Power Quality full report
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ABSTRACT

Power quality is essential for smooth functioning of industrial process. As industries expand, utilities become more interconnected and usage of electrically equipment increases, power quality is jeopardized. The quality of power in the power system is severely affected by the presence of harmonics. This harmonics adversely effects the power system performance. Some of the effects are over heating of metal parts, noise in motors, low efficiency in motors etc. The effects produced by the harmonics are reduced by adopting some corrective measures.

1. INTRODUCTION
Since last 25 years there has been an increase in the use of solid state electronic technology. This new, highly efficient, electronic technology provides product quality with increased productivity. Today, we are able to produce products at costs less than in the years passed, with the introduction of automation by using the solid state electronic technology .This new technology requires clear electric power.
The conventional speed control systems are being replaced by modern power electronic systems, bringing a verity of advantages to the users. Classic examples are DC $ AC drives, UPS, soft stators, etc. Since the thrusters converter technology is rapidly gaining in the modern industrial plants, the power supply systems are contaminated as the ideal sinusoidal current and voltage waveforms are getting distorted. This is in turn is affecting the performance of the equipment in the electrical network.

2. WHAT IS POWER QUALITY
Adequate to superior power quality is essential for the smooth functioning of critical industrial processes. As industries expand, utilities become more interconnected and usage of electronically controlled equipment increases, power quality is jeopardized. Most large industrial and commercial sites are served by overhead lines with feeders that are subject to unpredictable and sporadic events, e.g. lightning and contact with tree limbs. Most distribution circuits have resoling devices that clear temporary faults through a timed series of trip and close operations.
This minimizes the possibility of long-term outages but leads to a number of minor power disturbances. These typically occur several times a month. Many electric utilities have increased the voltage at which they distribute power. This allows a single circuit to serve more customers or deliver higher loads, and reduces energy losses in the system. But it often means the overhead distribution circuit is longer, with more exposure to disturbances. And disturbances travel farther because of lower system impedances associated with higher voltage circuits. Sophisticated new systems are providing vastly increased efficiency and control in critical processes. But with their high sensitivity even to brief variations in electric power quality, today's computer-driven devices fail when power is disturbed for even a few milliseconds.

3. HARMONICS-BASIC CONCEPTS
A pure sinusoidal voltage is conceptual quantity produced by an ideal AC generator build with finely distributed stator and field windings that operate in a uniform magnetic field. Since neither the winding distribution nor the magnetic field is uniform in a working AC machine, voltage waveform distortion is created, and the voltage time relation-ship deviates from the pure sine function. The distortion at the point of generation is very small (about 1%to 2%), but nonetheless it exists.
Because this is a deviation from a pure sine wave, the deviation is in the form of a periodic function and by definition, the voltage distortion contains harmonics. When a sinusoidal voltage is applied to a certain type of load, the current drawn by the load is proportional to the voltage and impedance and follows the envelope of the voltage wave form .These loads are referred to as linear loads (loads where the voltage and current follow one another without any distortion to their pure sine waves).examples of nonlinear loads are resistive heaters, incandescent lamps and constant speed induction and synchronous motors.
In contrast some loads cause the current to vary disproportionately with the voltage during each half cycle. These loads are classified as nonlinear loads and the current and voltage have waveforms that are non sinusoidal containing distortions where by 50 Hz waveform has numerous additional waveforms superimposed upon it creating multiple frequencies within the normal 50 Hz sine wave .The multiple frequencies are harmonics of the fundamental frequency.

Normally current distortion produce voltage distortions .However when there is a stiff sinusoidal voltage source there is a low impedance path from the power source which has sufficient capacity so that loads placed upon it will not affect the voltage one need not be concerned about current distortions producing voltage distortions Examples of non linear loads are battery chargers, electronic ballasts; variable frequency drives, and switched mode power supplies.
As nonlinear currents flows through a facility's electrical system and the distribution - transmission lines, additional voltage distortions are produced due to the impedance associated with the electrical network. Thus as electrical power is generated, distributed and utilized, voltage and current waveforms distortions are produced.
Power systems designed to function at the fundamental frequency which is 50 Hz in India are prone to unsatisfactory operation and at times failure when subjected to voltages and currents that contains substantial harmonic frequency elements. Very often the operation of electrical equipment may seem normal but under a certain combination of conditions the impact of harmonics is enhanced with damaging results.

4. THE AFFECTS
The actual problems of any building/industry will vary depending on the type and number of installed harmonics producing loads. Most electrical network can withstand nonlinear loads of up to 15% of the total electrical system capacity without concern but when the nonlinear loads exceed 15% some non expected negative consequences can be expected. .for electrical networks , they have on linear loading of more than 25% particular problems can be apparent.

