GE IAC77A Instructions Manual page 15

GEK-34055
PERIODIC CHECKS AND ROUTINE MAINTENANCE
In view of
the
vital role of
protective
relays
in the
operation
of a power
system, it
is important
that
a periodic test
program
be
followed.
It
is recognized that
the interval between periodic checks
will vary
depending
upon environment,
type of
relay and the
user's
experience
with periodic
testing. Until
the
user has
accumulated
enough experience
to select the test
interval
best
suited to his
individual requirements,
it is suggested that the points
listed below
be checked at an interval of from one to two years.
These
tests are intended
to make sure
that the
relays have
not
deviated from their original setting.
If deviations are encountered,
the relay must be retested and serviced as described in this manual.
TIME-OVERCURRENT UNIT
1.
Perform
the Pickup Test
as described
in the
ACCEPTANCE
TESTS
section for the tap in service.
2. Perform
the Time Test
as described
in the
ACCEPTANCE TESTS
section.
INSTANTANEOUS UNIT
1.
Check that the Instantaneous Unit picks up at
the desired current
level, as outlined in the ACCEPTANCE TESTS section.
TARGET AND SEAL-IN UNIT
1. Check that the unit picks up at the values shown in Table XI.
2. Check that the units drops out at 30% or more of tap value.
CONTACT CLEANING
For cleaning relay contacts,
a flexible burnishing tool should be
used.
This consists
of a flexible
strip of metal
with
an etch—
roughened
surface,
resembling in
effect a
superfine file.
The
polishing
action is so
delicate that no
scratched are
left, yet it
will clean off any corrosion thoroughly and rapidly.
Its flexibility
ensures
the cleaning
of the actual
points of
contact. Do
not use
knives,
files, abrasive
paper or
cloth of any
kind to clean
relay
contacts.
SYSTEM TEST
Although this
Instruction Book
is primarily written to check
and
set the
IAC relay, overall
functional
tests to check
the
system
operation are
recommended
at intervals
based on the
customer's
experience.
15