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Harmonic Distortion Sources and Effects
Events over the last several years have focused attention on certain types of load on the electrical system that results in power quality problems for the user and utility Equipment which has become common place in most of the facility. 
Non - linear loads generates voltage and current harmonics, which can have adverse effect on equipments, which are designed for operation as linear loads (i.e. Loads designed to operate on a sinusoidal waveform of 50 or 60 Hz.)

Effects of non-linear load:
Higher heating losses in the transformers Harmonic can have a detrimental effect on emergency generators, telephone and other sensitive electrical equipments. 

When receive power compensation (in the form of passive power factor improving capacitors) is used with non-linear loads, resonance condition can occur that may result in even higher levels of harmonic voltage and current distortion, thereby causing equipment failure, disruption of power services, and fire hazards in extreme conditions. The electrical environment has absorbed most of these problems in the past. However, the problem has now increased in a magnitude where Europe, the US, and other countries have proposed standards to responsible engineer system considering the electrical environment. IEEE 519-1992 and IEC 555 have evolved to become a common requirement cited when specifying equipment on newly engineered projects. The broad band harmonic filter was designed in part, to meet this specification. The present IEEE 519-1992 document establishes acceptable levels of harmonics (voltage and current) that can be introduced into the incoming feeders by commercial and industrial users. Where there may have been little cooperation previously from manufacturing to meet such specification, the adoption of IEEE 519-1992 and other similar world standards now attract the attention of everyone. 

Generation of harmonics:
Harmonics are sinusoidal wave forms. They have frequency in multiple of fundamental frequency. They are produced by equipment using frequency conversion technology. They are also generated due to power drawing pattern of non-linear loads.

Mitigation of Harmonic Distortion 
For resolution of harmonic problem, various techniques have been proposed to reduce the impact of load harmonic currents on the input current to an electrical system. Essentially, the intent of all these techniques is to make the input current more continuous so as to reduce the overall current harmonic distortion. The various techniques can be classified into four broad categories, 

a) The use of line reactors and / or DC link chokes 
b) Installation of passive filters (series, shunt, and low pass broad brand filters) 
c) Phase multiplication (12-pulse, 18-pulse rectifier system.)
d) Harmonic compensation by active filtering.

Harmonic protection filters are used for improvement of power factor and part elimination of harmonics. They are nothing but a combination of reactors and capacitors, suitably detuned. They are useful when distortion is 15 to 40 %.

Advantages of Harmonic Filters:
a) Protect capacitors from harmonic overloading.
b) Eliminate upto 97 % predominant harmonics.
c) Avoid harmonic amplification in the system. 
d) Improve power factor.

This system can be configured to operate in fully automatic mode. The objective is to eliminate high level of harmonic current to acceptable level to comply with utility regulation. They provide traps for individual harmonics frequency and provide reactive power compensation at fundamental frequency.

Harmonic filtering offers the following benefits:
1) Elimination of power factor penalty.
2) Improvement in reduction in energy bill.( due to improvement of PF)
3) Release of additional VA capacity in the system.
4) Improvement in voltage profile.
5) Reduction in line losses 
6) Reduction in harmonic currents.
7) Improvement in overall power quality. 
8) Improvement in life of electrical equipment.
9) Improvement in system reliability.

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