INTERPRET _ ANALYSIS-2

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					                    Interpretation and Analysis of Power Quality Measurements
                                    Christopher J. Melhom           Mark F. McGranaghan
                                   Electrotek Concepts, Inc.       Electrotek Concepts, Inc.
                                    Knoxville, Tennessee            Knoxville, Tennessee


                     ABSTRACT                                          0    Offer examples of Werent methods for
                                                                            presenting the results of power quality
    Thk paper describes advances in power quality                           measurements.
monitoring equipment and softwoe tools for analyzing                   0    Describe tools for analyzing and presentlng
power quality measurement results. Power quality                            the power quality measurement results.
monitoring has advanced from strictly problem solving
to ongoing monitoring of system performance. The                        Analysis tools for processing measurement data will
increased amount of data being collected requires more             be described. These tools can present the information as
advanced analysis t o o k    Types of power quality                individual events (d~sturbancewaveforms), trends, or
variations are described and the methods of                        statistical summaries.      By comparing events with
characterizing each type with measurements are                     libraries of typical power quality variation characteristics
presented     Finally, methods for summarizing the                 and correlating with system events (e.g. capacitor
information and presenting it in useful report formats
                                                                   switchmg), causes of the variations can be determined.
are described
                                                                   In the same manner, the measured data should be
                                                                   correlated with impacts to help characterize the
                  INTRODUCTION                                     sensitivity of end use equipment to power quality
                                                                   variations. This will help identrfy equipment that
     Power quality has become an important concern for             requires power conditioning and provide specifications
utility, facility, and consulting engineers in recent years.       for the protection that can be developed based on the
End use equipment is more sensitive to disturbances that           power quality variation characteristics.
arise both on the supplying power system and within the
customer facilities. Also, this equipment is more                          CATEGORIES OF POWER QUALITY
interconnected in networks and industrial processes so
that the impacts of a problem with any piece of                                    VARIATIONS
equipment are much more severe.
                                                                        It is important to first understand the lunds of power
     The increased concern for power quality has resulted          quality variations that can cause problems with sensitive
in si@cant advances in monitoring equipment that can               loads. Categories for these variations must be developed
be used to characterize disturbances and power quality             with a consistent set of definitions so that measurement
variations. This paper discusses the types of information          equipment can be designed in a consistent manner and so
that can be obtained from Werent kinds of monitoring               that information can be shared between different groups
equipment and methods for analyzing and presenting the             performing measurements and evaluations. An IEEE
infomution in a useful form.                                       Working Group has been developing a consistent set of
                                                                   definitions that can be used for coordination of
     Important objectives for the paper include the                measurements.[11
following:
                                                                        Power quality variations fall into two basic
    0   Describe important types of power quality                   categories:
        variations.
                                                                       1. Disturbances. Disturbances are measured by
   0    Identrfy categories of monitoring equipment                       triggering on an abnormality in the voltage or
        that can be used to measure power quality                         the current. Transient voltages may be
        variations.                                                       detected when the peak magnitude exceeds a
                                                                          specfied threshold. RMS voltage variations
                                                                          (e.g. sags or interruptions) may be detected


                                                               1
                                      Table 1. Summaw of Power Qualip Variation Categories
                                                                                                                Example
             Power Quality                     Method of                                                  Power Conditioning
           Variation Category               Characterizing                 Typical Causes                       Solutions
                                       Peak magnitude,                Lightning,                    Surge Arresters,
                                       Rise time,                     ElectroStatic Discharge,      Filters,
         lmpulsie Transients           Duration      -                Load Switching                Isolation Transformers      -
                                       Wawforms,                      LinelCable Switching,         Surge Arresters,
                                       Peak Magnitude,                Capacitor Switching,          Filters,
         Oscillatory Transients        Frequency Components           Load Switching                Isolation Transformers
                                                                                                    Femresonant Transformers,
                                       RMS vs. time,                                                Energy Storage Technologies',
         SagslSwells                   Magnitude, Duration            Remote System Faults          UPS
                                                                      System Protection             Energy Storage Technologies',
                                                                      (Breakers, Fuses),            UPS,
         Intemptions                   Duration                       Maintenance                   Backup Generators

