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Titlel~armonic currents generated by personal computers, their effects on the power system and
LanguageEnglish
File Size6.8 MB
Total Pages118
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Page 1

CURRENTS GENERATED BY PERSONAL COMPUTERS,

THEIR EFFECTS ON THE POWER SYSTEM AND

METHODS OF HARMONIC REDUCTION;

A DissertationPresentedto

The Faculty of the Russ College of Engineeringand

Technology

Ohio University

In Partial Fulfillment

of the Requirementsfor the Degree

Doctor of Philosophy

by

Hrair

June, 1994

Page 2

26

Page

1

8

TABLE OF CONTENTS

ChapterOne: .

ChapterTwo: Review of Recent Literature .

ChapterThree: The Nature of Harmonic Currents and their

Effects on the Distribution SystemNeutral Current

3.1 Time-domain Analysis 12

3.2 Changing the Values of Circuit Parameters

C and L 16

3.3 Harmonic Current Measurement 20

3.4 Time and FrequencyDomain Measurementsof

Input Currents of PC's

3.4.1 Monitor and Computer Currents Measured

Separately .

3.4.2 PersonalComputer Input Current Measurement

Results 31

3.5 The Magnitudes of the Harmonic Currents and

the Neutral Current 23

ChapterFour: Effects of PersonalComputer Harmonics on

the Distribution Transformer

4.1 Harmonic Current Effects on Transformer

Losses 42

4.2 Harmonic Analysis of the Transformer

Circuit 46

4.3 Three-phaseTransformerConnections 54

i

Page 59

47

• l.1 7
tmlt

D2

\i.-
t..,

C4I • 10
D4

a

Figure 4.1: Transformer PSpice model with nonlinear
rectifier load

is the mutual coupling of the transformerwindings and CORE

is the model name for a nonlinear magnetic inductor. The

model are defined as follows [13]:

AREA:

PATH:

GAP:

MS:

ALPHA:

A:

c:
K:

Mean magnetic crosi section area in cm2

Mean magnetic path length in cm

Effective air-gap length in cm

Magnetic saturationin Aim

Mean field parameter

Shapeparameter

Domain wall-flexing constant

Domain wall-pinning constant

Page 60

48

Program 1 of appendix 2 shows a copy of the Pspice

program that was used. Figure 4.2 shows the waveforms of

the primary(i1 ) , the secondary(i z) and the magnetization(i m)

currents of the transformerunder a nonsinusoidalrectifier

load (input section of a switch-modepower supply). The

magnetizationcurrent i m is equal to the difference i 1 - i 2 -

Figure 4.3 shows the magnitude spectraof these waveforms_

20

15

10

s 5
G)

"C
0:::3

C
0-
0
:E -5

-10

-15

-20
0 5 10 15 20

Time (msec)

25 30 35 40

Figure 4.2: Transformercurrent waveforms with
nonsinusoidalload obtainedby PSpice

Page 117

105

[19] Aintablian H.O., Hill H.W., Jr., "Harmonic Currents of

Personal Computers and t heir Effects on the Distribution

System Neutral Current," Proceedings of the Industrial

Applications Society Annual Meeting, Oct. 93, Toronto,

Ontario.

[20] Aintablian H. o. , Hill H. W. , Jr. , "The Effects of

Harmonic Currents of Personal Computers on the Distribution

Transformer," Proceeding,s of the North American Power

Symposium, Oct. 92, Reno, Nevada.

[21] Aintablian H.O., Hill H.W., Jr., "Harmonic Currents of

Personal Computers and their Effects on the Distribution

System Neutral Current." Proceedings of the International

Conference of Power Systems and Engineering, Aug. 92,

Vancouver, Be.

Page 118

Abstract

Aintablian, Hrair, OhannesPh.D. June 1994

Electrical and Computer Engineering

Harmonic Currents Generatedby PersonalComputers, their

Effects on the Power System and Methods of Harmonic

Reduction (105 pp.)

Director of Dissertation: H.W.Hill Jr.

The switching mode power supplies used in personal

computersare major sourcesof harmonic currents. Measured

and calculatedwaveforms and harmonic levels of input

currents of various types of personal computersare

presented.Harmonic currents of a group of personal

computers reinforce each other. Neutral currents resulting

from the addition of triplen harmonics are analyzedand

recommendationsare made to safeguardagainstpotential

problems. The impact of personal computer harmonic currents

on distribution transformer lossesare explored. Harmonic

currents result in the overheatingof transformerdue to

excessiveeddy current losses. In addition, the influence

of three-phasetransformerconnectionon the distribution

systemneutral current is examined. In the past ten years

severalmethods of power factor improvement through harmonic

elimination have been developedthat use high frequency

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