ABB KLF-1 User manual

41-748.31B
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KLF-1 Loss-of-Field Relay
21). The primary or current winding of the
long-reach-compensator TAhas 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 TCalso 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
1M±
--------------

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KLF-1 Loss-of-Field Relay
a spiral spring. The spring adjuster is also held in
place by a spring type clamp.
When the contacts close, the electrical connection is
mounted on the frame, with respect to t he upper pin
bearing, which is made through the stationary con-
tact 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 impedance unit: A
die-cast aluminum frame, an electromagnet, a mov-
ing element assembly, and a molded bridge.
The electromagnet has two series-connected polariz-
ing coils mounted diametrically opposite one another;
two series-connected operating coils mounted dia-
metrically opposite one another; two magnetic
adjusting plugs; upper and lower adjusting plug clips,
and two 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 aluminum cyl-
inder 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
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 spiral spring. The spring
adjuster is also held in place by a spring type clamp.
2.5 UNDERVOLTAGE UNIT
The voltage unit is an induction-cylinder unit.
Mechanically, the voltage unit is composed like the
directional unit, of four components: A die cast alumi-
num frame, an electromagnet, a moving element
assembly, and a molded bridge.
The electromagnet has two pairs of voltage coils.
Each pair of diametrically opposed coils is connected
in series. In addition one pair is in series with an
adjustable series resistor. These sets are in parallel
as shown in Figure 3 (page 21). The adjustable resis-
tor serves not only to shift the phase angle of the one
flux with respect to the other to produce torque, but it
also provides a pick-up adjustment.
Otherwise the undervoltage unit is similar in its con-
struction to the directional unit.
2.6 SOLID STATE TIME DELAY CIRCUIT
The telephone relay (X) is energized through a solid
state time delay circuit (TD) as shown in Figure 3.
The solid state time delay circuit shown in Figure 14
(page 27) consists basically of an adjustable integrat-
ing RC circuit with quick reset. The RC circuit is
adjusted to provide the voltage level to trigger the
SCR through a multi-layer silicon switch. The SCR in
turn energizes the relay.
2.7 INDICATING CONTACTOR SWITCH UNIT
(ICS)
The dc indicating contactor switch is a small clap-
per-type device. A magnetic armature, to which
leaf-spring mounted contacts are attached, is
attracted to the magnetic core upon energization of
the switch. When the switch closes, the moving con-
tacts bridge two stationary contacts, completing the
trip circuit. Also during this operation two fingers on
the armature deflect a spring located on the front of
the switch, which allows the operation indicator tar-
get 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, pro-
vides restraint for the armature and thus controls the
pickup of the switch.
3.0 OPERATION
The relay is connected and applied to the system as
shown in Figure 4 (page 22). The directional unit
closes its contacts for lagging var flow into the
machine., Its zero torque line has been set at -13°
from the R-axis. Its primary function is to prevent
operation of the relay during external faults. The
impedance unit closes its contacts when, as a result
of reduction in excitation, the impedance of the
machine as viewed from its terminals is less than a
predetermined value. The operation of both the

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KLF-1 Loss-of-Field Relay
impedance and directional units energize the time
delay circuit which operates the X unit after .4 ±.05
seconds.
The operation of impedance, directional and X unit
sounds an alarm, and the additional operation of the
under voltage unit trips the machine. This time delay
is to insure positive contact coordination under all
possible operating conditions. During a seismic event
which exposes the relay to a ZPA level of 5.7g, the
operate time of the X unit may vary from .25 second
to 1.25 seconds due to bounce induced in the Z and
D contacts. During normal conditions, all contacts
are open.
3.1 PRINCIPLE OF IMPEDANCE UNIT OPERA-
TION
The impedance unit is an induction cylinder unit hav-
ing directional characteristics. Operation depends on
the phase relationship between magnetic fluxes in
the poles of the electromagnet.
One set of opposite poles, designated as the operat-
ing poles are energized by voltage VAG modified by a
voltage derived from the long reach compensator TA.
The other set of poles (polarizing) are energized by
the same voltage VAG except modified by a voltage
derived from the short reach compensator TC: The
flux in the polarizing pole is so adjusted that the unit
closes its contacts whenever flux in the operating set
of poles leads the flux in the polarizing set.
Reach of the impedance unit is determined by com-
pensators TAand TCas modified by autotransformer
settings. Compensators TAand TCare designed
so that its mutual impedance ZAor ZChas known
and adjustable values as described below under
CHARACTERISTICS and SETTINGS. The mutual
impedance of a compensator is defined here as
the ratio of secondary induced voltage to primary
current and is equal to T. Each secondary com-
pensator voltage is in series with voltage VAG.
Compensator voltages are equal to IAZAfor long
reach compensator and IAZCfor short reach com-
pensator, where I, is the relay current.
Figure 5 (page 23) shows how the compensation
voltages IAZAand IAZCinfluence the R-X circle.
Note that ZAindependently determines the “long
reach”, while ZCindependently fixes the “short
reach”. With the reversing links in the normal posi-
tion (+ZC) the circle includes the origin; with the
opposite link position (-ZC) the circle misses the
origin. The following paragraphs explain this com-
pensator action.
Referring to Figure 6 (page 23) note that XCand
CCcause the polarizing voltage to be shifted 90°in
the leading direction. Thus, when the current is
zero, polarizing voltage VPOL leads the operating
voltage VOP by 90°, as shown in Figure 6(a). This
relation produces restraining torque. To illustrate
how ZAfixes the long reach, assume a relay cur-
rent which leads VAG by 90°and of sufficient mag-
nitude to operate the relay. This means the
apparent impedance is along the -X axis. Note in
Figure 6(b) that the ZAcompensation reverses the
operating voltage phase position. The relay bal-
ances when this voltage is zero. Note that this bal-
ance is unaffected by the ZCcompensation, since
this compensation merely increases the size of
VPOL.
For lagging current conditions note in Figure 6(c)
how VPOL is reversed by the ZCcompensation. In
this case ZAcompensation has no effect on the
balance point. This explains why the short reach
point is fixed independently by ZC.
Figure 6 (page 23) assumes that +ZCis positive
(circle includes origin). If the current coil link is
reversed, the compensation becomes -ZC. In Fig-
ure 6(b) this change would result in, VPOL being
reduced rather than increased by the compensa-
tion. As the current increases VPOL will finally be
reversed, re-establishing restraining torque. Thus,
the current need not reverse in order to obtain a
“short-reach”balance point. Instead the apparent
impedance need only move towards the origin in
the -X region to find the balance point. Therefore,
the circle does not include the origin with a
reversed link position.
4.0 CHARACTERISTICS
The type KLF-1 relay is available in one range. Long
Reach is 2.08 to 56 ohms. Short Reach is 0.79 to
18.0 ohms.
4.1 IMPEDANCE UNIT
The impedance unit can be set to have characteristic
circles that pass through the origin, include it, or
exclude it, as shown in Figure 5 (page 23).
The ZAand ZCvalues are determined by compensa-
tor settings and modified by autotransformer settings
S, L, and R. The impedance settings in ohms reach
can be made for any value from 2.08 to 56 ohms for
ZA, and from 0.79 ohm to 18 ohms for ZCin steps of
3 percent.

