Franklin 2007 manual Variable Speed Submersible Pump Operation, Inverter Drives

Application – Three-Phase Motors

Variable Speed Submersible Pump Operation, Inverter Drives

Franklin three-phase submersible motors are operable from variable frequency inverter drives when applied within guidelines below. These guidelines are based on present Franklin information for inverter drives, lab tests and actual installations, and must be followed for warranty to apply. Franklin two-wire and three-wire single-phase submersible motors are not recommended for variable speed operation.

WARNING: There is a potential shock hazard from contact with insulated cables from a PWM drive to the motor. This hazard is due to high frequency voltage content of a PWM drive output.

Load Capability: Pump load should not exceed motor nameplate service factor amps at rated voltage and frequency.

Frequency Range: Continuous between 30 Hz and rated frequency (50 or 60 Hz). Operations above rated frequency require special considerations, consult factory for details.

Volts/Hz: Use motor nameplate volts and frequency for the drive base settings. Many drives have means to increase effi ciency at reduced pump speeds by lowering motor voltage. This is the preferred operating mode.

Voltage Rise-time or dV/dt: Limit the peak voltage to the motor to 1000 V and keep the rise-time greater than 2 µsec. Alternately stated: keep dV/dt < 500 V/µsec. See Filters or Reactors below.

Motor Current Limits: Load no higher than motor nameplate service factor amps. For 50 Hz ratings, nameplate maximum amps are rated amps. See Overload Protection below.

Motor Overload Protection: Protection in the drive (or separately furnished) must be set to trip within 10 seconds at 5 times motor maximum nameplate amps in any line, and ultimately trip within 115% of nameplate maximum amps in any line.

Subtrol-Plus and SubMonitor: Franklin’s Subtrol-Plus and SubMonitor protection systems ARE NOT USABLE on VFD installations.

Start and Stop: One second maximum ramp-up and ramp-down times between stopped and 30 Hz Stopping by coast-down is preferable.

Successive Starts: Allow 60 seconds before restarting.

Filters or Reactors: Required if all three of the following

conditions are met: (1) Voltage is 380 or greater and

(2)Drive uses IGBT or BJT switches (rise-times < 2 µsec) and (3) Cable from drive to motor is more than

50 ft (15.2 m) A low-pass fi lter is preferable. Filters or reactors should be selected in conjunction with the drive manufacturer and must be specifi cally designed for VFD operation.

Cable Lengths: Per Franklin’s cable tables unless a reactor is used. If a long cable is used with a reactor, additional voltage drop will occur between the VFD and the motor. To compensate, set the VFD output voltage higher than the motor rating in proportion to the reactor impedance (102% voltage for 2% impedance, etc.).

Motor Cooling Flow: For installations that are variable-fl ow, variable-pressure, minimum fl ow rates must be maintained at nameplate frequency. In variable-

flow, constant pressure installations, minimum fl ow rates must be maintained at the lowest fl ow condition. Franklin’s minimum fl ow requirements for 4" motors : 0.25 ft/s (7.26 cm/sec) and for 6" and 8" motors: 0.5 ft/s (15.24 cm/sec)

Carrier Frequency: Applicable to PWM drives only. These drives often allow selection of the carrier frequency. Use a carrier frequency at the low end of the available range.

Miscellaneous: Franklin Electric three-phase motors are not declared “Inverter Duty” motors per NEMA MG1 standards. The reason is Part 31 of NEMA standard MG1 does not include a section covering encapsulated winding designs. However, Franklin submersible motors can be used with VFDs without problems and/or warranty concerns provided these guidelines are followed.

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