Toshiba Tosvert VF-A5 - Manual (Page 11)

4. Operation Precautions
Observe the following points when using the VF-A5 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 currertt 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 72, 73 for details.)
When using this inverter with a general purpose motor, the overload
protection of the VF-A5 is performed by use of an overioad 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 wiil 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 66)
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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