Electro-Magnetic Interference (Emi) And Leakage Currents - Mitsubishi Electric 800 Series Instruction Manual

Electro-magnetic interference (EMI) and leakage currents

3.1
Electro-magnetic interference (EMI) and
leakage currents
3.1.1
Leakage currents and countermeasures
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 countermeasures.
Select the earth leakage current breaker according to its rated sensitivity current, independently of the carrier frequency
setting.
To-earth (ground) leakage currents
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 leakage circuit breakers and earth leakage relays unnecessarily.
Countermeasures
• If the carrier frequency setting is high, decrease the Pr.72 PWM frequency selection setting.
Note that 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).
NOTE
• Long wiring will increase the leakage current.
• High motor capacity will increase the leakage current.
Line-to-line leakage currents
Harmonics of leakage currents flowing in static capacitances between the inverter output cables may operate the external
thermal relay unnecessarily. When the wiring length is long (50 m or more) for the 600 V class small-capacity models (FR-
A860-00170 or lower), the external thermal relay is likely to operate unnecessarily because the ratio of the leakage current to
the rated motor current increases.
Line-to-line leakage current example (600 V class)
Motor
Rated motor
capacity
current (A)
(kW)
0.75 1.1
1.5 2.0
2.2 3.2
3.7 5.2
5.5 7.8
7.5 9.9
.
Power
supply
Countermeasures
• 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. Selecting Pr.240 Soft-PWM operation selection makes 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.
Installation and selection of the molded case circuit breaker
68
PRECAUTIONS FOR USE OF THE INVERTER
Leakage current (mA)
Wiring length 50 m
1020
1110
1200
1320
1470
1605
MCCB MC
Inverter/
converter
Line-to-line leakage currents path
• Motor
• Carrier frequency: 14.5k Hz
Wiring length 100 m
• Used wire: 2 mm
1590
1680
1770
1890
2040
2175
Thermal relay
Line-to-line static
capacitances
2
, 4cores
Cabtyre cable
Motor
M