Document Sample
					       How to Specify POWER-QUALITY-TOLERANT Process Equipment

                  ITH THE INTENSE DRIVE FOR PROF-                  utility and industry to quickly identify the problem and
                  ITS, industrial plants are concerned about       eliminate it.
                  any kind of production shutdown. At the
                                                                   What Is Power Quality?
                  same time, sophisticated electronics are be-
                                                                   A power-quality problem is an occurrence manifested in a
ing rapidly introduced into most production processes.
                                                                   nonstandard voltage, current, or frequency deviation that
These are often in the form of such power-quality-sensitive
                                                                   results in a failure or a misoperation of end-use equipment.
equipment as
                                                                   Power quality is a reliability issue driven by end users.
   I   computers
                                                                   There are three concerns.
   I   telecommunications
                                                                      I   The characteristics of the utility power supply can
   I   electronic process controls
                                                                          have a detrimental effect on the performance of in-
   I   robotics
                                                                          dustrial equipment.

                                                                                                                                     IEEE INDUSTRY APPLICATIONS MAGAZINE • SEPT|OCT 2002 • WWW.IEEE.ORG/IAS
   I   adjustable-speed drives (ASDs).
                                                                                                 I   Harmonics produced by in-
The reliability of this type of
                                              BY JAMES A. OLIVER,
                                                                                                     dustrial equipment, such as
equipment is much more
                                              ROGER LAWRENCE, &
                                                                                                     rectifiers or ASDs, can have
closely tied to the quality of
                                            BASUDEB BEN BANERJEE
                                                                                                     a detrimental effect on the
the power supply, as compared
                                                                                                     reliability of the plant’s
to older or more traditional                                                                         electrical distribution sys-
equipment that may have had relay controls or electrical                  tem, the equipment it feeds, and on the utility system.
contactor controls.
                                                                      I   The characteristics of the current and voltage pro-
   For the past 15 years or so, there has been an increasing              duced by ASDs can cause motor problems.
awareness of the power-quality problem. In 1991, Busi-
                                                                      While power quality is basically voltage quality, it is
ness Week reported that spikes, sags, and outages cost the
                                                                   not strictly a voltage issue. Since the supply system has a fi-
nation US$26 billion in downtime. Contributing to this             nite, rather than an infinite, strength, currents outside the
cost is lost time, lost production, production of scrap, lost      direct control of the utility can adversely affect power qual-
sales, delivery delays, and damaged production equip-              ity. These are harmonic load currents, lightning currents,
ment. With utilities facing competition in who supplies            and fault currents. How do we quantify voltage aberrations
power, particularly to their major industrial customers,           indicative of power-quality problems? One must employ
mitigating power-quality problems are foremost on utili-           an accurate voltage-measuring device, such as an oscillo-
ties’ agendas.                                                     scope, to identify which of the voltage aberrations of Table
   There is a need to understand the power-quality issue.          1, and discussed here, is causing the problem.
The source of the power-quality problem is not a given; an
unacceptable quality of power may be a utility’s responsi-         Transients—Impulsive
bility, or it may be a self-generated responsibility of the in-    These are commonly known as switching surges or volt-
dustrial facility. With so much at stake, it behooves both         age spikes (Fig. 1). They can be caused by circuit breakers                      21
                                                   1077-2618/02/$17.00©2002 IEEE
                                                                          TABLE 1. CATEGORIES AND CHARACTERISTICS                   out of adjustment, capacitor switching, lightning, or
                                                                          OF VOLTAGE ABERATIONS                                     system faults. They are characterized by a sudden,
                                                                                                                                    nonpower frequency change, a high amplitude, fast
                                                                          Impulsive          Spectral     Typical        Voltage    rise and decay times, and high energy content.
                                                                          Transients         Content      Duration       p.u.
                                                                          Short              5-ns rise    < 50 ns
                                                                                                                                    This is a sudden, bidirectional, nonpower frequency
                                                                          Medium             1-µs rise    50 ns-1 ms                change: a ringing (Fig. 2). For high-frequency ring-
                                                                                                                                    ing over 500 kHz of 1-µs duration and for 5-500 kHz
                                                                          Long               .1-ms rise   > 1 ms                    ringing with tens of µs duration, it is likely the result
                                                                          Oscillatory Transients                                    of either the system response or the load response to
                                                                                                                                    an impulsive transient. With a frequency of less than
                                                                          Low Frequency      <5 kHz       0.3-50 ms      0-4        5 kHz and 0.3-50 ms duration, it could have one of a
                                                                          Medium                                                    number of causes.
                                                                                             5-500 kHz    20 µs          0-8
                                                                                                                                    Voltage Sag
                                                                          High Frequency     0.5-5 MHz    5 ms           0-4        This is a short-term, few-cycles duration, drop in
                                                                          Short Duration                                            voltage (Fig. 3) on the order of more than 10% to less
                                                                                                                                    than 90%. Typically, it lasts from 0.5 cycles to a min-
                                                                          Instantaneous                   0.5-30 Hz      < 0.1      ute. Voltage sags result from the voltage drop, from
                                                                                                                                    starting big motors across-the-line, or from a fault on
                                                                          Sag                             0.5-30 Hz      0.1-0.9
                                                                                                                                    an adjacent power line.
                                                                          Swell                           0.5-30 Hz      1.1-1.8
                                                                                                                                    Voltage Swell
                                                                          Momentary                                                 This is a short-term increase in voltage of a few cycles
                                                                          Interruption                    30 Hz-3 s      < 0.1      duration (Fig. 4). The magnitude of the increase is
                                                                                                                                    more than 10% and less than 80%. A swell can result
                                                                          Sag                             30 Hz-3 s      0.1-0.9    from a single line-to-ground fault that raises the volt-

