TYPE CN-33 P RELAY
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11!5"11.
IN-PHASE TRIPPING CHARACTERISTICS
OF THE CN-33P PRIMARY NETWORK RELAY
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Curve
471109
Fig,
8
Trip Sensitivity Characteristic ol the Type CN33P
Relay- Voltage
&
Current In Phase.
The upper end or line potential end of the voltage
vector is at the origin in this case. It will be noted
by referring to curve #1A of Fig. 5 that the relay
will just close its CLOSE contacts with approximate
ly 0.5 volts across the phasing circuit, in phase with
the network voltage.
The closing voltage adjusting screw, located on
the front panel, allows a range of adjustment of the
in-phase phasing voltage pickup from 0.5 to 2 volts.
Figure 6 and
7
show typical tripping phase angle
characteristic of the CN33P with 125 volts applied
to the potential coils. Lines drawn from the origin
to the curve are the currents which will produce a
torque in the relay just sufficient to cause its TRIP
contacts to make.
The curve shown in Fig.
7
re
presents a small section of the trip curve just
discussed plotted to a much larger scale in order to
show the operation of the relay on small current
values, such as the transformer magnetizing currents.
Fig. 8 shows the trip sensitivity characteristic,
which shows how it parallels the transformer exciting
current variations.
At zero voltage, the TRIP con
tacts are closed by spiral spring tension.
Voltage
only torque oppose this spring tension. Accordingly,
at zero current & some value of voltage, below 100
volts, the voltage-only torque opens the TRIP con
tacts. This voltage-only torque is overcome and the
TRIP contacts close when 2-4 rna in-phase current
flows toward the transformer.
SETTINGS
Set the voltage closing adjusting screw for the
desired value. Adjustment range is 0.5-2.0 phasing
volts, in phase with a network potential of 125 volts.
Factory adjustment is a nominal 0.5 volts. Refer to
Fig. 9 for the test circuit used to make this adjust
ment. (Close switches A, B
c.
A", B:' & C ". Ener
gize potential coils with 125 volts. Place switches
A
1,
B 1 &
c 1
in position 2.
Phasing voltage is
measured across the one ohm resistors.)
It is not intended that the factory adjustment of
the trip sensitivity characteristic be changed.
Note
that if the spiral spring setting is changed,
the
phasing voltage adjustment is affected .
INSTALLATION
The relays should be mounted on switchboard
panels or their equivalent in a location free from
dirt, moisture, excessive vibration, and heat. Mount
the relay vertically by means of the two mounting
holes through the case.
Either a mounting stud or
mounting screw may be utilized for grounding the
relay.
Electrical connections are made to the sta
tionary terminal blocks.
ADJUSTMENTS
&
MA INTENANCE
All characteristics described are based on normal
three-phase energization of the relay , with the phase
order being 1, 2, 3. Where in-phase relationships are
described, they are with respect to the individual
phase voltages and current. Nominal rated voltage is
125 volts 60 cycles.
Acceptance
&
Routine Maintenance checks
Connect the relay per Fig. 9 & perform the follow
ing checks:
A) Close swit ches A, B, C.
Adjust for 125 volts,
phase to neutral, on the potential coils. Preheat
for one hour.
B) Close switches A", B", & C". Place switches
A 1, B 1 & C 1 in position 1 & adjust the current
9
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