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KLF-1 Loss-of-Field Relay
The taps are marked as follows:
4.2 DIRECTIONAL UNIT
This unit is designed for potential polarization with an
internal phase shifter, so that maximum torque
occurs when the operating current leads the polariz-
ing voltage by 43 degrees. The minimum pickup has
been set by the spring tension to be approximately 1
volt and 5 ampere at maximum torque angle.
4.3 UNDERVOLTAGE UNIT
The undervoltage unit is designed to close its con-
tacts when the voltage is lower than the set value.
The undervoltage unit is energized with VPH-N. The
contacts can be adjusted to close over the range of
60 to 100 percent of normal system voltage. The
actual range of adjustment is 40 to 70 VL-N for relays
rated 69 Vac and 70-120 VL-N for relays rated 120
Vac. The dropout ratio of the unit is 98 percent or
higher.
4.4 TRIP CIRCUIT
The main contacts will safely close 30 amperes at
250 volts dc and the seal-in contacts of the indicating
contactor switch will safely carry this current long
enough to trip a circuit breaker.
4.5 TRIP CIRCUIT CONSTANT
Indicating Contactor Switch (ICS) Coil
4.6 BURDEN
4.7 THERMAL RATINGS
Potential: 75 volts (L-N) continuous (for relays rated
69 Vac)
132 volts (L-N) continuous (for relays rated
120 Vac)
Current: 8 amperes continuous
200 amperes for 1 second
5.0 SETTING CALCULATIONS
5.1 GENERAL SETTING RECOMMENDATIONS
The KLF-1 relay may be applied as a single-zone
device, or two relays may be used to provide
two-zone protection. The single-zone setting may be
fully offset (Zone-1) or may include the origin
(Zone-2). The two-zone application would require a
Zone-1 KLF-1 and a Zone-2 KLF-1, approximately
equivalent to two-zone step-distance line protection.
A generalized external schematic, which is applica-
ble to either Zone-1 or Zone-2 relays is shown in Fig-
ure 10 (page 25). The recommended settings and
relative advantages of these various configurations
are summarized in Table 1.
TA
2.4 3.16 4.35 5.93 8.3 11.5 15.8
TC
0.0 0.91 1.27 1.82 2.55 3.64 5.1
(SA, SC)
123
Ampere Pickup Ohms dc Resistance
0.2
1.0
2.0
8.5
0.37
0.10
MAMC ,()
values between taps .03, .06, .06±
---------------------------------------------------------------------------------------------
Current at 5 Amps
TA& TC
Settings
VA Angle of lag
60 Hz 50 Hz 60 Hz 50 Hz
Max. 12.05 10.6 58°53°
Min. 4.17 3.94 36°31°
Potential at 69 Volts
(Phase-to-Ground)
Phase 1 VA Angle of lag 60 Hz 50 Hz 60 Hz 50 Hz
S = 1
S = 2
S = 3
6.1
1.5
0.7
6.1
1.5
0.7
9°
9°
9°
7.5°
7.5°
7.5°
Phase 2 3.18 2.9 48°43°
Phase 3 2.76 2.55 43°38°
DC Circuit
Rating Watts @ Rated
125
250 3.9 7.8

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KLF-1 Loss-of-Field Relay
The single-zone and two-zone setting recommenda-
tions are modified when two or more machines are
bussed at the machine terminals. The voltage and
time delay considerations are treated in detail in
other sections of this leaflet. The recommended set-
tings are outlined in Table 2.
5.2 IMPEDANCE UNIT
Set the impedance unit to operate before the
steady-state stability limit is exceeded. Also, to allow
maximum output without an alarm, set the imped-
ance unit to allow the machine to operate at maxi-
mum hydrogen pressure and 0.95 per unit voltage
(lowest voltage for which the capability curve
applies). Where the maximum capability of the
machine cannot be realized without exceeding the
steady-state stability limit, set the impedance unit to
operate before the steady-state limit is exceeded.
Capability curves similar to Figure 7 (page 23) are
obtained from the generator manufacturer.
To determine the desired setting convert the capabil-
ity curve of Figure 7 to the impedance curve of Figure
8, by calculating where VTis the per unit
terminal voltage and (kVA)Cis the per unit output.
The angle of each point on the impedance curve is
the same angle as the corresponding point on the
capability curve.
For example, from Figure 7, an output of 0.6 per unit
kW on the 30# H2curve is -0.4 per unit reactive kVA.
Therefore,
per unit
and,
Converting to the impedance curve:
per unit
Since the angle remains the same, the impedance
plot conversion is:
, as shown in Figure 8 (page 23).
Continue this process with other points from curves
such as those of Figure 7 (page 23) until a complete
curve like that of Figure 8 (page 23) is obtained.
After plotting the steady-state stability limit and the
machine capability curves on the R-X diagram, plot
the impedance unit circle between the stability limit
and the capability curve. (Note in Figure 8 (page 23)
that the relay circle cannot be plotted within the 60# -
VT= 0.95 curve, since the machine is beyond the
steady-state stability limit for these conditions.) This
plot defines the desired reach ZAand radius R of the
relay circle. Then use the following procedure to
select tap settings.
where
Zbase = one per unit primary ohms/as seen
from the relay
kV = rated phase-to-phase voltage of
the machine.
kVA = rated kVA of the machine.
RC= the current transformer ratio.
RV= the potential transformer ratio.
The actual settings, ZAand ZCare:
ZA=(Z
Aper unit) x (Zbase)
ZC=(Z
Cper unit) x (Zbase)
=(2R-Z
A) x (Zbase)
where R = radius of circle in per unit.
The tap-plate settings are made according to equa-
tions:
(5)
where:
T = compensator tap value
S = autotransformer primary tap value
M = autotransformer secondary tap value
(M is a per-unit value determined by taking the sum
of the values between the L and R leads. The sign is
positive when L is above R and acts to lower the Z
setting. The sign is negative when R is above L and
acts to raise the Z setting).
The following procedure should be followed to obtain
an optimum setting of the relay:
VT2
kVA()
C
--------------------
kVA()
C0.6()
20.4–()
2
+0.721==
Θtan 1–0.4–
0.6
-----------

33.6°–==
ZVT2
kVA()
C
-------------------1.02
0.721
---------------1.39
===
Z1.39 33.6°–∠=
Zbase 1000 kV()
2RC
kVA()RV
------------------------------------ohms
=
ZAor ZC
()
TS
1M±
--------------
=