                                                                          Swell                           30 Hz-3 s      1.1-1.4    age on the other two phases. It can also result from
                                                                                                                                    dropping a large load or energizing a capacitor bank.
                                                                          Interruption                    3 s-1 min      < 0.1
                                                                                                                                    Ninety percent of the faults on overhead distribution
                                                                          Sag                             3 s-1 min      0.1-0.9    lines are of a temporary nature (Fig. 5). Typically,
                                                                                                                                    these faults result from lightning, tree limbs, or ani-
                                                                          Swell                           3 s-1 min      1.1-1.2
                                                                                                                                    mals causing grounds or shorts. Distribution lines are
                                                                          Long                                                      protected by a form of circuit breaker called a recloser.
                                                                                                                                    Reclosers interrupt faults, then automatically restore
                                                                          Interruption,                                             the circuit, or reclose, and, if the fault has cleared, the
                                                                                                          > 1 min        0.00
                                                                          Sustained                                                 recloser stays closed. If the fault still persists, the
                                                                          Undervoltages                   > 1 min        0.8-0.9    recloser trips and again automatically closes back in. It
                                                                                                                                    usually recloses three times before locking out.
                                                                          Overvoltages                    > 1 min        1.1-1.2
                                                                          Voltage                                                   Voltage Flicker
                                                                                                          Steady-state   0.05-0.2   Flicker comes from the aggravating, rapid on-off sen-
                                                                                                                                    sation of incandescent and fluorescent lamps as per-
                                                                          DC Offset                       Steady-state   0-0.01     ceived by the human eye. It results from the rapid
                                                                                             0-100th                                variation in voltage within the normal allowable
                                                                          Harmonics                       Steady-state   0-0.20     voltage range tolerance of 90-110% (Fig 6). Flicker
                                                                                                                                    can result from electric arc furnaces, welders, rapidly
                                                                          Interharmonics     0.6 kHz      Steady-state   0-0.02     cycling loads, or it can result from a large ASD with
                                                                          Notching                        Steady-state
                                                                                                                                    inadequate dc-link filtering on a weak distribution
                                                                                                                                    system. With inadequate dc-link filtering, the in-
                                                                                             Broad-                                 verter harmonics, which are a function of a
                                                                          Noise                           Steady-state   0-0.01
                                                                                             band                                   non-60-Hz fundamental, flow into the power sys-
                                                                                                                                    tem, causing a pulsating of the 60-Hz fundamental.
                                                                                             < 25 Hz      Intermittent   0.01-0.7
                                                                                                                                    Voltage Regulation
                                                                          Power                                                     Low voltage during peak load periods can result from
                                                                          Frequency                       < 10 s                    overloaded lines, improperly set transformer taps, or
22                                                                        Variations                                                maladjusted automatic voltage regulators. The volt-
                         1                                  2                                 3                               4

Impulsive transient               Oscillatory transient                                               Voltage swell.
voltage.                          voltage.                           Voltage sag.

                         5                                          6                                                         7

                                                                             Harmonic voltage distortion.
Momentary interruption.
                                  Voltage flicker.

age is less than the normal 90% lower limit. Symptoms are               Harmonics can cause such problems as telephone inter-
dim light bulbs, light bulbs burning out too often, and             ference, motor overheating, transformer overheating, ca-
electric motors failing to start.                                   pacitor fuse blowing, high neutral currents, and problems
                                                                    with electronic controls. Distorted time-domain voltage
Frequency Fluctuations                                              and current-wave shapes are evaluated with spectrum ana-
Normally, the variation in frequency is not significant             lyzer equipment utilizing Fourier transform algorithms to
enough to cause any problems. Frequency tends to lag a lit-         calculate frequency domain magnitudes and phase angles
tle during the day, as central plant generators are well            of individual harmonic components. Solutions to harmonic
loaded, but at night, with light load, the frequency leads a        problems include the use of transformer connections, har-
                                                                    monic filters, optimum spacing of conductors, shielding,

