Rockwell Automation 1902 Syncpro II - Manual (Page 42)

44 Rockwell Automation Publication 1902-IN001B-EN-E - April 2013
Chapter 5 Programming SyncPro II
Set Point 7: Incomplete Sequence Trip Time Delay
Once a synchronous starter has been commissioned, the acceleration and
synchronization times should remain fairly consistent provided that the starting
load does not vary significantly. The incomplete sequence timer can be set to a
time delay that is slightly higher than the slowest acceleration time. The
aforementioned squirrel-cage protection features protect the motor, but they also
let it go to its thermal limitations. The Incomplete Sequence Timing Relay
(ISTR) set point can be adjusted to take the starter off-line earlier than the
squirrel-cage protection trip time (set point 5) in the event of a field contactor
failure or some other mechanical problem that prevents synchronization. This
action minimizes motor heating during an equipment failure.
Set Point 8: Power Factor Trip
As discussed earlier, power factor can be sued to determine if a motor has pulled
out of synchronism due to loss of excitation, overloading or a severe undervoltage.
At this time, the motor should be taken off line to protect the stator and field.
Set Point 9: Power Factor Trip Time Delay
Once it is determined that the motor has a lagging power factor due to a pullout
condition, the trip condition can be time delayed to allow the motor a brief
opportunity to pull back into synchronism.
IMPORTANT The squirrel-cage winding of a synchronous motor has a very limited
capability. Generally, the stall time allowed by the squirrel-cage winding is less
than the time that the stator winding is capable of. It is possible that a motor
with a stator capable of a 20 second stall would have a rotor which can only
endure a stall condition of 5 seconds.
IST
t SP =
7
trip
PF SP =
8
Delay PF
t SP
_ 9
=