74
When the inverter is run in the low acoustic noise mode, more leakage
currents occur than in the non-low acoustic noise mode due to high-
speed switching operation. Be sure to use the inverter and motor after
grounding (earthing) them. In addition, always use the earth (ground)
terminal of the inverter to earth (ground) the inverter. (Do not use the
case and chassis)
When performing low-noise operation at higher carrier frequency,
electromagnetic noise tends to increase.
Therefore, refer to the following measure example and consider taking
the measures. Depending on the installation condition, the inverter
may be affected by noise in a non-low noise (initial) status.
The noise level can be reduced by decreasing the carrier frequency
(Pr.72)
.
The Filterpack or FR-BIF radio noise filter is useful to suppress
noise on AM radio broadcasting.
The Filterpack or FR-BSF01/FR-BLF line noise filter is useful for
preventing malfunction of sensors, etc.
As measures against induction noise from the power cable of the
inverter, an effect is produced by putting a distance of 30cm (at least
10cm) or more and using a shielded twisted pair cable as a signal
cable. Do not earth (ground) shield but connect it to signal common
cable.
Capacitances exist between the inverter I/O cables, other cables and
earth and in the motor, through which a leakage current flows. Since its
value depends on the capacitances, carrier frequency, etc., low
acoustic noise operation at the increased carrier frequency of the
inverter will increase the leakage current. Therefore, take the following
measures. Select the earth leakage breaker according to its rated
sensitivity current, independently of the carrier frequency setting.
(Refer
to page 69)
To-earth (ground) leakage currents
Line leakage current
Earth (Ground)
Noise
Inverter
Sensor
Use 4-core cable for motor
power cable and use one
cable as earthing (grounding)
cable.
Use a shielded twisted pair cable
Inverter
power
supply
Control
power
supply
Do not earth (ground) shield but
connect it to signal common cable.
Enclosure
Decrease
carrier frequency
Motor
M
Filterpack
FR-
BSF01
Do not earth (ground)
enclosure directly.
Do not earth (ground) control cable.
Separate inverter and power
line by more than 30cm (at
least 10cm) from sensor circuit.
Install line noise filter
on inverter output side.
FR- BLF
FR- BSF01
Power
supply
for sensor
Noise reduction examples
Leakage currents
Type
Influence and Measures
Influence
and
measures
Leakage currents may flow not only into the inverter's
own line but also into the other lines through the
earthing (grounding) cable, etc. These leakage
currents may operate earth (ground) leakage circuit
breakers and earth leakage relays unnecessarily.
Countermeasures
If the carrier frequency setting is high, decrease the
Pr.
72 PWM frequency selection
setting.
Note that motor noise increases. Select
Pr. 240 Soft-
PWM operation selection
to make the sound inoffensive.
By using earth leakage circuit breakers designed for
harmonic and surge suppression in the inverter's own
line and other line, operation can be performed with the
carrier frequency kept high (with low noise).
Undesirable
current
path
Type
Influence and Measures
Influence
and
measures
This leakage current flows via a static capacitance
between the inverter output cables.
The external thermal relay may be operated
unnecessarily by the harmonics of the leakage current.
When the wiring length is long (50m or more) for the
400V class small-capacity model (7.5kW or less), the
external thermal relay is likely to operate unnecessarily
because the ratio of the leakage current to the rated
motor current increases.
Countermeasures
Use
Pr. 9 Electronic thermal O/L relay
.
If the carrier frequency setting is high, decrease the
Pr.
72 PWM frequency selection
setting.
Note that motor noise increases. Select
Pr. 240 Soft-
PWM operation selection
to make the sound inoffensive.
To ensure that the motor is protected against line-to-
line leakage currents, it is recommended to use a
temperature sensor to directly detect motor
temperature.
Undesirable
current
path
Power
supply
Leakage
breaker
Leakage
breaker
NV1
NV2
Inverter
Motor
Motor
C
C
C
Power
supply
Thermal relay
Line-to-line static
capacitances
MCCB
MC
Line-to-line leakage currents path
Motor
Inverter
M
Содержание F720PJ-11KF
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