Post on 06-May-2015
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CHAPTER 1
INTRODUCTION
The aim of the power system has always been to supply electrical energy to customers.
Earlier the consumers of electrical energy were mere acceptors. Interruptions and other voltage
disturbances were part of the deal. But today electric power is viewed as a product with certain
characteristics which can be measured, predicted, guaranteed, improved etc. Moreover it has
become an integral part of our life. So the quality of the power supply has gained much
importance. The term ‘power quality’ emerged as a result of this new emphasis placed on the
customer utility relationship.
The fact that power quality has become an issue recently does not mean that it was not
important in the past. Utilities all over the world have for decades worked on the improvement of
what is now known as power quality. In the recent years, users of electric power have detected
an increasing number of drawbacks caused by electric power quality variations. These variations
already existed on the electrical system but only recently they are causing serious problems. This
is due to the increased sensitivity of equipments and devices used by customers. These end user
equipments are more interconnected in networks and industrial processes, that the impact of a
problem with any piece of equipment is much more severe. Also power quality of power systems
affects all connected electrical and electronic equipments and is a measure of deviations in
voltage, current, frequency, temperature, force, and torque of particular supply systems and their
components.
To fulfill the demand of required supply, the world is under tremendous pressure for
alternative sources of energy and has been inclined towards sustainable energy for future source
of energy. The energy sources like solar energy, wind energy, hydroelectric power, tidal power,
geothermal power and wave power are all important types of renewable energy. However if
these energy sources are coupled with the energy efficacy it is termed as sustainable energy
sources. Sustainable Energy is the provision of energy such that it meets the needs of the future
without compromising the ability of future generations to meet their own needs. It is required to
have more efficient means of converting and utilizing these energy. This will depend on the
quality of power supplied and the impact of end user equipments on that power. But power
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electronic equipments are mostly used in sustainable and renewable energies in different stages
for acquisition and conversion or inversion into useable form. Due to increasing sensitivity of the
equipments and devices used by the customers, power qualities of sustainable energy are
affected.
Poor Power Quality results in high costs and that is gradually rising. The poorer the
Power Quality, the more would be the initiatives required from concerned parties and regulating
bodies to adopt corrective measures to ensure better Power Quality. As a consequence, the
economy of a country is largely affected with even low tech industries suffering serious financial
losses. Especially for successful sustainable energy programe, Power Quality Monitoring can
help identify the cause of power system disturbances and the underlying problem conditions on a
system before they cause interruptions and disturbances. Due to this many power utilities
perform power quality monitoring as an essential service for their main customers. Essential
capabilities of a power quality monitoring system are reduced cost and remote data transmission
capability.
With the electrical industry undergoing change, increased attention is being focused on
reliability and power quality. Power providers and users alike are concerned about reliable
power, whether the focus is on interruptions and disturbances or harmonic distortion or flicker.
One of the most critical steps in ensuring reliability is monitoring power quality. Power quality
monitoring can help to identify the cause of power system disturbances and even help to identify
problem conditions before they cause interruptions or disturbances. Hence power quality
monitoring is a multi-pronged approach to identifying, analyzing, and correcting power quality
problems. To improve power quality with adequate solutions, it is necessary to know what kinds
of disturbances occurred. A power quality monitoring system that is able to automatically detect,
characterize and classify disturbances on electrical lines is therefore required. With power
quality monitoring, power engineers can eliminate some of their troubleshooting headaches.
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CHAPTER 2
POWER QUALITY
2.1 DEFINATION
The definition of power quality given in the IEEE dictionary is as follows
“Power quality is the set of parameters defining the properties of the power supply as delivered
to the user in normal operating conditions in terms of the continuity of voltage and voltage
characteristics”.
Modern electronic and power electronic devices are not only sensitive to voltage
disturbances; it also causes disturbances for other customers. These devices become the source
and victims of power quality problems. As such the term power quality is used to define the
interaction of electronic equipments within the electrical environment.
2.2 CAUSES OF POWER QUALITY PROBLEMS
The causes of power quality problems can be many. It is often difficult to point an exact cause
for a specific problem. Power quality monitoring equipments comes to aid in such situations.
Most of the causes of power quality problem can be divided into two categories
� Internal causes
Approximately 80% of electrical problems originate within a business facility. Potential culprits
may include large equipments start or shut down, improper wiring and grounding, overloaded
circuits or harmonics.
� External causes
About 20% of power quality problems originate with the utility transmission and distribution
system .The most common cause is a lightning strike; other possibilities include equipments
failure, vehicle accidents, weather conditions, neighboring business and even normal operation
of utility equipments.
