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6.4 Rotating Speed Start
Rotating speed start also as “flying start”, i.e. start the VFD when motor is already rotating. At this start mode, VFD
makes the speed (frequency) as the control target and use the actual speed (including direction) of the motor at
the start time to be the startup frequency. No matter the motor turning was forward or reverse before VFD starts,
the VFD can automatically track the actual speed, then smoothly start to the target speed and direction. This start
mode usually applies to the motor restart after power loss or motor running from constant speed running on the
grid changed to variable speed operation from VFD.
Firstly set the stop mode to free stop, when start mode is rotate speed start, before starting the VFD, the signal
board keeps detecting the speed of the motor. Once the start command is received, the VFD immediately outputs
the corresponding frequency at the speed, and on this basis accelerates and decelerates to reach the set
frequency, as shown in Figure 6-3.
Fig. 6-3 Switch Time Sequence
By setting HMI function “MV Loss Quick Break” and “MV Loss Self Restart”, the user can choose when lose the
MV, whether the VFD alarms heavy fault or not and whether the VFD will run automatically when the recover the
power.
6.5 MV Loss Solution
Before trying the synchronous switching, users need to check whether the setting of system parameters are
reasonable and meet the requirements or not, and must disable the commands or functions that may lead
to failure of the switching, such as speed curve, speed limit, set mode, etc that may change the VFD output
frequency during the synchronous switch, resulting in switching failure.
Using synchronizing switch function, it need to be equipped with synchronizing switch cabinet, reactor cabinet
and synchronizing switch sample board. Details see “Synchronizing switch cabinet manual”.
