Goodrive350 IP55 High-ingress Protection Series VFD
Troubleshooting
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7.7.3 Failure to stop and indicator shimmering due to motor cable coupling
Interference phenomenon:
1. Failure to stop
In a VFD system where an S terminal is used to control the start and stop, the motor cable and
control cable are arranged in the same cable tray. After the system is started properly, the S
terminal cannot be used to stop the VFD.
2. Indicator shimmering
After a VFD is started, the relay indicator, power distribution box indicator, PLC indicator, and
indication buzzer shimmers, blinks, or emits unusual sounds unexpectedly.
Solution:
1. Check and ensure that the exception signal cable is arranged 20 cm or farther away from
the motor cable.
2. Add a safety capacitor of 0.1
μF between the digital input terminal (S) and the COM
terminal.
3. Connect the digital input terminal (S) that controls the start and stop to other idle digital input
terminals in parallel. For example, if S1 is used to control the start and stop and S4 is idle,
you can try to connect connect S1 to S4 in parallel.
Note:
If the controller (such as PLC) in the system controls more than 5 VFDs at the same time
through digital input terminals (S), this scheme is not available.
7.7.4 Leakage current and interference on RCD
VFDs output high-frequency PWM voltage to drive motors. In this process, the distributed
capacitance between the internal IGBT of a VFD and the heat sink and that between the stator
and rotor of a motor may inevitably cause the VFD to generate high-frequency leakage current
to the ground. A residual current operated protective device (RCD) is used to detect the
power-frequency leakage current when a grounding fault occurs on a circuit. The application of
a VFD may cause misoperation of a RCD.
1. Rules for selecting RCDs
(1) VFD systems are special. In these systems, it is required that the rated residual current of
common RCDs at all levels is larger than 200 mA, and the VFDs are grounded reliably.
(2) For RCDs, the time limit of an action needs to be longer than that of a next action, and the
time difference between two actions need to be longer than 20 ms. For example, 1s, 0.5s,
and 0.2s.
(3) For circuits in VFD systems, electromagnetic RCDs are recommended. Electromagnetic
RCDs have strong anti-interference capability, and thus can prevent the impact of
high-frequency leakage current.
Electronic RCD
Electromagnetic RCD
Low cost, high sensitivity, small in volume,
susceptible to voltage fluctuation of the grid and
ambient temperature, weak anti-interference
capability
Requiring highly sensitive, accurate, and stable
zero-phase sequence current transformer, using
permalloy high-permeability materials, complex
process, high cost, not susceptible to voltage
fluctuation of the power supply and ambient
temperature, strong anti- interference capability