                                                                                                                                    IEEE INDUSTRY APPLICATIONS MAGAZINE • SEPT|OCT 2002 • WWW.IEEE.ORG/IAS
little, so that, at the end of a 24-hour period, all clocks are
correct. Deviations in frequency can occur in weak electric         and grounding schemes.
systems, such as, an island system with no main supporting
ties to the mainland or at an industrial plant with its own         Interharmonics
generating system. A weak system could develop during an            These are frequency components of distorted voltages that
area-wide system disturbance that separates one part of the         are not integer multiples of the fundamental 60-Hz fre-
system from another.                                                quency (Fig. 8). They can result from ASDs with insuffi-
                                                                    cient dc-link filtering. With inadequate dc-link filtering,
                                                                    inverter harmonics that are multiples of a non-60-Hz fun-
Voltage Distortion                                                  damental pass into the power system, where they appear as
Voltage distortion is the degree to which the voltage wave          nonmultiples of the 60-Hz fundamental. This phenome-
shape deviates from a sine wave. Distortion can result from         non can also occur with cycloconverter-type ASDs that
the following                                                       have no dc link and with arc furnaces that develop an infi-
   I harmonics                                                      nite spectrum of parasitic frequencies.
   I interharmonics
   I voltage notching
                                                                    Voltage Notching
   I noise
                                                                    Voltage notching is a periodic voltage disturbance result-
   I dc offset.
                                                                    ing from the normal operation of power electronic devices,
                                                                    such as thyristors. Notching (Fig. 9) is not normally a prob-
Harmonics                                                           lem since it is controlled by circuit elements associated
Voltage distortion (Fig. 7) is well understood; it is defined and   with the switching devices. It can be a significant problem
thoroughly discussed in IEEE Standard 519. Nonlinear ele-           on weak electric systems, where it can produce noise cur-
ments in power systems, such as, power electronic switches,         rents causing control system misoperation. Notching and
saturated magnetic components,
and arc furnaces, create current dis-                                       8
tortions. Harmonic currents flowing
through system impedances create
harmonic voltages. IEEE Standard                                                                                              9
519 suggests voltage and current
distortion limits at the connection
point between the industrial facility
and the electric utility, e.g., the
“point of common coupling.”                                                                                                                        23
                                           Voltage wave with interharmonics.        Distorted voltage with notching.
                                                                           TABLE 2. CAPABILITIES OF EMTP                                                                    ringing can cause extra zero crossings, resulting in equip-
                                                                                                                                                                            ment malfunction in some equipment. Typical accepted,
                                                                           Switching surge studies                                                                          defined value ranges for voltage aberrations are listed in
                                                                                                                                                                            Table 1.
                                                                           Line energizing                                                   Arrester duty
                                                                                                                                             Insulation                     Noise
                                                                           Single pole switching                                                                            Fast switching speed and high input impedance give insu-
                                                                                                                                                                            lated-gate bipolar transistor (IGBT) inverters the potential
                                                                                                                                             Static Var                     to produce stray currents resulting in electromagnetic in-
                                                                           reclosing                                                                                        terference (EMI). Stray currents can disrupt communica-
                                                                                                                                                                            tions equipment, ASD control, programmable controllers,
                                                                           Capacitor switching                                               Ferroresonance                 sensors, barcode scanners, and position sensing equipment.
                                                                                                                                                                            These common-mode noise currents (Fig. 10) are mainly
                                                                           Fault clearing                                                    Parallel resonance             conducted currents. They are superimposed on and can
                                                                           Transformer switching                                             Motor starting                 overwhelm low voltage control signals with these adverse
                                                                                                                                                                            effects. The magnitude of the stray currents is determined
                                                                           Reactor switching                                                 Harmonic analysis              by the amount of phase-to-ground stray capacitance cou-
                                                                                                                                                                            pling available during the approximate 0.05-0.1-µs time
                                                                                                                                             Power electronics
                                                                                                                                             harmonics                      period when the inverter voltage is transitioning to and
                                                                                                                                                                            from the dc-link voltage level.
                                                                           Lightning surges
                                                                                                                                                                            The Power-Quality Study
                                                                           Induced surges
                                                                                                                                                                            When there is a power-quality problem, it is often neces-
                                                                           Incoming surge                                                                                   sary to analyze both the utility electric supply system and
                                                                           at station                                                                                       the electric system of the industrial facility. A monitoring
                                                                                                                                                                            program is set up, and, at the same time, a model mathe-
                                                                                                                                                                            matical simulation is run. The latter is done to provide in-
                                                                                                                                                                            sight into the nature of the problem and to allow the
                                                                                                                                                                            simulation of a fix. The approach is as follows

                                                                                                                                                                               I identify the power-quality concerns
                                                                                                                  trise         tfall                                          I collect system data for both the utility system and
                                                                           DC Bus                                                                                                 the industrial plant
                                                                                                                                                                               I set up a monitoring program
                                                                                                                                                                               I set up a model and simulation program
                                                                                                                                                                               I from the results of the monitoring and the simula-
                                                                                                                                                                                  tion, develop solutions.
                                                                                                                                                                            Simulation Models
                                                                                                                                                                            There are several computer programs available for the
                                                                                                                                                                            power-quality study. Harmonic analysis programs can be
                                                                                                                                                                            used for calculating harmonics, notching, and noise. Elec-
                                                                          Common mode noise current.                                                                        tromagnetic transients programs (EMTP) are used for a va-
                                                                                                                                                                            riety of studies, as in Table 2 (from IEEE 1159).


                                                                                                                                                                              Change in Bus Voltage (%)
                                                                             Percent of Nominal Voltage

                                                                                                                                                                                                                                           Overvoltage Conditions
                                                                                                                 19 Per Year
                                                                                                                                                                                                                                        0.5 Cycle

                                                                                                           >700                            0-6 Per Year             150%                                  100
                                                                                                           Per Year                                       110%                                             50
                                                                                                                                0-200 Per Year            106%
                                                                                                             ANSI C84.1-1989 Steady-State Voltage Range                                                          Acceptable             Rated
                                                                                                                                                           87%                                              0
                                                                                                           >240                 20-140 Per Year            80%                                                     Power                Voltage
                                                                                                                                                                                                                              8.33 ms

