PQH 3rd chapter.pptx

UNIT-II Voltage Sag, Interruption and
Mitigation
Power Quality and
Harmonics
End user issues, ups system, Ferro-resonant transformers, super conducting
storage devices, dynamic voltage restorer and application of DSTATCOM
ADCET, Ashta Electrical Department

1. End user issues:
• Transient
• Impulsive Transient and Oscillatory Transient
• Long Duration Voltage Variation
• Over voltage, Under Voltage and Interruption.
• Short Duration Voltage Variation
• Voltage sang, Swell and interruption.
• Waveform Distortion
• Harmonics, Inter harmonics, DC offset, noise and notching.
• Voltage fluctuation
• Voltage imbalance
• Frequency variation

2. UPS (uninterruptable power supply) system:
1. Online UPS
2. Standby UPS
3. Hybrid UPS

2.1 Online UPS :
• In this design, the load is always fed through the UPS.
• The incoming ac power is rectified into dc power,
which charges a bank of batteries.
• This dc power is then inverted back into ac power, to
feed the load.
• If the incoming ac power fails, the inverter is fed from
the batteries and continue to supply the load.
• In addition to providing ride-through for power
outages, an on-line UPS provides very high isolation of
the critical load from all power line disturbances.
• However, the on-line operation increases the
losses and may be unnecessary for protection of many
loads.

2.2 Standby UPS :
• A standby power supply is sometimes termed off-line
UPS.
• since the normal line power is used to power the
equipment until a disturbance is detected and a
switch transfers the load to the battery backed
inverter.
• The transfer time from the normal source to the
battery-backed inverter is 8 ms is the lower limit Therefore a transfer time of 4 ms would
ensure continuity of operation for the critical load.
• A standby power supply does not typically
provide any transient protection or voltage regulation as does an on-line UPS.
• This is the most common configuration for commodity UPS units available at retail stores
for protection of small computer loads.

2.3 Hybrid UPS :
• Similar in design to the standby UPS, the hybrid UPS utilizes a voltage
regulator on the UPS output to provide regulation to the load and
momentary ride-through when the transfer from normal to UPS supply is
made.

3. Ferro-resonant transformers:
• Ferroresonant transformers, also called constant-
voltage transformers (CVTs), can handle most
voltage sag conditions.
• CVTs are especially attractive for constant, low-
power loads. Variable loads,
especially with high inrush currents, present more
of a problem for CVTs because of the tuned circuit
on the output.
• Ferroresonant transformers are basically 1:1 transformers which are excited high on their
saturation curves, thereby providing an output voltage which is not significantly affected
by input voltage variations.

4. super conducting (magnetic) storage devices :
• The energy storage in an SMES-based system is provided by the electric energy stored
in the current flowing in a superconducting magnet.
• Since the coil is lossless, the energy can be released almost instantaneously.
• Through voltage regulator and inverter banks, this energy can be injected into the
protected electrical system in less than 1 cycle to compensate for the missing voltage
during a voltage sag event.
• The SMES-based system has several advantages over battery-based UPS systems:
• SMES-based systems have a much smaller footprint than batteries for the same energy storage and power
delivery capability.
• The stored energy can be delivered to the protected system more quickly.
• The SMES system has virtually unlimited discharge and charge duty cycles. The discharge and recharge
cycles can be performed thousands of times without any degradation to the superconducting
magnet.

• Typical power quality–voltage regulator (PQ-VR) functional block diagram.

• SMES-based system providing ride-through during voltage sag event.

5. Dynamic Voltage Restorer :
• The DVR is a series connected power
electronic device used to inject voltage of
required magnitude and frequency.
• It contains the following components-
• Voltage Source Inverter (VSI)
• DC storage unit
• Filter circuit
• Series Transformer
• Basic Structure of DVR

• Voltage Source Inverter (VSI): The VSI consists of solid state switches like IGBT’s or
GTO’s used to convert the DC input to AC. It is used to inject the AC voltage to
compensate the decrease in the supply voltage. The switches of the VSI are operated
based on the pulse width modulation (PWM) technique to generate the voltage of
required magnitude and frequency.
• DC Storage Unit: The storage unit may consist of batteries, capacitors, flywheel, or
super magnetic energy storage (SMES). For DVR with internal storage capacity,
energy is taken from the faulted grid supply during the sag. Here a rectifier is used to
convert the AC voltage from the grid to DC voltage required by the VSI.
• Filter Circuit: An LC filter is connected at the output of the VSI to filter the
harmonics that are present in the output voltage of VSI. It also reduces the dv/dt
effect on the windings of the transformer.
• Series Transformer: A series transformer is used to connect the DVR with the
distribution feeder. In case of three phase system, three single phase transformers
are used to connect the DVR with the power network.

