E6581595
A-18
1
(2) CT
and
ammeter
If a CT and ammeter are connected externally to detect inverter output current, the leak current's high
frequency component may destroy the ammeter. If the wires are more than 50 meters long, it will be
easy for the high frequency component to pass through the externally connected CT and be
superimposed on and burn the ammeter with models having motors of low rated current (several A
(ampere) or less), because the leakage current will increase in proportion to the motor's rated current.
Remedies:
1. Use a meter output terminal in the inverter control circuit.
The load current can be output on the meter output terminal (FM). If the meter is connected, use an
ammeter of 1mAdc full scale or a voltmeter of 10Vdc full scale.
0-20mAdc (4-20mAdc) can be also output. (Refer to section 3.4)
2. Set
: PWM carrier frequency=4 kHz or less. However the motor magnetic noise is increased.
(Refer to section 6.11)
3. Use the monitor functions built into the inverter.
Use the monitor functions on the panel built into the inverter to check current values. (Refer to
section 8.2.1)
(4) Influence and remedy of the leakage current by long-distance wiring
Caution
Mandatory
action
As a remedy, when using an AC reactor (PFL series) for the output side of an inverter, Set
: PWM
carrier frequency=2 kHz or less.
This can also cause serious accidents through overheating and fire.
Make the wiring length between an inverter and a motor 100 m or less, and shorten as much as
possible.
When connecting two or more sets of motors, the wiring length is the total wiring length.
Over-current trip may be occurred according to the charging current which will flow into the electrostatic
capacity between cables if wiring length becomes long.
In that case, please cope with installing an AC reactor (PFL series) in the output side of an inverter, or
reduces the electrostatic capacity of a cable etc. by wiring by loose wires, etc.
