**5.1.1 Capacitors**

Capacitors are composed of standard units that are connected in series or parallel for obtain the desired overall voltage and KV rating [5]. The capacitor's are designed and chosen with the following considerations:


### **5.1.2 Inductors**

Inductors used in filter circuit need to be designed bearing in mind the high frequencies involved. Inductors rating depend mainly on the maximum RMS, current. The inductors and resistors form the ground side of a tuned filter [5]. The reactor current ratings are based on the following considerations:


#### **5.2 Tuned filter**

A single tuned filter is a series RLC circuit tuned to the frequency of one harmonic .its impedance is given by

$$\mathbf{Z}\_{\rm l} = \mathbf{R} + \mathbf{j} \text{ (wL-1/wC)}\tag{5.1}$$

Which at the resonant frequency fn reduces to R. There are two basic design parameters to be considered prior to the selection of R, L and C. these are the quality factor Q, and the relative frequency deviations. It is generally more convenient to deal with admittances rather than impedance in filter design

$$\mathbf{Y} \mathbf{=} \mathbf{1}/\mathbf{R} (\mathbf{1} + \mathbf{j} \mathbf{2} \mathbf{s} \mathbf{Q}) = \mathbf{G} \mathbf{i} + \mathbf{j} \text{ B} \tag{5.2}$$

Where

216 Power Quality Harmonics Analysis and Real Measurements Data

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

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

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

Capacitors are composed of standard units that are connected in series or parallel for obtain the desired overall voltage and KV rating [5]. The capacitor's are designed and chosen with

Inductors used in filter circuit need to be designed bearing in mind the high frequencies involved. Inductors rating depend mainly on the maximum RMS, current. The inductors and resistors form the ground side of a tuned filter [5]. The reactor current ratings are based

A single tuned filter is a series RLC circuit tuned to the frequency of one harmonic .its

 Z1=R + j (wL-1/wC) (5.1) Which at the resonant frequency fn reduces to R. There are two basic design parameters to be considered prior to the selection of R, L and C. these are the quality factor Q, and the relative frequency deviations. It is generally more convenient to deal with admittances

impressed upon specific parts of an electrical power system, or both [4,11].

on relevant IEEE Standards for capacitors and reactors [15].

Harmonic current peaks have a 100% coincidence.

Adherence to IEEE/ANSI peak and RMS voltage ratings.

The reactor core will not saturate for currents less than

Peak flux density of the core will be less than 1.2 – 1.4

250% of the fundamental current rating of the filter bank.

Tesla assuming all harmonic current peaks is 100% coincident.

Ambient voltage distortion equal to the limits set forth by IEEE 519.

frequency to shift slightly higher [6, 7].

**5.1 Filtre components 5.1.1 Capacitors** 

**5.1.2 Inductors** 

**5.2 Tuned filter** 

impedance is given by

the following considerations:

on the following considerations:

rather than impedance in filter design

Nominal System over-voltage of 5%.

$$\mathbf{G} = \mathbf{Q} / \mathbf{X}0(1 + \mathbf{4s^2Q^2}) \tag{5.3}$$

$$\mathbf{B} = 2\mathbf{s}\mathbf{Q}^2 / \mathbf{\hat{x}}\mathbf{0} (1 + 4\mathbf{s}^2\mathbf{Q}^2) \tag{5.4}$$

$$\chi\_0 = \sqrt{\frac{L}{C}}\tag{5.5}$$

The harmonic voltage at the filter bus bar is

$$\mathbf{V} = \mathbf{I}/\mathbf{Y}\_{\mathbf{I}} + \mathbf{Y}\_{\mathbf{s}} \tag{5.6}$$

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

$$\mathbf{V} = \mathbf{I} |(\mathbf{C}\mathbf{s} + \mathbf{1}/\mathbf{R}(1 + 4\mathbf{s}^2\mathbf{Q}^2))^2 + (\mathbf{B}\mathbf{s}\mathbf{-2s}\mathbf{Q}/\mathbf{R}(1 + 4\mathbf{s}^2\mathbf{Q}^2))^2|^{-1/2} \tag{5.7}$$