The following is a short summery of most problems caused by harmonics:
Blinking of incandescent lights-transformer saturation
Capacitor failure-harmonics resonance
Circuit breaker tripping-inductive heating and over loading
Computer malfunctioning-voltage distortion
Transformer failure-inducting
Motor failure-inductive heating
Fuses blowing for no apparent reason-inductive heating & over load
Electronic component shut down- voltage distortion
Flickering of florescent lights-transformer saturation

The heating effects of harmonic currents can cause destruction of equipment, conductors, and fires. The results can be unpredictable legal and financial ramifications apart from safety risks. Voltage distortions can lead to over heating of equipment failure, expensive down time and maintenance difficulties. Harmonic currents and voltage distortions are becoming the most severe and complex electrical challenge for the electrical industry .The problems associated with nonlinear loads were once limited to isolated devices and computer rooms, but now the problem can appear through the entire network and utility system

The point at which the harmonic limits are applied is called the point of common coupling (PCC). When the input transformer is the point of measurement then the PCC refers to this point where the facility electrical system is common to the facility of additional consumers. If there is a distortion present on the electrical power system at this point it may be experienced by the neigh boring facilities as well. So we need to avoid this situation

5. SOLUTION
Users of variable frequency drives often have strict demands placed on them to mitigate harmonic distortion caused by the nonlinear loads. Many choices are available to them including line reactors, harmonic traps, 12 pulse rectifier, 18 pulse rectifiers, and low pass filters.
5.1 LINE REACTORS
The input harmonic current distortion can be reduced by simple addition of input line reactance. The inductive reactance of an input line reactor allows 50 Hz or 60 Hz currents to pass easily but presents considerably higher impedance to all other harmonic frequencies. Harmonic currents are thus attenuated by the reactance offered by the line reactor.
These reactors are also used to solve the problems in variable frequency drive installations.Eg: harmonic attenuation , drive tripping .The line reactors are always used in the line side or input of the variable frequency drives. Thus they are called the line reactors. The line reactors cannot be used at the output of the variable frequency drives
Because the reactors are over heated due to the harmonic content of the output waveform of the VFD Harmonic compensated reactors can be used on the either side of the variable frequency drives .Due to the introduction of the Harmonic compensated reactors the following problems are eliminated: motor noise, low efficiency of the motors, temperature rise in motors and variable frequency drives short circuit problem.
5.2 HARMONIC FILTERS
In some cases, reactors alone will not be capable of reducing the harmonic current distortion to the desired levels. In these cases, a more sophisticated filter will be required. The common choices include shunt connected, tuned harmonic filters (harmonic traps) and series connected low pass filters (broad band suppressors). They consist of a capacitor and an inductor which are tuned to a single harmonic frequency. Since they offer very low impedance to that frequency, the specific (tuned) harmonic current is supplied to the drive by the filter rather than from the power source. If tuned harmonic filters (traps) are selected as the mitigation technique, then multiple tuned filters are needed to meet the distortion limits which are imposed.
When employing tuned harmonic filters, we need to take special precautions to prevent interference between the filter and the power system. A harmonic trap presents a low impedance path to a specific harmonic frequency regardless of its source. The trap cannot discern harmonics from one load versus another. Therefore, the trap tries to absorb that entire harmonic which may be present from all combined sources (non-linear loads) on the system. This can lead to premature filter failure.
Since harmonic trap type filters are connected in shunt with the power system, they cause a shift in the power system natural resonant frequency. If the new frequency is near any harmonic frequencies, then it is possible to experience an adverse resonant condition which can result in amplification of harmonics and capacitor or inductor failures. Whenever using harmonic trap type filters, one must always perform a complete system analysis. You must determine the total harmonics which will be absorbed by the filter, the present power system resonant frequency, and the expected system resonant frequency after the filter (trap) is installed. Field tuning of this filter may be required if adverse conditions are experienced.
5.3 12 PULSE RECTIFIERS
12 Pulse drives are frequently specified by the engineers for heating, ventilating and air conditioning applications because their ability to reduce harmonic current distortion. In the mid 1960s when power semiconductors were only available in limited ratings, twelve-pulse drives provided a simpler and more cost effective approach to achieving higher current ratings than direct paralleling of power semiconductors.
A typical diagram of a large twelve-pulse drive appears in figure the drive's input circuit consists of two six-pulse rectifiers, displaced by 30 electrical degrees, operating in parallel. The 30-degree phase shift is obtained by using a phase shifting transformer. The circuit in figure simply uses an isolation transformer with a delta primary, a delta connected secondary, and a second wye connected secondary to obtain the necessary phase shift. Because the instantaneous outputs of each rectifier are not equal, an inter phase reactor is used to support the difference in instantaneous rectifier output voltages and permit each rectifier to operate independently. The primary current in the transformer is the sum of each six-pulse rectifier or a twelve-pulse wave form.
Theoretical input current harmonics for rectifier circuits are a function of pulse number and can be expressed as:
h = (np + 1) where n= 1, 2, 3, and p = pulse number
For a six-pulse rectifier, the input current will have harmonic components at the following multiples of the fundamental frequency.
5, 7, 11, 13, 17, 19, 23, 25, 29, 31, etc.
For the twelve-pulse system shown in figure 1, the input current will have theoretical harmonic components at the following multiples of the fundamental frequency:
11, 13, 23, 25, 35, 37, etc.
Note that the 5th and 7th harmonics are absent in the twelve-pulse system. Since the magnitude of each harmonic is proportional to the reciprocal of the harmonic number, the twelve-pulse system has a lower theoretical harmonic current distortion.
12 PULSE RECTIFIERS
Figure shows the actual measurement of input current harmonic distortion for 12 pulse rectifier supplied from a balanced 3 phase voltage source while operating at full load conditions. For test purpose transformer has delta primary and delta,wye secondary windings. To obtain the best results, the bridge rectifier is connected in series so equal dc windings. To obtain the best results, the bridge rectifier is connected in series so equal dc

