Westinghouse Type KR, Installation & Operating Instructions Manual

Page: 45 / 124

connecting or disconnecting resistors R-7 3 and R-74
in the I
F stages.
The receiver oscillator ( Q- 2 and Q·3) is basic­
ally the same as the transmitter oscillator. The
frequency is 20-kc above the incoming signal
frequency.
The receiver channel frequency is determined by
the input filter and the oscillator crystal. The fre­
quency may be changed readily since both the filter
and the crystal are plug-in components.
Mixing i s accomplished by feeding the incoming
signal to the emitter and the receiver o scillator signal
to the base of the mixer Q- 1. Mixer oscillator re­
quirements are met through adjustment of potentio­
meter R-4. Injection into two sep arate elements, base
and emitter, provides a circuit capable of handling
greater signal level variations than one in which in­
jection is made into only a single element such as
the base.
This receiver us es an IF frequency of 20-kc. The
overall selectivity is determi ned primarily by the IF
filter FL- 2. Typical characteri stics of this fi lter are
shown in Fig.
15.
Th e IF ampl ifier consists of transi stors Q-4, Q-5
and Q- 6.
The detector i s a full wave bridge rectifier. This
rectifier in conjunction with the IF amplifier Q-6 ,
provides the necessary power to drive the D-C power
output stage Q-7.
Th e final output stage
Q- 7
will supply approxi­
mately 1 8 milli amperes to a s tandard 1700 ohm dis­
tance relay RRH co
il
and its a ssociated
5 00
ohm
a
l
a
rm coi l . It
may al so be used to dri v e oth er r el ay
coil s such as is shown by Fi g. 7, Supervi sory Con­
trol Connections.
Transmitter Control Circuits
In the standby condition, although the oscillator
is running , the transmitter driver has no emitter bias
which results in no output.
Positive voltage applied to terminal 15 supplies
this bias through a voltage dividing network , and
transmitter output results. The actual configuration of
the network is a function of supply voltage and ap­
plication ( Relaying, Telemetering, etc. ) and is
discussed in the Adjustments section.
Output may be stopped ·in several ways. The
method used with K-DAR relays is to remove the
po sitive voltage applied to terminal 15. In the case
of distance relaying with Westinghouse HZ/HZM
relays, application of a positive voltage to terminal
18 will stop the transmitter output. Output may also
be stopped by removal of negative battery from
terminal 18 .
Sl eet Detector
The Sleet Detector i s shown by Fig.
1 1.
Effe c­
tiv ely R- 1
is
a remote transmi tter output control . This
control is obtained through v ar ying th e dri v er stage
(Q- 10)
emitter bi as, and is effectiv e ov er
a
40- db
range of tr ansmitter output. The Sleet Detector
is
switched into service by S- 1. BY adjusting R- 1 for a
giv en receiver rel ay current at the
far
end of the
channel , a relativ e measure of th e channel attenua ­
tion may be obtained. Thi s is discu s sed further in
the section on Adjustments.
Communications
The transmitter output is reduced approximately
6-db when the Type KR voice adapter attachment is
used. Relaying takes preference, and full output i s
obtained since full voltage is supplied to terminal 1 5 .
Rel aying Control Circuits
Fi gs. 3, 4 and
5
show simpl ifi ed diagrams of the
relaying control circui ts.
1.
K-DAR and GCY Relaying (Figs. 4 and
5)
The control of the carrier set is obtained through
the CARRIER START and CARRIER STOP contacts.
These contacts are shown in their normal standby
condition.
The K-DAR or GCY relays operating from the
voltage and current on the transmission line, detect
and determine the direction of a line fault and there­
by control the carrier transmitter and receiver.
The control of the carrier set is such as to start
the transmission of carrier when fault power on the
transmi ssion line is flowing out of the line section
being protected. Conversely, when fault power is
flowing into this line section, the control is such as
to block the transmitter and keep it from being turned
on by secondary functions such as sleet detection
5
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