• The main operation of the DVR is to inject
voltage of required magnitude and
frequency when desired by the power
system network.
• During the normal operation, the DVR will
be in stand-by mode.
• During the disturbances in the system, the
nominal or rated voltage is compared with
the voltage variation and the DVR injects
the difference voltage that is required by
the load.

•
Control
Strategy
of
DVR:
(Flow
Chart)

• Applications of DVR:
• DVR can be used to compensate the load voltage harmonics and
improves the power quality of the system.
• DVR can be used under system frequency variations to provide the
real power required by the load. This is done by connecting a
uncontrolled rectifier at the input of the VSI.
• DVR can also protect the system against voltage swell or any other
voltage imbalances that occur in the power system.

6. D-STATCOM:
• D-STATCOM is a shunt connected
device designed to regulate the
voltage either by generating or
absorbing the reactive power. It
contains-
• DC Capacitor
• Voltage Source Inverter (VSI)
• Coupling Transformer
• Reactor

Operating Principle:
• A D-STATCOM is capable of compensating either bus voltage or line current. It
can operate in two modes based on the parameter which it regulates. They
are-
• Voltage Mode Operation: In this mode, it can make the bus voltage to which
it is connected a sinusoid. This can be achieved irrespective of the unbalance
or distortion in the supply voltage.
• Current Mode Operation: In this mode of operation, the D-STATCOM forces
the source current to be a balanced sinusoid irrespective of the load current
harmonics.
• The basic operating principle of a D-STATCOM in voltage sag mitigation is to
regulate the bus voltage by generating or absorbing the reactive power.
Therefore, the DSTATCOM operates either as an inductor or as a capacitor
based on the magnitude of the bus voltage.

Inductive Operation: If the bus voltage magnitude (VB) is more than the rated voltage
then the D-STATCOM acts as an inductor absorbing the reactive power from the system.
Capacitive Operation: If the bus voltage magnitude (VB) is less than the rated voltage
then the D-STATCOM acts as a capacitor generating the reactive power to the system.

Control Strategy:
• The main aim of the control strategy implemented to control a D-STATCOM
used
for voltage mitigation is to control the amount of reactive power exchanged
between the STATCOM and the supply bus.
• When the PCC voltage is less than the reference (rated) value then the D-
STATCOM generates reactive power and when PCC voltage is more than the
reference (rated) value then the D-STATCOM absorbs reactive power.
• To achieve the desired characteristics, the firing pulses to PWM VSI are
controlled.
• The actual bus voltage is compared with the reference value and the error is
passed through a PI controller.
• The controller generates a signal which is given as an input to the PWM
generator.
• The generator finally generates triggering pulses such that the voltage
imbalance is corrected.

•Applications of D-STATCOM:
The applications of the D-STATCOM are-
• Stabilize the voltage of the power grid
• Increase the transmission capacity
• Reactive power compensation
• Power Factor correction

UNIT-III Wiring and grounding
Power Quality and
Harmonics
Reasons for grounding, typical wiring and grounding
problem, solution to wiring and grounding problem.

• Grounding:
• A conducting connection, whether intentional or accidental, by
which an electric circuit or equipment is connected to the earth, or to some
conducting body of relatively large extent that serves in place of the earth.
• Grounded system:
• A system of conductors in which at least one conductor or point (usually the
middle wire or neutral point of transformer or generator windings) is
intentionally grounded, either solidly or through an impedance.
• Grounded solidly:
• Connected directly through an adequate ground connection in which no
impedance has been intentionally inserted.
• Grounded effectively:
• Grounded through a sufficiently low impedance such that for all system
conditions the ratio of zero sequence reactance to positive sequence
reactance (X0/X1) is positive and less than 3, and the ratio of zero sequence
resistance to positive sequence reactance (R0/X1) is positive and less than 1.

• Terminology used in National Electrical Cod (NEC) definitions:

3.1 Reasons for grounding
• Two important aspects to grounding requirements with respect to safety
and one with respect to power quality.
1. Personnel safety:
• Personnel safety is the primary reason that all equipment must have a safety
equipment ground.
• This is designed to prevent the possibility of high touch voltages when there is a fault
in a piece of equipment.

• There should be no “floating” panels or enclosures in the vicinity of
electric circuits.
• In the event of insulation failure or inadvertent application of moisture,
any electric charge which appears on a panel, enclosure, or raceway must
be drained to “ground” or to an object which is reliably grounded.
2. Grounding to assure protective device operation:
• A ground fault return path to the point where the power source neutral
conductor is
grounded is an essential safety feature.
• The NEC and some local wiring codes permit electrically continuous
conduit and wiring device enclosures to serve as this ground return path.
• An insulation failure or other fault that allows a phase wire to make
contact with an enclosure will find a low-impedance path back to the
power source neutral.
• The resulting overcurrent will cause the circuit breaker or fuse to
disconnect the faulted circuit promptly.