41-748.31B
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KLF-1 Loss-of-Field Relay
1. Select the lowest tap S which gives a product
of 18.6SAgreater than desired ZAand a
product of 6SCgreater than desired ZC.
2. Select a value of M that will most nearly
make it equal to: .
If the sign is negative, then the M taps are connected
with the R lead above the L lead to raise the setting.
5.3 SAMPLE CALCULATIONS
Assume that a KLF-1 relay is to be applied to the fol-
lowing machine:
3-phase, 60 cycles, 3600 rpm, 18 kV, rated at 0.9 pf,
183,500 kVA at 45# H2.
RC= 1400/1 RV= 150/1
If the recommended setting from Figure 8 (page 23)
is used:
The relay circle needed for a particular set of
machine capability curves may be obtained by trial
and error using a compass. The offset and radius of
the relay circle in Figure 8 were drawn by this
method.
ZAper unit = 1.68
ZCper unit = 2R -ZA= 2 x 0.94 -1.68 = 0.20
(1)
= 16.45 ohms
(2)
= 27.6 ohms
(3)
= 3.29 ohms
To set ZA= 27.6 ohms
Step 1:ThelowestS
Atap for 18.6 SAgreater than
ZA= 27.6 is 2. Set SAin tap 2.
Step 2:T
Anearest to = 13.8 is TA= 15.8.
Set TA in 15.8 tap.
Step 3: =
1.145 -1 = + .145
Set M = + .15. Place R lead in 0, L lead in upper .06.
The relay setting is now:
Actual
This is 99.7% of the desired setting.
To set ZC= 3.29 ohms:
Step 1: The lowest SCtap for 6SCgreater than
3.29 is SC= 1
Set SC= 1
Step 2:T
Cnearest to
Set TCin 3.64 tap.
Step 3:
= 1.107 -1 = +.107
Hence, the nearest MCvalue is +.12. Now set R lead
in 0.03 tap and L lead in the upper .06 tap.
(Since MChas plus sign, lead L must be over R).
Then, ohms, or
98.8% of the desired value.
5.4 UNDERVOLTAGE UNIT
A. The undervoltage unit is usually set to a value
corresponding to the minimum safe system volt-
age for stability. The voltage depends on many
factors, but is usually between 70 and 80 percent
of normal system voltage. The undervoltage unit
is set at the factory for 77 percent of normal sys-
tem voltage, or 53 volts line-neutral for relays
rated 69 Vac and 90 Vac for relays rated 120
Vac.
MTS
Z
--------1–=
Zbase 1000 kV()
2RC
(kVA)RV
------------------------------------1000 18
()×21400×
183 500 150×,
------------------------------------------------------==
ZAZAper unit()Zbase
()1.68()16.45()==
ZCZCper unit()Zbase
()0.20()16.45()==
27.6
2
-----------
MATASA
Z
------------- 1–=15.8 2×
27.6
---------------------1
–
ZATASA
1M±
-------------- 15.8 2
×
10.15+
---------------------31.6
1.15
----------- 27.5
== ==
3.29
1
----------- 3.29 is 3.64
=
MCTCSC
ZC
--------------1–3.64 1×
3.29
---------------------1
–==
ZCTCSC
1MC +()
-----------------------3.64 1
×
1.12
·
+
---------------------3.25===

41-748.31B
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KLF-1 Loss-of-Field Relay
B. In applications where multiple units are con-
nected to the same bus, loss-of-field of one unit
may not depress the bus voltage to the point
where the undervoltage unit will operate if it has
the standard setting. The following recommenda-
tions should be considered:
1. For cross-compound turbine generator appli-
cations, the dropout (contact closure of
“back”contact of voltage unit, i.e., the con-
tact which is in the trip circuit and is shown
closed on schematic) voltage of the under-
voltage unit should be set for 58 VL-N (equiv-
alent to 100 VL-L).
2. For water wheel generator applications, with
multiple machines tied to a common bus, the
dropout voltage of the undervoltage unit
should be set for 58 VL-N. (Equivalent to 100
VL-L.)
3. For all applications where the alarm function
is not to be used, the undervoltage unit con-
tact should be short circuited by means of a
jumper wire.
4. For industrial applications, with two or more
generators on the same bus, the undervolt-
age unit contact should be short circuited
and the alarm circuit not used.
5. For small synchronous condenser and large
motor applications, the undervoltage unit
contact should, in general, be short circuited
and the alarm circuit not used. In general
cases the machine may be treated as in 2,
above, where knowledge exist of expected
undervoltage level.
6. For gas turbine units, with high generator
impedance, the undervoltage unit may not
operate on loss-of-field. For these applica-
tions the undervoltage contacts should be
short circuited.
In cases where each generator is equipped
with its own transformer (unit connected) the
standard factory setting of 53 VL-N (corre-
sponding to 92.5 VL-L), or 90 VL-N for relays
rated 120 V, is usually satisfactory for the
undervoltage unit. It should operate at a level
commensurate with the minimum safe volt-
age for system stability.
NOTE: An electrical check of this particular set-
ting is outlined in this instruction leaflet,
under the heading “Acceptance Check”.
6.0 TIME DELAY CONSIDERATIONS
It may be conservatively stated that the rotor struc-
ture and stator heating, as a result of a shorted field
can be tolerated for 10 seconds on a conduc-
tor-cooled machine and 25 seconds for a conven-
tional machine. This time may be as low as 5
seconds for an open field (as opposed to a field
closed through a field discharged resistor on an
exciter armature) and as high as one minute where
the concern is protection of an adjacent tandem com-
pound unit against partial loss-of-excitation in the
faulted machine.
In view of the above considerations, it is often desir-
able to use an external timer in conjunction with the
KLF-1 Relay. The following examples are applica-
tions where an external timer would be desirable:
1. Cross-compound units, with undervoltage
unit setting of 58 volts VL-N (equivalent to
100 VL-L), should use an external timer to
assure tripping before thermal damage can
result. The timer is energized at the alarm
output and should be set for 10 seconds for
a cross-compound conductor cooled
machine. For a conventionally cooled
cross-compound machine, the external timer
should be set for 25 seconds. As an alterna-
tive to this, the KLF-1 with shorted
under-voltage contacts may be applied and
the alarm feature not used. With this
arrangement, tripping takes place after the
0.4 seconds time delay provided by the X
unit in the KLF-1 relay.
2. Machines connected to a common high volt-
age bus may be protected against partial
loss of voltage due to loss-of-excitation in an
adjacent machine by using a one-minute
timer driven by the alarm output of the
loss-of-field relay.
3. In some critical applications 2-zone
loss-of-field protection may be desirable. In
this case, the zone-1 KLF-1 impedance cir-
cle should be small and fully offset in the
negative reactance region. The long-reach
should be set above to synchronous reac-