                                                                                                           Events                                          70%
                                                                                                           Per Year             0-16 Per Year                                                              −50
                                                                                                                                                  0-10/yr                                                                                              Undervoltage Conditions
                                                                                                                 0.1 s 0.02 s                                  3s                                                0.0001 0.001 0.01                    0.1    1   10    100 1000
                                                                                                                                                                                                                                                    Time (s)
                                                                                                                                        Duration                       11                                                                                                        12
24                                                                        Power-quality field data.                                                                         Modified CEBEMA curve.
Initial Site Survey                                                 Mitigation Equipment
The initial site survey is used to develop basic information        Mitigation equipment exists for each of the above
for the power-quality study.                                        power-quality problem categories: voltage transients, voltage
   I The nature of the problem is determined, insofar as is         sags, interruptions, regulation, harmonics, flicker, and volt-
      possible.                                                     age unbalance. Some of this equipment is listed in Table 3.
   I An equipment list is made up with as many identify-
      ing characteristics listed as available, such as plant        Lightning and Surge Arresters
      identification name or number, nameplate informa-             Arresters are designed for lightning protection of transform-
      tion, rating in amperes, voltage, kilowatts, manufac-         ers and are not sufficiently voltage-limiting for protecting
      turer, model number, and serial number.                       sensitive electronic control circuits from voltage surges.
   I Identify the time of day when problems occur. Identify
      any coincident problems or simultaneous operations.             TABLE 3. POWER QUAILITY MITIGATION EQUIPMENT
   I Determine how the equipment is tied into the plant
                                                                      Problem                 Mitigation Device
      electrical system. Identify any existing power-condi-
      tioning equipment. Obtain a single-line diagram of              Voltage Transient
      the plant electrical system, with transformer ratings
      and impedances. Identify any power-factor correc-               Spike                   Surge Arresters
      tion capacitors.                                                Oscillation             Lightning Arresters
   I Look for loads that disrupt power quality, such as
      ASDs, arc furnaces, induction-heating units, weld-                                      Static Switch
      ers, or power electronic rectifiers.                                                    Controlled Switching
   I Identify loads that are sensitive, such as, computers,
      telecommunications systems, process controls, ro-                                       Energy Storage Systems
      botics, and ASDs.                                               Voltage Sag
   I Considerable insight into the problem can be ob-
      tained by discussing the problem with the plant en-                                     Energy Storage Systems
      gineers. Such a discussion would include a history of
                                                                                              Static Switch
      the problem, an evaluation of wiring, cable shielding

                                                                                                                                     IEEE INDUSTRY APPLICATIONS MAGAZINE • SEPT|OCT 2002 • WWW.IEEE.ORG/IAS
      and grounding practices, and identification of sensi-                                   Automatic Tap-
      tive equipment.                                                                         Changing Transformer
                                                                                              Dynamic Voltage Regulator
Monitoring Equipment
The basic measuring tools for the power-quality field test is the                             Static Var Compensator
power-quality monitor. Other useful tools are the ground-resis-
tance meter, megohmmeter, circuit tester, multimeter, infra-          Voltage Interruption
red scanner, and clamp-on current probes. There are a variety of      Momentary               Energy Storage Systems
power-quality monitors available. The correct monitor for the
job should be selected. Some of the key functions to consider in      Sustained               Static Switch
selecting a power-quality monitor include                                                     Automatic Tap-
    I multiple channels to monitor phase, neutral, and                                        Changing Transformer
       ground simultaneously
    I voltage and current measurements
                                                                                              Dynamic Voltage Regulator
    I waveform display                                                                        Static Var Compensator
    I continuous monitoring
    I harmonic analysis
    I scope mode                                                                              Automatic Tap-
    I simultaneous display of current and voltage wave forms                                  Changing Transformer
    I wide frequency response
                                                                      Undervoltage            Dynamic Voltage Regulator
    I event summaries to provide graphical plots of
       root-mean-square (rms) and high-frequency events                                       Static Var Compensator
    I capability to access the monitor over the Internet.
                                                                      Harmonics, Notching, Noise
    The power monitor should be placed at the location se-
lected in the test plan. To determine the overall power                                       Passive Filter
quality of the facility, place a monitor at the service en-
                                                                                              Dynamic Filter
trance. To investigate a power-quality test response for a
new manufacturing unit or for single new piece of equip-                                      Static Var Compensator
ment, place a monitor as close to the unit in question as
possible. It will be necessary to record current, voltage, and        Flicker
the response of the facility or new equipment over the pe-                                    Static Var Compensator
riod of time of each test segment.                                                                                                                  25
                                                                          Thyristor-Based Static Switch                                       such as uninterruptable power supply (UPS), batteries,
                                                                          The static switch is a versatile device for switching a new         superconducting magnet energy storage (SMES), storage ca-
                                                                          element into the circuit when voltage support is needed. It         pacitors, or even flywheels driving dc generators. The out-
                                                                          has a dynamic response time of about one cycle. To correct          put of these devices is supplied to the system through an
                                                                          quickly for voltage spikes, sags, or interruptions, the static      inverter on a momentary basis by a fast-acting electronic
                                                                          switch can be used to switch in one of the following                switch. Enough energy is fed to the system to replace the en-
                                                                             I capacitor                                                      ergy that would be lost by the voltage sag or interruption.
                                                                             I filter
                                                                             I alternate power line                                           Dynamic Voltage Regulator/Electronic Tap
                                                                             I energy storage system.                                         Changing Transformer
                                                                             The static switch can be used in the alternate power line        A voltage-regulating transformer with an electronic load
                                                                          application. This scheme requires two independent power             tap-changer is used with a single line from the utility. It
                                                                          lines from the utility. It protects against 85% of the inter-       regulates voltage drops up to 50% and requires a stiff sys-
                                                                          ruptions and voltage sags. It does not protect against              tem (short-circuit power-to-load ratio of 10:1 or better).
                                                                          area-wide voltage disturbances that affect both lines.              This has coarse steps and is intended for only occasional
                                                                                                                                              voltage variations.
                                                                          Energy Storage Systems
                                                                          Storage systems can be used to protect sensitive production         Static VAR Compensators
                                                                          equipment from shutdowns caused by voltage sags or mo-              Loads, such as rolling mills, mine hoists, cranes, welding
                                                                          mentary interruptions. These are usually dc storage systems,        machine, and arc furnaces, where the use of reactive power

