Mitsubishi Electronics FR-F700 instruction manual Leakage currents, Noise reduction examples

Noise

When performing low-noise operation at higher carrier frequency, electromagnetic noise tends to increase. Therefore, refer to the following measure example and consider taking the measures. Depending on the installation condition, the inverter may be affected by noise in a non-low noise (initial) status.

￿The noise level can be reduced by decreasing the carrier frequency (Pr. 72).

￿As measures against AM radio broadcasting noise and sensor malfunction, turning on the built-in noise reduction filter produces an effect. (For the switching method, refer to the instruction manual.)

￿As measures against induction noise from the power cable of the inverter, an effect is produced by putting a distance of 30cm (at least 10cm) or more and using a twisted pair shielded cable as a signal cable. Do not earth (ground) shield but connect it to signal common

cable.

Noise reduction examples

Install filter (FR-BLF,

Enclosure Decrease carrier frequency FR-BSF01) on inverter output side.

Inverter			FR-
power	EMC	Inverter		IM	Motor
			BLF
supply	filter

		Use 4-core cable for motor
Separate inverter and		power cable and use one cable
power line by more than		as earth (ground) cable.
30cm (at least 10cm)
from sensor circuit.		Use a twisted pair shielded cable
Control	Power	Sensor
power	supply for
	sensor
supply
Do not earth (ground)		Do not earth (ground) shield but
enclosure directly.		connect it to signal common cable.

Do not earth (ground) control cable.

Leakage currents

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 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 measures. Select the earth leakage breaker according to its rated sensitivity current, independently of the carrier frequency setting.

To-earth (ground) leakage currents

Type Influence and Measures

⋅Leakage currents may flow not only into the inverter's own line but also into the other lines through the earth (ground) cable, etc.These leakage currents may operate earth (ground) leakage circuit breakers and earth leakage relays unnecessarily.

Influence	￿ Countermeasures
	⋅	If the carrier frequency setting is high, decrease the Pr. 72
and
		PWM frequency selection setting.
measures
		Note that motor noise increases. Select Pr. 240 Soft-PWM
		operation selection to make 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).

		Inverter
Power	NV1	Motor
supply		C
Undesirable	Leakage
	breaker	C
current path
	NV2	Motor
	Leakage	C
	breaker

Line leakage current

Type Influence and Measures

⋅This leakage current flows via a static capacitance between the inverter output cables.

⋅The external thermal relay may be operated unnecessarily by the harmonics of the leakage current.When the wiring length is long (50m or more) for the 400V class small- capacity model (7.5kW or less), the external thermal relay is

Influence	likely to operate unnecessarily because the ratio of the
	leakage current to the rated motor current increases.
and	￿ Countermeasures
measures	⋅ 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. Select Pr. 240 Soft-PWM operation selection to make 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.

	MCCB	MC		Thermal relay	Motor
Undesirable	Power		Inverter		IM
	supply
current path
				line-to-line static
				capacitances
			Line-to-line leakage currents path

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