On line internet-based multi-location power system harmonics analysis and monitoring

On Line Internet-BasedMulti-Location PowerSystem Harmonics Analysisand Monitoring

HSIUNG CHENG LIN

Department of Automation Engineering, Chienkuo Technology University, No. 1, Chieh-Shou N. Road,

Changhua 500, Taiwan

Received 10 April 2007; accepted 4 July 2007

ABSTRACT: Traditional methods to measure power system harmonics employ the power

harmonic analyzer or a software package, such as Matlab or others, but they do have certain

limitations in the graphical programming environment, applications for remote monitoring

and control performance and for multi-point harmonic measurement. In this paper, a PC-based

virtual instrument (VI) based on Fast Fourier Transform (FFT) to implement a remote multi-

point power system harmonics analysis and monitoring using LabVIEW is proposed. The

nearby PC (Server) can collect real-time waveform data from different multi-locations and

transmit it to remote PCs (Clients) for on line harmonic analysis and monitoring via the

Internet. The history of Total Harmonic Distortion (THD) in the waveform signals from remote

locations can be also recorded and tracked in the data base. The strategies and guidelines

are also developed to enhance teaching and/or learning the basics of operating Internet-based

systems. Experimental results have testified its well performance and remote Web-based

capability. � 2009 Wiley Periodicals, Inc. Comput Appl Eng Educ 17: 241�252, 2009; Published online in

Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20175

Keywords: FFT; TCP/IP; THD; VI; power system harmonics; Internet

INTRODUCTION

When the extensive use of power electronic devices is

added to an industrial distribution power system, it is an

important engineering practice to design a model of

harmonic measurement and analysis approach in power

systems [1�8]. Power system harmonics are caused by

transformers, motors, and rectifiers; they have been

detected as early as the 1920s and 1930s [9]. A system

can still function adequately in the presence of limited

amounts of harmonics, and in the past amounts injected

into systems were generally considered insignificant.

Today, however, increased industrial and consumer

dependence on equipment with non-linear components

is aggravating the situation. Harmonics in a power systemCorrespondence to H. C. Lin ([email protected]).

� 2009 Wiley Periodicals Inc.

241

can result in communication interference, transformer

over heating, or the malfunction of solid-state devices,

and so on [10�12]. Current harmonics induced by non-

linear power electronic loads also present inefficient

operations of local and global power supply systems.

Harmonic measurements in industrial power

systems are essential to achieve three objectives.

Firstly, for the identification of the sources and

characteristics (magnitude, frequency, and location)

of the harmonics. Secondly, for the design and

installation of a filtering system to reduce the harmonic

impacts to the power system. Thirdly, to ensure that

total harmonic distortion, after compensation, will be in

compliance with the regulatory requirements such as

IEEE Standard 519�1992 [13]. Currently, general

purpose power spectrum instruments introduce a wide

variety of possible measurements from the proper

modes chosen. Some special purpose power system

harmonic analyzers give fewer modes for measure-

ments. The above analyzers have, however, a complex

control circuit system, limited frequency domain

display, and high operating cost.

This study proposes an alternative technique to

measure line current harmonics using human graphical

interface as well as remote harmonic analysis and Web

viewing from different checking points. The proposed

system is constructed by LabVIEW package using Fast

Fourier Transform (FFT) and TCP/IP communication

techniques [14�21]. Hence, it can implement on line

remote operation of the power system harmonics

measurement and monitoring between distant locations

via the Internet. This paper is organized as follows.

Background of Power System Harmonics Section gives

a background of power system harmonics. Structure of

the System Hardware Section provides the proposed

system hardware structure. In Description of the System

Software Section, the system software for data acquisi-

tion, transmission and analysis using LabVIEW

are provided. Internet Connections Section presents the

illustration of Internet connections. Experimental

Results With TCP/IP and Web Connection Section

provided the experimental results with TCP/IP and Web

connections. Conclusions and recommendations for

further application are given in Conclusions Section.