                                                                                                              APPENDIX: SURVEY OF SEVERAL INDUSTRIES
                                                                             T   o find out first hand what the industrial manufacturing
                                                                                 community’s concerns are about power quality, a se-
                                                                             ries of interviews were conducted with maintenance
                                                                                                                                              Power Equipment Supplier and Consultant
                                                                                                                                              In conducting a power-quality audit, this interviewer
                                                                                                                                              looks for the simple, easy-to-identify things first. His pro-
                                                                             and industrial engineers in manufacturing facilities             cedure includes
                                                                             throughout the country. These interviews yielded a vari-         - walk-through

                                                                             ety of insights.                                                 - identification of problems, including monitoring
                                                                                  As a general observation, large, well-established in-       - determination of the cost/benefit.
                                                                             dustrial manufacturing firms make power-quality train-           Sometimes the solution is too costly to consider. By plac-
                                                                             ing available to their engineering staff. Their engineers        ing the mitigation equipment as close to the problem as
                                                                             have an understanding of what the power-quality is-              possible, the costs can usually be minimized. Manage-
                                                                             sues are, and how to correct the problems. Manufac-              ment will not consider the mitigation project, unless a
                                                                             turing industries are using more and more ASDs for               detailed return on investment (ROI) is included.
                                                                             energy savings to reduce the cost of electricity. They
                                                                             know that ASDs can produce harmonics to the systems
                                                                                                                                              Automotive Finish Manufacturing
                                                                             and to the motor. They also know about using input
                                                                                                                                              More and more ASDs are being used for energy conser-
                                                                             transformers and input reactors in conjunction with
                                                                                                                                              vation. They are careful to design the ASD installation
                                                                             ASDs to prevent tripping on voltage spikes and to con-
                                                                                                                                              with input transformers, input reactors, or filters as
                                                                             trol harmonics to the system. They use shielded control
                                                                                                                                              needed for trouble-free, reliable operation. They are
                                                                             cable to control EMI.
                                                                                                                                              careful about specifying ASD sag and interruption
                                                                                  These engineers are under strict cost controls. Any
                                                                                                                                              ridethrough capability.
                                                                             power-quality mitigation devices must meet economic
                                                                             payback criteria. They prefer to design the ASD installa-
                                                                             tion correctly in the first place, rather than later resorting   Polyester Film Manufacturing
                                                                             to power-quality mitigation activities. In most cases, they      Ten or 12 years ago, they applied low speed flywheel gen-
                                                                             have the ability and persistence to get to the root cause        erators to back-up the power supply to their extruders and
                                                                             of the problem. There is a tendency for many of these            melt pumps to provide ridethrough capability for voltage
                                                                             firms to somehow acquire low-cost, substandard electric          interruptions. They have no specific problems now.
                                                                             motors in vendor packages for new projects. These mo-
                                                                             tors do not last long and are generally replaced with mo-        Photographic Paper Manufacturing
                                                                             tors with cast iron frames and inverter grade windings.          This facility generates 90% of its own power and pur-
                                                                                  Most feel that they get good quality power from the         chases 10%. An outage of the machine creates a pen-
                                                                             utility, and that the utility does a good job in making          alty of US$1 million per day, so they have been careful in
                                                                             power-quality training available.                                designing their ASD installations to minimize harmonics
                                                                                  Smaller, less-well-financed manufacturing companies         to their distribution system. They were concerned about
                                                                             have power-quality problems, but they may not recog-             lightning-created voltage spikes on the utility supply get-
                                                                             nize them as such. They have shutdowns, but unless they          ting into their electric system, so they are now using
                                                                             are of really significant duration, they take care of the        lightning arresters with better protective characteristics.
                                                                             problem and restart the operation. A few of the com-             Also, they have placed much of their power distribution
                                                                             ments by specific industries follow.                             system underground.

changes instantaneously, often cause rapid voltage fluctua-         at the 480-V bus or motor-control center (MCC) level, and
tions. If the effects are sufficiently large, production or op-     some at the control-voltage level. The lower voltage and
erational disturbances can result. This type of voltage             smaller kilovoltampere corrections are much less expensive
variation can be controlled with reactive power compensa-           than corrections at the transmission-voltage level. The Ap-
tion. Equipment is available in size ranges from 1-100              pendix provides results of interviews with engineers of a
megavoltamperes reactive (MVAR). This equipment utilizes
a combination of reactors, capacitors, and, depending on the
response time needed, thyristor or IGBT-based controls.
                                                                     TABLE 4. PQ DESIGN CHECKLIST
Passive Harmonic Filters
                                                                     Item                             √   Responsibility   √
Filters are used in some instances to effectively reduce or
eliminate certain harmonics. If possible, it is always prefera-      Power-Quality Study—Calc.            Customer
ble to use a 12-pulse or higher transformer connection,
rather than a filter. Tuned harmonic filters should be used           Sags
with caution and avoided when possible. Usually, multiple             Interruptions
filters are needed, each tuned to a separate harmonic. Each
filter causes a parallel resonance as well as a series resonance,     Spikes
and each filter slightly changes the resonances of other fil-         Surges
ters. Parallel resonances can occur near system harmonic fre-
quencies, exacerbating an existing problem or exciting                Harmonics
interharmonics. If the use of passive tuned harmonic filters is
anticipated, the power-quality study is definitely needed to
explore all the ramifications of using this equipment.               Power-Quality Study-History          Utility

