KLF Loss-of-Field Relay
41-748P
3
between the R and L lead. The actual per unit values
which appear on the tap plate between taps are
0,.03,.06, and.06.
The auto transformer makes it possible to expand the
basic ranges of the long and the short reach com-
pensators by a multiplier of
. Any relay ohm set-
ting can be made within
±
1.5 percent from 2.08
ohms to 56 ohms for the long reach and from 0 ohms
to 18 ohms for the short reach.
2.3 IMPEDANCE TRIPPING UNIT
The impedance unit is a four-pole induction-cylinder
type unit. The operating torque of the unit is propor-
tional to the product of the voltage quantities applied
to the unit and the sine of the phase angle between
the applied voltages. The direction of the torque so
produced depends on the impedance phasor seen
by the relay with respect to its characteristic circle.
Mechanically, the cylinder unit is composed of four
basic components: a die-cast aluminum frame, an
electromagnet, a moving element assembly, and a
molded bridge. The frame serves as a mounting
structure for the magnetic core. The magnetic core
which houses the lower pin bearing is secured to the
frame by a locking nut. The bearing can be replaced,
if necessary, without having to remove the magnetic
core from the frame.
The electromagnet has two sets of two series con-
nected coils mounted diametrically opposite one
another to excite each set of poles. Locating pins on
the electromagnet are used to accurately position the
lower pin bearing, which is mounted on the frame,
with respect to the upper pin bearing, which is
threaded into the bridge. The electromagnet is
secured to the frame by four mounting screws.
The moving element assembly consists of a spiral
spring, contact carrying member, and an aluminum
cylinder assembled to a molded hub which holds the
shaft. The hub to which the moving contact arm is
clamped has a wedge-and-cam construction, to pro-
vide low-bounce contact action. A casual inspection
of the assembly might lead one to think that the con-
tact arm bracket does not clamp on the hub as tightly
as it should. However, this adjustment is accurately
made at the factory and is locked in place with a lock
nut and should not be changed. Optimum contact
action is obtained when a force of 4 to 10 grams
pressure applied to the face of the moving contact
will make the arm slip from the condition of reset to
the point where the clamp projection begins to ride
up on the wedge. The free travel can vary between
15 and 20
°
.
The shaft has removable top and bottom jewel bear-
ing. 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 mag-
netic core. The stops are an integral part of the
bridge.
The bridge is secured to the electromagnet and
frame by two (2) mounting screws. In addition to
holding the upper pin bearing, the bridge is used for
mounting the adjustable stationary contact housing.
This stationary contact has .002 to.006 inch follow
which is set at the factory by means of the adjusting
screw. After the adjustment is made the screw is
sealed in position with a material which flows around
the threads and then solidifies. The stationary con-
tact housing is held in position by a spring type
clamp. The spring adjuster is located on the under-
side of the bridge and is attached to the moving con-
tact arm by a spiral spring. The spring adjuster is also
held in place by a spring type clamp.
When the contacts close, the electrical connection is
made through the stationary contact housing clamp,
to the moving contact, through the spiral spring and
out to the spring adjuster clamp.
2.4 DIRECTIONAL UNIT
The directional unit is an induction-cylinder unit oper-
ating on the interaction between the polarizing circuit
flux and the operating circuit flux.
Mechanically, the directional unit is composed of the
same basic components as the distance unit: A die-
cast aluminum frame, an electromagnet, a moving
element assembly, and a molded bridge.
The electromagnet has two series-connected polariz-
ing coils mounted diametrically opposite one another;
two (2) series-connected operating coils mounted
diametrically opposite one another; two (2) magnetic
adjusting plugs; upper and lower adjusting plug clips,
and two (2) locating pins. The locating pins are used
to accurately position the lower pin bearing which is
mounted on the frame, with respect to the upper pin
bearing, which is threaded into the bridge. The elec-
tromagnet is secured to the frame by four mounting
screws.
The moving element assembly consists of a spiral
spring, contact carrying member, and an aluminum
cylinder assembled to a molded hub which holds the
shaft. The shaft has removable top and bottom jewel
bearings. The shaft rides between the bottom pin
S
1
M
±
--------------