BACKGROUND OF POWERSYSTEM HARMONICS

The research focused on the distorted source line

current is now getting more attention as harmonic

problems have caused increasing concerns in power

systems in recent years. Using Fourier series expan-

sion, the periodic and distorted (non-sinusoidal)

source current isðtÞ can be expressed as a series of

sinusoidal harmonics, therefore the response to

each harmonic can be determined by the following

equations.

isðtÞ ¼ Idc þX1

n¼1;2;3;:::

ðancos not þ bnsin notÞ ð1Þ

where

Idc ¼1

2p

Z2p

0

isðtÞdot; an

¼ 1

p

Z2

0

isðtÞsin notdot; bn ¼ 1

p

Z2p

0

isðtÞcosnotdot

Usually there is symmetry, so Idc¼ 0, and isðtÞcan be expressed as

isðtÞ ¼X1

n¼1;2;3;:::

ffiffiffi2

pisnsinðnot þ jnÞ ð2Þ

where

jn ¼ tan�1 an

bn

; isn ¼ 1ffiffiffi2

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffia2

n þ b2n

q

The r.m.s. value of source current is defined as

follows.

is ¼D

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1

2p

Z2p

0

isðtÞ½ 2dot

vuuut

¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1

2p

Z2p

0

X1n¼1;2;3;:::

ffiffiffi2

pisnsinðnot þ jnÞ

" #2

dot

vuuut

¼ffiffiffiffiffiffiffiffiffiffiffiffiffiX1n¼1

i2sn

s¼

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffii2s1 þ i2s2 þ i2s3 þ . . .

qð3Þ

ih ¼�

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffii2s2 þ i2

s3 þ i2s4 þ . . .

qð4Þ

which is the r.m.s. value of input harmonic current.

The total harmonic distortion (THD) factor is the

ratio of the r.m.s. value of all the harmonic

components together to the r.m.s. amplitude of the

fundamental component as following definition.

Mathematically,

THD¼Dffiffiffiffiffiffiffiffiffiffiffiffiffiffii2s � i2s1

pis1

¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiP1

n¼2 i2sn

pis1

¼ ih

is1

ð5Þ

242 LIN

The power factor (PF) of a load fed from an AC

supply is defined as

PF¼D mean power

vsisð6Þ

Normally, the supply phase voltage can be taken as

being sinusoidal, hence there will be no power

associated with the harmonic current as follows.

mean power ¼ vs1is1cosj ð7Þ

Therefore in the usual AC supply system where

the current is sinusoidal, the power factor is the cosine

of the angle between current and voltage. The

converter circuit, however, draws non-sinusoidal

current from the AC system, hence the power factor

can not be defined simply as the cosine of the

displacement angle.

For a sinusoidal voltage supply, substituting the

Equation (7) into the Equation (6) yields.

PF ¼ vs1is1cosjvsis

¼ is1

is

cosj ¼ is1 cosjffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffii2s1 þ i2

s2 þ i2s3 þ . . .

pð8Þ

where vs1 ¼ vs without source voltage distortion.

When the supply voltage is sinusoidal, which is

generally true, the above PF can be defined as the ratio

of the fundamental component of current and the

total value of the current, multiplied by cosj where

j is the phase-angle difference (displacement angle)

between the fundamental components of the voltage

and current. The ideal value of this power factor is

unity. However, the current which contains harmonic

components results in its overall r.m.s. value being

higher than the r.m.s. value of its fundamental

component, that is, PF<cosj gets lower in this

case. For instance, variable-speed drives constructed

with semiconductor switches inevitably introduce

harmonics into AC system. Accordingly, the power

factor will be always further degraded than the ideal

case when there are harmonic components existing in

the supply current because the controlled hardware

system has been loaded into power systems.

STRUCTURE OF THE SYSTEM HARDWARE

The system hardware is shown as Figure 1. It can

perform remote on line harmonic detection and

monitoring by certified clients (remote PCs) simulta-

neously. The Server is to collect the waveform data

acquired from the DAQ card (National Instrument

PCI-6014) via the Current Waveform probe. Upon the

receipt of data transmitted from the Server (nearby

PC) via TCP/IP, the Client A then carries out the

instant harmonics analysis. The Client B is authorized

to view the harmonic analysis results from the

Web Site, that is, Internet Explorer, immediately.

The control of VI panel can be transferred to the

Client B under the protection of Fire wall. There are

up to 16 channels available for receiving various

waveform data that may contain serious harmonics at

different locations (checking points). The number of

clients can be also extended as necessary.

The basic facilities or modules required for the

proposed system are as follows.

