Mitsubishi Electric FR-F700PJ Series Manual page 74

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 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)
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).
 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.
Noise reduction examples
Enclosure
Inverter
power
Filterpack
supply
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.
74
FR- BLF
Install line noise filter
Decrease
FR- BSF01
carrier frequency
on inverter output side.
FR-
Motor
Inverter M
BSF01
Use 4-core cable for motor
power cable and use one
cable as earthing (grounding)
cable.
Use a shielded twisted pair 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 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
Type 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
Influence
 If the carrier frequency setting is high, decrease the Pr.
and
72 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).
NV1
Power
Undesirable
supply
current Leakage
breaker
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 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
Influence
motor current increases.
and
 Countermeasures
 Use Pr. 9 Electronic thermal O/L relay.
measures
 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
Undesirable
Power
current
supply
path
Line-to-line leakage currents path
Inverter
Motor
C
C
Motor
C
Thermal relay
Motor
Inverter M
Line-to-line static
capacitances