Input Single-Phase Rollback; Transformer Thermal Rollback; Field-Weakening Limit - Siemens 6SR41 series Product User Manual

Application and Operation
6.7 Drive Output Torque Limiting
6.7.3

Input Single-Phase Rollback

With Next Gen Control, input voltage unbalance (E
output torque. Figure "Drive Power (Pmax) as Function of Input Unbalance Voltage
(Eunbalance)" shows the reduction in drive power as a function of the unbalance voltage.
When the unbalance is less than 10%, the drive operates without any output limitation. There
is a linear reduction as the unbalance voltage increases from 10% to 30%, at which point the
input has a single-phase condition. When the input line voltage unbalance increases above
30%, the drive limits the amount of output power that can be delivered to the load to 40% of
rated.
Figure 6-7
A regulator is implemented to match the maximum drive power (P
flowing from the drive. The output of this regulator sets the output torque limit. The NXG
control provides menu settings for the proportional and integral gains of this regulator, as
well as an alarm setting for single-phase input detection.
6.7.4

Transformer Thermal Rollback

The input currents to the drive are monitored continuously. The largest among the three
input phase currents is limited to be at or below 105% of the nominal rating of the
transformer. Drive output torque is reduced when this current level is exceeded. An integral
regulator is implemented to limit the maximum input current to 105%. The output of this
regulator sets the output torque limit. The NXG Control provides a thermal gain parameter to
represent the integral gain of this regulator.
6.7.5

Field-Weakening Limit

The field-weakening limit is a torque limit that is based on the motor flux and motor leakage
inductance. This limit prevents the motor slip from exceeding pullout torque slip. Thus, it
prevents unstable operation of the motor. This limit normally occurs when motor flux is
reduced significantly during energy-saver operation, or when operating beyond the base
speed of the motor. Under such conditions, a large step (increase) in load will force the
output to be limited, resulting in a loss of speed rather than motor pullout.
126
Drive Power (P ) as Function of Input Unbalance Voltage (E
max
) is used for rolling back the drive
unbalance
MAX
Operating Instructions, Version AE 12/2009, A5E01454341C
)
unbalance
) with the actual power
Product User Manual