Modified CBEMA Curve                                                  Sags
The Electric Power Research Institute (EPRI), the Cana-               Interruptions
dian Electric Association (CEA), and the National Power
Laboratory (NPL) have assembled and combined their field              Spikes

                                                                                                                                  IEEE INDUSTRY APPLICATIONS MAGAZINE • SEPT|OCT 2002 • WWW.IEEE.ORG/IAS
data on voltage sags, spikes, and interruptions. Fig. 11 has          Surges
been prepared using this information. It shows the annual
distribution of power-quality aberrations for a typical in-           Harmonics
dustrial site. In 1996, based on this study, the Information
Technology Industry Council (ITIC), formerly the Com-
puter Business Equipment Manufacturers’ Association                  Power-Quality
(CBEMA), modified the well-known CEBEMA curve to                     Measurements at Point of             Utility
the shape shown in Fig. 12.                                          Common Coupling (PCC)
   The CEBEMA curve shows the power-quality withstand
goal of equipment manufacturers in this computer-related in-
dustry. Other industries are now evaluating the use of this curve                                         Equipment
                                                                     Equipment Specification
as a standard for power-quality withstand tolerance. The fol-                                             Supplier
lowing capability values have been picked from this new curve
                                                                      Power-Quality Tolerant for
   I momentary interruption—0 V for 20 ms
   I voltage sag—70% V for 0.5 s, 80% V for 10 s, 90%                 Sags
       V continuous
   I voltage spike—500% V for 0.01 cycle, 200% V for 1
       µs, 120% V for 0.5 s, 110% V continuous.                       Spikes

Constant-Voltage Transformers                                         Surges
and Coil Hold-In Devices                                              Harmonics
For many power-quality studies, it is possible to greatly
improve the sag and momentary interruption tolerance of a            Statement of
facility by protecting control circuits. Constant-voltage            Power-Quality Warranty
transformers (CVTs) can be used on control circuits to pro-           Utility Single Line Diagram
vide constant voltage with three-cycle ridethrough, or re-
lays and ac contactors can be provided with electronic coil           Plant single Line Diagram
hold-in devices to prevent misoperation from either low or           Information Furnish
interrupted voltage.                                                 w/Proposal

Applicability                                                         Short-Circuit MVA at PCC
Some of this equipment is more applicable to mitigation at            Ambient Harmonics
the transmission voltage level, others are more appropriate                                                                                      27
                                                                          number of industries on their views of                                                  The following historical data, from
                                                                          power-quality mitigation.                                                           the past few years for each supply circuit,
                                                                                                                                  WITH UTILITIES              is obtained from the utility
                                                                          How to Approach the Acquisition
                                                                          of New Process Equipment from
                                                                                                                                      FACING                      I interruptions, average annual
                                                                          the Power-Quality Perspective                        COMPETITION IN                     I momentary interruptions, average
                                                                          From this background review of                                                            annual number
                                                                          power-quality issues, how do we ap-                    WHO SUPPLIES                     I voltage sags, average annual num-
                                                                          proach the preparation of process equip-                                                  ber and percent sag
                                                                          ment specifications for industrial                          POWER,                      I voltage level range, maximum and
                                                                          eq u ip m ent tha t will pre c lude                                                       minimum
                                                                          power-quality problems when the equip-                   MITIGATING                     I ambient level of harmonics, total
                                                                          ment is placed in service and later
                                                                          throughout its operating life?                       POWER QUALITY                        harmonic distortion (THD) value
                                                                                                                                                                    for each harmonic.
                                                                              The equipment must be made to be
                                                                          tolerant of power-quality voltage aberra-
                                                                                                                                PROBLEMS ARE                      I minimum short-circuit kilo- or
                                                                                                                                                                    megavoltamperes at the point of
                                                                          tions and not produce harmonics in ex-                FOREMOST ON                         common coupling
                                                                          cess on IEEE Standard 519, considering                                                  I capacitors on the proposed supply
                                                                          quantity of equipment and the point of                       UTILITES                     circuit or circuits (Are the capaci-
                                                                          common coupling. Some knowledge of                                                        tors switched for voltage control?)
                                                                          the power system and the industrial facil-                AGENDAS.                      I single-line diagram of the utility
                                                                          ity is obviously needed. The utility may                                                  supply system showing power gen-
                                                                          have historical information on the fre-                                                   eration sources and transformers
                                                                          quency of voltage sags, momentary interruptions, and in-               with impedances and capacitors.
                                                                          terruptions on the circuit or circuits being considered for         The following information is to be obtained from the in-
                                                                          supplying the facility. Before the equipment is specified, dustrial system
                                                                          preliminary engineering needs to be done. This will pre-            I single-line diagram of plant electric system, includ-
                                                                          vent much grief later on. Preliminary information needs to             ing transformers, circuit breakers, and capacitors
                                                                          be obtained from the utility, the proposed equipment sup-