         Undeholtagesl                 RMS vs. Xme,                   Motor Starting,               Voltage Regulators,
         Owmltages                     Statistics                     Load Variations               Femresonant Transformers
                                       Harmonic Spectrum,                                           Filters (active or passiw),
                                       Total Harm. Distortion,        Nonlinear Loads,              Transformers (cancellation or
         Harmonic Distortion           Statistics                     System Resonance              zero sequence components) -
                                       Variation Magnitude,           Intermittent Loads,
                                       Frequency of Occurence,        Motor Starting,
         Voltage Flicker               Modulation Frequency           Arc Furnaces                  Static Var Systems
          M e : k e r g y Storage Technologies refers to a variety of aternative




      when the RMS variation exceeds a specified                                       Table 1 summarizes the Werent categories and lists
      level.                                                                       possible causes and power conditioning equipment
                                                                                   solutions for each category.
   2. Steady State Variations. These include
      normal RMS voltage variations and harmonic                                   Steady State Voltage Characteristics
      &stortion.     These variations must be
      measured by sampling the voltage and/or                                         There is no such thmg as steady state on the power
      current over time. The information is best                                   system. Loads are continually changng and the power
      presented as a trend of the quantity (e.g.                                   system is continually adjusting to these changes. All of
      voltage &stortion) over time and then                                        these changes and adjustments result in voltage
      analyzed using statistical methods (e.g.                                     variations that are referred to as long duration voltage
      average &stortion level, 95% probability of                                  variations. These can be undervoltages or overvoltages,
      not being exceeded, etc.).                                                   depenhng on the specific circuit conhtions.
                                                                                   Characteristics of the steady state voltage are best
    In the past, measurement equipment has been                                    expressed with long duration profiles and statistics.
designed to handle either the disturbances (e.g.                                   Important characteristics include the voltage m a p t u d e
&sturbance analyzers) or steady state variations (e.g.                             and unbalance.        Harmonic distortion is also a
voltage recorders, harmonics monitors). With advances                              characteristic of the steady state voltage but t h ~ s
in processing capability, new instruments have become                              characteristic is treated separately because it does not
available that can characterize the full range of power                            involve variations in the fundamental frequency
quality variations.      The new challenge involves                                component of the voltage.
characterizing all the data in a convenient form so that it
can be used to help idenhfy and solve problems.                                        Most end use equipment is not very sensitive to these
                                                                                   voltage variations, as long as they are withm reasonable
                                                                                   limits. ANSI C84.1 [7] specfies the steady state voltage

                                                                          2
tolerances for both magnitudes and unbalance expected                   phase angles of each individual harmonic component. It
on a power system. Long duration variations are                         is also common to use a single quantity, the Tofal
considered to be present when the limits are exceeded for               Harmonic Distortion, as a measure of the magmtude of
greater than 1 minute.                                                  harmonic distortion. For currents, the distortion values
                                                                        must be referred to a constant base (e.g. the rated load
  P O W 8010            June 14. 1992 a1 20.03.16 PONode Loco1          current or demand current) rather than the fundamental
  P h a x A-B Volt~ge                                                   component. llus provides a constant reference while the
  ss Rus
                                                                        fundamental can vary over a wide range.
                                                   Min   100 1

     103.51
      lQ4               I                          Mor1040
                                                                        Table 2. Example current waveformsfor various
                                                                                 nonlinear IC l .
                                                                                              b

                                                                               rypoflad




      1.0
       0.     !                    1

         2000 0000 04 00 0800 1 2 00 16 00 2~ -0                               SnnlOmVsler
                         lime
                                                   EMI/Elccirotck

Figure 1. Example 24 hour voltage profile illustrating
          long duration voltage variations.

