The following are reasons:
CAPEX is most significant for these equipment
Movable parts are prone to wear, and circuit
breaker duty will vary from the network supplied,
as well as network fault current levels.
Restoration times for the two pieces of equipment
are lengthy if no other planned or network
contingency has been established.
The tap changer has movable parts by definition,
and thus also requires periodic maintenance.
Furthermore, as the tap changer has been sited as
the second highest component failure next to
windings in a report of 2007 [6]. Jagers [5] finds
that tap changer failures represent 22% of the
failed components.
It enhances the Transformer model proposed by
Geldenhuis [1] by including the tap changer.
Failure in oil-filled circuit breakers has often been
found to be catastrophic. The insulating oil properties
deteriorate and become flammable during arcing or
thermal runaway. Reports indicate that damage to
neighbouring equipment occurs and even 3rd party
damage.
This plant health indicator will suffice as a short term
measure.
Equipment maintenance strategies
Asset management principles have developed over
years with many studies focused on the different
maintenance strategies:
Replace it when it fails
Time based maintenance
Condition-based maintenance
Reliability Centred maintenance
For these strategies, a study of the equipment is
conducted upfront. This study is known as Failure
Modes and Effects Analysis (FMEA). Such an
initiative entails identifying each component in the
equipment and describing the function, as well as
understanding the impact of its failure with respect to
the overall equipment function. Typical maintenance
tasks include routine inspections or visual inspections;
minor services, routine testing of major servicing or a
combination of them. This process involves a
coordinated approach between:
Equipment Designers
Manufacturers
Subject-matter experts
Maintenance crews