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2.3 POWER QUALITY DISTURBANCES
Power quality is concerned with the deviation of the voltage from the ideal waveform or the
deviation of the current from the ideal waveform. Such a deviation is called a power quality
phenomena or disturbances. It is important to first understand the kinds of power quality
disturbances that can cause problems with the sensitive loads. Categories of these disturbances
must be developed with a consistent set of definitions, so that the measurement equipments can
be designed in a consistent manner. Power quality phenomena can be divided into two basis
categories.
� Steady state variations
A characteristic of voltage or current is never exactly equal to its nominal or desired value.
The small deviations from the desired value are called voltage or current variations. A property
of any variation is that it has value at any moment in time. Monitoring of variations thus has to
take place continuously.
� Events
Occasionally, the voltage or current deviates significantly from the nominal or ideal wave
shape. These sudden deviations are called events. Monitoring of events take place by using a
triggering mechanism where recording of voltage or current starts the moment, a threshold is
exceeded.
STEADY STATE VARIATIONS
This category includes voltage and current variations which are relatively small
deviations of voltage and current characteristics around their nominal or ideal values. The two
basic characteristics are magnitude and frequency. On average voltage magnitude and voltage
frequency are equal to their nominal value but they are never exactly equal. Variations must be
measured by sampling the voltage and current over time. Information is best presented as a trend
of the quantity over time and then analyzed using statistical methods. An overview of voltage
and current variations are given below:
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� Voltage fluctuation
The fast changes or swings in the steady state voltage magnitude are called voltage
fluctuation. The change in voltage magnitude can be due to variations of total load of a
distribution system, action of transformer tap changers, switching of capacitor banks. If the
variations are large enough or in a certain critical frequency range, the performance of the
equipment can be affected.
Fig. 2.1
� Voltage and current unbalance
Unbalance or 3 phase unbalance is the phenomenon in a 3 phase system in which the
RMS values of voltages and phase angles between consecutive phases are not equal. The
primary source of voltage unbalance is the unbalanced load. This can be due to an uneven
spread of low voltage customers over the three phases but more commonly unbalance is due
to a large single phase load.
� Harmonic voltage and current distortion
Widespread use of electronic equipment in today’s commercial and industrial
environments make harmonic distortion an important but complicated power quality issue.
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Any power supply that converts AC to DC power will have a much distorted waveform at the
supply. The current waveform is always a picture of the way a load reacts to the AC supply.
The distorted voltage created by the return current through the impedance of the cable and
switchgear can cause the voltage waveform to distort. This voltage distortion will affect
every device connected to the corrupted circuit. Harmonic distortion of voltage and current
result, from the operation of non-linear loads and devices in the power system.
Fig. 2.2 Harmonic Distortion
� High frequency voltage noise
The non-periodic components in supply voltage can be called ‘noise’. Distinguishing
noise from other components is not always simple. An analysis is needed only in case where
noise leads to some problem with power system or end user equipments. Electrical noise can
be defined as the high frequency interference caused by a number of factors like arc welding
or operation of electrical motor.
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EVENTS
Events are the phenomena which happen once in a while. Power quality events are the
disturbances which can lead to the tripping of equipments, interruptions of production or plant
operation or endanger power system operation. Events are measured by a triggering mechanism.
An overview of various events is given below.
� Interruptions
A supply interruption is a condition in which the voltage at supply terminals is close to
zero. Interruptions are normally initiated by faults which subsequently trigger protection
measures. Interruptions can be subdivided based on their duration, thus based on the way of
restoring the supply.
1. Sustained Interruptions: These kinds of interruptions are terminated through manual
restoration or replacement of faulted components.
2. Temporary Interruptions: This refers to interruptions lasting less than 2 minutes. This
interruption is terminated through automatic restoration of pre-event situation.
3. Momentary Interruptions: These interruptions are terminated through self-restoration.
E.g. Interruption due to transients and other self-restoring events.
Fig. 2.3
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� Voltage sags / swells
A sag or swell is a decrease or increase in the RMS value of voltage ranging from a half
cycle to few seconds. The most likely kind of power quality problem is the voltage sag. Short
duration under voltages is called ‘voltage sags’ whereas, longer duration under voltages are
referred to as ‘under voltage’. Likewise over voltages of very short duration and high
magnitude are called ‘voltage swells’. Longer duration over voltage is called as ‘over
voltage’. Short duration voltage variations include variations in the fundamental frequency
voltage that lasts less than 1 minute.
