TYPE CN-33P R ELA Y
eeo
260
40
TYPICAL TRIP CURVE
FOR CN-33P
(CURRENT APPLIED DIRECT
'
THROUGH THE RELAY COILS,
SO
NO C.T.'S.)
100
110
120
Curve
471107
Fig.
6
Typical Tripping Phase Angle Curve for the CN33P Relay- High Current Values,
that is, that all feeders associated with the network
are open.
Now suppose that some network supply
line, other than the one to which the transformer
bank of Fig.
4
is connected is energized by closing
its breaker at the supply station.
The breaker on
that feeder will close and energize the network as
has been explained.
This energizes the network,
and the phase 1 and 3 potential coils and all phasing
circuits of the CN33P become energized.
The
phasing circuits of all phases have essentially full
voltage on them but since the voltage on the network
side of the breaker is the higher, a strong torque is
produced which keeps the TRIP contacts closed.
With the network energized, assume that the
primary supply breaker closes to energize the net
work transformer in question.
If the supply and
network voltages are in phase, the phasing voltage
will be zero . In this case there will be no electrical
torque produced,
except the "voltage only" torque
produced by the potential coils. This torque is suf
ficient to overcome the tension of the spiral spring.
Thus, the voltage only torque opens the TRIP con_
tact. However, there is not enough torque to close
the CLOSE contact, so the CN33P does not close the
breaker.
With the network energized, assume that the net
work transformer in question is energized, such that
the transformer secondary voltage is higher than the
network voltage, and substantially in phase with it.
In this case, the phasing coils in conjunction with
the potential coils will produce a torque which will
cause the moving contact of the CN33P relay to make
with the stationary CLOSE contact and close the
network breaker, thus connecting the transformer bank
to the network,
provided the CNJ contacts are
closed.
The instant the breaker closes, power starts to
flow from the transformer into the network.
This
causes current to flow in the current coils of the
relay. and produces a stronger torque in the closing
direction.
The network breaker will remain closed
even if conditions change so that there is no current
flowing through it.
As the current decreases to
7
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