How to Select a VFD for a Deep-Well Submersible Pump

Selecting a VFD for a deep-well submersible pump requires more than matching kilowatts. The drive is above ground, the motor is far below it, the motor cable may be long, the water level changes, and the pump must overcome both elevation and pipe losses. A package that looks correct on a price list can still fail to build pressure, cool the motor inadequately or trip unpredictably if those details are omitted.

A professional selection starts with the borehole, pump, motor, cable and hydraulic duty as one system. AUSENIST water-pump VFDs can be configured for submersible-pump applications, asynchronous or induction motors, and permanent-magnet synchronous motors. The correct series, voltage, settings, mounting and protection strategy depend on verified project data rather than a generic “deep-well mode.”

Define the Hydraulic Duty from Water Level to Delivery Point

The required pump head includes more than borehole depth. Use the dynamic water level while pumping, elevation from that level to the delivery point, required residual pressure, and friction losses through the riser, valves, filters and distribution pipe. Static water level is useful, but it may fall substantially when water is drawn.

Define at least the required flow and head at normal duty, expected minimum and maximum demand, lowest expected dynamic water level, pipe sizes and delivery-pressure target. Obtain the pump curve from the pump manufacturer. Confirm that the chosen impeller stages and speed can reach the duty point without operating outside the permitted region.

A VFD cannot correct an undersized pump. Increasing the frequency beyond the motor and pump manufacturer's approved limit is not a safe substitute for proper selection. At reduced speed, confirm that the pump still develops enough head to lift water and reach the pressure setpoint. Static head may establish a relatively high practical minimum speed even when demand is low.

Identify the Exact Submersible Motor

Record the motor's rated power, voltage, current, frequency, speed, phase, insulation information, service conditions and connection data directly from the nameplate and manufacturer. Determine whether it is an induction motor or a permanent-magnet synchronous motor. The two types require different control preparation and should not share an unverified parameter file.

YS620 and YS820 can be matched for both asynchronous or induction motors and PMSM applications. This compatibility is valuable to pump OEMs serving several markets, but “supports both” does not mean automatic interchangeability. AUSENIST needs the motor data and, where required, the motor manufacturer's technical information to prepare or review the configuration.

Also confirm how the submerged motor is cooled. Water movement past the motor, well diameter, flow sleeve, installation direction and minimum flow can affect temperature. The motor manufacturer's cooling and minimum-speed requirements take priority. A low frequency at which the pump still rotates may not be a permissible continuous operating point.

Match Voltage, Current and Power with Margin

Select the VFD around the actual supply and motor, not only the pump catalog power. Confirm input voltage and phase at the site, motor rated voltage, full-load current and expected supply variation. Check that the output arrangement is appropriate for the motor. An old project description such as “220 V well pump” is incomplete without phase and motor nameplate data.

AUSENIST supports standard 220 V and 380 V pump-drive projects. Confirmed 440 V and 460 V requirements can be evaluated as custom versions. A custom voltage project should be identified before drawings, labels, parameters and test plans are frozen. Do not assume that changing a keypad voltage value converts a standard unit into a different voltage class.

YS620 is documented from 0.75 to 7.5 kW, while YS820 extends from 0.75 to 22 kW. Motor current, overload duty, environmental derating and the required control functions remain part of selection. The next larger nominal kilowatt is not automatically correct unless its electrical ratings and application conditions have been reviewed.

Treat the Long Motor Cable as a Design Input

Deep-well installations often place considerable cable between the VFD and motor. Cable length, construction, conductor size, routing and joint quality affect voltage drop and the electrical stress seen by the motor. The fast-switched VFD output also behaves differently from a utility-frequency supply. These effects cannot be assessed from motor power alone.

Provide AUSENIST with the estimated total cable length from drive to motor, cable specification, supply voltage and motor insulation data. If output-side measures are needed, their selection should follow a project review rather than a universal distance threshold invented for every pump. Never place ordinary switching devices or compensation components on the VFD output without an approved design and operating sequence.

