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 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). • 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, 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 (400 V class) 48 3. PRECAUTIONS FOR USE OF THE INVERTER 3.1 Electro-magnetic interference (EMI) and leakage currents NOTE Motor capacity (kW) Rated motor current(A) Leakage current (mA) Condition Wiring length 50 m Wiring length 100 m 0.4 1.1 620 1000 • Motor: SF-JR 4P • Carrier frequency: 14.5 kHz • Cable:
2 mm2, 4 cores • Cabtyre cable 0.75 1.9 680 1060 1.5 3.5 740 1120 2.2 4.1 800 1180 3.7 6.4 880 1260 5.5 9.7 980 1360 7.5 12.8 1070 1450