Fig. 2.4
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� Transients
Transients are sub cycle disturbances of very short duration that vary greatly in
magnitude. Transients are used to refer to fast changes in the system voltage or current with
duration less than .5 cycles. Transients can be measured by triggering on the abnormality
involved. When transients occur, thousands of voltage can be generated into the electrical
system causing problems for equipments down the line. Transients can be divided into 2
categories:
1. Impulsive transient: Lightning striking a distribution line is normally an impulsive
transient where there is a large deviation of the wave form for a very short duration in
one direction, followed possibly by a couple of much smaller transients in both
directions.
2. Oscillatory transient: An oscillatory transient is one where there is a ringing signal or
oscillation following the initial transient. E.g.: switching of power factor correction
capacitor is considered the most prevalent type of transient.
Fig. 2.5
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2.4 INCREASED INTEREST IN POWER QUALITY
Power quality is an increasingly important issue for all business. A recent study by IBM
showed that power quality problems cost US business more than $15 billion a year. The
increased interest in power quality has resulted in significant advances in monitoring equipments
that can be used to characterize disturbances and power quality variations. The recent increased
interest in power quality can be explained in a number of ways.
• Equipments have become more sensitive to voltage disturbances
The electronic and power electronic equipments have especially become much more
sensitive to voltage disturbances than their counterparts 10 or 20years ago.
• Equipments cause voltage disturbances
Modern electronic and power electronic equipments are not only sensitive to voltage
disturbances but also cause disturbances for other customers. E.g. Non-sinusoidal current
drawn by rectifiers and inverters.
• Technical challenge taken up by utilities
Designing a system with a high reliability of supply at a limited cost is a technical challenge
which appealed too many in the power industry and hopefully still does in the future.
• Power quality can be measured.
The availability of electronic equipments to measure and show wave forms has certainly
contributed to the interest in power quality.
2.5 IMPACTS ON GLOBAL ECONOMY
The cost of energy or a KWH not supplied because of an outage is much higher than the
cost of a KWH that is supplied when needed. The global bill for poor power quality is more than
500 billion euros per year which is 50% of the turnover of the global electricity sector. For many
business uses, the cost of poor Power Quality is higher than the electricity bill and the cost is
rising. The global average energy consumption is steeply rising.
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Fig. 2.6 Projections of Indian average energy consumption
Due to high average increase of energy demand, India needs to have sustainable energy
productions to meet the huge energy requirements. The Government of India is trying to
accelerate solar power generation. By January 2014 the installed grid connected solar power had
increased to 2,208.36 MW, and India expects to install an additional 10,000 MW by 2017 and a
total of 20,000 MW by 2022. Poor Power Quality has serious impact on Indian economy. A joint
study by the manufacturers association of information technology(MAIT) and emersion network
power(India) has thrown up the finding that network power downtime costs Indian economy
more than Rs.43000 crores annually(2008) and this has been steeply rising. Similarly, economic
cost of outages of Bangladesh amounted to 1.72% (US $778millions) of the Country GDP in
2001. Industrial losses due to poor Power Quality had been estimated as $150- $200 billion
dollars for European Union (2001). Therefore, an efficient and intelligent monitoring is essential
to avoid staggering economic losses due to poor power quality and to meet the challenges.
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CHAPTER 3
POWER QUALITY MONITORING (PQM)
3.1 SOLAR ENERGY IN INDIA AND PQ MONITORING
Solar Energy is one of the cleanest and greenest technologies. Solar electric panels
produce DC. Necessary conversion is done for AC applications. A solar electric system may be
completely independent of the grid or designed to primarily feed power into the grid. The solar
radiation in India is very much satisfactory and most parts are suitable for generating power from
Solar Energy. In such case it is essential for India to install efficient power quality monitoring
systems to maintain quality and undertake exact mitigations in time. The support extended by
Government of India by way of providing attractive incentives under Jawaharlal Nehru National
Solar Mission (JNNSM) is generating significant interest in Solar Energy. India has
Geographical advantage with excellent solar radiation across the Country. In fact Rajasthan has
been recently termed as amongst the best in the world for Solar Energy. As an alternative source
of energy efforts are made to have larger production units from solar, wind mills sources etc. But
many systems (utility/customer) are affected due to absence of an effective PQM programme.
Integration of sustainable energy with the grid and use of power electronics, power quality
problems have increased in manifold. Monitoring within an industrial, residential or domestic
unit can reveal the origin of problems and give the necessary information for their solution.