Harmonic Distortion
    Harmonic distortion of the voltage and current
results from the operation of nonlinear loads and devices
on the power system. The nonlinear loads that cause
harmonics can often be represented as current sources of
harmonics.      The system voltage appears stif€ to
individual loads and the loads draw distorted current
waveforms. Table 2 illustrates some example current
waveforms for Merent types of nonlinear loads. The
                                                                              12pulrconvmta
weighting factors indicated in the table are being
proposed in the Guide for Applying Harmonic Limits on
the Power System (Draj? 2)[2] for preliminary evaluation
of harmonic producing loads in a facility.

     Harmonic voltage distortion results from the
interaction of these harmonic currents with the system
impedance. The harmonic standard, IEEE 519-1992 [2],
has proposed two way responsibility for controlling                          Harmonic distortion is a characteristic of the steady
harmonic levels on the power system.                                    state voltage and current. It is not a Qsturbance.
                                                                        Therefore, characterizing harmonic distortion levels is
    1. End users m s limit the harmonic currents
                    ut                                                  accomplished with profiles of the harmonic distortion
       injected onto the power system.                                  over time (e.g. 24 hours) and statistics. Figure 2
                                                                        illustrates a .typical profile of hhnonic voltage dtstortion
    2. The power supplier will control the harmonic                     on a feeder circuit over a one month period.
        voltage distortion by malung sure system
        resonant conditions do not cause excessive
        magmfication of the harmonic levels.

    Harmonic Qstortion levels can be characterized by
the complete harmonic spectrum with magnitudes and


                                                                    3
                                Time lrcnd      101       volioqe THO                                 crossing. Magrufication of the transient can be avoided
                      I         1                     I                  I
                                                                                                      by not using low voltage capacitors witlun the end user
                                                                                                      facilities. The actual equipment can be protected with
         I                                                                                            filters or surge arresters.

                                                                                                      Short Duration Voltage Variations
                                                                                                           Short duration voltage variations include variations
                      I         I I/    '             I '         I      I      I
                                                                                                      in the fundamental frequency voltage that last less than
         06I          I         I                     I                  I      I , , ,     1         one minute. These variations are best characterized by
          5
         0m          Mm!       MIOD              MI16                   MI?J   Mi3        Olfll
L                                                 Time                                                plots of the RMS voltage vs. time but it is often sufficient
Figure 2. Example Profile of Harmonic Voltage                                                         to describe them by a voltage mgmtude and a duration
          Distortion on a Distribution Feeder Circuit.                                                that the voltage is outside of specified thresholds. It is
                                                                                                      usually not necessary to have detailed waveform plots
Transients                                                                                            since the RMS voltage magnitude is of primary interest.

    The term transients is normally used to refer to fast                                                  The voltage variations can be a momentary low
changes in the system voltage or current. Transients are                                              voltage (voltage sag), h g h voltage (voltage swell), or
Isturbances, rather than steady state variations such as                                              loss of voltage (interruption). Interruptions are the most
harmonic distortion or voltage unbalance. Disturbances                                                severe in terms of their impacts on end users but voltage
can be measured by triggering on the abnormality                                                      sags can be more important because they may occur
involved. For transients, tlus could be the peak                                                      much more frequently. A fault conltion can cause a
magnitude, the rate of rise, or just the change in the                                                momenmy voltage sag over a wide portion of the system
waveform from one cycle to the next. Transients can be                                                even though no end users may experience an
Ivided into two sub-categories, impulsive transients and                                              interruption. This is true for most transmission faults.
oscillatory transients, depending on the characteristics.                                             Figure 4 is an example of tlus kind of event. Many end
                                                                                                      users have equipment that may be sensitive to these kinds
     Transients are normally characterized by the actual                                              of variations. Solving tlus problem on the utility system
waveform, although summary descriptors can also be                                                    may be very expensive so manufacturers are developing
developed (peak magnitude, primary frequency, rate-of-                                                ride through technologies with energy storage to handle
rise, etc.). Figure 3 gves a capacitor switching transient                                            these voltage variations on the end user side.
waveform. This is one of the most important transients
that is initiated on the utility supply system and can affect
the operation of end user equipment.