41-748.31B
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KLF-1 Loss-of-Field Relay
tance, Xd. The short-reach should be set
equal to one-half transient reactance, Xd/2.
The trip circuit should be energized directly,
with no time delay. The alarm circuit should
operate a timer which may be set from 0.4 to
1.0 seconds, depending on use preference.
If the condition persists, this timer permits
tripping.
The second-zone KLF-1 may be set with a
larger impedance characteristic and will
detect partial loss-of-field conditions. A typi-
cal setting would be to just allow the machine
to operate at maximum hydrogen pressure
and .95 per unit voltage. If a low voltage con-
dition occurs, it is recommended that tripping
be accomplished through a timer set for 0.6
seconds. Added to the X unit dropout time of
0.4 seconds, this gives an overall time of 1.0
second. If the voltage is maintained, then the
alarm circuit should start a “last ditch”timer.
This timer may be set anywhere from 10 sec-
onds to one minute, depending on machine
type and user preference.
7.0 SETTING THE RELAY
The type KLF-1 relay requires a setting for each of
the two compensators TAand TC, for each of the two
auto-transformers primaries SAand SC, and for the
undervoltage unit.
Table 1:
RECOMMENDED SETTINGS FOR KLF-1 RELAY
ZONE 1 (ALONE) ZONE 2 (ALONE) BOTH ZONE 1 &
ZONE 2
IMPEDANCE SETTING See Figure 11 (page 25) See Figure 12 (page 26) See Figure 11 & 12
VOLTAGE SETTING (a) Contact shorted or (b) Set at 80% for security 80% Zone 1 voltage contact shorted with Zone 2 set
at 80%
TD-1 1/4 to 1 sec
(1 sec preferred) 1/4 to 1 sec (1 sec preferred) Zone 1 timer = 1/4 sec Zone 2 timer = 1 sec
TD-2 Not required for (a) above.
(b) For above use 1 min. 1 min. 1 min.
ADVANTAGES
Less sensitive to
stable system swings 1) More sensitive to LOF condition
2) Can operate on partial LOF
3) Provide alarm features for
manual operation
(1) Same as 1), 2) and 3)
at left.
(2) Provides back-up
protection
Table 2:
SPECIAL SETTINGS FOR MULTI MACHINES BUSSED AT MACHINE TERMINALS
ZONE 1 (ALONE) ZONE 2 (ALONE) BOTH ZONE 1 & ZONE 2
IMPEDANCE SETTING See Figure 11 (page 25) See Figure 12 (page 26) See Figure 11 & 12
VOLTAGE SETTING (a) Contact shorted or
(b) Set at 87% for security 87% Zone 1 voltage contact
shorted with Zone 2 set at 87%
TD-1 1/4 to 1 sec
(1 sec preferred) 1/4 to 1 sec (1 sec preferred) Zone 1 timer = 1/4 sec Zone 2 timer = 1 sec
TD-2
Not required for
(a) above
(b) for above use 10 sec
for cond. cooled, 25
sec for conv. cooled
10 sec for cond. cooled.
25 sec for conv. cooled. 10 sec for cond. cooled 25 sec for conv. cooled

41-748.31B
10
KLF-1 Loss-of-Field Relay
7.1 COMPENSATOR (TAAND TC)
Each set of compensator taps terminates in inserts
which are grouped on a socket and form approxi-
mately three-quarters of a circle around a center
insert. This is the common connection for all taps.
Electrical connections between common insert and
tap inserts are made with a link. That is held in place
with two connector screws, one in the common and
one in the tap.
A compensator tap setting is made by loosening the
connector screw in the center. Remove the connec-
tor screw in the tap end of the link, swing the link
around until it is in position over the insert for the
desired tap setting, replace the connector screw to
bind the link to this insert, and retighten the connec-
tor screw in the center. Since the link and connector
screws carry operating current, be sure that the
screws are turned to bind snugly. DO NOT OVER-
TIGHTEN.
Compensator TCrequires an additional setting for
including or excluding the origin of R-X diagram from
the impedance unit characteristic. If the desired char-
acteristic is similar to that shown on Figure 5(b)
(page 23). The links should be set vertically in the
+TCarrow direction. If a characteristic similar to that
shown in Figure 5(c) is desired, set links horizontally
in the -TCarrow direction.
7.2 AUTOTRANSFORMER PRIMARY
(SAAND SC)
Primary tap connections are made through a single
lead for each transformer. The lead comes out of the
tap plate through a small hole located just below the
taps and is held in place on the proper tap by a con-
nector screw.
An S setting is made by removing the connector
screw, placing the connector in position over the
insert of the desired setting, replacing and tightening
the connector screw. The connector should never
make electrical contact with more than one tap at a
time.
7.3 AUTOTRANSFORMER SECONDARY
(MAAND SC)
Secondary tap connections are made through two
leads identified as L and R for each transformer.
These leads come out of the tap plate each through a
small hole, one on each side of the vertical row of M
tap inserts. The lead connectors are held in place on
the proper tap by connector screws.
Values for which an M setting can be made are from
-.15 to +.15 in steps of .03. The value of a setting is
the sum of the numbers that are crossed when going
from the R lead position to the L lead position. The
sign of the M value is determined by which lead is in
the higher position on the tap plate. The sign is posi-
tive (+) if the L lead is higher and negative (-) if the R
lead is higher.
An M setting may be made in the following manner:
Remove the connector screws so that the L and R
leads are free. Determine from the Table 3 (page
10). The desired M value and tap positions. Neither
lead connector should make electrical contact with
more than one tap at a time.
7.4 INDICATING CONTACTOR SWITCH (ICS)
There are no settings to make on the indicating con-
tactor switch (ICS).
7.5 UNDERVOLTAGE UNIT
The voltage unit is calibrated to close its contact
when the applied voltage is reduced to 53 volts. The
voltage unit can be set to close its contacts from 40
volts to 70 volts by adjusting the resistor located in
the rear, second from the bottom (RV). The spiral
spring is not disturbed when making any setting other
than the calibrated setting of 53 volts.
7.6 DIRECTIONAL SETTING
There is no setting to be made on directional unit.
8.0 INSTALLATION
The relays should be mounted on switchboard pan-
els or their equivalent in a location free from dirt,
moisture, excessive vibration, and heat. Mount the
relay vertically by means of the four mounting holes
on the flange for semi-flush mounting. The mounting
Table 3: TABULATED SETTINGS
Z M L Lead R Lead
0.87 TS
0.89 TS
0.92 TS
0.94 TS
0.97 TS
+.15
+.12
+.09
+.06
+.03
Upper .06
Upper .06
Lower .06
Upper .06
.03
0
.03
0
Lower .06
0
TS 0 0 0
1.03TS
1.06 TS
1.1 TS
1.14 TS
1.18 TS
-.03
-.06
-.09
-.12
-.15
0
Lower .06
0
.03
0
.03
Upper .06
Lower .06
Upper .06
Upper .06