• NEC Article 250-51 states that an effective grounding path
(the path to ground from circuits, equipment, and
conductor enclosures) shall;
• Be permanent and continuous.
• Have the capacity to conduct safely any fault current likely to be
imposed on it.
• Have sufficiently low impedance to limit the voltage to ground and
to facilitate the operation of the circuit protective devices in the
circuit.
• Not have the earth as the sole equipment ground conductor

3. Noise control:
• Noise control includes transients from all sources.
• This is where grounding relates to power quality.
• Grounding for safety reasons defines the minimum requirements
for a grounding system.
• Anything that is done to the grounding system to improve the
noise
performance must be done in addition to the minimum
requirements
defined in the NEC and local codes.
The primary objective of grounding for noise control is to create an
equipotential ground system.
• Potential differences between different ground locations can stress
insulation, create circulating ground currents in low-voltage cables,
and interfere with sensitive equipment that may be grounded in
multiple locations.

3.2 Typical wiring and grounding problem
• It is useful to be aware of these typical problems when performing site
surveys because many of the problems can be detected through simple
observations. Other problems require measurements of voltages,
currents, or impedances in the circuits.
1. Problems with conductors and connectors.
2. Missing safety ground.
3. Multiple neutral-to-ground connections.
4. Ungrounded equipment.
5. Additional ground rods.
6. Ground loops.
7. Insufficient neutral conductor.

• Problems with conductors and connectors.
• One of the first things to be
done during a site survey is to
inspect the service entrance,
main panel, and major
subpanels for problems with
conductors or connections.
• A bad connection (faulty, loose,
or resistive) will result in
heating, possible arcing, and
burning of insulation.

• Missing safety ground.
• If the safety ground is missing,
a fault in the equipment from
the phase conductor to the
enclosure results in line
potential on the exposed
surfaces of the equipment.
• No breakers will trip, and a
hazardous situation results.

• Multiple neutral-to-ground connections.
• The only neutral-to-ground bond should be at the service entrance.
• The neutral and ground should be kept separate at all panel boards
and junction boxes.
• Down line neutral-to-ground bonds result in parallel paths for the load
return current where one of the paths becomes the ground circuit.
• This can cause misoperation of protective devices.
• Also, during a fault condition, the fault current will split between the
ground and the neutral, which could prevent proper operation of
protective devices (a serious safety concern).
• This is a direct violation of the NEC .
• Refer 3 pin plug.

• Ungrounded equipment.
• Isolated grounds are sometimes used due to the perceived notion of
obtaining a “clean” ground.
• The proper procedure for using an isolated ground must be followed
• Procedures that involve having an illegal insulating bushing in the
power source conduit and replacing the prescribed equipment
grounding conductor with one to an “isolated dedicated computer
ground” are dangerous, violate code, and are unlikely to solve noise
problems.

• Additional ground rods.
• Ground rods should be part of a facility grounding system and
connected where all the building grounding electrodes are bonded
together.
• Multiple ground rods can be bused together at the service entrance to
reduce the overall ground resistance.
• One very important power quality problem with additional ground rods
is that they create additional paths for lightning stroke currents to
flow.
• With the ground rod at the service entrance, any lightning stroke
current reaching the facility goes to ground at the service entrance and
the ground potential of the whole facility rises together.
• With additional ground rods, a portion of the lightning stroke current
will flow on the building wiring (green ground conductor and/or
conduit) to reach the additional ground rods. This creates a possible
transient voltage problem for equipment and a possible overload
problem for the conductors.

• Ground loops.
• Ground loops are one of the most important grounding problems in
many commercial and industrial environments that include data
processing and communication equipment.
• If two devices are grounded via different paths and a communication
cable between the devices provides another ground connection
between them, a ground loop results.
• Slightly different potentials in the two power system grounds can
cause circulating currents in this ground loop if there is indeed a
complete path.
• Even if there is not a complete path, the insulation that is preventing
current flow may flash over because the communication circuit
insulation levels are generally quite low.

• Insufficient neutral conductor.
• Switch-mode power supplies and fluorescent lighting with electronic
ballasts are widely used in commercial environments.
• The high third harmonic content present in these load currents can
have a very important impact on the required neutral conductor
rating for the supply circuits.
• Third-harmonic currents in a balanced system appear in the zero
sequence circuit. This means that third-harmonic currents from three
single-phase loads will add in the neutral, rather than cancel as is the
case for the 60-Hz current.
• In typical commercial buildings with a diversity of switched-mode
power supply loads, the neutral current is typically in the range 140 to
170 percent of the fundamental frequency phase current magnitude.

