Figure 4.6 SLC Application Example
4.3.1
Submersible Pump Application
The system consists of a submersible pump controlled by a
Danfoss VLT
®
AQUA Drive and a pressure transmitter. The
transmitter gives a 4-20 mA feedback signal to the
adjustable frequency drive, which keeps a constant
pressure by controlling the speed of the pump. To design
an adjustable frequency drive for a submersible pump
application, there are a few important issues to consider.
Select the adjustable frequency drive according to motor
current.
1.
The motor is a so-called CAN motor with a
stainless steel can between the rotor and stator.
There is a larger and a more magnetic resistant
air-gap than on a normal motor, hence a weaker
eld, which results in the motors being designed
with a higher rated current than a normal motor
with similar rated power.
2. The pump contains thrust bearings that are
damaged when running below minimum speed,
which is normally 30 Hz.
3. The motor reactance is nonlinear in submersible
pump motors and, therefore, automatic motor
adaption (AMA) may not be possible. Normally,
submersible pumps are operated with long motor
cables that might eliminate the nonlinear motor
reactance and enable the adjustable frequency
drive to perform AMA. If AMA fails, the motor
data can be set from parameter group 1-3* Adv.
Motor Data (see the motor datasheet). Be aware
that, if AMA has succeeded, the adjustable
frequency drive will compensate for the voltage
drop in the long motor cables. This means that if
the advanced motor data are set manually, the
length of the motor cable must be considered to
optimize system performance.
4. It is important that the system be operated with
a minimum of wear and tear on the pump and
motor. A Danfoss sine-wave lter can lower the
motor insulation stress and increase lifetime
(check actual motor insulation and the adjustable
frequency drive dU/dt specication). Note that
most manufacturers of submersible pumps
require the use of output lters.
5. EMC performance can be dicult to achieve due
to the fact that the special pump cable, which is
able to withstand the wet conditions in the well
is normally non-shielded. A solution could be to
use a shielded cable above the well and x the
shield to the well pipe if it is made of steel. A
sine-wave lter also reduces the EMI from non-
shielded motor cables.
Application Examples
VLT
®
AQUA Drive FC 202
106 Danfoss A/S © 09/2014 All rights reserved. MG20N622
44
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