Rockwell Automation 1901 SyncPro - Manual (Page 7)

Product Description 1-3
1901-UM020C-EN-P – June 2013
Protection Features Theory of Operation
When the NOT STOP and START signals go high, a timer is
started (refer to Figure 7.1). 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 DTAM 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 (refer to programming of set point, Chapter 5),
the FIELD RELAY is energized. The power factor is now monitored
and displayed on the DTAM. If the power factor drops below the
programmed values, the TRIP and FIELD RELAY outputs will be
dropped and the DTAM 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 represent-
ing 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 are:
• maximum allowable starting times at the stalled condition
• 50% speed
• maximum programmed percentage of synchronous speed
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).