(1) Three PCs. One works as a Server for the

collection of current waveform data, and the

other two PCs are as the clients (A and B)

through TCP/IP and Web connection. Client A

is to perform the remote real-time harmonic

analysis, and Client B is to view its instant

analysis results obtained from Client A by the

Web Site.

(2) LabVIEW software package.

(3) One Data Acquire (DAQ) card (PCI-6014)

produced by National Instrument.

(4) Non-Linear Load (DC variable-speed motor or

other non-liner loads).

Figure 1 Structure of the proposed system hardware.

INTERNET-BASED POWER HARMONICS ANALYSIS 243

(5) Shunt (Current Waveform Sensing Probe).

(6) Amplifier (IC LM741).

DESCRIPTION OF THESYSTEM SOFTWARE

Besides the hardware system, the system software

using LabVIEW programming is needed to operate

the proposed system, described as follows.

Flowchart of the Server Programming

In the Server (nearby PC), it is to collect the waveform

data from the DAQ card, and then send the data to the

Client A for further signal processing. Figure 3 shows

its programming flowchart. The main programming

procedure is briefly described as follows.

(a) Initialize Analog Input (AI) Acquire Wave-

form.vi for acquiring waveform data from the

DAQ card. Detailed sub-vi is shown in Figure 2

and described as below.

(1) Device is assigned as 1 to the DAQ device

during configuration.

(2) Channel identifies the analog input channel

to measure. The input is set as channel

0�15.

(3) Number of samples is the number of

single-channel samples the VI acquires

before the acquisition completes. This

parameter is set as 1,000 samples.

(4) Sample rate is the requested number of

samples per second the VI acquires from

the specified channel. This parameter is set

as a rate of 1,000 samples/s. Note that the

sampling rate must be chosen higher than

the Nyquist sampling rate (twice the high-

est harmonic in the sampled data sequence)

[2]. For further information in the sampling

rate selection, please refer to the Refs.

[22�26].

(b) Activate the TCP/IP connection with Client A.

(c) Set the number of measured channels.

(d) Read waveform data from the assigned

channel of DAQ card.

(e) Display the current waveform signal in the

waveform chart.

(f) Send the waveform data to Client A via the

TCP/IP.

(g) Go back to step(d) until all checking points are

measured completely.

(h) Go back to step(c) until the TCP/IP is

disconnected (Fig. 3).

Flowchart of the Client A Programming

In Client A (remote PC), it receives the waveform data

from the Server, and analyze its harmonics instantly.

Its flowchart is shown in Figure 4.

The main programming procedure is briefly

described as follows.

(a) Initialize the TCP/IP connection with the

Server.

(b) Set the number (¼N) to read waveform data

from the Server.

(c) Read the waveform data transmitted from the

Server via the TCP/IP.

(d) Display the current waveform signal in the

waveform chart.

(e) Harmonic analysis using FFT.

(f) Go back to step(c) until every predefined

channel data is read completely. Note that the

number of the channel data (N) is the same as

the Server’s configuration.

(g) Display instant THD history and record it in

the data base.

(h) Go back to step(b) until the TCP/IP is

disconnected.

Flowchart of the Client B Programming

In Client B (remote PC), it views the harmonic

analysis results same as Client A by the Web Site

(Internet Explorer) simultaneously. Its flowchart is

shown in Figure 5.

Figure 2 AI Acquire Waveform.vi. [Color figure can be viewed in the online issue,

which is available at www.interscience. wiley.com.]

244 LIN

Figure 3 Flowchart of the Server programming. [Color

figure can be viewed in the online issue, which is available

at www.interscience.wiley.com.]

Figure 4 Flowchart of the Client A programming. [Color




The main programming procedure is briefly


(a) Publish the front panel of Client A to Web Site.

Details will be discussed in World Wide Web

Connection Between the Client A and Client B

Section.

(b) Check if the TCP/IP is authorized by Client A

until the TCP/IP is approved.

(c) View the front panel of the Client A via the

Internet Explorer.

(d) Go back to step(b) until the Web connection is

disconnected.

