Line-To-Line Leakage Current; Earth (Ground); Electromagnetic Interference (Emi); Leakage Current - Mitsubishi Electric FREQROL-CS80 Manual

 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.
EMI measure example
FR- BLF
Install common mode filter
FR- BSF01
on inverter input side.
Inverter
power
supply
Install capacitor type FR-BIF filter
on inverter input side.
Separate inverter and power
line by more than 30cm (at
least 10cm) from sensor circuit.
Control
power
supply
Do not earth (ground)
enclosure directly.
Do not earth (ground) control cable.
 leakage current
Capacitances exist between the inverter I/O cables, other cables
11
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
Type
• 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
Influence and
Pr.72 PWM frequency selection setting. However,
countermeasure
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).
Power
supply
Transmission
path
34
Install common mode filter
Decrease
Enclosure carrier frequency
on inverter output side.
FR- FR-
Inverter IM Motor
BSF01 BSF01
Use 4-core cable for motor
FR-
power cable and use one
BIF
cable as earthing cable.
Use a twisted pair shielded cable
Sensor
Power
supply
for sensor
Do not earth (ground) shield but
connect it to signal common cable.
Influence and countermeasure
Inverter
NV1
Motor
C
Leakage
breaker
C
NV2
Motor
C
Leakage
breaker

Line-to-line leakage current

Type
• This leakage current flows via a static capacitance
• The external thermal relay may be operated
Influence and
● Precaution
countermeasure
• Use Pr.9 Electronic thermal O/L relay.
• If the carrier frequency setting is high, decrease the
Power
Transmission
supply
path
FR- BLF
FR- BSF01
Influence and countermeasure
between the inverter output cables.
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.
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.
MCCB MC
Thermal relay
Inverter
Line-to-line static
capacitances
Line-to-line leakage currents path
Motor
IM