Electro-Magnetic Interference (Emi) And Leakage Currents - Mitsubishi Electric FR-A802-P 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. The amount of current leakage depends on the size of the capacitance. Take the following precautions to prevent
current leakage. Earth leakage circuit breakers should be selected based on their rated current sensitivity.
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 cause unnecessary operation of the earth leakage relays.
Precautions
• Use an earth leakage circuit breaker with a weak sensitivity in a high frequency range.
The output current of the inverter contains a high-frequency leakage current component, which gives relatively low impacts
to human bodies. These leakage currents may trip an earth leakage circuit breaker or earth leakage relay unnecessarily.
• Minimize the line-to-earth stray capacitance.
Use the line-to-earth insulated with low dielectric constant material, and perform wiring to make the wiring length between
the inverter and the motor to be as short as possible.
To-earth (ground) leakage currents
• Take caution as long wiring will increase the leakage current.
• Increasing the motor capacity increases 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.
Power
supply
Precautions
• Use Pr.9 Electronic thermal O/L relay.
• 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.
• Increase the external thermal overload relay setting by the amount of the leakage current.
• Minimize the stray capacitance between the lines.
Use the cables insulated with low dielectric constant material, and perform wiring to make the wiring length between the
inverter and the motor to be as short as possible.
Installation and selection of the molded case circuit breaker
Install a molded case circuit breaker (MCCB) on the power receiving side to protect the wiring at the inverter input side.
Select an MCCB according to the inverter input side power factor, which depends on the power supply voltage, output
frequency and load. Especially for a completely electromagnetic MCCB, a slightly large capacity must be selected since its
operation characteristic varies with harmonic currents. (Check it in the data of the corresponding breaker.) As an earth
leakage current breaker, use the Mitsubishi earth leakage current breaker designed for harmonics and surge suppression.
68
PRECAUTIONS FOR USE OF THE INVERTER
Inverter
Line-to-line leakage currents path
Thermal relay
Motor
M
Line-to-line static
capacitances