
done, complete with cost estimates and time
requirements. That way, during the large,
planned outage, maintenance work can be
performed effectively and efficiently.
Major Outage Repairs
After all of the assessments are completed
and recommendations are made during a minor
outage, the repair and retrofit work can
be planned for and carried out during a major
outage. By assessing and making estimates
months in advance, a maintenance team has
the elements necessary to ensure that the isolated
phase bus will be running at an optimal
level when the power plant is brought back
online.
These major overhauls can include replacement
of laminates (Figure 4), insulators,
expansion joints, and rubber bellows.
All of these components have lead times, and
there will be expediting fees if not ordered in
advance. When a plan is set months before
the outage, maintenance teams can be confident
in their preparation and ensure they have
all of the supplies they need to perform effective
work. Additionally, during the major
outage, any necessary welding can take place
along with silver plating.
Most importantly, it is critical that operators
have certified experts on the team that
does both the assessment/inspections during
the smaller outage and the major repairs
during the larger one. Knowledge and experience
are keys in providing accurate assessments
and necessary repairs to an isolated
phase bus system. These bus systems are
heavily relied upon to be operational and
keep the power plant online. With the costs
associated with repairs and unplanned shutdowns,
being able to count on the isolated
phase bus is critical. ■
-Cal Crader, PE is the CEO of SE Energy
LLC, a specialty electrical construction,
engineering, and consulting firm.
55
http://www.powermag.com
POWER April 2017

Table of Contents for the Digital Edition of POWER April 2017