41-748.31B
11
KLF-1 Loss-of-Field Relay
screws may be utilized for grounding the relay. The
electrical connections may be made directly to the
terminals by means of screws for steel panel mount-
ing or the terminal studs furnished with the relay for
thick panel mounting. The terminal studs may be
easily removed or inserted by locking two nuts on the
stud and then turning the proper nut with a wrench.
For detailed FT case information refer to I.L. 41-076.
9.0 ADJUSTMENTS AND
MAINTENANCE - FOR RELAYS RATED
AT 69 VAC
The proper adjustments to insure correct operation of
this relay have been made at the factory. Upon
receipt of the relay, no customer adjustments,
other than those covered under “SETTINGS’, should
be required.
9.1 ACCEPTANCE CHECK
The following check is recommended to insure that
the relay is in proper working order:
Note:The relay should be energized for at least
one hour.
A. Impedance Unit (Z)
1. Connect the relay as shown in Figure 9
(page 24) with the switch in position 2 and
the trip circuit de-energized.
2. Make the following tap settings:
TA= 11.5 TC= 2.55
SA= 2 SC= 1
MA= -.03(R/L) MC= -.09 (R/L)
TClink in middle block should be set for +TC
direction (vertical).
This setting corresponds to ZA= 23.7 ohms
and ZC= 2.80 ohms.
Adjust the phase shifter for 90°current lag-
ging the voltage.
3. With the terminal voltage at 50 volts,
increase current until contacts just close.
This current should be within ±3% of 2.11
amp (2.05 - 2.20 amp).
4. Adjust phase shifter for 90°current leading
the voltage.
5. With the terminal voltage at 50 volts increase
current until contacts just close. This current
should be within ±3% of 17.9 amps, (17.3 -
18.5 amps).
Contact Gap –The gap between the station-
ary contact and moving contact with the
relay in de-energized position should be
approximately .040”.
B. Directional Unit Circuit (D)
1. Connect the relay as shown in Figure 9
(page 24), with the switch in position 1 and
the trip circuit de-energized.
2. With a terminal voltage of 1 volt and 5
amperes applied, turn the phase shifter to
43°(current leads voltage). The contacts
should be closed. This is the maximum
torque position.
3. Raise the voltage to 69 volts and vary the
phase shifter to obtain the two angles where
the moving contact just makes with the
left-hand contact. These two angles (where
torque reverses) should be where the current
leads the voltage by 313°and 133°, (±4°).
4. Contact Gap –The gap between the station-
ary contact and moving contact with the relay
in the de-energized position should be
approximately .020”.
C. Undervoltage Circuit
1. Connect the relay as shown in Figure 9, with
switch in position 2 and the trip circuit
de-energized.
2. Decrease the voltage until the contacts close
to the left. This value should be 53 ±3% volts.
D. Solid State Time Delay Circuit
Block the contacts of the Z unit closed. Apply 125
volts dc with positive at terminal 10 and negative
at terminal 3. Manually close the contacts of the
D unit. Using oscilloscope measure the time
delay by observing the voltage block waveform
between the relay terminal 3 (-) and terminal 1
(+). Operate time should be 0.4 ± .05 seconds.
Close the main relay contacts and pass sufficient
dc current through the trip circuit to close the
contacts of the ICS. This value of current should
not be greater than the particular ICS nameplate
rating. The indicator target should drop freely.

41-748.31B
12
KLF-1 Loss-of-Field Relay
Repeat above except pass 85% of ICS name-
plate rating current. Contacts should not pickup
and target should not drop.
9.1.1 Routine Maintenance
All contacts should be periodically cleaned. A contact
burnisher Style #182A836H01 is recommended for
this purpose. The use of abrasive material for clean-
ing contacts is not recommended, because of the
danger of embedding small particles in the face of
the soft silver and thus impairing the contacts.
9.2 REPAIR CALIBRATION
A. Autotransformer Check
Autotransformers may be checked for turns ratio
and polarity by applying ac voltage to terminals 4
and 5 and following the procedures outlined
below:
1. Set SAand SCon tap number 3. Set the “R”
leads of MAand MCall on 0.0 and discon-
nect the “L”leads. Adjust the voltage for 90
volts. Measure voltage from terminal 5 to the
tap #1 of SA. It should be 30 volts (±1 volt).
From terminal 5 to tap #2 of SAshould be 60
volts (±1 volt). The same procedure should
be followed for taps #1 and #2 of SC.
2. Set SAand SCon Tap #1 and adjust the volt-
age at the relay terminals for 100 volts. Mea-
sure voltage drop from terminals 5 to each of
the MA and MCtaps. This voltage should be
equal to 100 (±1 volt) plus the sum of values
between R and tap being measured. Exam-
ple 100 (1 + .03 + .06) = 109 volts (±1 volt).
Transformers that have an output different
from nominal by more than 1.0 volt probably
have been damaged and should be replaced.
B. Impedance Unit (Middle Unit) Calibration
Make following tap plate settings:
TA= 15.8; TC= 5.1
SC= SC= 1
Make MA= MC= -.15 settings:
“L”lead should be connected to the “0”insert “R”
lead should be connected to the upper “.06”
insert. (-.03 -.06 -.06 = -.15 between L & R).
For the most accurate calibration preheat relay
for at least an hour by energizing terminals 4, 5,
6, & 7 with 70 volts, phase-to-neutral or terminals
5, 6, 7 with 3-phase 120 volts phase-to-phase
voltages.
The links in the middle tap block should be set
for the + TCdirection (vertical)
1) Contact Gap Adjustment
The spring type pressure clamp holding the sta-
tionary contact in position should not be loos-
ened to make the necessary gap adjustments.
With moving contact in the opened position, i.e.
against right stop on bridge, screw in stationary
contact until both contacts just make (use neon
light for indication). Then screw the stationary
contact away from the moving contact 1-1/3 turn
for contact gap of .040”.
2) With relay de-energized adjust the restraint
spring so that contact arm just floats.
C. Impedance Characteristic Check
1) Maximum Torque Angle
Adjust the adjustable reactor for about 5 turns
out.
Applying 60 volts ac to terminals 5 and 4 and
passing 4.8 amperes, through the current circuit
turn the phase shifter until the moving contact
opens. Turn the phase shifter back (few degrees)
until contacts close. Note degrees. Continue to
turn the phase shifter until contact opens, then
swing phase shifter back until contact closes
again. Note degrees. The maximum torque angle
should be (±1°) computed as follows:
Degrees to Close Contacts at Left +
Degrees to Close Contacts at Right = 90°
Adjust reactor XCuntil the correct maximum
torque angle is obtained.
2) Sensitivity Adjustment
Using the connections of Figure 9 (page 24).
apply 5 volts at 90°leading, to terminals 4 and 5
pass .325 amperes through current circuit termi-
nals 9 and 8. The spiral spring is to be adjusted
2

