**5. Filter design**

Harmonic filters are designed to suppress system harmonics as well as to improve power factor. They allow a system to meet IEEE Standard 519 harmonic limits while avoiding power factor penalties. Filter designs are tailored to individual project objectives such as meeting a harmonic limit and/or a power factor level. This is a complex and involved engineering task, where alternative designs are checked to ensure that the final one will meet study objectives [14].

Typically, single tuned shunt filters are designed with a reactor and capacitor in series, connected as a shunt load on the system. In more complex studies, other types of filters, like 2nd or 3rd order, C-type, and/or double tuned filters are designed. In a complex filter design,

Harmonics Effect in Industrial and University Environments 217

Yf=1/R(1+j2s Q) =Gf + j Bf (5.2)

Gf=Q/X0(1+4s2Q2) (5.3)

Bf=2sQ2/X0(1+4s2Q2) (5.4)

 V=I/Yf+Ys (5.6) Therefore, to minimize the voltage distortion it is necessary to increase the overall admittance of the filter in the parallel with the a.c system. The harmonic voltage increases

V=I{(Gs+1/R(1+4s2Q2))2+(Bs-2sQ/R(1+4s2Q2))2}-1/2, (5.7)

**6. University Personnel Computers (PC) effect on line currents harmonics** 

cables, error of power electronic equipments operations and telephone interference.

block the harmonics or withstand the heating effects of the harmonics.

Many desktop personal computers still present a nonlinear load to the AC supply. This is because they have a power supply design known as a "capacitor input switch mode power supply". Much of today's Information Technology equipment including servers, routers, hubs, and storage systems almost universally use a different power supply design known as "Power Factor Corrected". These devices present a very linear load to the AC supply and do not generate harmonic currents. In fact they are one of the cleanest loads on the power grid and generate less harmonic current than many other devices such as fluorescent lighting or variable speed drives. The 3rd harmonic currents, the predominant harmonic in PC power supplies, causes overloaded neutrals, overheated transformers, and annoyance circuit breaker tripping. Very high price may be spent on equipment which will either filter or

Studies on the monitoring of power quality at computer sites have been conducted as early as 1969, [16, -18], and continuing interest in this area has maintained regular publications thereafter [19-21]. Most early studies were concerned with the effects of power disturbances

Power Quality problems are increasing with the proliferation of nonlinear devices, which draw none sinusoidal current waveforms when supplied by a sinusoidal voltage source. When these devices are present in an electric power system, they cause harmonic distortion of voltages and currents. Individually, single phase nonlinear load may not pose many serious harmonic problem, but large concentrations of these loads have the potential to raise harmonic voltages and currents to unacceptable high levels which results in increased neutral currents in four wire system, over heating of distribution system components and may cause mechanical oscillations in generators and motors. Other unwanted effects are capacitor and insulation failure due to harmonic resonance, malfunction of installed protection systems, transient voltage fluctuations, over heating of system transformer and

with (s) [4]. In term of Q and s can be equation (6) can be written as follows:

*C* (5.5)

X0= *<sup>L</sup>*

The harmonic voltage at the filter bus bar is

Where

**6.1 Introduction** 

a combination of filter types could be required. A generic term used to describe those types of equipment whose purpose is to reduce the harmonic current or voltage flowing in or being impressed upon specific parts of an electrical power system, or both [4,11].

The filter is tuned slightly below the harmonic frequency of concern. This allows for tolerances in the filter components and prevents the filter from acting as a direct short circuit for the offending harmonic current. Further allows the filter to perform its function while helping to reduce the duty on the filter components. It also minimizes the possibility of dangerous harmonic resonance should the system parameters change and cause the tuning frequency to shift slightly higher [6, 7].

Once the filter type and the components (reactors, capacitors and resistors) are determined, the design program is used to model these filters. Overall power system operation can then be analyzed to determine the effectiveness of the filtering scheme. Ratings of all filter components along with the protection schemes and control methods are identified, and detailed specifications are developed for the manufacture of the filters. All designs are based on relevant IEEE Standards for capacitors and reactors [15].
