9
information may be gained by
operating the breaker several times
after it is deenergized, measuring the
contact resistance of each pole
initially and after each operation.
operating the breaker several times
after it is deenergized, measuring the
contact resistance of each pole
initially and after each operation.
5.5.2. Influence of normal duty.- The
relative severity of duty imposed by
load switching, line dropping, and
fault interruptions depends upon the
type of circuit breaker involved. In
circuit breakers which employ an oil
blast generated by the power arc, the
interruption of light faults or the
interruption of line charging current
may cause more deterioration than
the interruption of heavy faults within
the rating of the breaker because of
low oil pressure. In some designs
using this basic principle of
interruption, distress at light
interrupting duty is minimized by
multiple breaks, rapid contact travel,
and turbulence of the oil caused by
movement of the contact and mech-
anism. In designs employing a
mechanically driven piston to supple-
ment the arc-driven oil blast, the
performance is more uniform. Still
more uniform performance is usually
yielded by designs which depend for
arc interruption upon an oil blast
driven by mechanical means. In the
latter types, erosion of the contacts
may appear only with heavy
interruptions. The mechanical
stresses which accompany heavy
interruptions are always more severe.
relative severity of duty imposed by
load switching, line dropping, and
fault interruptions depends upon the
type of circuit breaker involved. In
circuit breakers which employ an oil
blast generated by the power arc, the
interruption of light faults or the
interruption of line charging current
may cause more deterioration than
the interruption of heavy faults within
the rating of the breaker because of
low oil pressure. In some designs
using this basic principle of
interruption, distress at light
interrupting duty is minimized by
multiple breaks, rapid contact travel,
and turbulence of the oil caused by
movement of the contact and mech-
anism. In designs employing a
mechanically driven piston to supple-
ment the arc-driven oil blast, the
performance is more uniform. Still
more uniform performance is usually
yielded by designs which depend for
arc interruption upon an oil blast
driven by mechanical means. In the
latter types, erosion of the contacts
may appear only with heavy
interruptions. The mechanical
stresses which accompany heavy
interruptions are always more severe.
These variations of characteristic
performance among various designs
must be considered when judging the
need for maintenance from the
service records and when judging the
performance of a breaker from
evidence on inspection. Because of
these variations, the practice of
evaluating each fault interruption as
performance among various designs
must be considered when judging the
need for maintenance from the
service records and when judging the
performance of a breaker from
evidence on inspection. Because of
these variations, the practice of
evaluating each fault interruption as
equivalent to 100 no-load operations,
employed by some companies, is
necessarily very approximate
although it may be a useful guide in
the absence of any other information.
employed by some companies, is
necessarily very approximate
although it may be a useful guide in
the absence of any other information.
5.5.3. Influence of severe duty.-
Erosion of the contacts and damage
from severe mechanical stresses may
occur during large fault interruption.
The most reliable indication of the
stress to which a circuit breaker is
subjected during fault interruptions is
afforded by automatic oscillograph
records. Deterioration of the circuit
breaker may be assumed to be
proportional to the energy dissipated
in the breaker during the interruption.
T h e e n e r g y d i s s i p a t e d i s
approximately proportional to the
current and the duration of arcing;
that is, the time from parting of the
contacts to interruption of the current.
However, the parting of contacts is
not always evident on the
oscillograms, and it is sometimes
necessary to determine this from
indicated relay time and the known
time for breaker contacts to part.
Where automatic oscillograph records
are available, they may be as useful
in guiding oil circuit breaker
maintenance as in showing relay and
system performance.
Erosion of the contacts and damage
from severe mechanical stresses may
occur during large fault interruption.
The most reliable indication of the
stress to which a circuit breaker is
subjected during fault interruptions is
afforded by automatic oscillograph
records. Deterioration of the circuit
breaker may be assumed to be
proportional to the energy dissipated
in the breaker during the interruption.
T h e e n e r g y d i s s i p a t e d i s
approximately proportional to the
current and the duration of arcing;
that is, the time from parting of the
contacts to interruption of the current.
However, the parting of contacts is
not always evident on the
oscillograms, and it is sometimes
necessary to determine this from
indicated relay time and the known
time for breaker contacts to part.
Where automatic oscillograph records
are available, they may be as useful
in guiding oil circuit breaker
maintenance as in showing relay and
system performance.
Where automatic oscillographs are
not available, a very approximate, but
nevertheless useful, indication of fault
duty imposed on the circuit breakers
may be obtained from relay operation
targets and accompanying system
conditions. All such data should be
tabulated in the circuit breaker
maintenance file.
not available, a very approximate, but
nevertheless useful, indication of fault
duty imposed on the circuit breakers
may be obtained from relay operation
targets and accompanying system
conditions. All such data should be
tabulated in the circuit breaker
maintenance file.
(FIST 3-16 1/92)