Emerson Epsilon Eb Series Reference Manual page 58

During current foldback the Torque Command Actual will be limited to 80 percent
continuous motor torque. Current foldback is cancelled when the RMS Foldback level falls
below 70 percent. This could take several seconds or several minutes depending on the load.
The RMS Foldback value is dependent on both torque and velocity. At low speeds (<20
percent of maximum motor speed) the RMS Foldback will closely follow the Torque
Command Actual. At high speeds (>50 percent of maximum motor speed) the RMS Foldback
will read higher than the Torque Command Actual.
The time constant for RMS Foldback is 10 seconds. This means that if the load is 150 percent
of continuous, it will take about 10 seconds to reach the foldback trip point.
Figure 30: RMS Foldback Trip Point (this graph is accurate to ±5 percent)
Stall Foldback (E Series Only)
Stall Foldback prevents overheating of the Power Stage. It activates in any mode when the
motor velocity is 100 RPM or less and the Torque Command causes the current to exceed the
stall current threshold for 100 ms or more.
Note
The stall current threshold is not the same as the drives continuous current rating. For
example, the E -204 has a continuous rating of 4.5 Amps but a stall current threshold of
N
7 Amps.
Stall Foldback will also be triggered when the drive sees repeated high currents in one of the
three motor phases. This can occur when a motor is indexed back and forth between two of
its electrical poles.
• For 4 pole motors such as MG-205 or MG-208 this distance is 90° mechanical.
• For 6 pole motors such as MG-316 through the MG-4120 this distance is 60° mechanical.
• For 8 pole motors this distance is 45° mechanical.
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Operational Overview
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