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

#### **6.1 Introduction**

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

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

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

Harmonics Effect in Industrial and University Environments 219

that has only recently begun to be recognized in the building industry, as more and more computers and similar equipment are installed, turning the modern office or factory into a

The objective of section six is to investigate the effect of an University-PC and other harmonic contributing sources on the line currents that may have influence on processing

Although harmonics is the subject of several international standards [16], the difficulties of regulating harmonics emissions from small, individual devices employing switched mode technology, such as a personal computer, is compounded by the fact that the harmonic generation capabilities of these devices varies according to the number of parallel connected

In the last decade, power quality has become a major issue for electric utilities and their customers, and indirectly to almost all manufacturers of equipment that depend on sinusoidal supply voltage waveforms. The proliferation of solid-state switching devices in both industry and home has increased the harmonic levels found on electricity supply systems. In the past, sources of harmonics were limited and in most cases tolerable. However today, virtually all high performance electronic equipment uses switched mode power converters, conducting current for part of a cycle through multiple paths in order to efficiently convert alternating current to direct current. In response to this increased demand some countries encouraged the development of more efficient ways of getting full benefits

On the other hand a new technique of manufacturing circuits called integrated electronic circuits have been invented and led directly to increasingly complex systems such as in industry ,communications, domestic appliances … etc because its size, weight and cost. These circuits, although increased speed of operations and complexity of tasks, typically use

The majority of modern electronic units use switched mode power supplies (SMPS). The advantage–to the equipment manufacturer– is the size, cost and weight is significantly reduced and the power unit can be made in almost any required factor [28]. But unfortunately switch mode power supplies act as non–liner loads or they can be considered

Equipments with switch mode circuits are usually more sensitive to main variations and disturbances than liner loads [30]. For this reason power quality has become a major issue for electric utilities and their costumers and almost all manufactures of equipment that despond on sinusoidal supply voltage waveforms. The increasing of solid state switch devices such as Personal computers in both industry and homes will draw rather than continuous current from the supply; the power supply unit will draw pluses of current

The switching mode power supplies used in personal computers are major sources of harmonic currents. An experiment [26, 28, and 32] has been done for different types of computers to measure the harmonic generated by each type and the result was scheduled

modes and to measure the actual Total Harmonic Distortion during such modes.

high-tech computer environment. [28]

devices.

as:

**7. Power quality issues related to computers** 

from electrical energy by various switching methods.

a technique called switch mode power supplies [26- 29].

which contain large amount of harmonics [29, 32].

as a noise generators which get down the quality of the electricity supply.

on the correct operation of the computer facility. However, with the advent of relatively inexpensive personal computers (PC), the emphasis of computer power quality monitoring has also moved towards investigating the effects that large concentrations of PCs can have on other utility customers.

Personal computing impacts on power quality are increasing due to the common place usage of switched mode power supplies (SMPS) for converting single phase AC into low voltage DC for supplying processing electronics. Such power supplies, which are responsible for the generation of odd line current harmonics, are the main concern of this paper. However, in turn harmonically polluted line currents can distort supply voltages causing power quality problems for other consumers connected at a point of common coupling [22]. Additionally, and somewhat ironically, the switched mode power supply itself can be affected by non-sinusoidal supply voltages [23], which can increase or decrease current harmonics depending on the nature of the voltage distortion.

Switched mode power supplies are by no means restricted to PCs and can be found in a variety of other widely used electrical equipment including low energy lighting, battery chargers, televisions and their peripherals.

A recent study [24] has shown that the line current harmonics from a single PC differed considerably to the harmonics generated collectively by several PCs of the same type. One widely held theory [25] regarding this effect introduces the concepts of *attenuation* and *diversity*. Attenuation describes the reduction in harmonic magnitude, and change in phase angle, as a load connected to a SMPS increases, and attributes this effect to the change in the spectrum of the line current pulse which widens to allow more power flow through the SMPS. Attenuation is also observed where several identical loads share the same source impedance. Diversity describes a The influence of personal computer processing modes on line current harmonics similar effect where a reduction, or even cancellation, of harmonics is possible due to loads of different levels, or connected through different impedances, presenting differing phase angles to the supply. These findings have not been proved using large-scale studies; although predictions based on results taken from individual computers have been reported [26].