The data shows when the current through both sets of the rectifiers is equal, harmonics can be as low as 10% to 12% total harmonic current distortion, at full load. Current sharing reactors will help parallel connected bridge rectifiers to share current equally. Even with balanced current harmonic current distortion can increase appreciably at light loaded conditions. Even with perfectly balanced line voltages, the resultant % total harmonic current distortion increases as the load increases. As the load reduced, that is 23% total harmonic current distortion at 20% load.
5.4 18 PULSE RECTIFIER
A typical diagram of a series connected eighteen pulse drive constructed from a standard six-pulse drive, two external rectifiers and a conventional 18 pulse isolation transformer appears in figure 1. The drive has terminals available to connect a DC link choke. These terminals are used to connect the two external rectifiers in series with the drives internal rectifier. The eighteen pulse transformer is designed to provide one third the normal input voltage to each of the three rectifiers at a 20 degree phase displacement from each other. The 20-degree phase shift is obtained by phase shifting the transformers secondary windings. The circuit in figure 1 simply uses an isolation transformer with a delta primary, and three delta connected secondary windings, one shifted + 20 degrees, one shifted -20 degrees and one in phase with the primary.
The primary current in the transformer is the sum of each six-pulse rectifier or an eighteen-pulse wave form.
Theoretical input current harmonics for rectifier circuits are a function of pulse number and can be expressed as:
h = (np ± 1) where n= 1, 2, 3,... and p = pulse number
For a six-pulse rectifier, the input current will have harmonic components at the following multiples of the fundamental frequency.
5, 7, 11, 13, 17, 19, 23, 25, 29, 31, 35, 37, 41, 43, 47, 49, 53, 55, etc.

For the eighteen-pulse system shown in figure 1, the input current will have theoretical harmonic components at the following multiples of the fundamental frequency:
17, 19, 35, 37, 53, 55, etc.
Note that the 5th and 7th, 11th and 13th harmonics are absent in the theoretical eighteen-pulse system. Since the magnitude of each harmonic is proportional to the reciprocal of the harmonic number, the eighteen-pulse system has a lower theoretical harmonic current distortion.
To determine how an eighteen-pulse drive system operates under unbalanced line voltage conditions, we constructed a 30 HP eighteen-pulse drive from a conventional isolation transformer and standard six-pulse drive using the series bridge connection shown in figure 1. An auto transformer could have been used in place of the isolation transformer. The auto transformer costs less and requires less mounting space, but the isolation transformer was selected because it provides better performance and is readily available as a modified standard transformer.
Care was taken in the physical construction of the transformer to balance the leakage reactance and output voltage of the three secondary windings. The system was tested with line voltage unbalance ranging from 0% to 3% and with loads ranging from 5% to 100%. The input total harmonic current distortion, THID, is shown in figure 3. THID varied from 7.4% at full load with balanced line voltages to 59% at 30% load with a 3% unbalance. The data show that the harmonic performance of eighteen-pulse drives degrades rapidly with increasing line voltage unbalance and decreasing load.
Simply focusing on harmonic performance under the best operating conditions, perfectly balanced line voltages and full load, is not a useful indicator of performance under practical operating conditions. In heating, ventilating and air conditioning applications where drives will operate for long periods of time at 30% to 60% load eighteen pulse drives to not meet expectations.