    I




    1
    I

    I
              -I 0
                           n
                                            \
                                                                                                               0   005 01 0 1 5 0 2 0 2 5 0 3 035 0 4   Live




                                                      h e (mS)
    Figure 3. Capacitor Switching Transient.                                                          Figure 4. Voltage Sag Caused by a Remote Fault
                                                                                                                Condition.
            Transient problems are solved by controlling the
        transient at the source, changing the characteristics of the
        system affecting the transient or by protecting equipment
        so that it is not impacted. For instance, capacitor
        switching transients can be controlled at the source by
        closing the breaker contacts close to a voltage zero


                                                                                                  4
                                       Table 3.
                   Meter            Circuit                                          Distorted           Light            Triangle
                                                                                      Wave             Dimmer              Wave

                                                  l
                                                  i
                                                                                                     1
                                                                                                     -
                                                                                                     i                  E,
           I        Peak
                   Method    1   Peak I 1.414       100 %               82 %           184 %             113 %              121 %




                                                  1
           I

                                                    100 %           110 %              60 %              84 %               96 %
               Respondmg

                                                    100 %           100 %              100 %             100 %              100 %



                    TYPES EQUIPMENT
                        OF          FOR                                               clean sinusoidal signal, thls average value is
                                                                                      related to the R M S value by the constant,
                   MONITORING
                            POWER QUALITY                                             k=l.l. This value k is used to scale all
                                                                                      waveforms measured.
         Multimeters or DMMs
              After initial tests of wiring integrity, it may also be             3. True RMS. The RMS value of a signal is a
         necessary to make quick checks of the voltage andor                         measure of the heating whch will result if the
         current levels within a facility. Overloading of circuits,                  voltage is impressed across a resistive load.
         under- and over-voltage problems, and unbalances                            One method of detecting the true R M S value
         between circuits can be detected in this manner. These                      is to actually use a thermal detector to
         measurements just require a simple multimeter. Signals                      measure a heating value. More modem
         to check include:                                                           &@tal meters use a &@tal calculation of the
                                                                                     R M S value by squaring the signal on a
               0    phase-to-ground voltages                                         sample by sample basis, averaging over a
                                                                                     period, and then takrng the square root of the
                    phase-to-neutral voltages                                        result.
               0    neutral-to-ground voltages
                                                                                    These different methods all give the same result for a
               0    phase-to-phase voltages (three phase system)               clean, sinusoidal signal but can give sigruficantly
                                                                               Merent answers for distorted signals. Thus is very
                    phasecurrents                                              important because sigmficant &stortion levels are quite
                    neutral currents                                           common, especially for the phase and neutral currents
                                                                               within the facility. Table 3 can be used to better illustrate
             The most important factor to consider when                        this point.
         selecting and using a multimeter is the method of
         calculation used in the meter. All of the commonly used                   Each waveform in Table 3 has an R M S value of 1.0
         meters are calibrated to give an R M S indication for the             pu (100.0%). The correspondmg measured value for
         measured signal. However, a number of different                       each type of meter is displayed under the associated
         methods are used to calculate the RMS value. The three                waveforms, per-unitized to the 1.O pu RMS value.
         most common methods are:

               1. Peak Method. The meter reads the peak of
                                                                               Oscilloscopes
                  the signal and divides the result by 1.414                       An oscilloscope is valuable when performing real
                  (square root of 2) to obtain the RMS.                        time tests. Looking at the voltage and current waveforms
                                                                               can tell a lot about what is going on, even without
               2. Averaging Method. The meter determines                       performing detailed harmonic analysis on the waveforms.
                  the average value of a rectified signal. For a               You can get the magnitudes of the voltages and currents,


