Mitsubishi Electric FR-A700 Series, Technical Manual

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SELECTION
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LECTION
3
3.3.4 Brake motor
When a motor with magnetic brake is operated by the
inverter, the power for the brake must be supplied from the
primary side of the inverter. (Modifications must be made to
a motor with brake where the motor terminals are
connected with the brake terminals inside the motor, e.g. a
current type brake which operates the brake using a large
starting current.)
To stop the motor with the magnetic brake, turn ON the
output stop signal (MRS) of the inverter, and at the same
time, turn OFF the start input signal (STF or STR). If MRS
signal is not used, the braking force will reduce at the time
of braking and/or a lock current will flow in the motor,
causing the electronic thermal relay to be activated by the
current limit function which has been activated for a long
time.
Other instructions
1) The brake should be used at a speed of 1800 r/min or
less. If the motor running at high speed is brought
to a sudden stop, the braking capacity of the
electromagnetic brake may be insufficient
depending on the value of load J (moment of
inertia).
2) When the motor is provided with the NB brake,
continuous low-speed operation below 900 r/min
may cause noise to be generated due to the
looseness of the brake disc, which does not cause
a functional problem. This type of motor can be
used without fault if operated at low speed for a
short duration, e.g. positioning to a stop.
Setting of factory shipment is AC synchronous
OFF connection. For further reduction of the
coasting time, DC OFF is available.
3.3.5 Pole changing motor
Since a pole-change motor has difference in rated current
from a general-purpose motor, the inverter should be
selected after checking the rated motor current. The
number of poles must be changed after stopping the motor.
If it is changed during rotation, the inverter is brought to a
fault as indicated in the table on the right and proper
operation cannot be performed.
3.3.6 Submersible motor
Since its rotor and other parts rotate under water, a water
seal type submersible motor is larger in both mechanical
loss and rated current than a general-purpose motor.
Select the inverter capacity so that its rated output current
is more than 1.1 times greater than the rated current of the
submersible motor. (An inverter of one rank higher capacity
may be required for the motor.)
When large torque is required due to lodged sand etc., an
inverter of one rank higher capacity may be selected to
raise its overload capacity and the motor capacity may also
be increased. Alternatively, the torque boost ([
Pr. 0 ]) setting
value may be increased.
Other instructions
1) As compared to the one driven by a commercial
power supply, the submersible motor driven by an
inverter is slightly higher in motor temperature
rise. Particularly in a canned system, the increase
in can loss causes the submersible motor driven
by the inverter to be about 15% higher in
temperature than the one driven by a commercial
power supply.
2) Protection of submersible motor
Since the submersible motor may be installed
deep in a well, it is difficult to detect its fault from
the ground, and its permissible lock time is short.
Hence, an appropriate protection relay must be
selected to protect the submersible motor.
Ideally, the installation of a thermal detector, e.g.
thermistor, on the motor for the detection of coil
temperature ensures safety, which detects faults
occurring in a low-speed range (ambient water
temperature rise, overload operation). Generally,
provide a thermal relay between the inverter and
motor, and set zero in electronic thermal O/L relay
([
Pr. 9 ]) of the inverter. Set the overload protection
of the thermal relay to the rated motor current and
set the lock protection to within 5 seconds (3
seconds preferable).
3) When the cable length between the motor and
inverter is long, use a large-diameter cable to
prevent the motor torque from decreasing due to
the voltage drop over the cable.
4) Using an existing submersible motor
The inverter power supply generates a surge
voltage, causing the voltage to rise sharply (dV/dt
is large). Therefore when using an installed
submersible motor, a high voltage developed by
the inverter may burn out the motor if insulation is
lower than 10M
Ω
. Check that the insulation of the
submersible motor has not deteriorated.
5) Installation of a leakage current relay
The installation of a leakage current relay informs
of an alarm or an insulation fault of the
submersible motor and cable, allowing measures
to be taken in advance. Larger in normal leakage
current and longer in cable length than a land
motor, the submersible motor should be selected
with consideration given to a large leakage
current.
Switching from high-speed
operation to low-speed
operation Overcurrent (OC3) or regenerative
overvoltage (OV3) is activated to
coast the motor to a stop.
Switching from low-speed
operation to high-speed
operation
Overcurrent (OC1) is activated to
coast the motor to a stop.