4.4. MAINTENANCE PROCEDURES
FOR MEDIUM-VOLTAGE OIL CIRCUIT
BREAKERS.- The following suggestions
are for use in conjunction with the
manufacturer's instruction books for the
maintenance of medium-voltage oil circuit
a. Check the condition, alignment,
and adjustment of the contacts.
b. Thoroughly clean the tank and
other parts which have been in con-
tact with the oil.
c. Test the dielectric strength of the oil
and filter or replace the oil if the
dielectric strength is less than 22 kV.
The oil should be filtered or replaced
whenever a visual inspection shows
an excessive amount of carbon, even
if the dielectric strength is
d. Check breaker and operating
mechanisms for loose hardware and
missing or broken cotter pins, retain-
ing rings, etc.
e. Adjust breaker as indicated in in-
f. Clean and lubricate operating
g. Before replacing the tank, check to
see there is no friction or binding that
would hinder the breaker's operation.
Also check the electrical operation.
Avoid operating the breaker any more
than necessary without oil in the tank
as it is designed to operate in oil and
mechanical damage can result from
excessive operation without it.
h. When replacing the tank and refill-
ing it with oil, be sure the gaskets are
undamaged and all nuts and valves
are tightened properly to prevent leak-
4.5. MAINTENANCE PROCEDURES
FOR MEDIUM-VOLTAGE VACUUM
CIRCUIT BREAKERS.- Direct inspection
of the primary contacts is not possible as
they are enclosed in vacuum containers.
The operating mechanisms are similar to
the breakers discussed earlier and may
be maintained in the same manner. The
following two maintenance checks are
suggested for the primary contacts:
a. Measuring the change in external
shaft position after a period of use
can indicate extent of contact erosion.
Consult the manufacturer's instruction
b. Condition of the vacuum can be
checked by a hi-pot test. Consult the
manufacturer's instruction book.
SECTION 5 - MAINTENANCE OF
HIGH-VOLTAGE CIRCUIT BREAKERS
5.1. FREQUENCY OF INSPECTIONS.-
Most manufacturers recommend com-
plate inspections, external and internal, at
intervals of from 6 to 12 months. Ex-
perience has shown that a considerable
expense is involved, some of which may
be unnecessary, in adhering to the
manufacturer's recommendations of in-
ternal inspections at 6- to 12-month
intervals. With proper external checks,
part of the expense, delay, and labor of
internal inspections may be avoided
without sacrifice of dependability.
5.1.1. Inspection schedule for new
breakers.- A temporary schedule of
frequent inspections is necessary
after the erection of new equipment,
(FIST 3-16 1/92)