18 PULSE RECTIFIER
To determine how an eighteen-pulse drive system operates under unbalanced line voltage conditions, we constructed a 30 HP eighteen-pulse drive from a conventional isolation transformer and standard six-pulse drive using the series bridge connection shown in figure 1. An auto transformer could have been used in place of the isolation transformer. The auto transformer costs less and requires less mounting space, but the isolation transformer was selected because it provides better performance and is readily available as a modified standard transformer. Care was taken in the physical construction of the transformer to balance the leakage reactance and output voltage of the three secondary windings. The system was tested with line voltage unbalance ranging from 0% to 3% and with loads ranging from 5% to 100%. The input total harmonic current distortion, THID, is shown in figure 3. THID varied from 7.4% at full load with balanced line voltages to 59% at 30% load with a 3% unbalance. The data
show that the harmonic performance of eighteen-pulse drives degrades rapidly with increasing line voltage unbalance and decreasing load. Simply focusing on harmonic performance under the best operating conditions, perfectly balanced line voltages and full load, is not a useful indicator of performance under practical operating conditions. In heating, ventilating and air conditioning applications where drives will operate for long periods of time at 30% to 60% load eighteen pulse drives to not meet expectations.

Figure 3
Obviously, any unbalance in the eighteen-pulse transformer's leakage reactance and output voltage will degrade performance. Unfortunately perfect transformers can not be built. Output voltage depends on turns ratios which are limited to plus or minus one turn. As a result the output voltage of the three secondary windings cannot be perfectly balanced. Leakage reactance is a function of coil position and volume. Clever Mechanical design of the transformer windings will help to minimize the differences in leakage reactance between the three groups of secondary windings but perfect balance can not be achieved. Data for the transformer used in this test appears in Tables 1 and 2.
Transformer Design
Secondary
Winding Phase Shift
Degrees Leakage
Reactance
% Nominal Output Voltage
Based on Turns Ratios
Volts
0 3.67 160.00
-20 4.73 160.50
+20 5.33 160.50
Table 1
Transformer Full Load Data
Secondary
Winding
Phase Shift
Degrees Secondary Phase Voltage
At Full Load Unbalance
Per
Secondary
Group
% Unbalance
Across
Secondary
Groups
%
Volts
A B C Average
0 154.3 154.4 154.1 154.26 0.10
-20 157.9 157.0 157.6 157.50 0.32
+20 156.6 155.4 156.9 156.30 0.57
Average 156.02 1.12
Table 2
The addition of 5% line reactors at the input to each of the three rectifiers results in a significant improvement in the operation Drives are applied in heating, ventilating, and air conditioning applications because loads are variable and users demand energy efficiency and comfort. Varying loads result in load unbalances within building power distribution systems which add to the utility line voltage unbalance at the point of common coupling. Harmonic mitigation techniques which are not effective with line voltage unbalances of 1% to 3% at the point of utilization will not as a practical matter achieve useful results. The data in this report show that a standard six-pulse drive fed from a low pass Matrix Filter provides superior harmonic performance to an eighteen-pulse drive in applications with variable loads and line voltage unbalances ranging from 0% to 3%.
5.5 LOW PASS HARMONIC SUPPRESSORS
Low pass harmonic filters, also referred to as broad band harmonic suppressors, offer a non-invasive approach to harmonic mitigation. Rather than being tuned for a specific harmonic, they filter all harmonic frequencies, including the third harmonic. They are connected in series with the non-linear load with a large series connected impedance, therefore they donâ„¢t create system resonance problems. No field tuning is required with the low pass filter.
Due to the presence of the large series impedance, it is extremely difficult for harmonics to enter the filter / drive from the power source. Rather they are supplied to the drive via the filter capacitor. For this reason, it is very easy to predict the distortion levels which will be achieved and to guarantee the results.
A low pass (broad band) harmonic filter can easily offer guaranteed harmonic current levels, right at the drive / filter input, as low as 8% to 12% THID. (To achieve 8% maximum current distortion one can typically select the broad band harmonic suppressor based on a HP / KW rating which is 25-30% larger than the total drive load to be supplied). In most cases, this results in less than 5% THID at the facility input transformer and meets most international standards.

Fig. 6 Actual input current waveform for VFD fitted with Broad Band Harmonic Suppressor.
The low pass filter not only offers guaranteed results, it is also more economical than 12 or 18 pulse rectifier systems, active filters or in many cases even harmonic traps. They are intended for use with 6-pulse drives having a six diode input rectifier in variable torque applications. This typically means fan and pump applications. For the sake of economy, a single Broad Band Harmonic Suppressor may be used to supply several drives (VFDs). When operating at reduced load, the THID at the filter input will be even lower than the guaranteed full load values.

