Page 92 - Power Quality in Electrical Systems

Chapter
6

Power Harmonic Filters

In this chapter, we will discuss methods of reducing harmonic
distortion in line voltages and currents through the use of
filters. Filters can be implemented with either passive
components (capacitors and magnetics) or active filters. Here,
we will examine filtering techniques applied to harmonics of
60 Hz, and to high-frequency “interharmonics” as well. The
eventual goal of the use of such filters is to reduce harmonic
distortion to within IEEE Std. 519 limits.

Introduction
Industrial and commercial power systems usually incorporate power
capacitors to improve the power factor and provide reactive power for
voltage support [6.1]. When the system includes sources of harmonic cur-
rent, such as power electronic converters or adjustable speed drives
(ASDs), the capacitors may be used in power harmonic filters to mini-
mize the harmonic voltage applied to the system load at the point of
common coupling (PCC).
The current harmonics produced by power converters, usually
polyphase rectifiers, can be reduced in one of three ways: (1) series reac-
tors in the input line; (2) the use of a 12-pulse, or higher, connection of
the rectifier bridges, and (3) use of pulse-width modulation of the line
current. When these measures do not reduce the current harmonics to
an acceptable level, power harmonic filters can be introduced to obtain
further reduction.
The current harmonics, of themselves, are seldom the problem, such
as when the third harmonic produces overheating in the three-phase
feeder neutral conductor. The problem occurs when a higher-order current
harmonic is resonant with the capacitors and system reactance to pro-
duce excessive voltages at the point of common coupling (PCC).

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