•The possible solutions to neutral conductor overloading
include the following:
• Run a separate neutral conductor for each phase in a three-phase circuit
that serves single-phase nonlinear loads.
• When a shared neutral must be used in a three-phase circuit with single-
phase nonlinear loads, the neutral conductor capacity should
be approximately double the phase conductor capacity.
• Delta-wye transformers designed for nonlinear loads can be used to limit
the penetration of high neutral currents.
• Filters to control the third-harmonic current that can be placed at the
individual loads are becoming available.
• Zigzag transformers provide a low impedance for zero-sequence harmonic
currents and, like filters, can be placed at various places along the three-
phase circuit to shorten the path of third-harmonic currents and better
disperse them.

3.3 Solution to wiring and grounding problem
1. Proper grounding practices
2. Ground electrode (rod)
3. Service entrance connections
4. Panel board
5. Isolated ground
6. Separately derived systems
7. Grounding techniques for signal reference
8. More on grounding for sensitive equipment

• Proper grounding practices

• Ground electrode (rod)
• The ground rod provides the electrical connection from the power
system ground to earth.
• There are three basic components of resistance in a ground rod:
• Electrode resistance: Resistance due to the physical connection of
the grounding wire to the grounding rod.
• Rod-earth contact resistance: Resistance due to the interface
between the soil and the rod. This resistance is inversely proportional
to the surface area of the grounding rod (i.e., more area of contact
means lower resistance).
• Ground resistance: Resistance due to the resistivity of the soil in
the vicinity of the grounding rod. The soil resistivity varies over a
wide range, depending on the soil type and moisture content.

• Service entrance connections
• The primary components of a properly grounded system are found at
the service entrance.
• The neutral point of the supply power system is connected to the
grounded conductor (neutral wire) at this point.
• This is also the one location in the system (except in the case of a
separately derived system) where the grounded conductor is
connected to the ground conductor (green wire) via the bonding
jumper.
• The ground conductor is also connected to the building grounding
electrode via the grounding-electrode conductor at the service
entrance.
• For most effective grounding, the grounding-electrode conductor
should be exothermically welded at both ends.

• Panel board
• The panel board is the point in the system where the various branch
circuits are supplied by a feeder from the service entrance.
• The panel board provides breakers in series with the phase
conductors; connects the grounded conductor (neutral) of the branch
circuit to that of the feeder circuit; and connects the ground
conductor (green wire) to the feeder ground conductor, conduit, and
enclosure.
• It is important to note that there should not be a neutral-to-ground
connection at the panel board.
• This neutral-to-ground connection is prohibited in the NEC as it
would result in load return currents flowing in the ground path
between the panel board and the service entrance.
• In order to maintain an equipotential grounding system, the ground
path should not contain any load return current.

• The noise performance of the supply to sensitive loads can some times be
improved by providing an isolated ground to the load.
• This is done using isolated ground receptacles, which are orange in color.
• If an isolated ground receptacle is being used down line from the panel board,
the isolated ground conductor is not connected to the conduit or enclosure in
the panel board, but only to the ground conductor of the supply feeder.
• The conduit is the safety ground in this case and is connected to the
enclosure.
• A separate conductor can also be used for the safety ground in addition to the
conduit.
• This technique is described in the NEC, Article 274, Exception 4 on
receptacles.
• It is not described as a grounding technique.

• Separately derived systems

• Grounding techniques for signal reference

• The most important characteristic of a signal reference ground is that
it must have a low impedance over a wide range of frequencies.

• More on grounding for sensitive equipment
• Whenever possible, use individual branch circuits to power sensitive
equipment.
• Conduit should never be the sole source of grounding for sensitive
equipment. It can cause interference with communications and
electronics.
• Green-wire grounds should be the same size as the current-carrying
conductors.
• Use building steel as a ground reference, whenever available. The
building steel usually provides an excellent, low-impedance ground
reference for a building.

UNIT-IV Power quality monitoring
Power Quality and
Harmonics
Monitoring considerations, power quality measurement
equipment, and assessment of power quality, power
quality monitoring and standard.

Power quality monitoring:
• Power quality monitoring is the process of gathering, analyzing, and
interpreting raw measurement data into useful information.
• The process of gathering data is usually carried out by continuous
measurement of voltage and current over an extended period.
• The process of analysis and interpretation has been traditionally
performed manually, but recent advances in signal processing and
artificial intelligence fields have made it possible to design and
implement intelligent systems to automatically analyze and interpret
raw data into useful information with minimum human intervention.
• Power quality monitoring programs are often driven by the demand
for improving the system wide power quality performance.
• Many industrial and commercial customers have equipment that is
sensitive to power disturbances, and, therefore, it is more important
to understand the quality of power being provided.