6. BENEFITS
MOTOR TEMPERATURE REDUCTION
Motors operated on a VFD tend to run warmer than when they are operated on pure 60hz, such as in an across-the-line stator application. The reason is that the output waveform of the VFD is not pure 60hz,, but rather it contains harmonics which are currents flowing at higher frequencies. The higher frequencies cause additional watts loss and heat to be dissipated by the iron of the motor, while the higher currents cause additional watts loss and heat to be dissipated by the copper windings of the motor. Typically the larger horsepower motors (lower inductance motors) will experience the greatest heating when operated on a VFD.
Reactors installed on the output of a VFD will reduce the motor operating temperature by actually reducing the harmonic content in the output waveform. A five percent impedance, harmonic compensated reactor will typically reduce the motor temperature by 20 degrees Celsius or more. If we consider that the typical motor insulation system has a "Ten Degree C Half Life" (Continual operation at 10 degrees C above rated temperature results in one half expected motor life), then we can see that motor life in VFD applications can easily be doubled. Harmonic compensated reactors are actually designed for the harmonic currents and frequencies whereas the motor is not.
MOTOR NOISE
Because the carrier frequency and harmonic spectrum of many Pulse Width Modulated (PWM) drives is in the human audible range, we can actually hear the higher frequencies in motors which are being operated by these drives. A five percent impedance harmonic compensated reactor will virtually eliminate the higher order harmonics (11th & up) and will substantially reduce the lower order harmonics (5th & 7th). By reducing these harmonics, the presence of higher frequencies is diminished and thus the audible noise is reduced. Depending on motor size, load, speed, and construction the audible noise can typically be reduced from 3 - 6 dB when a five percent impedance harmonic compensated reactor is installed on the output of a PWM drive. Because we humans hear logarithmically, every 3dB cuts the noise in half to our ears. This means the motor is quieter and the remaining noise will not travel as far.
MOTOR EFFICIENCY
Because harmonic currents and frequencies cause additional watts loss in both the copper windings and the iron of a motor, the actual mechanical ability of the motor is reduced. These watts are expended as heat instead of as mechanical power. When a harmonic compensated reactor is added to the VFD output, harmonics are reduced, causing motor watts loss to be reduced. The motor is able to deliver more power to the load at greater efficiency. Utility tests conducted on VFD's with and without output reactors have documented efficiency increases of as much as eight percent (at 75% load) when the harmonic compensated reactors were used. Even greater efficiency improvements are realized as the load is increased.
SHORT CIRCUIT PROTECTION
When a short circuit is experienced at the motor, very often VFD transistors are damaged. Although VFD's typically have over correct protection built-in, the short circuit current can be very severe and its rise time can be so rapid that damage can occur before the drive circuitry can properly react. A harmonic compensated reactor (3% impedance is typically sufficient) will provide current limiting to safer values, and will also slow down the short circuit current rise time. The drive is allowed more time to react and to safely shut the system down. You still have to repair the motor but you save the drive transistors.
The above methods solve other problems on the load side of VFD's in specialized applications also. Some of these include: Motor protection in IGBT drive installations with long lead lengths between the drive and motor, Drive tripping when a second motor is switched onto the drive output while another motor is already running, and Drive tripping due to current surges from either a rapid increase or decrease in the load.

7. CONCLUSION
VFD users have many choices when it comes to harmonic filtering. Of course they may do nothing, or they may choose to employ one of the many techniques of filtering available. Each filtering technique offers specific benefits and has a different cost associated with it. Some may have the potential to interfere with the power system while others will not.
For best overall results when using reactors or harmonic filters, be sure to install them as close as possible to the non-linear loads which they are filtering. When you minimize harmonics directly at their source you will be cleaning up the internal facility mains wiring. This will also reduce the burden on upstream electrical equipment such as circuit breakers, fuses, disconnect switches, conductors and transformers. The proper application of harmonic filtering techniques can extend equipment life and will often improve equipment reliability and facility productivity.

