E6580516
4.
Operation
Precautions
Observe the following points when using the VF-AS inverter
4.1 Cautions Regarding Motor
Comparison with
com-
mercial power source
operation:
Running at low-speeds:
Adjustment of overload
protection
level:
Running at speeds
exceeding
60Hz:
Load equipment lubrication
method:
Ultra-light loads and low-
inertia loads:
Measures for
instability
phenomena:
The
VF-A5 inverter uses a sinusoidal-wave PWM method, but the
output voltage and output current
will be distorted waveforms which
closely approximate sinusoidal waveforms, instead of complete
sinusoidal waveforms. In comparison to operating with the commercial
power source, the motor temperature rise, noise and vibration will
increase slightly.
When the inverter is used in combination with a general purpose
motor and run at
low speeds,
the
motor's cooling effect will decrease.
Therefore, the output load must be reduced to
less than the rated
load. If the motor is to be run at the rated torque even at low speeds,
use a
Toshiba"VF motor" specially designed for use with inverters.
When used with a
VF motor, the inverter's overload protection level
must be adjusted. (Refer to pages 77, 78 for details. )
When using this inverter with a general purpose motor, the overload
protection of the
VF-A5 is performed by use of an overload detection
circuit
(electronic thermal relay) that meets a general purpose motor's
reduced load characteristics. The reference current
value for this
electronic thermal relay is set to the inverter's rated current value;
therefore, this may need adjustment depending on the motor.
When operating at a frequency that exceeds
60Hz, motor vibration
and noise
will increase. Furthermore, this type of operation may be
limited by the motor's
mechanical strength and bearing construction,
so please contact the motor manufacturer for further information.
When driving an
oil-lubricated speed reduction gear or geared motor,
the
lubrication may deteriorate at low-speeds, so contact the speed
reduction gear manufacturer for information on
usable variable-speed
areas.
Instability phenomena, such as abnormal vibration or overcurrent
trips, may occur when operating with an
ultra-light load at a load ratio
of
5%
or less, or with a load having
an
extremely small moment of
inertia.
In these cases, lower the carrier frequency. (Refer to page 71)
Instability phenomena may also occur when using the inverter with the
following types of motors or loads, so always confirm applicability
before use.
(1)
Combination with motor exceeding recommended applicable motor rating.
(2)
Combination with special motors such as explosion-proof motors.
(3)
Combination with special loads having severe rotational
fluctuations, such as piston-type movements.
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