Westinghouse KC-4, Инструкция по установке, эксплуатации и обслуживанию

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T Y P E S B F U STAT I C CI RCU I T B R E A K ER F AI L U R E
" 1" output ( 1 5 to 20 volts). A knob on the rheostat
shaft i s used
to
obtain the desired operate p oint.
A locking feature prevents the knob from being
accidentally changed.
Beside the setting circuit the overcurrent unit
modul e consists of a d-e rectifier, input sensing
circuit , a feedback circuit and a switching amplifi er.
The phase spl itting adj ustment potentiometer and
feedback potentiometer are also located on the
module . These potentiometers are factory adjusted
and should not require changing. The output can be
checked by means of the red and black test point
j ack s mounted on the front of the modul e. The actual
electrical connections can be seen by referring to
the internal schematic drawin g of the modul e.
Breaker F a i l u re Log i c Modu l e
This module receives the output o f the over­
current unit. It also receives the 62X and 62Y signal
and performs the necessary logic function. Some
relays are wired with a seal-in circuit as shown in the
particular logic dwg. An 8MS time delay is used in some
types to prevent undesirable operation of the seal-in
0
circuit due to capacitive surges. In addition the input
buffer is designed to respond to input signals greater
than half battery voltage (Fig. 27). Figure 31 shows
breaker failure logic module with high capacitive surge
immunity.
Adj ustabl e Timer Module
The timer adj ust potentiometer is mounted at
the front of the module along with a dial plate. A knob
is mounted on the potentiometer shaft and can be held at
0
the desired setting by means of a locking device. Some
relays come supplied with two timer modules (see Fig. 38).
Trip Module
A trip module is supplied when the SBFU out­
put is a thyristor switch. It contains the circuitry
for isolating the thyristor trip supply voltage from
the SB FU control voltage as well as the thyristor
gate driving circuit.
Power Suppl y
The power supply i s a transistor and Zener
regulated d-e supply which is located on the power
supply m odule . The module is used in conjunction
with two ext ernal resi stors (RA and RB) , whose
value depend on whether a 48-volt or 1 25-volt d-e
control voltage is available . The output voltage is
approximately 2 0VDC.
Output Rel ay
The output relay, when used, is the Westinghouse
0
high speed Type AR with 4 normally open contacts. At
least one normally open contact is connected to a terminal
strip for tripping duty. �he relay driver circuit is
located on the power supply module or breaker failure
module.
O P E R A T I O N
The overall operation can best be explained by
referring to the d-e schematic and logic diagram
20 1C845. The 62X and 6 2Y input from the primary
or backup rel ays are introduced in a lo gic "AND "
with the overcurre nt unit fault detector. The output
of the breaker failure logic module then operates
the adju stable timer module. The timer output then
drives either a relay driver or thyristor dep ending
on the type of output. An i nductor
Ll
is used in
conjunction with the thyristor to provide immunity
to line transients.
A supplementary instruction leaflet is provided
for some SBFU relays not co nt ained in this booklet .
Refer to nameplate for this number.
Overcu rrent U n i t
T h e line C T current flo ws through the SBFU
input transformer producing a secondary voltage
proportional to the current. The secondary voltage
value is affec ted by the setting rheostat. The sec­
ondary voltage is connected to a p hase splitter
consisting of a capacitor and fixed resi stor and a
potentiom eter which produce a three-phase voltage.
This voltage is fed into a three-phase full wav e
rectifier. The output of the rectifier goes to a Zen er
comparer. When thi s voltage is high enough, the
Zener conduct s and allows current to flow into the
b ase of the Q 1 transistor. When transistor Q 1 turns
on, transistor Q 2 also turns on c ausing the voltage
at the output terminal of the module to rise from
appro ximatel y 0 ( logic 0) to approximately 20 volts
(logic 1) . At the same tim e , a current feeds back to
the input. The amount of feedback current is ad­
justed by a potentiometer in the feedback p ath which
is factory calibrated for a dropout of approximately
95% of p ickup .
Breaker Fai l u re Logic Module
The 62X and 62Y inputs are connected to two
buffer circuits which consist of two Zener diodes,
three resistors, o ne capacitor and one diode. This
circuitry provides immunity to transients that may
be p icked up by the leads l e ading to t he input of
the SBFU. The buffers are connected to a NOR
circuit consisting of a transistor and resi stor. The
output of the NOR circuit connects to a NAND
3
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