8. REFERENCES
¢ INDUSTRIAL REFERENCE MAY 2003 PAGE 178
¢ WWW://POWERQUALITY.COM
¢ WWW://ECONOMICSOULTIONSTOMEETHARMONICDISTORTION.COM
¢ WWW://POWERQUALITYUSINGREACTORS.COM


CONTENTS
1. INTRODUCTION 1
2. WHAT IS POWER QUALITY 2
3. HARMONICS BASIC CONCEPT 3
4. THE AFFECTS 5
5. SOLUTION 7
5.1. LINE REACTORS 7
5.2. HARMONIC TRAPS 8
5.3. 12 PULSE RECTIFIER 9
5.4.18 PULSE RECTIFIER 12
5.5. LOW PASS SUPPRESSORS 17
6. BENEFITS 19
7. CONCLUSION 22
8. REFERENCES 23

ACKNOWLEDGEMENT
I express my sincere gratitude to Dr.Nambissan, Prof. & Head, Department of Electrical and Electronics Engineering, MES College of Engineering, Kuttippuram, for his cooperation and encouragement.
I would also like to thank my seminar and presentation guide Mrs. Nafeesa K. (Lecturer, Department of EEE), Asst. Prof. Gylson Thomas. (Staff in-charge, Department of EEE) for their invaluable advice and wholehearted cooperation without which this seminar and presentation would not have seen the light of day.
Gracious gratitude to all the faculty of the department of EEE & friends for their valuable advice and encouragement.
Use Search at http://topicideas.net/search.php wisely To Get Information About Project Topic and Seminar ideas with report/source code along pdf and ppt presenaion
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INTRODUCTION
Power quality is a measure of how well electric power service can be utilized by customers.

The power quality is an electrical property that allows electrical systems to function in their intended manner without significant loss of performance.

Complexity of the system enables compromised quality of power.

Supply interruptions and low voltage levels are a constant source of concern for Indian consumers.

Parameters of Power Quality

Continuity of service.
Variation in voltage magnitude.
Transient voltages and over currents.
Harmonic content in the waveforms.

Transient Overvoltage
Transient over voltages are brief, high-frequency increases in voltage on AC mains.


Generally two different types of transient over voltages are observed:
a) Low frequency transients
b) High frequency transients (surges, spikes etc.)






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presented by:
G.HARINATHAREDDY


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Abstract
In little more than ten years, electricity power quality has grown from obscurity to a major issue. Electronic converters and power electronics gave birth to numerous new applications, offering unmatched comfort, flexibility and efficiency to the customers.These equipments are highly sensitive to poor power quality. These require reliable and good power quality free from all power quality issues.However, their proliferation during the last decade is creating a growing concern and generates more and more problems: not only these electronic loads pollute the AC distribution system with harmonic currents, but they also appear to be very sensitive to the voltage distortion. Then, electricity power quality is becoming a major issue for utilities and for their customers, and both are quickly adopting the philosophy and the limits proposed by the new
Today, recent advances in power electronic technology are providing an unprecedented capability for conditioning and compensating harmonic distortion generated by the non-linear loads. This new innovative active conditioner appears to be the easiest of use, the most flexible, the most efficient and cost effective one Power quality monitors assist the troubleshooter to identify and solve many power quality problems. The paper presents examples showing how to analyze these clues, but also shows that similar disturbance wave shapes may still have radically different causes.
INTRODUCTION:
The power quality problem is defined as any problem manifested in voltage, current or frequency deviations that results in mal-operation of customer equipment. The power quality problem causes the deterioration of performance of various sensitive electronic and electric equipments. The good quality of power can be specified as The supply voltage should be within guaranteed tolerance of declared value.The waveshape should be pure sine wave within allowable limits for distortion.The voltage should be balanced in all three phases.Supply should be reliable i.e continuous availability without interruption Modern industrial machinery and commercial computer networks are prone to many different failure modes. When the assembly line stops, or the computer network crashes for no apparent reason, very often the electric power quality is suspected. It is a convenient culprit, as it is invisible and not easy to defend. Power quality problems may be very difficult to troubleshoot, and often the electric power may not have any relation to the actual problem. For example, in an industrial plant the faults of an automated assembly machine may ultimately be traced to fluctuations in the compressed air supply or a faulty hydraulic valve. Or in an office building, the problems on a local area network may be find their root cause with coaxial cable tee locations that are too close together, causing reflections and signal loss. Monitoring after the event has already happened tells us little about the past.
Why power quality is so important?
Power quality is an increasingly important issue for all businesses. Problems with powering and grounding can cause data and processing errors that affect production and service quality.
 Lost production: Each time production is interrupted, your business loses the margin on the product that is not manufactured and sold.
 Damaged product: Interruptions can damage a partially complete product, cause the items to be rerun or scrapped.
 Maintenance: Reacting to a voltage disruption can involve restoring production, diagnosing and correcting the problem, clean up and repair, disposing of damaged products and, in some cases, environment costs.
 Hidden costs: If the impact of voltage sag is a control error, a product defect may be discovered after customer delivery. The costs of losing repeat sales, product recalls and negative public relations can be significant and hard to quantify.
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Power Quality full report


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Overview: In a general sense, power quality is, quality power supply. However, because people look at problems from different perspectives, so far, the technical meaning of power quality, there are still different understanding, it can not give an accurate and uniform definition.
Over the years, the concept of power quality and reliability of electricity supply is almost identical. How to describe the interaction of both supply and power and influence, and gives the definition of appropriate technology is still the people continue to explore the issue. No matter what kind of power quality are given the definition of power quality of the content should include the following aspects of the content, a general consensus has been made to solve power quality test equipment, using power quality analyzer.

