Leakage Current And Interference On Rcd - Kruger Ecowatt K320 Series Operation Manual

Ecowatt Drive K320 series
®

7.7.4 Leakage current and interference on RCD

The VFD outputs high-frequency PWM voltage to drive motors. In this process, the distributed
capacitance between the internal IGBT of the 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 the 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
Low cost, high sensitivity, small in
volume, susceptible to voltage fluctuation
of the grid and ambient temperature,
weak anti-interference capability
2. Solution to RCD misoperation (handling the VFD)
(1) Try to remove the jumper cap at "EMC/J10" on the middle casing of the VFD.
(2) Try to reduce the carrier frequency to 1.5 kHz (P00.14=1.5).
(3) Try to modify the modulation mode to "3PH modulation and 2PH modulation"
(P08.40=0).
3. Solution to RCD misoperation (handling the system power distribution)
(1) Check and ensure that the power cable is not soaking in water.
(2) Check and ensure that the cables are not damaged or spliced.
(3) Check and ensure that no secondary grounding is performed on the neutral wire.
(4) Check and ensure that the main power cable terminal is in good contact with the air
switch or contactor (all screws are tightened).
(5) Check 1PH powered devices, and ensure that no earth lines are used as neutral wires by
these devices.
Note: Do not use shielded cables as VFD power cables and motor cables.
Electromagnetic RCD
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
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Troubleshooting