Page 54 - Energize June 2022

TECHNICAL

Series-passive THD and maintaining a good power factor. However, AFEs have some serious drawbacks. In
The most straightforward series-passive order to maintain a small form factor, lower switching frequencies are used, which result in
solution can be achieved using a line high switch ripples on the voltage waveform. This can cause other sensitive equipment like
reactor. This is a low-cost way to reduce PLCs and telemetry and communications networks to nuisance trip and malfunction.
current harmonics, while adding a level of Also, although this unit may at first seem to eliminate harmonics, it must be noted that
protection to the rectifier. with the AFE in addition to the VSD, there are now two drives in the circuit producing twice
the heat. Twice the heat with a 200 kW AFE will soon add up. For the panel builder or system
Shunt-passive integrator, bigger cooling systems are needed to cope with the excessive heat.
Shunt passive is power factor correction,
often using fixed capacitor banks, tuned Shunt-active
and detuned contactor-based units, Active filters provide the most efficient harmonic compensation in a compact unit that has
thyristor capacitor banks and fine-tuned little loss, is insensitive to grid conditions, cannot be overloaded and is easy to retrofit. All of
passive filters. These methods were this comes at a slightly higher cost, which is offset by the better return on investment over
principally developed to resolve reactive the longer term.
power and not specifically for harmonic
mitigation. Today, one would hope that Conclusion
no one is installing capacitor banks by Understanding the subtle differences between various harmonic filtering technologies can
themselves and, at the very least, using yield better cost savings, reduce complexity and prolong equipment life. Getting your head
de-tuned ones – with an inductor, for around what options are available really is worth it in the long run.
example.
Contact John Mitchell, CP Automation, john.mitchell@cpaltd.net, www.cpaltd.net
Series-active
Series-active takes the form of an Active- About CP Automation
Front-End (AFE) VSD. It replaces the CP Automation is a specialist in the repair and replacement of automation equipment
rectifier diodes in a regular VSD with including electronic boards, PLCs and Ac and DC drives. It was established to provide an
an IGBT controlled rectifier to eliminate independent maintenance service, without exclusive ties to any manufacturer. However,
switching based signal noise. it does have strong relationships with the principal inverter, encoder, resistors and motor
AFEs are great at significantly lowering manufacturers.

3

1

2

1: Distorted waveform composed of fundamental and 3rd harmonic (EATON)
2. Power factor correction equipment (ABB)
3. Power factor correction equipment (ABB)

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