Voltage Quality: Given the actual voltage and the deviation between the ideal voltage to reflect the distribution of electricity power sector to the user is qualified. Voltage quality usually includes a voltage bias, voltage and frequency deviation, voltage unbalance, electromagnetic transient phenomena, voltage fluctuation and flicker, short duration voltage variation, voltage harmonics, voltage inter-harmonics, voltage gap, under voltage, over voltage.
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Power Quality full report



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INTRODUCTION
Power quality


Power quality is one of the most important topics that electrical engineers have been noticed in recent years. Electric power quality means different things to different people. To most electric power engineers, the term refers to a certain sufficiently high grade of electric service but beyond that there is no universal agreement. The measure of power quality depends upon the need of the equipment that is being supplied. What is good power quality for an electric motor may not be good enough for a personal computer. Usually the term power quality refers to maintaining a sinusoidal waveform of bus voltages at rated voltage and frequency. In its broadest sense, power quality is a set of boundaries that allows electrical systems to function in their intended manner without significant loss of performance or life.


Cost of poor Power Quality

Poor Power Quality can be described as any event related to the electrical network that ultimately results in a financial loss. Possible consequences of poor Power Quality include
Unexpected power supply failures (breakers tripping, fuses blowing)
Equipment failure or malfunctioning
Equipment overheating (transformers, motors) leading to their lifetime reduction.
Damage to sensitive equipment (PC‟s, production line control systems)
Electronic communication interferences
Increase of system losses
Need to oversize installations to cope with additional electrical stress with consequential increase of installation and running costs and associated higher carbon footprint.


Sag
A "dip" (in British English) or a "sag" (in American English - the two terms are equivalent) is the opposite situation where the RMS voltage is below the nominal voltage by 10 to 90% for 0.5 cycle to 1 minute. The main causes for sag are faults on the transmission and distribution network mostly on parallel feeders, faults in consumer’s installation, connection of heavy loads and startup of motors. This leads to malfunction of microprocessor-based control systems (PCs, PLCs, ASDs, etc.) that may lead to process stoppage, tripping of contactors and electromechanical relays, disconnection and loss of efficiency in electric rotating machines.

Swell
It occurs when the RMS voltage exceeds the nominal voltage by 10 to 80% for 0.5 cycle to 1 minute. This voltage swell may be caused by switching of heavy loads, badly dimensioned power sources, badly regulated transformers mainly during off-peak hours. The various consequences of voltage swell are data loss, flickering of lighting and screens and stoppage or damage of sensitive equipment.

Surge
It is a rapid short-term increase in voltage. Surges often are caused when high power demand devices such as air conditioners turn off and the extra voltage is dissipated trough the power line. Surges are also caused by over-voltages resulting from lightning,switching on the utility power system and other causes without forewarning. Surges normally can be filtered out of the power system at the customer level.


Spike
An extremely high and nearly instantaneous increase in voltage with a very short duration measured in microseconds. Spikes are often caused by lightning or by events such as power coming back on after an outage. A spike can damage or destroy sensitive electronic equipment and of insulating materials, data processing errors or data loss and electromagnetic interference. Turn the equipment off during a power outage. Wait a few minutes after power is restored before turning it on, then turn on one device at a time.

Noise
Noise is a disturbance in the smooth flow of electricity. Often technically referred to as electro-magnetic interference (EMI) or radio frequency interference (RFI). “Harmonics” are a special category of power line noise that causes distortions in electrical voltage. Noise can be caused by motors and electronic devices in the immediate vicinity or far away. Noise can affect performance of some equipment and introduce glitches and errors into software programs and data files.

Outage
Total loss of power for some period of time. Outages are caused by excessive demands on the power system, lightning strikes and accidental damage to power lines. In addition to shutting down all types of electrical equipment, outages cause unexpected data loss.


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seminar flower
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08-08-2012, 04:32 PM

Power Quality


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ABSTRACT:-

”The Energy is neither be created nor be destroyed”. “Energy saved is energy produced”
Power quality is simply the interaction of electrical power with equipment. If electrical equipment operates correctly and reliably without being damaged or stressed ,we would say that the electric power is good quality. On the other hand, if the electrical equipment malfunctions, is unreliable or is damaged during normal usage, we would suspect that the power quality is poor.

