Delta CT2000 Series, User Manual

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Chapter 19 EMC Standard Installation Guide

CT2000 Series
19-18
C
AVI/ACI/AUI
ACM
Ferrite core
19-5.2 Harmonic Interference
The AC motor drive’s input current is non-linear, the input rectifier generates harmonics. Harmonics must be
limited to within a certain range to avoid impact the mains power and to avoid current distortion to ensure
surrounding devices are not influenced. An AC Motor Drive with built-in DC reactor suppresses harmonic currents
(Total Harmonic Current Distortion THID) effectively and therefore reduces the harmonic voltage peaks (Total
Harmonic Voltage Distortion).
Harmonic Current at the Power Supply Side
(A) Fundamental Sine Wave
(60Hz)
(B) Harmonic
(1 80Hz)
3
rd
(C) Harmonica lly
Distorted Wave
(B) Harmonic
(300H z)
5 th
(C) Harmoni cally
Distorted Wave
(A) Fundamental Sine Wave
(60Hz)
Suppression of Harmonic Currents
When a large portion of lower order harmonic currents (5
th
, 7
th
, 11
th ,
etc) occur at the power input,
surrounding devices will be disturbed and the power factor will be low as a result of reactive power. Installing a
reactor at the AC Motor Drive’s input effectively suppresses lower order harmonic currents.
AC Reactor
Installed in series with the power supply and is effective in reducing low order current harmonics.
Features of an AC reactor include:
1. Reduces the harmonic currents to the AC Motor Drive and increases the impedance of the power supply.
2. Absorbs interferences generated by surrounding devices (such as surge voltages, currents, and mains surge
voltages) and reduce their effect on the AC Motor Drive.
3. Increases the power factor.
DC Reactor
A DC-Reactor is installed between the rectifier and the DC-bus capacitor to suppress harmonic currents and
to achieve a higher power factor.