Mitsubishi Electric FREQROL-CS80, Manual

Page: 34 / 40

34
Pr
eca
utions for Periph
er
al De
vice
Selection
11
 Earth (ground)
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 the high-speed switching operation. Be sure to earth (ground) the
inverter and motor before use. In addition, always use the earth
(ground) terminal of the inverter to earth (ground) the inverter. (Do
not use the case or chassis)
 Electromagnetic interference (EMI)
For the low acoustic noise operation with high carrier frequency,
electromagnetic noise tends to increase. Take precautions by
referring to the following examples. Depending on the installation
conditions, noise may also affect the inverter in the normal operation
(initial status).
• Decrease the carrier frequency (
Pr.72 ) setting to lower the EMI
level.
• As measures against AM radio broadcasting noise, radio noise
filter FR-BIF produces an effect.
• As measures against sensor malfunction, line noise filter
FRBSF01, FR-BLF produces an effect.
• 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.
 leakage current
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 static 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 precaution. Select the earth leakage
current breaker according to its rated sensitivity current,
independently of the carrier frequency setting. (Refer to
page 31 )
To-earth (ground) leakage currents
Line-to-line leakage current
Type Influence and countermeasure
Influence and
countermeasure
• Leakage currents may flow not only into the inverter's
own line but also into the other line through the earth
(ground) 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. However,
the motor noise increases. Selecting Pr.240 Soft-
PWM operation selection makes 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).
Transmission
path
Inverter
Sensor
Use 4-core cable for motor
power cable and use one
cable as earthing cable.
Use a twisted pair shielded cable
Inverter
power
supply
Control
power
supply
Do not earth (ground) shield but
connect it to signal common cable.
Enclosure
Decrease
carrier frequency
Motor
IM
FR-
BSF01 FR-
BSF01
FR-
BIF
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 common mode filter
on inverter output side.
FR- BLF
FR- BSF01
Install capacitor type FR-BIF filter
on inverter input side.
Install common mode filter
on inverter input side.
FR- BLF
FR- BSF01
Power
supply
for sensor
EMI measure example
Power
supply
Leakage
breaker
Leakage
breaker
NV1
NV2
Inverter
Motor
Motor
C
C
C
Type Influence and countermeasure
Influence and
countermeasure
• 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 model, the external thermal relay
is likely to operate unnecessarily because the ratio of
the leakage current to the rated motor current
increases.
● Precaution
• Use Pr.9 Electronic thermal O/L relay .
• If the carrier frequency setting is high, decrease the
Pr.72 PWM frequency selection setting. However,
the motor noise increases. Selecting Pr.240 Soft-
PWM operation selection makes the sound
inoffensive. To protect motor securely without being
subject to the influence of the line-to-line leakage
current, direct detection of the motor temperature
using a temperature sensor is recommended.
Transmission
path
Power
supply
Thermal relay
Line-to-line static
capacitances
MCCB MC
Line-to-line leakage currents path
Motor
Inverter IM