41-748.31B
13
KLF-1 Loss-of-Field Relay
such that the contacts will just close. De-ener-
gize the relay. The moving contact should return
to open position against the right-hand stop.
3) Impedance Check
a. Adjust voltage to be 50 volts.
For current lagging 90°the impedance unit
should close its contacts at 2.60 - 2.76
amp. Reverse current leads, the imped-
ance unit should close its contacts 8.1 - 8.6
amperes.
b. Reverse the links in the middle tap block to
-TCposition (Horizontal). Apply current of
8.6 amps. The contacts should stay open.
Reverse current leads to original position.
The contacts should open when current is
increased above 8.1 amperes and
reduced below 2.8 Amps.
Set links back to +TCposition (vertical).
Change SAand SCto setting “2”. Keeping
voltage at 50 volts, 90°leading, check
pickup current. It should be 1.30 - 1.40
amperes. Now set the phase shifter so that
voltage lags the current by 90°. Impedance
unit should trip now at 4.05 - 4.3 amperes.
c. Change SA, SC= 3. Check pickup. It
should be 2.70 - 2.90. Reverse current
leads. Pickup should now be .87 - .93
amp.
D. Directional Unit (Top Unit)
1. Contact Gap Adjustment
The spring type pressure clamp holding the
stationary contact in position should not be
loosened to make the necessary gap adjust-
ments.
With moving contact in the open position,
i.e., against right stop on bridge, screw in
stationary contact until both contacts just
make. Then screw the stationary contact
away from the moving contact 3/4 of one turn
for a contact gap of .22”.
2. With relay de-energized adjust the restraint
spring so that contact arm just floats.
3. Maximum Torque Angle Check
With 50 volts and 5 amperes applied, vary
the phase shifter to obtain the two angles
where the moving contacts just close. These
two angles (where torque reverses) should
be where the current leads the voltage by
313°±4°and 133°±4°. Readjust the bottom
resistor located in the rear for correct read-
ing.
4. Sensitivity Adjustment
Apply 1.0 volt to terminals 4 and 6. Observ-
ing polarities as per schematic, apply 5
amperes current leading the voltage by 43°,
the spiral spring is to be adjusted such that
the contacts will just close. The spring type
clamp holding the spring adjuster should not
be loosened prior to rotating the spring
adjuster. The adjustment of the spring is
accomplished by rotating the spring adjuster
which is located on the underside of the
bridge. The spring adjuster has a notched
periphery so that a tool may be used to
rotate it. Plug Adjustment for Reversing of
Spurious Torques
a. Set TC= 0.0. Connect a heavy current
lead from TAcenter link to terminal 8.
b. Short circuit terminals 4 and 6.
c. Screw in both plugs as far as possible
prior to starting the adjustment.
d. Apply 80 amps only momentarily, and
the directional unit need not be cooled
during initial rough adjustment. But, the
directional unit should be cool when final
adjustment is made.
e. When relay contact closes to the left,
screw out the right-hand plug until spuri-
ous torque is reversed.
f. When plug adjustment is completed
check to see that there is no closing
torque when relay is energized with 40
amps and voltage terminals 4 and 6
short-circuited.
E. Undervoltage Unit (Lower Unit)
NOTE: The moving contact is in closed position
to the left when de-energized.

41-748.31B
14
KLF-1 Loss-of-Field Relay
1) Contact Gap Adjustments
a. L.H. (Normally Closed) Contact Adjustment
With the moving contact arm in the closed
position, against left-hand side of bridge,
screw the left-hand contact in to just touch
the moving contact (use neon light for indica-
tion) and then continue for one more com-
plete turn.
b. R.H. (Normally Open) Contact Adjustment
With moving contact arm against the left-
hand stationary contact, screw the right-hand
stationary contact until it just touches the
moving contact. Then back the right-hand
contact out two-thirds of one turn to give
0.020 inch contact gap.
2) Sensitivity Adjustment
a. Apply voltage to terminals 4 & 7. Connect
the brush lead of the adjustable resistor, RV,
that is located in the rear (second from the
bottom) to maximum. Adjust the spring so
that contacts make (to the left) at 40 volts.
The contact should open when unit is ener-
gized with 41 or more volts.
b. Relay is set for 53 volts. This is accom-
plished by lowering resistance value of RV
until contacts make at 53 volts and open
when unit is energized with 54 or more volts.
The spring should not be used for this set-
ting.
F. Indicating Contactor Switch (ICS)
Initially adjust unit on the pedestal so that arma-
ture fingers do not touch the yoke in the reset
position. (Viewed from top of switch between
cover and frame.) This can be done by loosening
the mounting screw in the molded pedestal and
moving the ICS in the downward position.
1. Contact Wipe –Adjust the stationary contact
so that both stationary contacts make with
the moving contacts simultaneously and
wipe 1/64”to 3/64”when the armature is
against the core.
2. Target –Manually raise the moving contacts
and check to see that the target drops at the
same time as the contacts make or up to
1/16”ahead. The cover may be removed and
the tab holding the target reformed slightly if
necessary. However, care should be exer-
cised so that the target will not drop with a
slight jar.
3. Pickup –The unit should pickup at 98% rat-
ing and not pickup at 85% of rating. If neces-
sary, the cover leaf springs may be adjusted.
To lower the pickup current use a tweezer or
similar tool and squeeze each leaf spring
approximately equal by applying the tweezer
between the leaf spring and the front surface
of the cover at the bottom of the lower win-
dow.
If the pickup is low, the front cover must be
removed and the leaf spring bent outward
equally.
G. Solid State Delay Circuit
Refer to Figure 14 (page 27) for the following
test.
a. Connect a jumper between the “D”contacts
(top unit) and connect a switch between the
D-contact and relay terminal 10.
b. Connect a scope probe, common and exter-
nal trigger to relay terminals 1, 3 and contact
“D”respectively.
c. Connect a rated dc power supply between
relay terminals 10 (+) and 3 (-).
d. Turn on the dc power supply and then turn
on the switch. The voltage at terminal 1
should jump from 0 to the rated voltage after
a time delay of 0.4 ± 10% seconds. A trimpot
on the PC board can be adjusted to obtain
the desired time delay from 0.3 to 0.5 sec-
onds.
H. Compensator Check
Accuracy of the mutual impedance T of the com-
pensators is set within very close tolerances at
factory and should not be changed under normal
conditions. The mutual impedance of the com-
pensators can be checked with accurate instru-
ments by the procedure outlined below:
1. Set TAon the 15.8 tap
TCon the 5.1 tap