Choose Pressure, Level or Flow Feedback Deliberately

A borehole system may control discharge pressure, tank level, reservoir level or a process flow. Identify the main controlled variable and where it will be measured. For constant pressure, a correctly ranged pressure sensor should represent the delivery point or header that the system is intended to regulate. For tank filling, an external level controller or suitable sensor may provide commands according to the project design.

AUSENIST can support compatible sensor options and parameter customization, but the exact signal, range, wiring and control behavior must be confirmed. Do not describe every sensor as interchangeable. A voltage signal, current signal and switch contact require different treatment, and a level-control project should not be assumed to use the same factory file as a pressure-booster package.

Build Water-Shortage Protection Around Real Evidence

A falling source level is a central risk in deep-well pumping. Water-shortage protection should stop the pump before prolonged dry running damages it, but it must also distinguish source shortage from a blocked inlet, air leak, wrong rotation, damaged impeller, closed valve or a speed too low to overcome static head.

YS620 and YS820 include documented water-shortage protection as part of their pump-control functions. The detection method, delay and restart strategy should be commissioned for the actual well and pump. An aggressive setting can create nuisance trips during normal recovery; a permissive one can allow excessive dry-running exposure. External level or well probes may also be part of the project where required, but their use and interface must be defined rather than assumed.

Coordinate Minimum Speed, Sleep and Check-Valve Behavior

At low demand, a pressure-controlled well pump may slow until it approaches the lowest speed that can still lift water. If it remains below that hydraulic threshold, it can run without recovering pressure. Establish minimum speed from the pump curve, dynamic water level, motor cooling and field tests, then coordinate it with sleep logic.

After sleep, a functioning check valve should help retain column and system pressure as designed. A leaking valve can drain the riser or header, cause repeated wakes and produce long recovery times. Do not mask that symptom by endlessly widening the pressure differential. Test pressure decay and valve sealing as hydraulic functions.

Plan the Above-Ground Installation

The drive environment can differ greatly from the submerged motor environment. Confirm ambient temperature, altitude, ventilation, dust, water exposure, sunlight, access, cable entry and enclosure arrangement. AUSENIST YS620 and YS820 have documented IP54 protection, but the completed assembly depends on the glands, connectors, covers and workmanship as well as the VFD housing.

For a YS620 installation above 1,000 m, use its documented altitude derating rule. No altitude derating is required below 1,000 m; capacity is derated by 1% for every additional 100 m. This calculation can change the selected drive size. High-altitude compatibility must never be marketed as operation without limits.

Commission with Measured Data

Test startup, normal duty, reduced demand, sleep, wake, water-shortage response and recovery after a controlled demand change. Compare current and hydraulic performance with the motor nameplate and pump curve. Investigate discrepancies rather than adjusting limits until the result looks acceptable.

Retain a commissioning record with the pump and motor identifiers, cable specification and length, sensor type and range, approved parameters, protection tests and baseline readings. This information is much more useful to remote support than a photo of one fault code.

Turn One Installation into a Controlled OEM Package

AUSENIST customization can cover pump and motor matching, YS620 or YS820 selection, induction-motor or PMSM control, voltage review, sensor compatibility, parameter presets, communication, system-control behavior, cabinet or mounting concept, documentation, packaging, and OEM or private-label presentation.

Communication needs should be decided early. YS620 provides dual RS485 across its documented 0.75–7.5 kW range. YS820 covers 0.75–22 kW; its 220 V 0.75 and 2.2 kW versions use single RS485, while the 380 V versions use dual RS485. A project that needs one connection for pump coordination and another for external monitoring should reflect this distinction in series selection.

The result should be a defined application envelope: approved pumps and motors, supply options, maximum reviewed cable arrangement, hydraulic duty range, sensor configuration, altitude rules, mounting drawing and test criteria. That is how a deep-well VFD package becomes reproducible without claiming that one parameter file fits every borehole.