New EMC Filters Minimize Earth Leakage Currents

TDK Corporation presents the EPCOS LeaXield^TM active filter module, a new solution for the minimization of earth leakage currents in power drive systems with frequency converters. Leakage current can cause RCDs (residual current devices) to trip. In some applications this means that RCDs with low thresholds such as 30 mA cannot be used or only used with substantial additional expense. The LeaXield active filter module is connected between the RCD and the EMC input filter of the converter in standard three-phase industrial power grids and does not require an additional power supply.

LeaXield detects the common-mode currents on the load side via a current sensing transformer. An amplifier generates an inverse of the leakage currents and feeds them to the power line via a capacitor network. This produces almost complete cancellation of the leakage currents. LeaXield is now designed for rated currents up to 150 A for 3-phase grids at frequencies of 50/60 Hz and a rated voltage of 520 V AC. The new active filter can be used in systems with leakage currents up to 1000 mA.

In addition to minimizing earth leakage currents, LeaXield active filter modules can also improve the EMC performance of power drive systems in the range to approximately 500 kHz. The new active filter module achieves typical common-mode attenuation values of up to 30 dB at 4 kHz, 40 dB at 10 kHz, and 15 dB at 150 kHz.

The EPCOS LeaXield module can be retrofitted into existing converter-based installations in order to improve their EMC and RCD compatibility of the power drive system. Moreover, LeaXield circuits can be integrated into new EMC filter solutions in order to downsize the expensive current-compensated filter chokes.

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