1. Monitoring considerations:
• Before embarking on any power quality monitoring effort,
one should clearly define the monitoring objectives.
• The monitoring objectives often determine the choice of
monitoring equipment, triggering thresholds, methods for data
acquisition and storage, and analysis and interpretation
requirements.
• Monitoring to characterize system performance.
• Monitoring to characterize specific problems.
• Monitoring as part of an enhanced power quality service.
• Monitoring as part of predictive or just-in-time maintenance.

Monitoring considerations
1.1 Monitoring as part of a facility site survey.
1.2 Determining what to monitor.
1.3 Choosing monitoring locations.
1.4 Options for permanent power quality monitoring equipment.
1.5 Disturbance monitor connections.
1.6 Setting monitor thresholds.
1.7 Quantities and duration to measure.
1.8 Finding the source of a disturbance.

1.1 Monitoring as part of a facility site survey:
• Site surveys are performed to evaluate concerns for power quality
and equipment performance throughout a facility.
• The survey will include inspection of wiring and grounding concerns,
equipment connections, and the voltage and current characteristics
throughout the facility.
• Power quality monitoring, along with infrared scans and visual
inspections, is an important part of the overall survey.
•

• The initial site survey should be designed to obtain as much information as
possible about the customer facility.
• Nature of the problems (data loss, nuisance trips, component failures, control system
malfunctions, etc.)
• Characteristics of the sensitive equipment experiencing problems (equipment design
information or at least application guide information)
• The times at which problems occur
• Coincident problems or known operations (e.g., capacitor switching) that occur at the
same time
• Possible sources of power quality variations within the facility (motor starting, capacitor
switching, power electronic equipment operation, arcing equipment, etc.)
• Existing power conditioning equipment being used
• Electrical system data (one-line diagrams, transformer sizes and impedances, load
information, capacitor information, cable data, etc.)
• Once these basic data have been obtained through discussions with the customer,
a site survey should be performed to verify the one-line diagrams, electrical
system data, wiring and grounding integrity, load levels, and basic power quality
characteristic.

• Form for recording supply
transformer test data.

1.2 Determining what to monitor:
• Power quality encompasses a wide variety of conditions on the power system.
• Important disturbances can range from very high frequency impulses caused by lightning
strokes or current chopping during circuit interruptions to long-term overvoltage caused by
a regulator tap switching problem.
• The range of conditions that must be characterized creates challenges both in terms of the
monitoring equipment performance specifications and in the data-collection requirements.
• Various categories of power quality variations:
• Transient
• Impulsive Transient and Oscillatory Transient
• Long Duration Voltage Variation
• Over voltage, Under Voltage and Interruption.
• Short Duration Voltage Variation
• Voltage sang, Swell and interruption.
• Waveform Distortion
• Harmonics, Inter harmonics, DC offset, noise and notching.
• Voltage fluctuation
• Voltage imbalance
• Frequency variation

• Extensive monitoring of all the different types of power quality
variations at many locations may be rather costly in terms of
hardware, communications charges, data management, and report
preparation.
• Hence, the priorities for monitoring should be determined based on
the objectives of the effort.

1.3 Choosing monitoring locations:
• Obviously, we would like to monitor conditions at virtually all locations
throughout the system to completely understand the overall power
quality.
• However, such monitoring may be prohibitively expensive and there are
challenges in data management, analysis, and interpretation.
• Fortunately, taking measurements from all possible locations is usually not
necessary since measurements taken from several strategic locations can be
used to determine characteristics of the overall system.
• Thus, it is very important that the monitoring locations be selected carefully
based on the monitoring objectives.

• Since the primary objective was to
characterize power quality on
primary distribution feeders,
monitoring was done on the actual
feeder circuits.
• One monitor was located near the
substation, and two additional sites
were selected randomly.
• By randomly choosing the remote
sites, the overall project results
represented power quality on
distribution feeders in general.
• It may not be realistic, however, to
assume that the three selected
sites completely characterized
power quality on the individual
• Typical distribution feeder monitoring scheme.

1.4 Options for permanent power quality monitoring equipment:
• Permanent power quality monitoring systems, such as the system illustrated in Fig., should
take advantage of the wide variety of equipment that may have the capability to record
power quality information.

• Some of the categories of equipment that can be
incorporated into an overall monitoring system
include the following:
• Digital fault recorders (DFRs)
• Smart relays and other IEDs
• Voltage recorders
• In-plant power monitors
• Special-purpose power quality monitors
• Revenue meters

1.5 Disturbance monitor connections:
• The recommended practice is to provide input power to the monitor
from a circuit other than the circuit to be monitored.
• Some manufacturers include input filters and/or surge suppressors on their
power supplies that can alter disturbance data if the monitor is powered from
the same circuit that is being monitored.
• The grounding of the power disturbance monitor is an important
consideration.
• The disturbance monitor will have a ground connection for the signal
to be monitored and a ground connection for the power supply of the
instrument.
• Both of these grounds will be connected to the instrument chassis.
For safety reasons, both of these ground terminals should be
connected to earth ground.
• However, this has the potential of creating ground loops if different
circuits are involved.

