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6.1.3 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 VLT AQUA Drive, which keeps a constant pressure by controlling the speed of the pump. To design a drive for a submersible pump application,
there are a few important issues to take into consideration. Therefore, the drive used must be chosen according to motor current.

The motor is a what is known as a “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 field which results in the motor being designed with a higher rated current than a
norm motor with similar rated power.

The pump contains thrust bearings which are damaged when run below minimum speed, which is normally 30 Hz.

The motor reactance is nonlinear in submersible pump motors and therefore Automatic Motor Adaption (AMA) may not be possible. However,
normally submersible pumps are operated with very long motor cables that might eliminate the nonlinear motor reactance and enable the drive
to perform AMA. If AMA fails, the motor data can be set from parameter group 1-3* (see motor datasheet). Be aware that if an AMA has been
successful, the drive will compensate for voltage drop in the long motor cables, so if the advanced motor data are set manually, the length of
the motor cable must be taken into considerations to optimize system performance.

It is important that the system be operated with a minimum of wear and tear of the pump and motor. A Danfoss Sine-Wave filter can lower the
motor insulation stress and increase lifetime (check actual motor insulation and the adjustable frequency drive du/dt specification). It is rec-
ommended to use a filter to reduce the need for service.

EMC performance can be difficult to achieve due to the fact that the special pump cable, which is able to withstand the wet conditions in the
well, is normally unshielded. A solution could be to use a shielded cable above the well and fix the screen to the well pipe if it is made of steel
(can also be made of plastic). A Sine-Wave filter will also reduce the EMI from unshielded motor cables.

The special “can motor” is used due to the wet installation conditions. The drive needs to be designed for the system according to output current to be
able to run the motor at nominal power.

To prevent damage to the thrust bearings of the pump, it is important to ramp the pump from stop to min. speed as quickly as possible. Well-known
manufacturers of submersible pumps recommend that the pump be ramped to min. speed (30 Hz) in max. 2 -3 seconds. The new VLT© AQUA Drive is
designed with initial and final ramp for these applications. The initial and final ramps are 2 individual ramps, where Initial Ramp, if enabled, will ramp the
motor from stop to min. speed and automatically switch to normal ramp, when min. speed is reached. Final ramp will do the opposite from min. speed
to stop in a stop situation.

Pipe-Fill mode can be enabled to prevent water hammering. The Danfoss adjustable frequency drive is capable of filling vertical pipes using the PID
controller to slowly ramp up the pressure with a user specified rate (units/sec). If enabled, the drive will enter pipe fill mode, when it reaches min. speed
after startup. The pressure will slowly be ramped up until it reaches a user-specified filled setpoint, after which the drive automatically disables pipe fill
mode and continues in normal closed-loop operation.
This feature is designed for irrigation applications.

Electrical Wiring

Typical parameter settings

Typical/recommended settings in brackets().

Parameters:

Motor Rated Power

Par. 1-20 / par. 1-21

Motor Rated Voltage

Par. 1-22

Motor Current

Par. 1-24

Motor Rated Speed

Par. 1-28