Rockwell Automation 1902 Syncpro II - Manual (Page 9)

Rockwell Automation Publication 1902-IN001B-EN-E - April 2013 9
Product Description Chapter 1
Protection Theory Theory of Operation
When the NOT STOP and START signals go high, an internal timer is started
(see
Figure 4 and Figure 5 ). The START signal must be dropped before another
start can be initiated. The timer is preset based on the slip frequency of the
motor. If the timer expires prior to achieving the maximum asynchronous speed,
the starting sequence will halt, the TRIP output will be dropped and the
PanelView will display a message indicating the faulted condition. The TRIP
signal is restored when there are no faults and the Fault/Reset PB input is
received.
NOTE: The NOT STOP and START can be tied together to indicate a RUN
condition to control the device without separate signals. The RUN output
follows the start input if the motor is permitted to start, (i.e. no faults and the
EQUIPMENT SHUTDOWN is high).
If the programmed percentage of synchronous speed is obtained within set time
limits, the FIELD RELAY is energized. The power factor is now monitored and
displayed on the PanelView. If the power factor drops below the programmed
values, the TRIP and FIELD RELAY outputs will be dropped and the
PanelView 300 will display a message indicating the faulted condition. Under
normal conditions the FIELD RELAY is maintained until the NOT STOP
signal is removed.
The slip frequency is calculated from a square wave input representing the slip
frequency. Based on this frequency, the allowable starting time is calculated. This
calculation is based on three set points which are entered by the user, as well as a
‘function order’ used to shape the curve. The three required set points for
squirrel-cage protection trip time are:
• Set Point 4: at synchronizing = 95%
• Set Point 5: at 50% speed
• Set Point 6: at stalled
The time curve between stalled frequency and 50% speed is assumed to be linear.
The time between 50% speed and the synchronizing speed is to the nth order
such that unity makes it linear, 2-5 makes it exponential in nature. The higher the
order, the shorter the times near to 50% speed and the higher the times near the
synchronous speed set point (i.e. bottom of curve (time vs. frequency) is flatter
and then rises more steeply).
NOTE: If the time set point at the maximum programmed percentage of
synchronous speed is set below that of the extended stall (i.e. 50% speed curve),
the function between 50% speed and synchronous speed will also be treated as
linear. (For example, the slope between 50% speed and synchronizing speed is
flatter than the slope between stalled and 50% speed).