1.6 Setting monitor thresholds:
• Disturbance monitors are designed to detect conditions that are
abnormal. Therefore, it is necessary to define the range of conditions that
can be considered normal.
• Some disturbance monitors have preselected (default) thresholds that
can be used as a starting point.
• The best approach for selecting thresholds is to match them with the
specifications of the equipment that is affected.
• This may not always be possible due to a lack of specifications or
application guidelines.
• An alternative approach is to set the thresholds fairly tight for a period of
time (collect a lot of disturbance data) and then use the data collected to
select appropriate thresholds for longer-duration monitoring.

1.7 Quantities and duration to measure:
• Sometimes, when characterizing system disturbances, it is sufficient
to monitor only the voltage signals.
• For instance, the voltages provide information about the quality of
power being delivered to a facility and characterize the transients and
voltage sags that may affect customer equipment.
• However, there is a tremendous amount of information in the
currents associated with these disturbances that can help determine
the cause and whether or not equipment was impacted.
• Also, current measurements are required if harmonics are a concern
since the currents characterize the harmonic injection from the
customer onto the power system.

1.8 Finding the source of a disturbance:
• The first step in identifying the source of a disturbance is to
correlate
the disturbance waveform with possible causes.
• Once a category for the cause has been determined (e.g., load
switching, capacitor switching, remote fault condition, recloser
operation), the identification becomes more straightforward.
• The following general guidelines can help:
• High-frequency voltage variations will be limited to locations close to
the source of the disturbance.
• Power interruptions close to the monitoring location will cause a very
abrupt change in the voltage.
• The highest harmonic voltage distortion levels will occur close to
capacitors that are causing resonance problems.

2. Power Quality Measurement Equipment:
• It is clear that power quality phenomena cover a wide range of
frequencies.
• They include everything from very fast transient overvoltages
(microsecond time frame) to long-duration outages (hours or days
time frame).
• Power quality problems also include steady-state phenomena, such
as harmonic distortion, and intermittent phenomena, such as voltage
flicker.
• This wide variety of conditions that make up power quality makes the
development of standard measurement procedures and equipment
very difficult.

Types of instruments:
• Although instruments have been developed that measure a wide
variety of disturbances, a number of different instruments may be
used, depending on the phenomena being investigated.
• Basic categories of instruments that may be applicable include:
■ Wiring and grounding test devices
■ Multimeters
■ Oscilloscopes
■ Disturbance analyzers
■ Harmonic analyzers and spectrum analyzers
■ Combination disturbance and harmonic analyzers
■ Flicker meters
■ Energy monitors

■ Wiring and grounding test devices :
• Many power quality problems reported by end users are caused by problems
with wiring and/or grounding within the facility.
• These problems can be identified by visual inspection of wiring, connections, and
panel boxes and also with special test devices for detecting wiring and grounding
problems.
• wiring and grounding test device include;
• Detection of isolated ground shorts and neutral-ground bonds.
• Ground impedance and neutral impedance measurement or indication.
• Detection of open grounds, open neutrals, or open hot wires.
• Detection of hot/neutral reversals or neutral/ground reversals.
• Three-phase wiring testers should also test for phase rotation and
phase-to-phase voltages.

■ Multimeters :
• After initial tests of wiring integrity, it may also be necessary to
make quick checks of the voltage and/or current levels within a
facility.
• Overloading of circuits, undervoltage and overvoltage problems,
and unbalances between circuits can be detected in this manner.
• These measurements just require a simple multimeter. Signals
used to check for these include
■ Phase-to-ground voltages
■ Phase-to-neutral voltages
■ Neutral-to-ground voltages
■ Phase-to-phase voltages (three-phase system)
■ Phase currents
■ Neutral currents

■ Digital Camera :
• Photographs are extremely useful for documentation purposes.
• Those conducting the measurements often get distracted trying to get
instruments to function properly and tests coordinated. They are
rushed and fail to write down certain key data that later turn out to
be important.
• Unfortunately, human memory is unreliable when there are dozens of
measurement details to remember.
• The modern digital camera has become an indispendable tool when
taking field measurements.
• It is a simple matter to take photographs to document the tests. The
photographer can immediately tell if the shot failed and retake it with
a different exposure.
• Typical items to record photographically during field measurements
include:
• Nameplates of transformers, motors, etc., Instrumentation setups, Transducer and probe
connections, Key waveform displays from instruments, Substations, switchgear arrangements,
arrester positions, etc. and Dimensions of key electrical components such as cable lengths.

