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Application – Three-Phase Motors
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.
Variable Speed Submersible Pump Operation, Inverter Drives
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-
fl ow, 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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