GEI-50261
The negative-sequence voltage will be proportional to the unbalance in the line
voltages.
When a balanced three-phase voltage of correct phase sequence is
connected to the relay studs 5, 6 and 7, as shown in Figure 8, then the voltage
across the relay coil, TR, which is proportional to the negative-sequence voltage,
will be zero.
When the voltages supplied to the relay are unbalanced in either of
the two possible ways, as illustrated in Figure 9, then the voltage across the
relay coil will be proportional to the voltage unbalance, as demonstrated in the
section on CALCULATIONS.
On reverse phase voltages, the relay will pick up even on
balanced voltage.
It should be noted that other non-motor load connected to the bus will in most
cases tend to increase the unbalance in the voltages. Thus, if the relay is set to
detect a single-phase condition with only motors on the system, then any additional
non-motor load, such as lighting, will either make the relay's operation more
positive or leave it unchanged.
and
Time
To avoid confusion and to facilitate tests, we shall define the relay pickup
voltage, VR, as the single-phase voltage that, when connected to the relay as shown
in Figure 10, will just cause the relay to pick up.
This will be between 10 and 20
volts for the 120 volt relay and between 17 and 34 volts for the 208 volt relay.
The corresponding negative phase-sequence voltages are 5.8 - 11.5 for the 120 volt
relay and 10 - 20 for the 208 volt relay.
The operating characteristics are shown in Figures 4 and 5.
Figure 4 shows the
time to open the normally-closed contact, and the time to close the normally-open
contact, as functions of multiples of pickup.
The dropout time, or the time to
�,
return the contacts to their normal positions when the unbalanced voltage is
removed, is shown in Figure 5.
RATINGS
RELAY MODEL
RATED VOLTAGE
RATED FREQUENCY
PICKUP VOLTS, MIN.-MAX.(±10%)
12NBV11A1A
120
60 Hz
10-20
12NBV11A2A
120
50 Hz
10-20
12NBV11A3A
208
60 Hz
17-34
12NBV11A4A
240
60 Hz
20-40
12NBV11A5A
208
50 Hz
17-34
12NBV11A7A
216
60 Hz
17-34
The relay will withstand rated voltage continuously with normal phase sequence and
for 60 minutes with reverse phase sequence.
The relay will withstand single-phase
rated voltage continuously.
Contacts
The telephone-type relay contact ratings are shown in Table I.
4
www
. ElectricalPartManuals
. com
