Earth (Ground); Noise; Leakage Currents - Mitsubishi Electric FR-D700 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 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 and chassis)

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, radio noise
filter FR-BIF produces an effect.
As measures against sensor malfunction, line noise filter FR-
BSF01, 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.
Noise reduction examples
FR- BLF
Install common mode filter
FR- BSF01
on inverter input side. Enclosure
Inverter
FR-
power
Inverter
BSF01
supply
Install capacitor type FR-BIF filter
FR-
on inverter input side.
BIF
Separate inverter and power
line by more than 30cm (at
least 10cm) from sensor circuit.
Control
Power
power supply
supply for sensor
Do not earth (ground)
enclosure directly.
Do not earth (ground) control cable.
FR- BLF
Install common mode filter
Decrease
FR- BSF01
carrier frequency
on inverter output side.
FR-
IM Motor
BSF01
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.

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 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 measures. Select the earth leakage
current breaker according to its rated sensitivity current,
independently of the carrier frequency setting. (Refer to page 26)
To-earth (ground) leakage currents
Type Influence and Measures
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
Influence and If the carrier frequency setting is high, decrease the Pr.
measures 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).
NV1
Power
supply
Undesirable
Leakage
breaker
current path
NV2
Leakage
breaker
Line leakage current
Type 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 model, the external thermal relay is likely to
operate unnecessarily because the ratio of the leakage
current to the rated motor current increases.
Influence and Countermeasures
measures • 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.
MCCB MC
Power
Undesirable
supply
current path
Line-to-line leakage currents path
Inverter
Motor
C
C
Motor
C
Thermal relay
Motor
IM
Inverter
Line-to-line static
capacitances
30