                                                                          5




. .
. . ..
look for obvious distortion, and detect any major                     1000u
variations in the signals.                                                                                                   1
     There are numerous makes and models of
oscilloscopes to choose from. A digital oscilloscope with
data storage is valuable because the waveform can be
saved and analyzed. Oscilloscopes in h s category often
have waveform analysis capability (energy calculation,
spectrum analysis) also.        In adhtion, the &@tal
oscilloscopes can usually be obtained with
communications so that waveform data can be uploaded
to a PC for additional analysis with a software package.
                                                                     -lOOOu ?00.%WDlu UERTICFI;       5.0'MS;DIU   'HO,',.
                                                                                    PH C-NEUT      AE
                                                                                                  W U SHAPE FAULT
Disturbance Analyzers
                                                                    Figure 5. Graphics Based Analyzer Output
     Disturbance analyzers and disturbance monitors
form a category of instruments which have been                      Spectrum Analyzers and Harmonic Analyzers
developed specifically for power quality measurements.
They typically can measure a wide variety of system                      Many instruments and on line monitoring equipment
disturbances from very short duration transient voltages            now include the capability to sample waveforms and
to long duration outages or under-voltages. Thresholds              perform FFT calculations. The capabilities of these
can be set and the instruments left unattended to record            instruments vary widely and the user must be careful that
&sturbances over a period of time. The information is               the accuracy and information obtained is adequate for the
most commonly recorded on a paper tape but many                     investigation.      The following are some basic
devices have attachments so that it can be recorded on              requirements for harmonic measurements used to
h s k as well.                                                      investigate a problem:

    There are basically two categories of these devices:                   Capability to measure both voltage and
                                                                           current simultaneously so that harmonic
    1. Conventional analyzers that summarize                               power f o information can be obtained.
                                                                                  lw
       events with specific information such as
                                                                           Capability to measure both magnitude and
       overlunder voltage magnitudes, sagdsurge
                                                                           phase angle of inhvidual harmonic
       magnitude and duration, transient magnitude
                                                                           components (also needed for power flow
       and duration, etc.
                                                                           calculations).
   2. Graphics-Based analyzers that save and                               Synchronization and a h g h enough sampling
      print the actual waveform along with the                             rate for accurate measurement of harmonic
      descriptive information which would be                               components up to at least the 37th harmonic
      generated by one of the conventional                                 ( h s requirement is a combination of a h g h
      analyzers.                                                           sampling rate and a sampling interval based
                                                                           on the 60 Hz fundamental).
    It is often difiicult to detennine the characteristics of
a disturbance or a transient from the summary                              Capability to characterize the statistical
information available from conventional disturbance                        nature of harmonic distortion levels
analyzers. For instance, an oscillatory transient cannot                   (harmonics levels change with changing load
be effectively described by a peak and a duration.                         conditions and changing system conhtions).
Therefore, it is almost imperative to have the waveform                 Harmonic distortion is a continuous phenomena. It
capture capability in a hsturbance analyzer for detailed            can be characterized at a point in time by the frequency
analysis of a power quality problem (Figure 5). However,            spectrums of the voltages and currents. However, for
a simple conventional disturbance monitor can be                    proper representation, measurements over a period of
valuable for initial checks at a problem location.                  time must be made and the statistical characteristics of
                                                                    the harmonic components and the total &stortion
                                                                    determined.


                                                                6
                                                                                                                                                   ~




' I53
   W0E                           Apd    22. 1992 at 2 4321 iocol R E D
                                                     1            GB A           November '9. 1991 al 060756 PONode .ocoI Bu503Y                                                                 Uoy 09. 1992 at ' 3 04 07 a d
  Phase C-A Vollaqe                                      lriqqer Phase A Volloqe                                  Trigger 'hose A Currenl
1 RUS Jarlalion                                                  UOVP fault                                               is Wave




                                                 96 77
                                                 mar
                                                   0
                                                  I1 1

                                                                        0   t   o   m   J   o   1   o   y   I   o   1   o

                      Time (mSeconds)            wriuiroie~                         Time (mSeconos)                             Uncoibioled Dalo

Figure 6. Output From Combination Disturbance and Harmonic Analyzer

                                                                                                                                           -
Combination Disturbance and Harmonic
                                                                                                                                                                                                   m)
                                                                                                                                               P   W       :
                                                                                                                                                           :
                                                                                                                                               Guullly     ;
Analyzers                                                                                                                                     7"
                                                                                                                                             - , "
                                                                                                                                            ................   .. ........ . ...,. ..,. .,. ..       .................
    The most recent instruments combine limited
harmonic sampling and energy monitoring functions
with complete lsturbance monitoring functions as well
(Figure 6). The output is graphically based and the data
is remotely gathered over phone lines into a central
database. Statistical analysis can then be performed on
the data. The data is also available for input and
manipulation into other programs such as spreadsheets
and other graphical output processors.