                                                                                                                                              I any harmonic producing equipment, such as rectifi-
                                                                          pliers, assuming that there is more than one and competi-              ers, ASDs, or other
                                                                          tive bidding is anticipated. If partnering is expected,             I any power-quality mitigation equipment
                                                                          preliminary information is still needed.                            I if the equipment is to be added to an existing plant,
                                                                              It is recommended that a power-quality study be made               harmonic measurements on each supply bus and at
                                                                          of the facility, or of the proposed facility, if it is a new one.      the point of common coupling
                                                                          This will involve modeling the utility system, the indus-           I large motors that are started across-the-line, voltage
                                                                          trial plant’s electric supply system, and the new equipment            and horsepower.
                                                                          using a program such as EMTP.                                       This information is to be determined from the
                                                                                                                                            power-quality study
                                                                             TABLE 5. POWER-QUALITY CHECKLIST                                 I voltage sag study: expected voltage sag level from
                                                                             FOR EQUIPMENT INSTALLATION                                          line-to-line faults, from line-to-ground faults, and
                                                                             Item                        √     Responsibility          √
                                                                                                                                                 from motor starting
                                                                                                                                              I expected duration or any momentary interruptions,
                                                                             Control and Power                 A/E Firm and                      in cycles
                                                                             Cable Separation                  Contractor                     I level of voltage spikes to be expected from any capac-

                                                                             Correct Grounding                 A/E Firm and
                                                                                                                                                 itor switching or from circuit breaker operations on
                                                                             Practices                         Contractor                        the utility system
                                                                                                                                              I expected harmonic levels from adding the new
                                                                             Power Cable                                                         equipment
                                                                                                               A/E Firm
                                                                             Ampacity                                                         I any potential electric harmonic resonances.

                                                                                                              A/E Firm                     Equipment Specification
                                                                                                                                           The new process equipment specification needs address the
                                                                            ASDs Six-Pulse ver-                                            reliability of the equipment. Reliability should not be
                                                                            sus 12- or Higher
                                                                                                              Supplier                     compromised by power-quality problems, and the equip-
                                                                                                                                           ment should not cause power-quality problems, e.g., har-
                                                                            Power-Quality Tol-                Equipment                    monics in excess of IEEE Standard 519 recommendations,
                                                                            erant Features                    Supplier                     or EMI/radio-frequency interference (RFI) radiation suffi-
                                                                                                                                           cient to cause any reliability problems. The specification
                                                                            Provisions for
                                                                                                              Equipment                    should request a three-year guarantee against shutdown
                                                                                                              Supplier                     from any power-quality problem based on specified ex-
28                                                                          Testing
                                                                                                                                           pected power-quality characteristics of the power supply.
    Based on information obtained from                                            New Process Equipment Test Plan
the power-quality study, the specifica-                                           Working with the electric utility and
tion should specify expected values for                       A                   utilizing available portable test rig facili-
the following
    I voltage sags, amplitude and du-
                                                POWER-QUALITY ties totest plan is power-quality anoma-
                                                                                  lies, a
                                                                                                      made for verifying the
        ration                                      PROBLEM IS                    performance of the new equipment in-
    I momentary interruptions, ampli-                                             stallation as regards susceptibility to
        tude and duration                      MANIFESTED IN A power-quality disruptions. Depending
    I voltage spike amplitudes                                                    on test rig capability and the availability
    I ambient harmonic level                     NONSTANDARD                      of any utility voltage control capacitors
    I expected circuit resonant fre-                                              near the industrial facility, it may be pos-
        quencies.                                     VOLTAGE,                    sible to test for the new equipment re-
    The specification should include sin-
gle-line diagrams of the utility power             CURRENT, OR                    sponse to the following
                                                                                      I voltage sag of specified amount
supply and of the proposed industrial
plant with the point of common cou-
                                                    FREQUENCY                             and duration
                                                                                      I unbalanced phase voltage of speci-
pling identified. The minimum avail-            DEVIATION THAT                            fied amount
able short-circuit megavoltamperes                                                    I low steady-state voltage of speci-
(MVA) from the utility at the point of              RESULTS IN A                          fied amount
common coupling needs to be specified.                                                I response to capacitor switching
If any ASDs are included in the equip-             FAILURE OR A                           transient voltage
ment being purchased, the specification                                               I voltage interruption.
s h o u l d a d d re ss lim its o n the          MISOPERATION                         The test plan includes written proce-
kilovoltampere rating of equipment as
regards six-pulse and 12-pulse units and
                                                    OF END-USE                    dures for each simulation describing the
                                                                                  test rig set-up and the monitoring equip-
allowable THD limits from the ASDs.                 EQUIPMENT.                    ment to be used.
    The specification should specify the                                              Portable power-quality test simula-
tests that should be carried out by the ven-                                      tors are available for rent, along with
dor to demonstrate compliance with the                                            technicians, at the 100-A/480-V and

