POWER SENSOR TR IP
GENERAL DESCRIPTION
All
AK-3 Type Air Circuit Breakers contain
Power Sensor Overcurrent Trip Devices. The
Power Sensor Trip functions with solid state
components with the exception of the Magnetic
Trip Device which is used to trip the breaker on
signal from the Power Sensor Unit. The Power
Sensor Overcurrent Trip Device consists of four
major components.
1 . The m�gnetic coils around the breaker con
ductors (Figure
14).
2.
The Power Supply which provides both the
tripping energy and the comparison basis for
overcurrent detection (Figure 1 5) .
3 .
The Power Sensor Unit with the various pick
up settings and time delay selection taps
(Figure 1 6).
4.
The Magnetic Trip Device which physically
trips the breaker (Figure 17).
In addition
to
the phase overcurrent protection,
a ground fault sensing feature may be provided.
The Ground Sensing Device works on the principle
that the instantaneous value of current flowing in
the three conductors (or; in four conductors on
four wire systems)
must add to zero unless
ground current is flowing.
Therefore,
if
the
electrical system is a four wire wye system with
the neutral grounded at the transformer, the fourth
sensing coil (Figure
1 8)
must be included on the
neutral conductor with its secondary combined
with the secondaries of the three phase sensors
which are mounted on the breaker. On Draw-out
breakers, the output of the external neutral sensor
must enter the breaker by a control disconnect
(Figure 19) which is mounted low and on the center
line on the back of the breaker. Refer to Figure
20 for Power Sensor Cabling diagram.
MAINTENANCE
When mal-functioning of the Power Sensor Trip
is indicated the trouble should be traced to one
or more of these four components involved, and
that component should be replaced as a unit. The
following steps should be taken to detect a mal
functioning unit.
Figure 14. (804 1 866} Magnetic Coils
2 5
www
. ElectricalPartManuals
. com