                    POWER
            ANALYZING   QUALITY                                                                                                                                                                                          Event
                                                                                                                                                                                                                         formatio
                        DATA
              MEASUREMENT                                                                                               Site
                                                                                                                     nformatio
     Analyzing power quality measurements has become
increasingly more sophisticated within the past few years.
It is not enough to simply look at RMS quantities of the
voltage and current. Disturbances that occur on the
power system have durations in the milli-second time
frame, equipment is more sensitive to these disturbances,
and there is more equipment connected to the power
systems that cause lsturbances or power quality
problems. For these reasons, it is often necessary to                                                                -igure 7. Example Data Analysis System.
continuously monitor system performance and
characterize possible impacts of disturbances.                                                                           Different types of power quality variations require
                                                                                                                    different types of analysis to characterize system
     The data analysis system must be flexible enough to                                                            performance. Some examples are given in the following
 handle data from a variety of monitoring equipment and                                                             sections. With a flexible system, these applications can
 maintain a database that can be used by many different                                                             be customized to individual user needs.
 applications. The concept is illustrated in Figure 7.
                                                                                                                    Transients
                                                                                                                        Transients are normally characterized by the actual
                                                                                                                    waveform, although summary descriptors can also be
                                                                                                                    developed for:

                                                                                                                            0      peakmagmtude


                                                                                                        7
          primary frequency                                                                 and duration is shown. Figure 10 illustrates t l u s type of
                                                                                            plot
          time of occurrence
          rateofrise                                                                                          F M s ~ t l + a p M e v r ~ b S G u t

    An example of tlus data in statistical form is
presented in Figure 8.
                                    Tronsicnl Uoqniludc


                                                                                                         M

                                                                                   -
                                                                               0
                                                                              '6
                                                                                   -
                                                                                   -
                                                                                   Y
                                                                                   -
-                                                                                  's
5                                                                               a"
                                                                              a-
                                                                              :
                                                                                   3
                                                                              m
                                                                                            Figure 10. Three Dimensional RMS Variation Bar
                                                                              0
    00                    a3                 IO                   I S        20                        Graph.
                                     Lloqnnuae (pr-""d)
Figure 8. Bar Chartfor Transient Peak Voltage.
                                                                                            Harmonics
RMS Variations                                                                                   Harmonics are characterized by individual snapshots
    R M S variations are generally characterized by the                                     of voltage and current with the associated spectrums. It
R M S value vs. time or by the minimum magnitude of the                                     is important to understand that the harmonic distortion
voltage during the event vs. the duration of the event.                                     levels are always changmg and these characteristics
Figure 1 was an illustration of a plot of magrutude vs.                                     cannot be represented with a single snapshot. Therefore,
Time for a 24 hour period.                                                                  time trends and statistics are needed. An example time
                                                                                            trend plot for one month was included in Figure 2. Figure
     This method is fine for looking at single sites and                                    11 shows the statistics of the harmonic current level.
single events. But when a whole system is involved,                                         T h s would be good for comparison with IEEE-519
either customer or utility, it may be preferable to look at a                               limits.
range of events (e.g. one month, one year, etc.) for                                        I                     Hirlwram for Hoimonic QMS Cuiienl        1
multiple sites. This would gwe an indication as to what
type of R M S events are occurring on a gwen system.
The magrutude duration plot in Figure 9 illustrates the
minimum voltage (in percent) during the event and the
duration of the event (time in cycles that voltage was out
of the thresholds).




                                                                                            Figure 11. Histogram for Harmonic RMS Currentfor
                                                                                                       Approximately Four Months.

