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3
PRECAUTIONS FOR USE OF THE CONVERTER
UNIT
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 I/O cables or other cables of the inverter or the converter unit 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 or the converter unit'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, converter
unit's own line and other line, operation can be performed with the carrier frequency kept high (with low noise).
To-earth (ground) leakage currents
• Take caution as long wiring will increase the leakage current. Decreasing the carrier frequency of the inverter reduces the
leakage current.
• High motor capacity will increase the leakage current.
Line-to-line leakage currents
Harmonics of leakage currents flowing in static capacitances between the output cables of the inverter or the converter unit
may operate the external thermal relay unnecessarily.
Power
supply
Countermeasures
• Use Pr.9 Electronic thermal O/L relay.
• 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.
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.
52
3. PRECAUTIONS FOR USE OF THE CONVERTER UNIT
3.1 Electro-magnetic interference (EMI) and leakage currents
MCCB
MC
Converter
Line-to-line leakage currents path
Thermal relay
Inverter
unit
Motor
M
Line-to-line static
capacitances
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