Efficient power quality monitoring will provide the information needed to validate compliance,
improve system stability, and minimize unplanned downtime. It is therefore an important issue
for the successful and efficient operation of existing as well as future energy systems. In such
conditions, monitoring of power quality is the real challenge. An intelligent power quality
monitoring system is an essential requirement of the future energy system. The PQM should be
capable to detect most (and almost all) of the power quality events and disturbances. Intelligent
PQM is the need for smart grid due to principal functionality characteristics of Smart Grids.
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3.2 OBJECTIVES OF PQ MONITORING
The objectives of a monitoring program determine the choice of measuring equipments
and triggering thresholds, the methods for collecting data, data storage and analysis requirements
and the overall level of effort needed. General classification of objectives for power quality
monitoring is explained in the following section.
� Proactive approach:
This approach of monitoring is intended to characterize the system performance. A power
producer may find this objective important because this helps to understand the system
performance and then be able to match the system performance with customer needs.
� Reactive approach:
This kind of monitoring is intended to characterize a specific problem. Many services
solve power quality problems by performing short term monitoring at specific customers or at
different loads.
3.3 DEVLOPMENT OF SYSTEM
The aim of this work is to develop a method that is suitable for efficient monitoring of
power qualities in sustainable energy system like solar energy etc. The emphasis is therefore on
low computational power required to perform the necessary calculations. Stress is also laid on
the possibility to detect as many categories of PQ disturbances as possible.
An intelligent power monitoring system can be developed by designing virtual
instruments using LabVIEW software and NI’s DAQ system and sensors. Along with LabVIEW,
Higher order statistics (HOS) and quadratic discriminant analysis techniques are employed to
classify and analyze the huge amount of acquired data to determine the condition of the
waveforms. The system shows fast response with accuracy in monitoring and analysis of the
desired power qualities.
Initially, the distortions have been simulated in the labs and measured with the help of the
developed virtual instruments (VIs) using graphical programming in LabVIEW. Different types
of disturbances measurements are done with front panel created on PC monitor. The huge
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amount of acquired data has been analyzed using quadratic discriminant analysis technique to
determine the quality of the supply. The quadratic function is estimated treating a sample from
the data as a training data. The data can be exported in different formats in a text file or directly
in common software products like Excel etc. The test results of the simulated and the prototype
system show the desired performance of the system and thus validate the proposed technique.
The beauty of the system is that it can be used for monitoring of power qualities in both existing
power system and sustainable energy systems with provisions for switching-over.
In this application, we generate a graphical user interface through which the user can
monitor and adjust different parameters to customize the monitoring tasks. On the other hand, a
National Instruments Data Acquisition card is chosen to interface the analog AC signal as a
second step after using step-down transformer along with voltage divider circuit for signal
conditioning. For voltage measurements, magnetic voltage transformers are used (upto 5 KHz).
However current probes and Hall Effect voltage transducers are employed to acquire voltage and
current signals for accurate sensing.
Fig. 3.1 Block diagram of power quality monitoring system
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3.4 POWER QUALITY MONITORS
The first step to troubleshooting power quality problems is to have a monitor that
accurately measures voltage and current waveforms. The role of monitor for troubleshooting
power quality problems is undeniable. Power quality monitoring devices come in a variety of
shapes and sizes. Commercially available monitors fall into two categories: 1) portable
monitors and 2) permanent monitors.
� PORTABLE MONITORS
Handheld and portable instruments have made great improvements in testing capability in
recent years and are helpful in uncovering small localized problems. But these are used for
troubleshooting after an event has taken place. Installing a power quality monitor after the
occurrence of the event tells us little about the past. Portable monitors are again subdivided into
two classes:
1. Voltage recorders
These instruments record voltage and current strip chart data. Portable monitors are used for
continuous monitoring of steady state voltage variations. These recorders digitize voltage and
current signals by taking samples of voltage and current over time. The most important factor
to consider when selecting and using a voltage recorder is the method of calculation of the
RMS value of the measured signal.
2. Disturbance analyzer
Disturbance analyzer and disturbance monitors form a category of instruments which have
been developed specifically for power quality measurements. The analyzers are designed to
capture events affecting sensitive devices. They typically can measure a wide variety of
system events from very short duration transients to long duration outages. Thresholds can
be set and the instrument is left unattended to record disturbances over a long period of
time. Recording starts the moment, a threshold value is exceeded.