The primary aim of this investigation is to investigate how the mode of operation of a PC affects the harmonics produced in the line current. This is an area barely mentioned in previous literature although these effects are closely related. One published study has made limited investigations of this type, but, again, only for individual computers [27]. In new construction or renovation, many power disturbances can be prevented or significantly lessened by designing for power quality assurance, at surprisingly small cost.

In view of the concerns regarding cumulative effects of large collections of PCs, this study was conducted within a University library building containing over 370 PCs. Furthermore, the study was intended to investigate the primary effect on line current harmonics caused by mode of operation, in isolation from additional secondary effects caused by distorted supply voltages. Investigation of this primary effect was achieved by monitoring during periods when the PCs represented the only load on the transformer supplying the library building and consequently the supply voltage waveforms were relatively undistorted. Most of these disturbances originate right within the building. Personal computers, laser printers and other switched-mode power supply equipment within your building are usually the culprits for most of the power supply irregularities affecting other computers. It's a problem

on the correct operation of the computer facility. However, with the advent of relatively inexpensive personal computers (PC), the emphasis of computer power quality monitoring has also moved towards investigating the effects that large concentrations of PCs can have

Personal computing impacts on power quality are increasing due to the common place usage of switched mode power supplies (SMPS) for converting single phase AC into low voltage DC for supplying processing electronics. Such power supplies, which are responsible for the generation of odd line current harmonics, are the main concern of this paper. However, in turn harmonically polluted line currents can distort supply voltages causing power quality problems for other consumers connected at a point of common coupling [22]. Additionally, and somewhat ironically, the switched mode power supply itself can be affected by non-sinusoidal supply voltages [23], which can increase or decrease

Switched mode power supplies are by no means restricted to PCs and can be found in a variety of other widely used electrical equipment including low energy lighting, battery

A recent study [24] has shown that the line current harmonics from a single PC differed considerably to the harmonics generated collectively by several PCs of the same type. One widely held theory [25] regarding this effect introduces the concepts of *attenuation* and *diversity*. Attenuation describes the reduction in harmonic magnitude, and change in phase angle, as a load connected to a SMPS increases, and attributes this effect to the change in the spectrum of the line current pulse which widens to allow more power flow through the SMPS. Attenuation is also observed where several identical loads share the same source impedance. Diversity describes a The influence of personal computer processing modes on line current harmonics similar effect where a reduction, or even cancellation, of harmonics is possible due to loads of different levels, or connected through different impedances, presenting differing phase angles to the supply. These findings have not been proved using large-scale studies; although predictions based on results taken from individual computers

The primary aim of this investigation is to investigate how the mode of operation of a PC affects the harmonics produced in the line current. This is an area barely mentioned in previous literature although these effects are closely related. One published study has made limited investigations of this type, but, again, only for individual computers [27]. In new construction or renovation, many power disturbances can be prevented or significantly

In view of the concerns regarding cumulative effects of large collections of PCs, this study was conducted within a University library building containing over 370 PCs. Furthermore, the study was intended to investigate the primary effect on line current harmonics caused by mode of operation, in isolation from additional secondary effects caused by distorted supply voltages. Investigation of this primary effect was achieved by monitoring during periods when the PCs represented the only load on the transformer supplying the library building and consequently the supply voltage waveforms were relatively undistorted. Most of these disturbances originate right within the building. Personal computers, laser printers and other switched-mode power supply equipment within your building are usually the culprits for most of the power supply irregularities affecting other computers. It's a problem

lessened by designing for power quality assurance, at surprisingly small cost.

current harmonics depending on the nature of the voltage distortion.

chargers, televisions and their peripherals.

on other utility customers.

have been reported [26].

that has only recently begun to be recognized in the building industry, as more and more computers and similar equipment are installed, turning the modern office or factory into a high-tech computer environment. [28]

The objective of section six is to investigate the effect of an University-PC and other harmonic contributing sources on the line currents that may have influence on processing modes and to measure the actual Total Harmonic Distortion during such modes.
