1

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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20

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.