INTERNET CONNECTIONS

For simplicity, there are only three checking points

involved to demonstrate the proposed scheme in this

case. However, the number of checking points can be

easily extended up to sixteen as needed. Two kind

of Internet connections required in the system are


TCP/IP Connection Between the Serverand Client A

In the Server side, initially set Port Number to listen

for connection and set time out limit of 5 s. Send data

to the TCP port specified once a connection has been

detected. Numeric data is cast into string data and sent

via TCP Write. The first TCP Write sets the amount

of data to send and second TCP Write sends the

data. Error checking the loop will stop the loop if a

connection error occurs. Close connection once the

waveform data has been sent. Convert connection

errors to warnings and check for additional errors. The

program (Block Diagram) for TCP/IP connection is

shown in Figure 6.

In the Client A side, open connection with port

and IP address. Read the data at the port specified and

the data into a numeric representation. First TCP Read

acquires the size of the data and the second TCP

Read reads the data and passes it to the chart. Error

checking in the loop will stop the loop if a connection

error occurs. Close connection when the reading

procedure is done. Convert connection errors to

warnings and check for additional errors. The main

program for TCP/IP connection as well as waveform

spectrum using FFT is shown in Figure 7.

World Wide Web Connection Between theClient A and Client B

In Client A, LabVIEW front panel displays its

working status on line, as shown in Figure 8. Every

waveform and its spectrum can be viewed in the

graph, including the individual frequency and its

amplitude. The waveform THD (%) is also presented

immediately and recorded in the data file, that is,

a:\IO.txt. Once the THD (%) is over the predefined

limit, for example 25%, the warning LED will be

operated (on).

Figure 5 Flowchart of the Client B programming. [Color



246 LIN

Figure 6 TCP/IP connection program for Server. [Color figure can be viewed in the

online issue, which is available at www.interscience.wiley.com.]

Figure 7 TCP/IP connection program for Client A. [Color figure can be viewed in the

online issue, which is available at www.interscience.wiley.com.]

Figure 8 VI panel of the Client A. [Color figure can be viewed in the online issue, which

is available at www.interscience. wiley.com.]

The VI panel is published to World Wide Web

that can be viewed by Client B via Internet Explorer.

Figure 9 shows the Web Publishing Tool to display the

VI front panel. The document is then saved within

the web Server’s root directory. The URL should be

created to access this page from a browser, shown as

in Figure 10.

Note that m513-lin in the URL path (shown

in Fig. 10) should be replaced by the Server’s IP

address, for example 163.23.59.150, to be viewed and

Figure 9 VI panel for web publishing tool. [Color figure can be viewed in the online

issue, which is available at www.interscience.wiley.com.]

Figure 10 VI panel for URL access. [Color figure can be viewed in the online issue,

which is available at www.interscience.wiley.com.]

248 LIN

controlled by the client B (remote PC) via World Wide

Web. For security considerations, the Fire wall has

been set up to avoid a stranger (or hacker) invasion,

shown as in Figure 11.

As can be seen, only the certified IP address,

that is, 163.23.59.135 and 163.23.59.142, can be

permitted to view the system simultaneously,

and all others are prohibited. Note that IP

(163.23.59.135) is also allowed to control the system

via Web Site.

EXPERIMENTAL RESULTS WITHTCP/IP AND WEB CONNECTION

The proposed system under on line real-time per-

formance via TCP/IP as well as Web connection was

Figure 11 VI panel for Brower access. [Color figure can be viewed in the online issue,


Figure 12 VI panel of the Server. [Color figure can be viewed in the online issue, which

is available at www.interscience.wiley.com.]


implemented successfully. The front panel of the

Server was illustrated in Figure 12. It was to collect

and display the waveform data from the checking

points via the DAQ card.

Figure 13 showed the VI panel of the Client A.

The three waveforms were displayed in the waveform

charts, respectively. The individual VI panel showed

not only the waveform’s THD but also its individual

frequency and amplitude. The path to save the THD

history in the data base was set up in the system. A

warning sign was switched on if the THD was

beyond the predefined limit. As can be seen, there

Figure 13 VI panel of the Client A. [Color figure can be viewed in the online issue,


Figure 14 Web front panel of the Client B. [Color figure can be viewed in the online

issue, which is available at www.interscience.wiley.com.]

250 LIN

were up to 50 THD results (THD history) displayed in

the waveform chart for all checking points at the

same time. The preset THD limit is shown in the chart

for easily investigating the THD status.