                                                                                                                                  IEEE INDUSTRY APPLICATIONS MAGAZINE • SEPT|OCT 2002 • WWW.IEEE.ORG/IAS
power-quality tolerance of the equipment to the specified 200-A/480-V levels. The 100-A equipment is intended for
system power-quality characteristics.                           component testing. The 200-A equipment is intended for
    Under information to be furnished with the proposal, in use at the MCC. These devices can simulate the following
addition to the technical information on the performance anomalies
of the equipment, there should be the following                     I voltage sag
power-quality information                                           I voltage unbalance
    I preliminary harmonic study results: voltage and cur-          I voltage swell
        rent THD harmonic levels at the point of common             I low steady-state voltage.
        coupling                                                    To simulate a voltage interruption, the supply
    I preliminary EMTP study results, defining voltage          breaker is opened and closed. If there is a utility capaci-
        sag levels and frequency, momentary interruption tor bank in the region of the test site, the effect of capaci-
        duration and frequency, voltage spike amplitude, tor switching transient could be observed with the
        and frequency of occurrence                             power-quality monitor.
    I if ASDs and motors are part of the equipment pack-
        age, the vendor should address the nonsusceptibility      TABLE 6.
        of the motors to winding failures or bearing failures     CHECKLIST FOR POWER-QUALITY TESTS
        from inverter output voltage characteristics.
    With the proposal, the vendor should furnish a state-         Item                      √   Responsibility            √
ment of warranty regarding equipment reliability of opera-
tion considering the specified expected system                    Test
power-quality characteristics. It should specify the tests        Procedure
that will be performed during commissioning to verify the         Test                          Equipment
reliability of the equipment to the specified system              Technicians                   Supplier
power-quality characteristics.
                                                                  Test                          Equipment
Checklist of Procedures                                           Equipment                     Supplier
for Design, Installation, and Testing                                                           Equipment
                                                                  Test Schedule
Tables 4-6 will help the industrial utility customer                                            Supplier
through the design, installation, and testing phases of the
new process equipment acquisition from the point of view          Equipment
of eliminating later power-quality problems.                      Availability

                                                                          Summary                                                               “HarmFlo Workstation for Windows. [Online]. Available:
                                                                          Understanding the power-quality issue leads to a systems      
                                                                          approach to the acquisition of new process equipment as re-
                                                                          gards its tolerance to power-quality aberrations. Equip-              “PSCAD/EMTDC” Powerful Transients Simulation Software by Mani-
                                                                          ment specifications are designed to make production                      t ob a H V D C R e s e a r c h C e n t r e . [ O n l i n e ] . A v a i l a b l e :
                                                                          equipment power-quality tolerant. To prepare these speci-      
                                                                          fications correctly, a power-quality study is needed to de-
                                                                          termine what can be expected from both electric utility               WebPASS Web Monitoring of Power Quality Data from BMI 8010 and
                                                                          power quality and internal facility power quality when the               8020 PQNodes. [Online] Available:
                                                                          new equipment is placed into service. Post startup testing
                                                                          for equipment tolerance to power-quality aberrations may              PQWeb Monitoring Power Quality via World Wide Web. [Online]
                                                                          be appropriate.                                                         Available:

                                                                          References and Additional Reading                                     TOP, The Output Processor Power System Analysis and Display Soft-
                                                                                                                                                   ware. [Online]. Available:
                                                                          L. Tang and J. Daniel, “Power quality book 1,” presented at the ABB
                                                                              Industrial Power Quality Seminar, Turgi, Switzerland, 1999.       PQView Power Quality Database Management and Analysis Software.
                                                                                                                                                   [Online]. Available:
                                                                          R.C. Dugan, M.F. McGranaghan, and H.W. Beaty, Electric Power Sys-
                                                                             tems Quality. New York: McGraw-Hill, 1996.                         WebPES Web Monitoring of Data from Dranetz-BMI 7100 PQNodes
                                                                                                                                                  and PQPagers. [Online]. Available:
                                                                          “Trouble-shooting guide for low-voltage ASD/motor systems,” Jarsco
                                                                             Engineering Corp., Corona, CA, EPRI TR-111097, 1998.               Fluke VR1101S Voltage Event recorder System. [Online]. Available:
                                                                          R. Bingham, “The power quality survey,” NETA World, Summer 1998.

                                                                                                                                                R. Dwyer, L. Tang, and S.G. Ashmore “Application of C-filters in steel
                                                                          “Superconductiong magnet energy storage smooths voltage sags,”
                                                                                                                                                   mill power systems,” ABB Electric Systems Technology Institute,
                                                                             Maintenance Technology, May, 1999.
                                                                                                                                                   Raleigh, NC, 1998.

                                                                          “Solutions for Power Quality,” ABB Power Systems.
                                                                                                                                                M.M. Swamy and S.L. Rossiter, “Harmonic interaction between
                                                                          “TCSC–thyristor controlled series capacitors, ABB Power Systems.        1500-kVA supply transformer and VFD load at an industrial
                                                                                                                                                  plant,” in Conf. Rec. 1997 IEEE IAS Annual Meeting, vol. 2, pp.
                                                                          “We don’t have a flicker problem…,” ABB Power Systems.                  1352-1359.

                                                                          “Minimum flicker, optimum active power and…,” ABB Power Sys-          G.T. Heydt, R. Ayynar, and R. Thallam, “Power Acceptability,” IEEE
                                                                             tems.                                                                 Power Eng. Rev., vol. 21, pp. 12-15, Sept. 2001.

                                                                          “The electromagnetic transients program—EMTP.” [Online]. Avail-       James A. Oliver ( is with Jarsco Engi-
                                                                             able:                                    neering Corp. in Corona, California, USA. Roger Lawrence and
                                                                                                                                                Basudeb Ben Banerjee are with EPRI in Palo Alto, California,
                                                                          “SuperHarm” Harmonic Simulation Software. [Online]. Available:        USA. This article first appeared in its original format at the
                                                                                                             2000 IEEE Petroleum and Chemical Industry Conference.


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