Xylem IM226R02 CP-Series Submersible Motors - Manual (Page 12)

10 CP-Series Submersible Motors Installation, Operation and Maintenance Manual
V. Guidelines For VFD Control of
CentriPro CP-Series Rewindable
Submersible Motor
Variable Frequency Drives together with submersible pumps are today often being used when water demand
varies over time. The pump will run with the VFD at a speed optimal to the actual demand, leading to possible
energy savings.
There are a wide number of different frequency drives available on the market and they often have different
characteristics. Therefore it is important to choose a VFD and other electric components that will work
satisfactory together with the motor. VFDs generate voltage peaks and if the peaks are too high and too steep
they will damage the windings in any submersible motor.
The CentriPro CP Series submersible motors can be used with Variable Frequency Drives if the following
guidelines are followed.
Frequency Limitations
You should never run the motor with the VFD on a higher frequency than the data plate on the motor states.
With a higher frequency than stated, overload and overheating problems could occur. Generally you are never
allowed to run the pump with a frequency below 30Hz. Always make sure that the flow around the motor is
enough to cool the motor at all the duty points of operation. Values for the flow can be found in the
submersible motor technical catalogue.
Ramp Up and Ramp Down Time
The ramp up time to the minimum running frequency should be set as quick as possible (maximum 1s) to ensure
the correct lubrication of the thrust bearing in the motor. The ramp down time (from the minimum running
frequency to 0 Hz) should be set as quick as possible (maximum 1s) as well.
Filters
Filters for reducing voltage peaks and steepness generated by the VFD are recommended and should be speci-
fied by the VFD manufacturer according to the below voltage peak and rise time limits.
Voltage Drop with Long Cables
The VFD should be installed as close as possible to the motor. When this is not possible a maximum of 4%
voltage drop at the motor is acceptable.
Use of VFD with CentriPro CP Series Submersible HT Motors (high temperature version)
It is always recommended the use of HT motors with VFD operation. The reason for this is that the
HT version has a higher tolerance for voltage peaks. For HT motors the voltage peaks to the pump may never
exceed 1000 Volts and the voltage rise time dV/dt should be lower than 500V/μs. If the VFD can not fulfil this
recommendation filters between the VFD and the motor has to be used. The requirement will then be that the
VFD together with the filters does not generate higher peaks than 1000V and that the voltage rise time dV/dt
should be lower than 500V/μs. The following indications are also recommended: use of dV/dt filters in case
of motors cable length ≤ 100 and use of sine wave filters for longer cable.
Guidelines for VFD Control