From the World Wide Web, the Client B can view

the VI panel that is the same front panel as the VI

panel of the Client A, as shown in Figure 14. In

particular, the control of VI panel can be transferred to

the client with the protection of Fire wall. Therefore,

the Client B can be allowed to take over the Server to

carry out a remote monitoring and control function.

The waveform’s THD was recorded once for

every 30 min (i.e., time delay) so that its history can be

easily tracked by the data base. For simplification,

there are only 18 THD records shown in Table I. Note

that time delay can be varied according to the user’s

requirement.

The proposed Internet-based algorithm using FFT

has been applied successfully to multi-location

power system harmonics analysis and monitoring,

particularly perfect for stationary signals as above.

However, the FFT analysis in non-stationary signals

may lead to incorrect results because of the problem

of leakage effect. Accordingly, this approach should

add a data window such as Hanning window function

for reducing the spectral leakage for non-stationary

signals in advanced industrial applications [10].

CONCLUSIONS

The objective of this paper is to introduce the

background needed for electrical/automation engi-

neering students in understanding system harmonics

as well as the Internet extension to multi-location

power harmonic measurement using graphic pro-

gramming. Particularly, this paper introduced illus-

trative techniques for waveform data transmission

between the server and the clients via TCP/IP. The

paper also presented the potential capability of

graphical programming and Internet connection that

is easy for extension to on line applications.

These techniques, in fact, are becoming more

important to develop learning skills about advanced

ideas in the electrical engineering and automated

industry fields.

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Table I THD History

Iteration Date Time THD0 (%) Status THD1 (%) Status THD2 (%) Status

0 2007/2/19 00:00 PM 17.79 Norm. 6.09 Norm. 9.06 Norm.

1 2007/2/19 00:30 PM 27.31 High 19.81 Norm. 8.71 Norm.

2 2007/2/19 01:00 PM 22.57 Norm. 5.07 Norm. 7.84 Norm.

3 2007/2/19 01:30 PM 23.53 Norm. 13.27 Norm. 5.97 Norm.

4 2007/2/19 02:00 PM 16.68 Norm. 10.69 Norm. 9.12 Norm.

5 2007/2/19 02:30 PM 27.74 High 9.59 Norm. 8.93 Norm.

6 2007/2/19 03:00 PM 21.75 Norm. 6.41 Norm. 10.79 Norm.

7 2007/2/19 03:30 PM 6.10 Norm. 5.55 Norm. 5.95 Norm.

8 2007/2/19 04:00 PM 17.74 Norm. 13.74 Norm. 5.70 Norm.

9 2007/2/19 04:30 PM 29.61 High 10.79 Norm. 10.92 Norm.

10 2007/2/19 05:00 PM 26.46 High 4.35 Norm. 5.14 Norm.

11 2007/2/19 05:30 PM 29.50 High 15.74 Norm. 7.13 Norm.

12 2007/2/19 06:00 PM 5.57 Norm. 7.73 Norm. 7.90 Norm.

13 2007/2/19 06:30 PM 27.35 High 10.59 Norm. 4.85 Norm.

14 2007/2/19 07:00 PM 30.10 High 15.76 Norm. 4.90 Norm.

15 2007/2/19 07:30 PM 25.62 High 20.17 Norm. 4.50 Norm.

16 2007/2/19 08:00 PM 8.74 Norm. 19.43 Norm. 5.71 Norm.

17 2007/2/19 08:30 PM 25.00 High 12.00 Norm. 5.91 Norm.


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BIOGRAPHY

Hsiung Cheng Lin was born in Chang

Hua in Taiwan on September 3, 1962. He

graduated from National Taiwan Normal

University for his bachelor degree in 1986,

Taiwan. He received Master and PhD degrees

from Swinburne University of Technology,

Australia, in 1995 and 2002 respectively.

His employment experience included lec-

turer and associate professor at Chung

Chou Institute of Technology, Taiwan. He is currently a professor

in the Department of Automation Engineering at Chienkuo

Technology University (CTU), Taiwan. He was honored with an

excellent teaching award from CTU in 2005, 2006 and 2007. He was

also nominated and included in the First Edition of Who’s Who in

Asia 2007 and 10th Who’s Who in Science and Engineering 2007.

His special fields of interest include power electronics, neural

network, network supervisory system and adaptive filter design.

252 LIN

Documents

On line internet-based multi-location power system harmonics analysis and monitoring