Westinghouse KRD-4, Installation, Operation, & Maintenance Instruction

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Westinghouse
I.L. 41 - 1 37.4
INSTALLATION
•
OPERATION
•
MAINTENANCE
INSTRUCTIONS
A P P L I C A T I O N
The SRGU is a high sp e ed dual-polarized dire c-
tion a! over current ground relay. It may be used as a
current or potential polarized relay. It is suitabl e
for overreaching pilot systems where the pilot aux­
iliary provides a coordinating delay of at l e ast 15
ms during a sudden reversal in the direction of fault­
power flow due to a sequentially cl e ared external
fault. This SRGU design is not suitable for under­
reaching applications, pilot or no n-pilot, since the
overcurrent unit is not designed for minimum tran­
sient overreach and the dire ctional-unit reset during
a reversal is as much. as 1 2 ms.
C O N S T R U C T I O N A N D O P E R A T I O N
As s hown in Fig. 1 , 2, & 3 the relay contains a
power supply, a directional unit and overcurrent unit
in a 19 inc h rack unit.
Di rectional Unit
The directional unit co nsist of air gap current
transformers, T 2 and T3 , a voltage transformer T 1,
a p hase shifting network, and two printed circ uit
boards (dual dire ctional and dire ctional amplifier).
Transformer T1 and T2 are used in the current
pol arizing circuit and in t h e operating circuit. The
operating current transformer has two sep arat e
secondary windings.
The p hase s hifting n etwork consist of a cap a­
citor (C6), resistor ( R 1) and a reactor (L 1 ) in voltage
polarizing circuit and a reactor ( L 2) in current
p olarizing circuit. Fig. 3 s hows t he connections of
the transformers and the p hase shifting netwo rk to
the ring modul ator.
The dire ctional circuit board consist of two
sets of ring modul ators, an amplifier, a tim er, a
filter and an output transistor.
The ring modulator consist s of four diodes. The
anode of each diode is connect ed to the cat hode of
N EW I NF O RMATION
the followin g diod e to
d
roduce a m.aximum outf)ut
'
' '
voltage of 1 . 4 volts or two diodes forward voltage
drop .
Amplifier: The amplifier consist of the two NPN
transistors 1 Q l , and 1 Q3. The second stage of t h e
amplifier is an emitter follower which provides an
output to the next st age.
The turn on tim er consists of a potentiometer
1 R 1 4, a re sistor 1R1 2, a unij unction transistor 2Q1,
a cap acitor 1C3, and norm ally conducting transistor
1Q4 for a rapid discharge of the capacitor.
The filt er consists of a diode 2D 1, a capacitor
2C 1 and t he resistor 2R 3. There are two outp uts one
of which is the directional unit output. The other
controls the overcurrent unit. The directional out­
put s of a NPN 2Q2 and PNP 2Q3 with a diode 2D2
and zener diode 2Z 1 for the prot e ction of output unit
from the surge. The control output unit consist of
two NPN transistors 2Q4 and 2Q5 in which 2Q5 i s
normally conducting.
I n stantaneou s Overcu rrent Unit
The overcurr ent unit co nsists of an input trans­
former T4, a setting circuit, a phase splitter circuit,
a se nsing circuit, a voltage regulator circuit, a
feedback circuit and a transistor output.
1. Inp ut Transformer - A two winding typ e with a
non-tapped prim ary winding and a tapped second­
ary winding, the secondary is connected to the
setting circuit and from the fix ed t ap to the
p hase splitter circuit.
2. Setting Circuit - The setting circuit is connected
acro ss the se condary winding of the input trans­
former and consists of two branches, a re sistor
and a rheostat, connected in p arallel with a
resistor and zener diode. This circuit loads the
transform er and produces a seco ndary voltage
proportional to the input current. T he rheost at
has a lo cking feature to minimize the accidental
change of current setting.
E F FECT I V E AUGUST 1 968
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