Page 4
react with the
flux
in the air gap producing
a torque. This torque is balanced against a
spring torque to determine the balance po
sition of the relay disk and its associated
contacts.
Assume 120 volts has been applied to the
relay long enough for the moving contact to
come to rest at the 120 volt point on the re
lay scale. If the applied voltage were in
creased to 121 volts, the increased electro
magnetic torque would move the moving con
tact to the 121 volt point on the scale. If
the voltage were reduced to 119 volts the de
creased electro-magnetic torque would al
low the spring torque to move the contacts
to the 119 volt position.
A permanent damping magnet is mounted
on the relay with the induction disk between
the pole faces of this magnet and the magnet
keeper. \Vhenever the induction disk moves
through the unidirectional
flux
produced by
this permanent magnet a restraining force is
produced to control the time required to
change from one balanced position to another
for a given change in voltage.
The position of the stationary 90R and
90L contacts determines the voltage level at
which they will be closed to initiate tap
changer operation to correct the voltage.
If the voltage falls below the setting of the
left hand contact long enough for the disk
operated 90R contact to close, the relay AR
is energized and seals itself in through the
normally closed 120Y relay contact. Closing
the AR motor control relay contact operates
the tap changer to raise the voltage. Before
the tap changer arcing contact has opened,
a cam operated 120 switch in the tap changer
closes to energize the 120X relay, which in
turn takes over the sealing of the AR relay
through its 120X contact and also operates
the 120Y slug delayed relay. The normally
open 120Y relay contact closes and shunts
the reactor with a 3,000 ohm resistor which
increases the current through the voltage
coil 90 and tends to rotate the disk to open
contact 90R. Thus for small
devi
ations there will be a short
between
successive
After
the tap changer arcing contact has closed on
position, the 120 pilot switch opens, allowing
the 120X relay to release theAR relay. The
tap changer motor is stopped by the motor
brake. If the voltage is not corrected, the
sequence is repeated until the voltage is
corrected or a tap changer limit position is
reached.
A rise in voltage to close the right hand
contact 90L would initiate a similar se
quence of operations to lower the voltage.
In the latter instance the closing of the 120Y
normally open contact will place a shunt
through another 3000 ohm resistor around
the potential coil 90 to produce compounding
that tends to rotate the disk to open contact
90L.
VOLTAGE SENSING
r-- --
ELEMENT
r----,
I
I
I
UPPER POLE
1 1
I
WINDING
TRANSFORMER
WINDING
POTENTIAL
SOURCE
CU RRENT
TRANSF.
-
----
---
l
r--.,
, ---, '
1
I
I
1
1
I
1
I
I
I
L
___
J
I
I
__
.J
RESISTOR
Fig.
2
-
Schematic Diagram of the CVR-1
Relay Voltage Sensing Circuit
Bandwidth and Balance Voltage
The bandwidth of the voltage regulating re
lay is the difference in volts between the 90R
and 90L contact setting.
Balance voltage is defined as the voltage
midway between the 90R and 90L voltage
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