                                                                                                                       SUMMARY
     0
    10-
           .
               10-
                     :I
                               18             Id             Id         Id
                                                                                                     Systematic procedures for evaluating power quality
                                     Dudton (60 )h Cycler)                                      concerns can be developed but they must include all
Figure 9. Example Magnitude Duration Plot.                                                      levels of the system, from the transmission system to the
                                                                                                end user facilities. Power quality problems show up as
    Another method for displaying tlus type of data is a                                        impacts within the end user facility but may involve
three dimensional bar graph where the count, magnitude,                                         interaction between all levels of the system.

                                                                                        8
    A consistent set of definitions for Merent types of          2. IEEE Std. 519-1992,        IEEE Recommended
power quality variations is the starting point for                  Practices and Requirements for Harmonic Control
developing evaluation procedures. The definitions                   in Electrical Power Systems, IEEE, New York,
permit standardzed measurements and evaluations                      1993.
across Merent systems.
                                                                 3. “Electrical Power System Compatibility with
     A data analysis system for power quality                                                         -
                                                                    Industrial Process Equipment Part 1: Voltage
measurements should be able to process data from a                  Sags,” Paper by the IEEE Working Group P1346,
variety of instruments and support a range of applications          Proceedings of the Industrial and Commercial
for processing data. With continuous power quality                  Power Systems Conference, 94CH3425-6, May,
monitoring, it is very important to be able to summarize            1994.
variations with time trends and statistics, in adhtion to
characterizing individual events.                                4. CENELEC Standard CLC/B’ITF 686 (Sec) 23,
                                                                    “Voltage Characteristics of Electricity Supplied by
                   BIOGRAPHIES                                      Public Distribution Systems,” June, 1993.

Christopher J. Melhorn received an ASE from York                 5.   IEC Standard 1000-2-2, “Compatibility Levels for
College of Pennsylvania in 1986 and a BSEET from the                  Low Frequency Conducted Disturbances and
Pennsylvania State University in 1989. Chns has been                  Signalling in Public Low Voltage Power Supply
employed with Electrotek Concepts, Inc. since 1990. His               Systems.”
experience at Electrotek includes workmg with EPRI and
utilities on case studies involving power quality issues.        6. IEC Standard 1000-4-7, “General guide on
He was also extensively involved in the EPRI DPQ                    harmonics and interharmonics measurements and
project site selection phase. Chns is presently involved            instrumentation, for power supply systems and
in developing new software for the power systems                    equipment connected thereto.”
engineering environment and workmg to increase
Electrotek‘s industrial based clientele.                         7. ANSI C84.1-1989, American National Standard
                                                                    for Electric Power Systems and Equipment -
Mark F. McGranaghan received a BSEE and an MSEE                      Voltage Ratings (60 Hertz).
from the University of Toledo and an MBA from the
University of Pittsburgh. Mark serves as Manager of              9. M. McGranaghan, D. Mueller, and M. Samotqj,
Power Systems Engineering at Electrotek Concepts, Inc.,             “Voltage Sags in Industrial Plants,” IEEE
Mark is responsible for a wide range of studies, seminars,          Transactions on Industry Applications, Vol. 29,
and products involving the analysis of power quality                No. 2, MarcWApril, 1993.
concerns. He has worked with electric utilities and end
users throughout the countq performing case studies to           10. L. Conrad, K. Little, and C. Grigg, “Prdcting
characterize power quality problems and solutions as part            and Preventing Problems Associated with Remote
of an extensive Electric Power Research Institute (EPRI)             Fault-Clearing Voltage Dips, IEEE Transactions
                                                                                                  “



project. He has also been involved in the EPRI                       on Industry Applications, vol. 27, pp. 167-172,
Distribution Power Quality Monitoring Project whch is                January, 1991.
establishing the baseline power quality characteristics of
U.S. dstribution systems through a multi-year                    11. V. Wagner, A. Andreshak, and J. Staniak, “Power
monitoring effort. Mark was involved in the design and               Quality and Factory Automation, “ Proceedings of
specification of the instrumentation and software for thrs           the L4SAnnual Meeting, vol. 35, no. 6, pp. 1391-
project.                                                             1396.


                    REFERENCES
   1. IEEE Working Group P1159, Recommended
      Practice for Monitoring Electric Power QualiQ -
      Draft 7, December, 1994.



                                                             9

				
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