Diagnostico De Cables

Workshop 2000, Alexandria, Virginia, 13 & 14 September 2000

paper No.: 3

THE ROLE OF DIAGNOSTIC TESTING AND MONITORING IN
TRANSMISSION CABLE MAINTENANCE PROGRAMS.
Gerry Sheerin P.Eng, EHV Power Inc. Markham, Ontario, Canada.

Abstract:
The structure of a traditional transmission
cable maintenance program is reviewed
together with a discussion of the business
perspective that nowmakes these practices
unattractive. Included is consideration of
changing expectations in the maintenance
environment, including the heightened
expectation that the maintenance engineer
can accurately predict the probability of
reliable cable operation.
A review of the eventual consequences of
unfocused maintenance is presented,
illustrated by several examples from past
experience. Alsoincluded are the effects of
changes in the cable system operational
environment and a discussion of the
measures necessary to protect system
integrity from external adverse effect.
The
application
of
the
“predictive
maintenance”
philosophy
to
cable
maintenance programs is discussed,
together with the impact this philosophy has
had on cable maintenance in the past two
decades.
Abroad overview of the results of a 22 year
cable oil sampling program is presented with
a discussion of the insights this program has
provided into cable condition.
A Variety of diagnostic tools, both intrusive
and non-intrusive, which have been used in
the past is reviewed. The role of some of
these techniques in complementing the

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moderntransmission maintenance program
is discussed.
Based on the severity of the consequences
of component failures, a priority list of
diagnostic needs is developed. A discussion
of the likelihood of the successful
incorporation of diagnostic tools to satisfy
these needs is provided. The potential for
successful incorporation of partial discharge
testing into the maintenance program is
discussed.1.0 Background
There have been many different approaches
to HV cable maintenance evident within the
electrical utility industry. Many of these were
driven by a belief that if anything went wrong
with a HV cable, it was necessary to have
crews available to immediately carry out
repairs. (In part this thinking is a reflection of
a strategy that had proven itself to be very
effective foroverhead transmission lines.
However, HV transmission cable repair has
little in common with an emergency repair
for overhead lines.)
Where cable crews have been established
as an insurance against extended repair
times, there has been a need to keep those
crews occupied during non-emergency
times. Many of the maintenance programs

3-1

that have emerged from this type of workenvironment have a unique “flavour”. This
has a lot to do with the recurring problem of
what tasks to assign to crews of cable
jointers on days when there is no jointing to
be done. As a result, a lot of maintenance
programs have elements such as “clean and
polish cable termination insulators” and
carry out annual overhauls repeated at
regular intervals.
This is not a criticism of the desire tomaintain H V cable termination insulators
free of contamination or to have confidence
in the reliable operation of a pumping plant.
Rather, it is recognition there is a basic
incompatibility between maintaining an “in
house” emergency repair capability and
performing planned maintenance programs.
The “clean polish and check” school of HV
cable system maintenance had as it’s major
benefit acomfort zone that if anything went
wrong, the resources were available to fix it
while in the meantime something was
always being done to “keep the system
running”.
A “pesky” outsider with a business
background might suggest that a proper test
of the value of this approach would be the
degree to which a trend toward a reduced
frequency of emergencies in the HV cable
system has...