41-748.31B
15
KLF-1 Loss-of-Field Relay
2. Disconnect the L-leads of sections MAand
MC.
3. Pass 10 amperes ac current in terminal 9
and out of terminal 8.
4. Measure the compensator voltage with an
accurate high resistance voltmeter (5000
ohms/volt).
5. Compensator A voltage should be checked
between lead LAand terminal 5.
a. For TA= 15.8 the voltage measured
should be 158 volts ±3%.
6. Compensator C voltage should be checked
between lead LCand terminal 5.
a. For TC= 5.1, the voltage should be 51
volts (±3%).
7. For all other taps the compensator voltage is
IT (±3%).
where I = relay current
T = tap setting.
10.0 ADJUSTMENTS AND
MAINTENANCE –FOR RELAYS RATED
AT 120 VAC
The proper adjustments to insure correct operation of
this relay have been made at the factory. Upon
receipt of the relay, no customer adjustments,
other than those covered under “SETTINGS”, should
be required.
10.1 ACCEPTANCE CHECK
The following check is recommended to insure that
the relay is in proper working order:
Note:The relay should be energized for at least
one hour.
A. Impedance Unit (Z)
1. Connect the relay as shown in Figure 9 (Dia-
gram of Test Connections for KLF-1 Relay
on page 24) with the switch in position 2 and
the trip circuit de-energized.
2. Make the following tap settings:
TA= 11.5 TC= 2.55
SA= 2 SC= 1
MA= -.03 (R/L) MC= -.09 (R/L)
The reversing links should be set for +TC
direction (vertical).
This setting corresponds to ZA= 23.7 and ZC
= 2.80 ohms.
Adjust the phase shifter for 90°current lag-
ging the voltage.
3. With the terminal voltage at 90 volts,
increase current until contacts just close.
This current should be within ±3% of 3.80
amp (3.686 - 3.914 amp).
4. Adjust phase shifter for 90°current leading
the voltage.
5. With the terminal voltage at 90 volts increase
current until contacts just close. This current
should be within ±3% of 32.14 amps, (31.18 -
33.11 amps).
Contact Gap –The gap between the station-
ary contact and moving contact with the
relay in de-energized position should be
approximately .040”.
B. Directional Unit Circuit (D)
1. Connect the relay as shown in Figure 9 (Dia-
gram of Test Connections for KLF-1 Relay
on page 24), with the switch in position 1 and
the trip circuit de-energized.
2. With a terminal voltage of 1 volt and 5
amperes applied, turn the phase shifter to
43°(current leads voltage). The contacts
should be closed. This is the maximum
torque position.
3. Raise the voltage to 120 volts and vary the
phase shifter to obtain the two angles where
the moving contact just makes with the
left-hand contact. These two angles (where
torque reverses) should be where the current
leads the voltage by 313°and 133°, (±4°).
4. Contact Gap –The gap between the station-
ary contact and moving contact with the relay
in de-energized position should be approxi-
mately .020”.
C. Undervoltage Circuit
1. Connect the relay as shown in Figure 9 (Dia-
gram of Test Connections for KLF-1 Relay
on page 24), with switch in position 2 and the
trip circuit de-energized.

41-748.31B
16
KLF-1 Loss-of-Field Relay
2. Decrease the voltage until the contacts close
to the left. This value should be 90 ±3% volts.
D. Solid State Time Delay Circuit
Block the contacts of the Z unit closed. Apply 125
volts dc with positive at terminal 10 and negative
at terminal 3. Manually close the contacts of the
D unit. Using oscilloscope measure the time
delay by observing the voltage block waveform
between the relay terminal 3 (-) and terminal 1
(+). Operate time should be 0.4 ± .05 second.
E. Indicating Contactor Switch (ICS)
Close the main relay contacts and pass sufficient
dc current through the trip circuit to close the
contacts of the ICS. This value of current should
not be greater than the particular ICS nameplate
rating. The indicator target should drop freely.
Repeat above except pass 85% of ICS name-
plate rating current. Contacts should not pickup
and target should not drop.
10.1.1 Routine Maintenance
All contacts should be periodically cleaned. A contact
burnisher Style #182A836H01 is recommended for
this purpose. The use of abrasive material for clean-
ing contacts is not recommended, because of the
danger of embedding small particles in the face of
the soft silver and thus impairing the contacts.
10.2 REPAIR CALIBRATION
A. Autotransformer Check
Autotransformers may be checked for turns ratio
and polarity by applying ac voltage to terminals 4
and 5 and following the procedures outlined below:
1. Set SAand SCon tap number 3. Set the “R”
leads of MAand MCall on 0.0 and discon-
nect the “L”leads. Adjust the voltage for 90
volts. Measure voltage from terminal 5 to the
tap #1 of SA. It should be 30 volts (±1). From
terminal 5 to tap #2 of SAshould be 60 volts.
The same procedure should be followed for
taps #1 and #2 of SC.
2. Set SAand SCon Tap #1 and adjust the volt-
age at the relay terminals for 100 volts. Mea-
sure voltage drop from terminals 5 to each of
the MA and MCtaps. This voltage should be
equal to 100 (±1) plus the sum of values
between R and tap being measured. Exam-
ple 100 (1 + .03 + .06) = 109 volts.
Transformers that have an output different
from nominal by more than 1.0 volt probably
have been damaged and should be replaced.
B. Impedance Unit (Middle Unit) Calibration
Make following tap plate settings:
TA= 15.8; TC= 5.1
SC= SC= 1
Make MA= MC= -.15 settings:
“L”lead should be connected to the “0”insert “R”
lead should be connected to the upper “.06”
insert. (-.03 -.06 -.06 = -.15 between L & R).
For the most accurate calibration preheat relay
for at least an hour by energizing terminals 4, 5,
6, & 7 with 70 volts, phase-to-neutral or terminals
5, 6, 7 with 3-phase 120 volts phase-to-phase
voltages.
The reversing links should be set for the + TC
direction (vertical).
1) Contact Gap Adjustment
The spring type pressure clamp holding the sta-
tionary contact in position should not be loos-
ened to make the necessary gap adjustments.
With moving contact in the opened position, i.e.
against right stop on bridge, screw in stationary
contact until both contacts just make (use neon
light for indication). Then screw the stationary
contact away from the moving contact 1-1/3 turn
for contact gap of .040”.
2) With relay de-energized adjust the restraint
spring so that contact arm just floats.
C. Impedance Characteristic Check
1) Maximum Torque Angle
Applying 100 volts ac to terminals 5 and 4 and
passing 7.8 amperes, through the current circuit
turn the phase shifter until the moving contact
opens. Turn the phase shifter back (few degrees)
until contacts close. Note degrees. Continue to
turn the phase shifter until contact opens, then
swing phase shifter back until contact closes
again. Note degrees. The maximum torque angle

