Appendix A. EMC Standard Installation GuideVFD-ED
A-5 Solution to EMC: Filter
A-5-1 Filter
Electromagnetic interference is transmitted in two ways, by radiation and by conduction. The most
effective and economical method of reducing radiated interference is to use shielding and of reducing
conducted interference is to use an electromagnetic filter.
Noise interference can be divided into two categories: high frequency (150 kHz–300 MHz) and low
frequency (100–3000 Hz). High-frequency noise fades more over distance and has a shorter wave-
length, while low-frequency noise fades less over distance and has a longer wave-length. Both types
of interference are transmitted through power cables and power leads, affecting the power supply side.
High-frequency interference at the power side can be eliminated or attenuated by mounting a filter.
The filter consists of coils and capacitors. Some drives do not have a built-in filter, in which case the
installation of an external option filter is required. Figure A-20 below shows a standard filter diagram.
A filter is composed of a Differential Mode section (to eliminate noise below 150 kHz) and a Common
Mode section (to eliminate noise above 150 kHz). For high-frequency noise, the inductor acts as a
high impedance to form an open circuit and the capacitor acts as a low impedance to form a short
circuit. Proper design and dimensioning of inductors and capacitors give a resonant circuit to absorb
harmonic currents. Capacitor Cy is earthed to lead the harmonic currents to the ground.
External Filter
The filter and the AC drive should be installed in the control cabinet or on the mounting plate that is
earthed to ground. The motor cable must be shielded and as short as possible. Use the filters
recommended by Delta to ensure compliance with EMC standards.
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