IEEE Standard 1531- 2003

Harmonic distortion on the power system is caused by nonlinear devices that produce distorted or non sinusoidal waveforms. Examples include electronically controlled devices (such as rectifiers and power controllers), arcing loads (such as arc furnaces and arc welders), and magnetic devices to a lesser degree (such as rotating ac machinery and transformers).

Excessive harmonic voltage and/or current can cause damage to equipment and the electrical system. One of the common ways of controlling harmonic distortion is to place a passive shunt harmonic filter close to the harmonic producing load(s). The harmonic-producing device can generally be viewed as a source of harmonic current. The objective of the harmonic filter is to shunt some of the harmonic current from the load into the filter, thereby reducing the amount of harmonic current that flows into the power system.

The simplest type of shunt harmonic filter is a series inductance/capacitance (LC) circuit. More complex harmonic filters may involve multiple LC circuits, some of which may also include a resistor.

Key filter design considerations include the following:

a) Reactive power (kilovar) requirements
The major components of a harmonic filter generally include capacitors, reactors, and resistors (if any) designed to achieve acceptable harmonic control. Because of the capacitors, the harmonic filter provides power frequency capacitive reactive power to the power system.

b) Harmonic limitations
System harmonic limitations are generally defined to ensure that equipment does not malfunction or fail due to excessive harmonic distortion.

c) Normal system conditions, including ambient harmonics
The normal system operating conditions are generally evaluated to assure that the harmonic filter design will meet specific reactive power (kilovars) and harmonic performance requirements for normal system operating conditions.

d) Normal harmonic filter conditions
Filters are seldom tuned to their exact calculated values. It is necessary to allow for the following parameter variations when evaluating the performance of the harmonic filters:
            Component tolerances.
            Ambient temperature variations
            Capacitor element or unit failures.

e) Contingency system conditions, including ambient harmonics
The contingency system operating conditions are generally evaluated to assure that the harmonic filter design will be rated adequately to handle these conditions although the normal system distortion limits may be exceeded:
            Application of filters tuned to the same frequency
            System frequency variation
            Power system configurations
            Characteristic and uncharacteristic harmonics
            Unknown harmonic sources

f) Contingency harmonic filter conditions
When multiple harmonic filters are applied at the same location, the outage of a complete harmonic filter is often considered in rating the filter components. In some applications, the outage of a single harmonic filter may require that the other harmonic filters be disconnected so that their ratings are not exceeded.

These considerations can be grouped into performance and rating criteria. The performance criteria relate to normal expected operating conditions and include capacitive reactive power requirements, harmonic limitations, normal system conditions, and normal harmonic filter conditions.

The rating criteria relate to unusual conditions that may place a more severe duty on the equipment. These unusual conditions include contingency system conditions and contingency harmonic filter conditions. Under the contingency conditions, it may be acceptable to have a more relaxed harmonic limitation

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