ABB KA-4, Инструкция, Страница: 4 / 16

41-923.4M
4
shaft. The shaft has removable top and bottom jewel
bearings. The shaft rides between the bottom pin
bearing and the upper pin bearing with the 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 holding
the upper pin bearing, the bridge is used for mount-
ing the adjustable stationary contact housing. The
stationary contact housing is held in position by a
spring type clamp. The spring adjuster is located on
the underside of the bridge and is attached to the
moving contact arm by a spiral spring. The spring
adjuster is also held in place by a spring type clamp.
With the contacts closed, the electrical connection is
made through the stationary contact housing clamp,
to the moving contact, through the spiral spring out to
the spring adjuster clamp.
When the current in the overcurrent unit exceeds the
pick-up value the contacts open, allowing positive
potential to be applied to the carrier transmitter.
A transformer and current limiting reactor is used in
conjunction with the cylinder unit. The transformer
supplies one set of coils on the cylinder unit with volt-
age shifted by approximately 90° from the residual
current supplied directly to another set of coils. The
transformer and reactor are of the saturating type
which limits energy to the cylinder unit and reduces
the burden on the transmission line CT.
2.2. AUXILIARY UNITS
These are two solenoid-type contactor switches des-
ignated as CSP and CSG. The plunger of the contac-
tor switch has a circular conducting disc mounted on
its lower end and as the plunger travels upward, the
disc bridges three silver stationary contacts. The
CSP switch is energized by the operation of the sec-
ond zone or KD-10 distance relay, and the CSG
switch, by the operation of the directional and over-
current units of the KRD-4 ground relay. The contacts
of the two switches are connected in parallel as
shown in the internal schematic. The operation of
either of these switches connects the carrier control
circuit to negative to stop carrier, and energizes the
RRT operating coil of the receiver relay unit.
2.3. RECEIVER UNIT
The receiver unit consists of an armature and con-
tacts mounted on a leaf spring supported symmetri-
cally within a magnet frame. The armature rides in
the front air-gap of the frame with the contacts pro-
jecting outside. The poles of a permanent magnet
clamp directly to each side of the frame. Two adjust-
able shunts are located across the rear air-gaps.
These change the reluctance of the magnetic path as
shown in Figure 7 so as to force some of the flux thru
the moving armature which is fastened to the frame
midway between the two rear air gaps. Flux in the
armature polarizes it and creates a magnetic bias,
causing it to move towards either the left or right,
depending upon the adjustment.
Two stationary contact screws are mounted to the left
(front view) of the moving contact assembly and
adjusted for normally open contacts. These contacts
are designated, RRP and RRG, and are connected in
the phase and ground trip circuit respectively. These
contacts are operated by two concentric coils, RRT
and RRH, which are placed around the armature and
within the magnetic frame. RRT is the operating coil
and receives its energy from the local battery when
either CSP or CSG is closed. RRH is the holding coil
and receives its energy from the carrier transmitted
either from the local transmitter or the one at the end
of the line section. These two coils are connected in
oppose each other with the operating coil, RRT oper-
Figure 6. Typical Time Characteristics of carrier start over-
current unit of the type KA-4 Relay.