Danfoss VLT AQUA Drive FC 202 Design Manual

Also see for VLT AQUA Drive FC 202: Service guide Installation guide Installation guide Operating guide Installation guide

Contents

4.3.1 Submersible Pump ApplicationThe system consists of a submersible pump controlled by aDanfoss VLT® AQUA Drive and a pressure transmitter. Thetransmitter gives a 4-20 mA feedback signal to thefrequency converter, which keeps a constant pressure bycontrolling the speed of the pump. To design a frequencyconverter for a submersible pump application, there are afew important issues to consider. Select the frequencyconverter according to motor current.1. The motor is a so-called CAN motor with astainless steel can between the rotor and stator.There is a larger and a more magnetic resistantair-gap than on a normal motor, hence a weakerfield, which results in the motors being designedwith a higher rated current than a normal motorwith similar rated power.2. The pump contains thrust bearings that aredamaged when running below minimum speed,which is normally 30 Hz.3. The motor reactance is nonlinear in submersiblepump motors and, therefore, automatic motoradaption (AMA) may not be possible. Normally,submersible pumps are operated with long motorcables that might eliminate the nonlinear motorreactance and enable the frequency converter toperform AMA. If AMA fails, the motor data can beset from parameter group 1-3* Adv. Motor Data(see the motor datasheet). Be aware that, if AMAhas succeeded, the frequency converter willcompensate for the voltage drop in the longmotor cables, so if the advanced motor data areset manually, the length of the motor cable mustbe considered to optimise system performance.4. It is important that the system be operated witha minimum of wear and tear on the pump andmotor. A Danfoss sine-wave filter can lower themotor insulation stress and increase lifetime(check actual motor insulation and the frequencyconverter dU/dt specification). Note that mostmanufacturers of submersible pumps require theuse of output filters.5. EMC performance can be difficult to achieve dueto the fact that the special pump cable, which isable to withstand the wet conditions in the wellis normally unscreened. A solution could be touse a screened cable above the well and fix thescreen to the well pipe if it is made of steel. Asine-wave filter also reduces the EMI fromunscreened motor cables.The special CAN motor is used due to the wet installationconditions. The frequency converter needs to be designedfor the system according to output current to be able torun the motor at nominal power.To prevent damage to the thrust bearings of the pump,and to ensure sufficient motor cooling as quickly aspossible, it is important to ramp the pump from stop tominimum speed as quick as possible. Well-known manufac-turers of submersible pumps recommend that the pump isramped to min. speed (30 Hz) in max. 2–3 s. The VLT®AQUA Drive FC 202 is designed with initial and final rampfor these applications. The initial and final ramps are 2individual ramps, where initial ramp, if enabled, ramps themotor from stop to minimum speed and automaticallyswitches to normal ramp, when minimum speed isreached. Final ramp will do the opposite from minimumspeed to stop in a stop situation. Consider also enablingadvanced minimum speed monitoring as described inchapter 4.2 Selected Application Features.To achieve additional pump protection, use the dry-rundetection function. Refer to the programming guide forfurther information.Pipe-fill mode can be enabled to prevent waterhammering. The Danfoss frequency converter is capable offilling vertical pipes using the PID controller to ramp upthe pressure slowly with a user specified rate (units/second). If enabled, the frequency converter enters pipe-fillmode when it reaches minimum speed after start-up. Thepressure is slowly ramped up until it reaches a user-specified filled set point, where the frequency converterautomatically disables pipe fill mode and continues innormal closed-loop operation.Electrical Wiring130BA727.10MPEL1 L3 U V W 12 18 27 13 54L2 PEMains2 wire 4-20mAPressureTransmitterStartStopIllustration 4.7 Wiring for Submersible Pump ApplicationApplication Examples Design Guide102 Danfoss A/S © 09/2014 All rights reserved. MG20N60244