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Fig. 3.2 PORTABLE MONITOR
� PERMANENT MONITORS
In the past, measurement equipments were designed to handle either the events or steady
state variations. With advances in processing capability, new instruments have become available
that can characterize the full range of power quality variations. The new challenge involves
characterizing all the data in a convenient form, so that it can be used to identify and solve
problems. This highlights the features of permanent monitors.
Permanently installed full system monitors strategically placed on pieces of equipments
throughout the facility, lets the users know, what happened, where it happened as soon as it
happened. The main feature of these kinds of monitors is that they characterize full range of
power quality variations. They record both the triggered and sampled data. Triggering is based
upon the RMS thresholds for RMS variations and on wave shape for transient variation. The
simplest monitoring system could be a self-contained circuit monitor; however the real value of
monitoring is in automatic data downloading from the measuring instruments. Monitoring
system should fully utilize the networking infrastructure. A more apt term for these efficient
monitoring systems would be ‘real time monitoring systems’.
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Fig. 3.3 Permanently Installed Full System Monitor
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CHAPTER 4
ANALYSIS OF POWER QUALITY MEASUREMENTS
4.1 MONITORING OBSERVATIONS OF POWER QUALITIES
A large number of readings were recorded during observations of monitoring performed
by the developed system. Fig. 4.1 show some typical distortions or disturbances captured during
monitoring of simulated disturbances in the laboratory.
Fig. 4.1 PQ disturbances monitored by the developed method.
The waveforms captured show different power quality events or disturbances, including
voltage sag, swell, interruptions, transients, harmonics etc.
The table I shows the summary report of power quality monitoring of 200 KVA UPS
Input at NIT Silchar Systems. And table II shows the summary report of power quality
monitoring of 200 KVA UPS Output at NIT Silchar System.
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The tables I and II show extract of actual recordings, which would be helpful for assessment of
power quality of the systems. UPS input has about 15% input current harmonics distortion as it
has 12 pulse rectifier at the input. Similarly it has been observed that the blower motors which
have thyristor rectifiers at input are affected due to a lot of input current harmonic distortion.
Thus this system is showing monitoring of harmonics (THD), supply voltage and current.
4.2 DATA ANALYSIS
Acquired data can be exported in different formats in a text file, HTML or directly in
common software products or evaluation software provided by National Instruments. It has been
found during investigations and analysis that the sources of disturbances can be determined by
simultaneous measurement or monitoring of voltage and current. Analysis tools for processing
measured data present the information as individual events i.e. disturbance wave forms, trends or
statistical summaries. By comparing the captured events with libraries of typical power quality
variation characteristics and correlating with system events, causes of variations can be
determined. The data analysis system should be flexible enough to handle data from a variety of
monitoring equipments and maintain a database that can be used by many different applications.
4.3 BENEFITS OF POWER QUALITY MONITORING
The benefits of power quality monitoring are many. The following section mentions some of
them.
� Ensures power system reliability.
� Identify the source and frequency of events.
� Helps in the preventive and predictive maintenance.
� Evaluation of incoming electrical supply and distribution to determine if power quality
disturbances are impacting.
� Determine the need for mitigation equipments.
� Reduction of energy expenses and risk avoidances.
� Process improvements – monitoring systems allows to identify the most sensitive
equipments and install power conditioning systems where necessary.
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CHAPTER 5
CONCLUSION
Global economy has been affected due to poor PQ of the supply systems. Power qualities
of sustainable energy are also affected due to increasing sensitivity of the equipments and
devices used by the customers, and need proper monitoring and analysis for mitigation purposes.
Traditional monitoring methods are based on the RMS measurements and constrained by their
accuracies. Recently proposed approaches for automated detection and classification of power
quality disturbances are based on wavelet analysis, artificial neural networks, hidden Markov
model and bispectra. The use of such advanced techniques makes the power quality monitoring
system more accurate and the power system more reliable.
The configuration complexity of a monitoring system depends primarily upon the number
of instruments used to acquire information and the number of people who need to utilize it. The
simplest monitoring system could be a self-contained circuit monitor built into a sensitive load.
However the real value of monitoring system is in automatic data downloading from the
measuring instruments and hence today, a lot of emphasis is given on the design of ‘real time
monitoring systems’.
5.1 FUTURE OF POWER QUALITY
In 10 years’ time, it may well be that equipment has become fully compatible with the power
supply and does not cause any disturbance to the customers. However, there is no indication that
this will happen soon. So right now the emphasis is on mitigation equipments and on intelligent
power quality monitoring systems which enables the automatic classification and analysis of the
measured data.