3-4
BE1-46N Functional Description
BE1-46N relays are featured with the following settings:
&
TAP ADJUST and TAP ADJUST CAL to establish a reference level (full load stator current)
&
ALARM and PICKUP
&
K SET
&
MAX TIME (X 10 SEC)
I
n
Reference Level (Tap Value)
An adjustment is provided to establish the stator full load current reference level I
n
. This adjustment has a
range of 3.0 to 5.0 amperes. This is provided by a 10 position switch and vernier control. The switch
positions are marked from position A through J and provide a TAP VALUE as follows:
A
-
3.2
B
-
3.4
C
-
3.6
D
-
3.8
E
-
4.0
F
-
4.2
G
-
4.4
H
-
4.6
I
-
4.8
J
-
5.00
The vernier calibration control (CAL) is provided to adjust the full load current reference level I
n
in between
the TAP ADJUST range settings.
Alarm and Pickup
The I
2
output of the filter network is applied to the alarm and trip level detector circuits. The alarm circuit
pickup adjustment is settable from 0.01 to 0.50 which represents the ratio of magnitude of the negative
sequence current to the full load current rating of the machine. The alarm circuit compares the level of I
2
from the filter network to the selected ALARM pickup setting. When I
2
is greater than or equal to the setting
and exists for three seconds (a fixed three second time delay), the alarm output contact closes. The alarm
setting is usually set lower than the trip level to warn the station operator that corrective action is required.
After pickup (I
2
pu
I
2
÷I
n
), the trip level detector circuit applies the sensed negative sequence current I
2
pu
to the minimum and maximum trip timers and the network which integrates the value (I
2
)
2
dt equal to the
machine constant K. The minimum trip time circuitry, after a 0.2 second time delay, applies a signal to
initiate the operation of the oscillograph (optional). The maximum trip time circuitry maintains the same I
2
pu and triggers the output trip contact when the time delay expires. The setting of the maximum trip time
setting is based upon the maximum time allowed for a particular K constant. For a conventionally cooled
synchronous generator, the permissible (I
2
)
2
rating is 30 (reference C37.102-1987). Therefore, a setting of
0.35 pu would allow the generator to carry a negative sequence current condition for 245 seconds without
damage. For I
2
currents of less than 0.35 pu, the generator will be adequately protected.
When the value of I
2
pu applied to the microprocessor integrator network falls below the pickup setting, the
integration will cease and reset at a linear rate of 2.5 seconds per percent of full scale trip time. This linear
reset approximates generator cooling.
K Setting
The K setpoint should be set so that the (I
2
t characteristic of the relay matches the permissible heating
characteristic of the generator.
MAX TIME
The maximum timer function prevents negative sequence current from being above pickup for long periods
of time. The maximum timer is ORed with the inverse timer such that if either time out occurs, the unit trips.
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