■ Oscilloscopes :
• An oscilloscope is valuable when performing real-time tests. Looking
at the voltage and current waveforms can provide much information
about what is happening, even without performing detailed harmonic
analysis on the waveforms.
• One can get the magnitudes of the voltages and currents, look for
obvious distortion, and detect any major variations in the signals.
• A digital oscilloscope with data storage is valuable because the
waveform can be saved and analyzed.
• In addition, the digital oscilloscopes can usually be obtained with
communications so that waveform data can be uploaded to a
personal computer for additional analysis with a software package.

■ Disturbance analyzers :
• Disturbance analyzers and disturbance monitors form a category of
instruments that have been developed specifically for power quality
measurements.
• They typically can measure a wide variety of system disturbances
from very short duration transient voltages to long-duration outages
or undervoltages.
• Thresholds can be set and the instruments left unattended to record
disturbances over a period of time.
• The information is most commonly recorded on a paper tape, but
many devices have attachments so that it can be recorded on disk as
well.

■ Harmonic analyzers and spectrum analyzers :
• Instruments in the disturbance analyzer category have very limited
harmonic analysis capabilities.
• Some of the more powerful analyzers have add-on modules that can
be used for computing fast Fourier transform (FFT) calculations to
determine the lower-order harmonics.
• However, any significant harmonic measurement requirements will
demand an instrument that is designed for spectral analysis or
harmonic analysis.
•

• Important capabilities for useful harmonic measurements
include;
 Capability to measure both voltage and current simultaneously so
that harmonic power flow information can be obtained.
 Capability to measure both magnitude and phase angle of individual
harmonic components (also needed for power flow calculations).
 Synchronization and a sampling rate fast enough to obtain accurate
measurement of harmonic components up to at least the 37th
harmonic (this requirement is a combination of a high sampling rate
and a sampling interval based on the 60-Hz fundamental).
 Capability to characterize the statistical nature of harmonic distortion
levels (harmonics levels change with changing load conditions
and changing system conditions).

■ Combination disturbance and harmonic analyzers :
• The most recent instruments combine harmonic sampling
and energy monitoring functions with complete disturbance
monitoring functions as well.
• The output is graphically based, and the data are remotely
gathered over phone lines into a central database.
• Statistical analysis can then be performed on the data.
• The data are also available for input and manipulation into
other programs such as spreadsheets and other
graphical output processors.

■ Flicker meters :
• Over the years, many different methods for measuring flicker have been
developed.
• These methods range from using very simple rms meters with flicker curves to
elaborate flicker meters that use exactly tuned filters and statistical analysis to
evaluate the level of voltage flicker.
Flicker standards. Although the United States does not currently have a
standard for flicker measurement, there are IEEE standards that address
flicker.
IEEE Standards 141-19936 and 519-19927 both contain flicker curves that
have been used as guides for utilities to evaluate the
severity of flicker within their system.

■ Smart Power Quality monitors:
• All power quality measurement instruments previously described are
designed to collect power quality data.
• Some instruments can send the data over a telecommunication line to a
central processing location for analysis and interpretation.
• However, one common feature among these instruments is that they do
not possess the capability to locally analyze, interpret, and determine what
is happening in the power system. They simply record and transmit data for
post processing.
• An emerging trend in power quality monitoring practice is to collect the
data, turn them into useful information, and disseminate it to users.
• All these processes take place within the instrument itself. Thus, a new
breed of power quality monitor was developed with integrated intelligent
systems to meet this new challenge.
• This type of power quality monitor is an intelligent power quality monitor
where information is directly created within the instrument and
immediately available to the users.

• The system consists of data acquisition, data aggregation, communication, Web-
based visualization, and enterprise management components.
• The data acquisition component (DataNode) is designed to measure the actual
power system voltages, currents, and other quantities.
• The data aggregation, communication, Web-based visualization, and enterprise
management components are performed by a mission-specific computer system
called the InfoNode.
• The communication between the data acquisition device and the InfoNode is
accomplished through serial or Ethernet communications.

• Power quality measurement equipment capabilities.

3. Assessment of power quality
• As utilities and industrial customers have expanded their power
quality monitoring systems, the data management, analysis, and
interpretation functions have become the most significant challenges
in the overall power quality monitoring effort.
• In addition, the shift in the use of power quality monitoring from off-
line benchmarking to on-line operation with automatic identification
of problems and concerns has made the task of data management
and analysis even more critical.
• There are two streams of power quality data analysis, i.e., off-line
and on-line analyses.
• The off-line power quality data analysis, as the term suggests, is
performed off-line at the central processing locations.
• The on-line data analysis is performed within the instrument itself for
immediate information dissemination.