INTRODUCTION:-

Our technological world has become deeply dependent upon the continuous availability of electrical power .In most countries, commercial power is made available via nationwide grids, interconnecting numerous generating stations to the loads. The grid must supply basic national needs of residential, lighting, heating, refrigeration, air conditioning, and transportation as well as critical supply to governmental, industrial, financial, commercial, medical and communications communities. Commercial power literally enables today’s modern world to function at its busy pace. Sophisticated technology has reached deeply into our homes and careers, and with the advent of e-commerce is continually changing the way we interact with the
rest of the world.

Oscillatory

An oscillatory transient is a sudden change in the steady-state condition of a signal's voltage, current, or both, at both the positive and negative signal limits, oscillating at the natural system frequency. In simple terms, the transient causes the power signal to alternately swell and then shrink, very rapidly. Oscillatory transients usually decay to zero within a cycle (a decaying oscillation). These transients occur when you turn off an inductive or capacitive load, such as a motor or capacitor bank. An oscillatory transient results because the load resists the change. This is similar to what happens when you suddenly turn off a rapidly flowing faucet and hear a hammering noise in the pipes. The flowing water resists the change, and the fluid equivalent of an oscillatory transient occurs.

Under voltage

Under voltages are the result of long-term problems that create sags. The term “brownout” has
been commonly used to describe this problem, and has been super ceded by the term under voltage. Brownout is ambiguous in that it also refers to commercial power delivery strategy during periods of extended high demand. Under voltages can create overheating in motors, and can lead to the failure of nonlinear loads such as computer power supplies. The solution for sags also applies to under voltages. However, a UPS with the ability to adjust voltage using an inverter first before using battery power will prevent the need to replace UPS batteries as often. More importantly, if an under voltage remains constant, it may be a sign of a serious equipment fault, configuration problem, or that the utility supply needs to be addressed.

Over voltage

Over voltages (can be the result of long-term problems that create swells. An overvoltage can be
thought of as an extended swell. Over voltages are also common in areas where supply transformer tap settings are set incorrectly and loads have been reduced. This is common in seasonal regions where communities reduce in power usage during off-season and the output set for the high usage part of the season is still being supplied even though the power need is much smaller. It’s like putting your thumb over the end of a garden hose. The pressure increases because the hole where the water comes out has been made smaller, even though the amount of water coming out of the hose remains the same. Overvoltage conditions can create high current draw and cause the unnecessary tripping of downstream circuit breakers, as well as overheating and putting stress on equipment.

Frequency Variations:-

Frequency variation is extremely rare in stable utility power systems, especially systems
interconnected via a power grid. Where sites have dedicated standby generators or poor power
infrastructure, frequency variation is more common especially if the generator is heavily loaded. IT equipment is frequency tolerant, and generally not affected by minor shifts in local generator frequency. What would be affected would be any motor device or sensitive device that relies on steady regular cycling of power over time. Frequency variations may cause a motor to run faster or slower to match the frequency of the input power. This would cause the motor to run inefficiently and/or lead to added heat and degradation of the motor through increased motor speed and/or additional current draw.
To correct this problem, all generated power sources and other power sources causing the frequency variation should be assessed, then repaired, corrected, or replaced.

CONCLUSIONS:

The widespread use of electronics has raised the awareness of power quality and its affect on the critical electrical equipment that businesses use. Our world is increasingly run by small microprocessors that are sensitive to even small electrical fluctuations. These microprocessors can control blazingly fast automated robotic assembly and packaging line systems that cannot afford downtime. Economical solutions are available to limit, or eliminate, the affects of power quality disturbances. However, in order for the industry to communicate and understand power disturbances and how to prevent them, common terms and definitions are needed to describe the different phenomena. This paper has attempted to define and illustrate power quality disturbances.
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seminar flower
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06-10-2012, 05:10 PM

Power quality


.doc   Power quality.doc (Size: 24.5 KB / Downloads: 30)

INTRODUCTION

Power quality is a measure of how well electric power service can be utilized by customers.
The power quality is an electrical property that allows electrical systems to function in their intended manner without significant loss of performance.
Complexity of the system enables compromised quality of power.
Supply interruptions and low voltage levels are a constant source of concern for Indian consumers.

Parameters of Power Quality

Continuity of service.
Variation in voltage magnitude.
Transient voltages and over currents.
Harmonic content in the waveforms.

Transient Overvoltage

Transient over voltages are brief, high-frequency increases in voltage on AC mains.
Generally two different types of transient over voltages are observed:
a) Low frequency transients
b) High frequency transients (surges, spikes etc.)
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