TYPE KAB HIGH IMPEDANCE
BUS DIFFERENTIAL RELAY
a \'Oltage limiting suppressor ( varistor), an adjust
able reactor and capacitors for completing a tuned
ci rcuit.
Overvoltage Unit V
The wltage uni t is a product i nduction cylinder
type unit operating on the interaction between th e
polarizing circuit flux and the operating circuit flux.
1\Iecllanically, the voltage unit is composed of
tour basic components: A di e-cast aluminum frame,
an electromagnet, a moving element assembly, and
a molded bridge.
The frame serves as the mounting structure for
the magnetic core. Tlw magnetic core which houses
thP 10\rer pin bearing is secured to the frame by a
locking nut. Th e bearing can be replaced, if neces
sary, without lla\'ing to remove the magnetic core
from the frame.
The electromagnet has two series-connected
polarizing coils mounted diam eterically opposite one
another; two series-connected operating coils mounted
diametrically opposite one another; two magnetic
adjusting plugs; upp er and lower adjusting plug
clips , and two locating pins . The locating pins are
used to accuratPly position the lower pin bParing,
which is threaded into the bridge. The electromagnet
is secured to th e frame by four mounting screws .
The rnodng element assembly consists o f a s piral
spring, contact carrying member, and an aluminum
cylinder ass embled to a molded hub which holds th e
shaft. The shaft has remO\'able top and bottom je wel
bearing. The shaft rides betwe en th e bottom Pin
bearing and the upper pin bearing with th e cylinder
rotating in an air gap formed by the electromagnet
and the magnetic core.
The bridge is secured to the electromagnet and
frame by two mounting screws. In addition to h olding
the upper pin bearing , the bridge is use d for mounting
the adjustable stationary contact housing. The sta
tionary contact housing is h eld in position by a
spring type clamp. The spring adjus ter is located on
the underside o f the bridge and is attache d to th e
moving contact arm by a spiral spring. The spring
adj uster is also held in place by a spring ty-pe clamp.
With the contacts close d, the electrical connec
tion is made through the stationary contact housing
2
clamp, to the mo ving contact. through th e s piral
spring out to the spring adjuster clamp.
Overcurrent Unit (IT)
The instantaneous unit is a small a-c operated
clapper type device. A magnetic armature, to which
leaf-spring mounted contacts are attached, is at
tached to the magnetic core upon energization of the
switch. When the switch close s , the moving contacts
bridge two stationary contacts completing the trip
circuit.
A core screw acces sible from the top of th e
switch provides th e adjustable pickup range .
The coil is tapped and the taps brought out to
a tap block. By means of the Hi and L o tap and the
adjustabl e core, a pickup range of
16
to
1
m ay be
obtained.
Varistor
The varistor is an non-linear voltage dependent
resistor. It consists of four discs of electrical grade
silicon carbide material mounted between cooling
fins and connected in serie s . They are as sembled
in an integral mechanical assembly and should not
be taken apart.
Reactor
The adj ustable reactor is an air-gap type h aving
two iron screws which are used at the factory to
tune the circuit for maximum current at rated fre
quency . This feature all ows retuning of th e circuit
in the event other parts of the circuit are replaced.
I ndicating Contactor Switch Unit (ICS)
The indicating contactor switch is a small d-e
operated clapper type device. A m agnetic armature ,
t o which leaf-spring mounted contacts are attached,
is attracted to the magnetic core upon energization
of the switch. When the switch closes, the moving
contacts bridge two stationary contacts, com pleting
the trip circuit. Also during this operation two fin
gers on the armature deflect a spring located on the
front of the s witch , which allows the operation
indicator target to drop. The target is reset from the
outside of the case by a push rod located at the
bottom of the cover.
The front spring, in addition to holding the target,
provide s restraint for the armature and thus control s
the pickup value o f th e switch.
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