1. Off-line power quality data assessment:
• Off-line power quality data assessment is carried out separately from
the monitoring instruments.
• Dedicated computer software is used for this purpose.
• Large-scale monitoring projects with large volumes of data to analyze
often present a challenging set of requirements for
software designers and application engineers.
• First, the software must integrate well with monitoring equipment and
the large number of productivity tools that are currently available. The
storage of
vast quantities of both disturbance and steady-state measurement
data requires an efficient and well-suited database.
• Data management tools that can quickly characterize and load power
quality data must be devised, and analysis tools must be integrated with
the database.
• Automation of data management and report generation tasks must be
supported, and the design must allow for future expansion and
customizing.

• The off-line power quality data assessment software usually performs the
following functions:
■ Viewing of individual disturbance events.
■ RMS variation analysis which includes tabulations of voltage sags
and swells, magnitude-duration.
■ Steady-state analysis which includes trends of rms voltages, rms currents, and
negative- and zero-sequence unbalances.
■ Harmonic analysis where users can perform voltage and current harmonic
spectra, statistical analysis of various harmonic indices, and
trending overtime.
■ Transient analysis which includes statistical analysis of maximum
voltage, transient durations, and transient frequency.
■ Standardized power quality reports (e.g. daily reports, monthly
reports, statistical performance reports, executive summaries, customer power
quality summaries). Analysis of protective device operation (identify problems).
■ Analysis of energy use.
■ Correlation of power quality levels or energy use with important parameters
(e.g., voltage sag performance versus lightning flash
density).
■ Equipment performance as a function of power quality levels (equipment
sensitivity reports).

• On-line power quality data assessment:
• On-line power quality data assessment analyzes data as they are
captured.
• The analysis results are available immediately for rapid
dissemination.
• Complexity in the software design requirement for on-line
assessment is usually higher than that of off-line.
• Most features available in off-line analysis software can also be
made available in an online system.
• One of the primary advantages of on-line data analysis is that it
can provide instant message delivery to notify users of specific
events of interest.
• Users can then take immediate actions upon receiving the
notifications.

4. Power quality monitoring and standard
• Standards are very important in the area of power quality monitoring.
• Power quality levels must be defined consistently and characterized
using the same methods if they are going to be compared from one
site to another and from one system to another.
• IEEE 1159 is the IEEE Working Group that coordinates the
development of power quality monitoring standards.
• The existing IEEE 1159 provides general guidelines and definitions for
monitoring power quality, and there are three separate task forces
that are working on more specific guidelines and requirements.
• IEEE 1159.1
• IEEE 1159.2
• IEEE 1159.3

1. IEEE 1159: Guide for power quality monitoring:
• IEEE Standard 115915 was developed to provide general guidelines
for power quality measurements and to provide standard definitions
for the different categories of power quality problems.
• These definitions were provided previously in Chap. 2 and provide the
basis for a common language in describing power quality phenomena.
Power quality monitoring equipment can use this language to
correctly differentiate between different power quality variations and
disturbances.
• After publication of the basic monitoring guidelines, working groups
were established for development of more advanced guides for
power quality monitoring. Three working groups were established.

1. IEEE 1159.1:
• Working Group is developing guidelines for instrumentation requirements
associated with different types of power quality phenomena.
• These requirements address issues like sampling rate requirements,
synchronization, A/D sampling accuracy, and number of cycles to sample.
2. IEEE 1159.2:
• Working Group is developing guidelines for characterizing different power
quality phenomena.
• This includes definition of important characteristics that may relate to the
impacts of the power quality variations. Example waveforms have been
collected illustrating the importance of different characteristics of the power
quality variations.
• IEEE 1159.1 and 1159.2 Working Groups has been combined into a single task
force and is being coordinated with the development on an international
standard .

3. IEEE 1159.3:
• Working Group is defining an interchange format that can be used to
exchange power quality monitoring information between different
applications.
• IEEE developed the COMTRADE format for exchanging waveform data
between fault recorders and other applications, such as relay testing
equipment.
• A more complete data interchange format is needed for power quality
data, which can include harmonic spectra, rms envelopes, characterized
power quality data, and statistical power quality data, as well as steady-
state and disturbance waveforms.
• The new Power Quality Data Interchange Format (PQDIF) has been defined,
and the standard is being balloted at the time of this writing.
• The common data interchange format will allow software developers to
develop applications for analyzing power quality events and problems
independently from the manufacturers of the actual power quality
monitoring equipment.

2. IEC 61000-4-30: Testing and Measurement Techniques—
Power Quality Measurement Methods:
• IEC standards for monitoring power quality phenomena are provided
in a series of documents with the numbers 61000-4-xx. The individual
standards in this series cover specific requirements for each type of
power quality variation or concern.
• This standard provides detailed requirements for the measurement
procedures and the accuracy requirements of the measurements.
• Class A performance is for measurements where very precise
accuracy is required.
• Class B performance still indicates that the recommended procedures
for characterizing power quality variations are used but that
the exact accuracy requirements may not be met.

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