Filter
Top Products
FOR CORRECT OPERATION
Application to Motors
For operation at higher than 60Hz, it is required to examine the allowable torque of the motor, useful life of bearings, noise, vibration,
etc. In this case,
be sure to consult the motor manufacturer as the maximum allowable rpm differs depending on the motor capacity, etc.
The torque characteristics of driving a general-purpose motor with an inverter differ from those of driving it using commercial power
(starting torque decreases in particular). Carefully check the load torque characteristic of a connected machine and the driving torque
characteristic of the motor.
Application to general-purpose motors
Operating frequency
Torque characteristics
An inverter-driven general-purpose motor heats up quickly at lower speeds. Consequently, the continuous torque level (output) will
decrease at lower motor speeds. Carefully check the torque characteristics vs speed range requirements.
Motor loss and
temperature increase
When run by an inverter, a general-purpose motor audible slightly greater than with commercial power.
Noise
When run by an inverter at variable speeds, the motor may generate vibration, especially because of (a) unbalance of the rotor
including a connected machine, or (b) resonance caused by the natural vibration frequency of a mechanical system. Particularly, be
careful of (b) when operating at variable speeds a machine previously fitted with a constant speed motor. Vibration can be minimized
by (1) avoiding resonance points using the frequency jump function of the inverter, (2) using a tireshaped coupling, or (3) placing a
rubber shock absorber beneath the motor base.
Vibration
Under continued, low-speed operation, oil lubrication can deteriorate in a power transmission mechanism with an oil-type gear box
(gear motor) or reducer. Check with the motor manufacturer for the permissible range of continuous speed. To operate at more than
60Hz, confirm the machine's ability to withstand the centrifugal force generated.
Power transmission
mechanism
The allowable rotation range of continuous drive varies depending on the lubrication method or motor manufacturer.
(Particularly in case of oil lubrication, pay attention to the low frequency range.)
Application to special motors
Gear motor
For use of a brake-equipped motor, be sure to connect the braking power supply from the primary side of the inverter.
Brake-equipped motor
There are different kinds of pole-change motors (constant output characteristic type, constant torque characteristic type, etc.), with
different rated current values. In motor selection, check the maximum allowable current for each motor of a different pole count. At
the time of pole changing, be sure to stop the motor. Also see: Application to the 400V-class motor.
Pole-change motor
The rated current of a submersible motor is significantly larger than that of the general-purpose motor. In inverter selection, be sure
to check the rated current of the motor.
Submersible motor
Inverter drive is not suitable for a safety-enhanced explosion-proof type motor. The inverter should be used in combination with a
pressure-proof explosion-proof type of motor.
*Explosion-proof verification is not available for SJ700/SJ700D/SJ700B Series.
Explosion-proof motor
In most cases, the synchronous (MS) motor and the high-speed (HFM) motor are designed and manufactured to meet the
specifications suitable for a connected machine. As to proper inverter selection, consult the manufacturer.
Synchronous (MS) motor
High-speed (HFM) motor
A single-phase motor is not suitable for variable-speed operation by an inverter drive. Therefore, use a three-phase motor.
Single-phase motor
Application to the 400V-class motor
Notes on Use
Drive
Run or stop of the inverter must be done with the keys on the operator panel or through the control circuit terminal. Do not operate
by installing a electromagnetic contactor (MC) in the main circuit.
Run/Stop
When the protective function is operating or the power supply stops, the motor enters the free run stop state. When an emergency
stop is required or when the motor should be kept stopped, use of a mechanical brake should be considered.
Emergency motor stop
A max. 400Hz can be selected on the SJ700/SJ700D/SJ700B Series. However, a two-pole motor can attain up to approx. 24,000
rpm, which is extremely dangerous. Therefore, carefully make selection and settings by checking the mechanical strength of the
motor and connected machines. Consult the motor manufacturer when it is necessary to drive a standard (general-purpose)motor
above 60Hz. A full line of high-speed motors is available from Hitachi.
High-frequency run
Repetitive operation on starting or plugging
Operation use in highlands beyond 1,000m above sea level
About frequent repetition use (crane, elevator, press, washing machine) , a power semiconductor (IGBT, a rectification diode, thyristor) in the inverter may
come to remarkably have a short life by thermal fatigue.
The life can be prolonged by lower a load electric current. Lengthen acceleration / deceleration time. Lower carrier frequency. or increasing capacity of the inverter.
Due to the air density decreasing, whenever standard inverters are used for altitudes above 1000m, the following conditions are additionally required for
proper operation. In application for operation over 2500m, kindly contact your nearest sales office for assistance.
1. Reduction of inverter rated current
Current rating has to be reduced 1% for every 100m that exceeds from an altitude of 1000m.
For example, for inverters placed at an altitude of 2000m, the rated current has to be reduced 10% (Rated current x0.9) from its original amount.
{(2000m-1000m)/100m*-1%=-10%}
2. Reduction of breakdown voltage
Whenever an inverter is used at altitudes beyond 1000m, the breakdown voltage decreases as follows:
1000m or less: 1.00 / 1500m: 0.92 / 2000m: 0.90 / 2500m: 0.85. As mentioned in the instruction manual, please avoid any pressure test.
A system applying a voltage-type PWM inverter with IGBT may have surge voltage at the motor terminals resulting from the cable constants including
the cable length and the cable laying method. Depending on the surge current magnification, the motor coil insulation may be degraded. In particular,
when a 400V-class motor is used, a longer cable is used, and critical loss can occur, take any of the following countermeasures:
(1) install the LCR filter between the inverter and the motor,
(2) install the AC reactor between the inverter and the motor, or
(3) enhance the insulation of the motor coil.
37