Chapter 3 Precautions For Use Of The Inverter; Electro-Magnetic Interference (Emi) And Leakage Currents; Leakage Currents And Countermeasures - Mitsubishi Electric 800 Series Instruction Manual

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. When the wiring length is long (50 m or more) for the 400 V class small-capacity models (FR-
E840-0170(7.5K) 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 (200 V class)
Motor capacity
(kW)
0.4 1.8
0.75 3.2
1.5 5.8
2.2 8.1
3.7 12.8
5.5 19.4
7.5 25.6
*1 The leakage currents of the 400 V class are about twice as large.
90
3. Precautions for Use of the Inverter

3.1 Electro-magnetic interference (EMI) and leakage currents

Rated motor
current (A)
Wiring length 50 m
310
340
370
400
440
490
535
*1
Leakage current (mA)
Wiring length 100 m
500
530
560
590
630
680
725
Condition
• Motor: SF-JR 4P
• Carrier frequency: 14.5 kHz
2
• Cable: 2 mm , 4 cores
• Cabtyre cable