KSB S 100D - Operation with Frequency Inverter

60 Hz Submersible Borehole Pumps
6
Pump Operation with Frequency Inverter
In principle, the motors of submersible borehole pumps can
also be run on a frequency inverter. As submersible motors
differ from conventional standardized motors in terms of
bearings, moment of inertia, insulation, temperature increase,
loss distribution and heat distribution, the following parameters
must be observed:
-- Maximum allowable acceleration time (start ramp)
-- Maximum allowable deceleration time (stop ramp)
-- Minimum frequency
-- Maximum operating frequency
-- Maximum permissible voltage increase velocity and peak
voltages
-- Control principle of frequency inverter
Maximum Allowable Acceleration Time (Start
Ramp) and Deceleration Time (Stop Ramp)
The plain bearings of the submersible motor operation below
the minimum frequency f
min
do not tolerate (operation in mixed
lubrication range).
For this reason, the acceleration period from standstill to
minimum frequency f
min
should not exceed 2s. The same
applies to the deceleration period.
Minimum Frequency
Minimum frequency f
min
(Hz)
Motor size
Vertical
installation
Horizontal
installation
DN 100
3
0
30
DN 150
30
-- --
UMA 150D
UMA 200D
2
0
3
0
UMA 250D
2
0
3
0
UMA 300D /2
UMA 300D /4 30 35
Maximum Operating Frequency
Frequency inverter operation above the nominal frequency
(50Hz / 60Hz) of the pump unit must be avoided so as, to
prevent motor overload.
Maximum Permissible Voltage Increase Velocity
and Peak Voltages
Excessive voltage increase velocities and excessive peak
voltages will reduce the service life of the winding insulation.
For this reason, the following limits must be adhered to:
-- Maximum voltage increase velocity:
du/dt ≤ 500 V/µs
-- Maximum peak voltages to earth:
Low-voltage motors ≤ 1 kV: J1 insulation ≤ 600 V
J2 insulation ≤ 800 V
Note: Compliance with these limits can usually be assured by
means of a sine filter or
du
/
dt
filter.
Control Principle of Frequency Inverter
The control principle of the frequency inverter must correspond
to linear U/f curve control. If other control principles are
employed, such as field-oriented inverters, inverters with DTC
or NOF, the manufacturer of the frequency inverter must ensure
that the special requirements of submersible motors (very small
moment of inertia, electrical data) are taken into account.