41-748.31B
17
KLF-1 Loss-of-Field Relay
should be (±1°) computed as follows:
Degrees to Close Contacts at Left +
Degrees to Close Contacts at Right = 90°
Adjust resistor, RB, until the correct maxi-
mum-torque angle is obtained.
2) Sensitivity Adjustment
Using the connections of Figure 9 (Diagram of
Test Connections for KLF-1 Relay on page 24),
apply 10 volts ac 90°leading, to terminals 4 and
5 pass 0.63 amperes through current circuit ter-
minals 9 and 8. The spiral spring is to be
adjusted such that the contacts will just close.
De-energize the relay. The moving contact
should return to open position against the
right-hand stop.
3) Impedance Check
a. Adjust voltage to be 90 volts.
For current lagging 90°the impedance unit
should close its contacts at 4.68 - 4.98
amp. Reverse current leads, the imped-
ance unit should close its contacts 14.55 -
15.45 amperes.
b. Reverse the links in the middle tap block to
-TCposition (horizontal). Apply current of
15.45 amps. The contacts should stay
open. Reverse current leads to original
position. The contacts should open when
current is increased above 15.45 amperes
and reduced below 4.98 Amps.
Set links back to +TCposition (vertical).
Change SAand SCto setting “2”. Keeping
voltage at 69 volts, 90°leading check
pickup current. It should be 1.80 - 1.90
amperes. Now set the phase shifter so that
voltage lags the current by 90°. Impedance
unit should trip now at 5.32 - 5.95
amperes.
c. Change SA, SC= 3. Check pickup. It
should be 3.68 - 3.96. Reverse current
leads. Pickup should now be 1.20 - 1.28
amp.
D. Directional Unit (Top Unit)
1. Contact Gap Adjustment
The spring type pressure clamp holding the
stationary contact in position should not be
loosened to make the necessary gap adjust-
ments.
With moving contact in the open position,
i.e., against right stop on bridge, screw in
stationary contact until both contacts just
make. Then screw the stationary contact
away from the moving contact 3/4 of one turn
for a contact gap of .22”.
2. With relay de-energized adjust the restraint
spring so that contact arm just floats.
3. Maximum Torque Angle Check
With 120 volts and 5 amperes applied, vary
the phase shifter to obtain the two angles
where the moving contacts just close. These
two angles (where torque reverses) should
be where the current leads the voltage by
313°± 4°and 133°±4°. Readjust the bottom
resistor located in the rear for correct read-
ing.
4. Sensitivity Adjustment
Apply 1.0 volt to terminals 4 and 6. Observ-
ing polarities as per schematic, apply 5
amperes current leading the voltage by 43°,
the spiral spring is to be adjusted such that
the contacts will just close. The spring type
clamp holding the spring adjuster should not
be loosened prior to rotating the spring
adjuster. The adjustment of the spring is
accomplished by rotating the spring adjuster
which is located on the underside of the
bridge. The spring adjuster has a notched
periphery so that a tool may be used to
rotate it.
5. Plug Adjustment for Reversing of Spurious
Torques
a. Set TC= 0.0. Connect a heavy current
lead from TAcenter link to terminal 8.
b. Short circuit terminals 4 and 6.
c. Screw in both plugs as far as possible
prior to starting the adjustment.
d. Apply 80 amps only momentarily, and
2

41-748.31B
18
KLF-1 Loss-of-Field Relay
the directional unit need not be cooled
during initial rough adjustment. But, the
directional unit should be cool when final
adjustment is made.
e. When relay contact closes to the left,
screw out the right-hand plug until spuri-
ous torque is reversed.
f. When plug adjustment is completed
check to see that there is no closing
torque when relay is energized with 40
amps and voltage terminals 4 and 6
short-circuited.
E. Undervoltage Unit (Lower Unit)
NOTE: The moving contact is in closed position
to the left when de-energized.
1) Contact Gap Adjustments
a. L.H. (Normally Closed) Contact Adjustment
With the moving contact arm in the closed
position, against left-hand side of bridge,
screw the left-hand contact in to just touch
the moving contact (use neon light for indica-
tion) and then continue for one more com-
plete turn.
b. R.H. (Normally Open) Contact Adjustment
With moving contact arm against the left-
hand stationary contact, screw the right-hand
stationary contact until it just touches the
moving contact. Then back the right-hand
contact out two-thirds of one turn to give
0.020 inch contact gap.
2) Sensitivity Adjustment
a. Apply voltage to terminals 4 & 7. Connect
the brush lead of the adjustable resistor,
RV, that is located in the rear (second from
the bottom) to maximum. Adjust the spring
so that contacts make (to the left) at 70
volts. The contact should open when unit
is energized with 71 or more volts.
b. Relay is set for 90 volts. This is accom-
plished by lowering resistance value of RV
until contacts make at 90 volts and open
when unit is energized with 91 or more
volts. The spring should not be used for
this setting.
F. Indicating Contactor Switch (ICS)
Initially adjust unit on the pedestal so that arma-
ture fingers do not touch the yoke in the reset
position. (Viewed from top of switch between
cover and frame.) This can be done by loosening
the mounting screw in the molded pedestal and
moving the ICS in the downward position.
1. Contact Wipe –Adjust the stationary contact
so that both stationary contacts make with
the moving contacts simultaneously and
wipe 1/64”to 3/64”when the armature is
against the core.
2. Target –Manually raise the moving contacts
and check to see that the target drops at the
same time as the contacts make or up to
1/16”ahead. The cover may be removed and
the tab holding the target reformed slightly if
necessary. However, care should be exer-
cised so that the target will not drop with a
slight jar.
3. Pickup –The unit should pickup at 98% rat-
ing and not pickup at 85% of rating. If neces-
sary, the cover leaf springs may be adjusted.
To lower the pickup current use a tweezer or
similar tool and squeeze each leaf spring
approximately equal by applying the tweezer
between the leaf spring and the front surface
of the cover at the bottom of the lower win-
dow.
4. If the pickup is low, the front cover must be
removed and the leaf spring bent outward
equally.
G. Solid State Time Delay Circuit
Refer to Figure 14 (page 27) for the following
test:
a. Connect a jumper between the “D”contacts
(top unit) and connect a switch between the
D-contact and relay terminal 10.
b. Connect a scope probe, common and exter-
nal trigger to relay terminals 1, 3 and contact
“D”respectively.
c. Connect a rated dc power supply between
relay terminals 10 (+) and 3 (-).
d. Turn on the dc power supply and then turn
on the switch. The voltage at terminal 1

41-748.31B
19
KLF-1 Loss-of-Field Relay
should jump from 0 to the rated voltage after
a time delay of 0.4 ± 10% seconds. A trimpot
on the PC board can be adjusted to obtain
the desired time delay from 0.03 to 0.5 sec-
onds.
H. Compensator Check
Accuracy of the mutual impedance T of the com-
pensators is set within very close tolerances at
factory and should not be changed under normal
conditions. The mutual impedance of the com-
pensators can be checked with accurate instru-
ments by the procedure outlined below:
1. Set TAon the 15.8 tap
TCon the 5.1 tap
2. Disconnect the L-leads of sections MAand
MC.
3. Pass 10 amperes ac current in terminal 9
and out of terminal 8.
4. Measure the compensator voltage with an
accurate high resistance voltmeter (5000
ohms/volt).
5. Compensator A-voltage should be checked
between lead LAand terminal 5.
a. For TA= 15.8 the voltage measured
should be 158 volts ±3%.
6. Compensator C voltage should be checked
between lead LCand the front terminal of the
reactor (XD).
a. For TC= 5.1, the voltage should be 51
volts (±3%).
7. For all other taps the compensator voltage is
IT (±3%).
where I = relay current
T = tap setting.
11.0 RENEWAL PARTS
Repair work can be done most satisfactorily at the
factory. However, interchangeable parts can be fur-
nished to the customers who are equipped for doing
repair work. When ordering parts, always give the
complete nameplate data.

41-748.31B
20
KLF-1 Loss-of-Field Relay
Figure 1. Type KLF-1 Class 1-E Relay
Directional Unit
TA Tap Plate Impedance Unit UnderVoltage Unit
ICS
RB
TACompensator
TAAutotransformer
RV
Directional Unit Maximum Torque Angle Adjustment
TCCompensator
TCAutotransformer
TC Tap Plate
Front View Rear View
Telephone
Relay
(X Unit)