Noise; Leakage Currents; Line Leakage Current; Noise Reduction Examples - Mitsubishi Electric FR-F700 Manual

Noise

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).
As measures against AM radio broadcasting noise and
sensor malfunction, turning on the built-in noise
reduction filter produces an effect. (For the switching
method, refer to the instruction manual.)
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
twisted pair shielded cable as a signal cable. Do not
earth (ground) shield but connect it to signal common
cable.

Noise reduction examples

Enclosure Decrease carrier frequency
Inverter
power
EMC
supply filter
Separate inverter and
power line by more than
30cm (at least 10cm)
from sensor circuit.
Power
Control
supply for
power
sensor
supply
Do not earth (ground)
enclosure directly.
Do not earth (ground) control cable.

Leakage currents

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.
To-earth (ground) leakage currents
Type
⋅
Leakage currents may flow not only into the inverter's own
line but also into the other lines through the earth (ground)
cable, etc.These leakage currents may operate earth
(ground) leakage circuit breakers and earth leakage relays
unnecessarily.
Countermeasures
Influence
⋅
If the carrier frequency setting is high, decrease the Pr. 72
and
PWM frequency selection setting.
measures
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).
Power
supply
Undesirable
current path
61
Install filter (FR-BLF,
FR-BSF01) on
inverter output side.
FR-
Inverter
IM
BLF
Use 4-core cable for motor
power cable and use one cable
as earth (ground) cable.
Use a twisted pair shielded cable
Sensor
Do not earth (ground) shield but
connect it to signal common cable.
Influence and Measures
Inverter
NV1
Motor
C
Leakage
breaker
C
NV2
Motor
C
Leakage
breaker

Line leakage current

Type
⋅ This leakage current flows via a static capacitance between
⋅ The external thermal relay may be operated unnecessarily
Influence
and
⋅ Use Pr. 9 Electronic thermal O/L relay.
measures
⋅ If the carrier frequency setting is high, decrease the Pr. 72
Undesirable
current path
Motor
Influence and Measures
the inverter output cables.
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
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.
MCCB MC
Thermal relay
Power
Inverter
supply
Line-to-line leakage currents path
Motor
IM
line-to-line static
capacitances