Goodrive300-01A-RT series integrated machine Common EMC problems and troubleshooting
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E.4 Leakage current and residual current device (RCD)
As the VFD outputs high frequency PWM voltage to drive the motor, the distributed capacitance
against the radiator from internal IGBT and between rotor and stator of the motor may cause the VFD
to generate high frequency leakage current against the ground. While the RCD is used to detect the
power frequency leakage current when grounding fault occurred to electrical circuit, the application of
VFD may cause mal-operation of RCD.
How to select RCD:
Due to the specialty of VFD system, it is required that the rated residual operating current should be
above 200mA for regular RCDs at all levels, and the VFD must be grounded with proper technics.
As for the setting time of RCD, the time limit of preceding action should be longer than the secondary
action and time gap between them should be set to a value larger than 20ms e.g. 1s, 0.5s and 0.2s.
It is recommended to use electromagnetic RCD for the electrical circuit of VFD system. Such RCD
carries strong anti-interference capacity to prevent the RCD from being affected by high frequency
leakage current.
Low cost, high sensitivity, small size,
vulnerable to voltage fluctuation of the grid
and ambient temperature, weak
anti-interference capacity.
Require the zero sequence current
transformer to be quite sensitive, precise and
stable, made from permalloy material with
high permeability, complicated process and
high cost, immune to voltage fluctuation of the
grid and ambient temperature, strong
anti-interference capacity.
Solution to mal-operation of RCD (on the part of VFD)
Try to decrease the carrier frequency to 1.5kHz (P00.14=1.5).
Try to change the modulation mode to “3PH modulation and 2PH modulation” (P8.40=00).
Solution to mal-operation of RCD (on the part of system distribution)
Check and confirm the power cable is not immersed in water.
Check and confirm the cable is not broken or switched over.
Check and confirm if secondary grounding occurred to the null line.
Check and confirm if power cable terminal is in the air switch or the contactor is poorly
contacted (loose screws).
Check the single-phase electric equipment and confirm if the ground line is misused as null
line.
VFD power cable and motor cable should not be shielded ones.
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