Operation - ABB KLF Instruction Leaflet

Otherwise the undervoltage unit is similar in its
construction 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
ure 3. The solid state time delay circuit shown in
Figure 4 consists basically of an adjustable inte-
grating 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
contacts bridge two stationary contacts, complet-
ing 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 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, provides restraint for the arma-
ture and thus controls the pickup of the switch.
Figure 5. External Schematic of Type KLF Relay
Fig-

3. OPERATION

The relay is connected and applied to the system
as shown if Figure 5. 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 reduc-
tion in excitation, the impedance of the machine as
viewed from its terminals is less than a predeter-
mined value. The operation of both 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 the D contacts. Dur-
ing normal conditions, all contacts are open.
3.1 Principle of Distance Unit Operation
The distance 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.
41-748.21C
Sub 3
1487B21
5