41-748.31B
2
KLF-1 Loss-of-Field Relay
2 1 ) . T h e p r i m a r y o r c u r r e n t w i n d i n g o f t h e
long-reach-compensator T
A
has seven taps which
terminate at the block. They are marked 2.4, 3.16,
4.35, 5.93, 8.3, 11.5, 15.8. The primary winding of
the short-reach compensator T
C
also has seven taps
which terminate at this tap block. They are marked
0.0, 0.91, 1.27, 1.82, 2.55, 3.64, 5.1. A voltage is
induced in the secondary which is proportional to the
primary tap and current magnitude. This proportion-
ality is established by the cross sectional area of the
laminated steel core, the length of an air-gap which is
located in the center of the coil, and the tightness of
the laminations. All of these factors which influence
the secondary voltage proportionality have been pre-
cisely set at the factory. The clamps which hold the
laminations should not be disturbed by either tighten-
ing or loosening the clamp screws.
The secondary winding is connected in series with
the relay terminal voltage. Thus a voltage which is
proportional to the line current is added vectorially to
the relay terminal voltage.
2.2
AUTOTRANSFORMER
The autotransformer has three taps on its main wind-
ing, S, which are numbered 1, 2, and 3 on the tap
block. A tertiary winding M has four taps which may
be connected additively or subtractively to inversely
modify the S setting by any value from -15 to +15
percent in steps of 3 percent.
The sign of M is negative when the R lead is above
the L lead. M is positive when L is in a tap location
which is above the tap location of the R lead. The M
setting is determined by the sum of per unit values
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 autotransformer makes it possible to expand the
basic ranges of the long and short reach compensa-
tors by a multiplier of
. Any relay ohm setting
can be made within
±
1.5 percent from 2.08 ohms to
56 ohms for the long reach and from .79 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 vector 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 one-fourth of its total free
travel. Free travel is the angle through which the hub
will slip from the condition of reset to the point where
the clamp projection begins to ride up the wedge.
The free travel can vary between 15° to 20°.
The shaft has removable top and bottom jewel bear-
ings. 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 mounting screws. In addition to holding
the upper pin bearing, the bridge is used for mount-
ing 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 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
S
1
M
±
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