Chapter 3 Precautions For Use Of The Inverter; Electro-Magnetic Interference (Emi) And Leakage Currents; Leakage Currents And Countermeasures - Mitsubishi Electric FR-A800 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.
For the separated converter type, refer to the "PRECAUTIONS FOR USE OF THE INVERTER" in the FR-A802 (Separated
Converter Type) Instruction Manual (Hardware).
For the IP55 compatible model, refer to the "PRECAUTIONS FOR USE OF THE INVERTER" in the FR-A806 (IP55/UL Type
12 specification) Instruction Manual (Hardware).
3.1
Electro-magnetic interference (EMI) and leakage
currents
3.1.1

Leakage currents and countermeasures

Capacitance exists between the inverter I/O cables, other cables and earth and in the motor, through which a leakage current
flows. The amount of current leakage depends on the factors such as the size of the capacitance and the carrier frequency.
Low acoustic noise operation at an increased carrier frequency of the inverter will increase current leakage. Take the following
precautions to prevent current leakage. Earth leakage circuit breakers should be selected based on their rated current
sensitivity, 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 devices, 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 capacitance 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-
A840-00250(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.
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3. PRECAUTIONS FOR USE OF THE INVERTER

3.1 Electro-magnetic interference (EMI) and leakage currents

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