Three-phase motors
Use three-phase motors with the proper motor starter to ensure the
motor is protected against damage from low voltage, phase failure,
current imbalance and overload current.
Use a proper starter with ambient-compensated, class 10, extra
quick-trip overload relays or an MP 204 to provide the best possible
motor winding protection.
Each of the three motor legs must be protected with overloads.
The thermal overloads must trip in less than 10 seconds at locked
rotor (starting) current. A three-phase motor wiring diagram is
indicated in the figure below.
Ensure that the pump is completely submerged before
checking the direction of rotation. Severe damage may be
caused to the pump and motor if they are run dry.
6
1
5
4
3
2
TM050038
Three-phase wiring diagram for Grundfos motors and other motor
manufacturers
Pos.
Description
1
Power supply
2
Fused disconnect switch
3
Pressure switch
4
Well seal
5
Magnetic starter
6
Green
6.7.3 Variable-frequency drive operation
Grundfos motors
Three-phase Grundfos motors can be connected to a variable
frequency drive (VFD).
During variable-frequency drive operation, do not run the
motor at a frequency higher than the nominal frequency
and not lower than 30 Hz for asynchronous motors or 55
Hz for synchronous motors. In connection with pump
operation, never reduce the frequency (and consequently
the speed) to such a low level that the necessary flow of
the cooling liquid past the motor is no longer ensured.
If a Grundfos MS motor with temperature transmitter is
connected to a variable frequency drive, a fuse
incorporated in the transmitter melts, and the transmitter
becomes inactive. The transmitter cannot be reactivated.
This means that from that point on, the motor operates
like a motor without a temperature transmitter.
To enable the motor temperature monitoring, install a
Pt100 or Pt1000 sensor.
To avoid damage to the pump, make sure that the motor stops
when the pump flow falls below 0.1 x rated flow.
Depending on the type of the variable frequency drive, it may
expose the motor to detrimental voltage peaks.
The variable frequency drive must have an output sine-wave filter to
limit voltage peaks (Upeak) and to reduce dU/dt (or dV/dt) which
causes stress on the insulation of the submersible motor. For sine-
wave filter location placement within the system, see the
figure Location of the sine-wave filter in the system.
Protect the motor from voltage peaks (Upeak) and excess
dU/dt (or dV/dt) by using a sine-wave filter if one or more
of the following conditions are present:
•
The motor nameplate voltage is above 379 V.
•
The variable frequency drive (VFD) uses pulse width modulation
(PWM) and/or IGBT-BJT switches.
•
The VFD voltage rise time is less than 2 msec (NEMA MG
1-2011).
•
The power cable length from the VFD to the submersible motor
terminals is 0 to 1500 ft (0 to 457 m).
•
The power quality is not stable.
•
Keep the motor peak voltage (U
peak
) and dU/dt within the limits
listed in the table below.
For recommended best practice, use a resistor-inductor-
capacitor (RLC) type sine-wave filter. An equivalent type
LC sine-wave filter is acceptable.
Consult the VFD manufacturer for specific sine-wave filter
recommendation.
16
English (US)
Summary of Contents for SP 1100S
Page 2: ......
