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3. Precautions for Use of the Inverter
3.1 Electro-magnetic interference (EMI) and leakage currents
3
Precautions for Use of the Inverter
This chapter explains the precautions for use of this product.
Always read the instructions before use.
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 power system of the inverter but also into the other power systems through the
earthing (grounding) cable, etc. These leakage currents may operate earth leakage circuit breakers and earth leakage relays
unnecessarily.
Precautions
• 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 to suppress harmonics and surge voltage in the power system of the
inverter and other power systems, 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. The leakage current of the 400 V class is larger than that of the 200 V
class.
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.
Line-to-line leakage current example (600 V class)
Motor capacity
(kW)
Rated motor
current (A)
Leakage current (mA)
Condition
Wiring length 50 m
Wiring length 100 m
0.75
1.1
1020
1590
• Motor
• Carrier frequency: 14.5 kHz
• Cable: 2 mm
2
, 4 cores
• Cabtyre cable
1.5
2.0
1110
1680
2.2
3.2
1200
1770
3.7
5.2
1320
1890
5.5
7.8
1470
2040
7.5
9.9
1605
2175
Power
supply
Thermal relay
Line-to-line static
capacitances
MCCB
MC
Line-to-line leakage currents path
Motor
Inverter
M
