A Technical Seminar Report OnELECTRIC POWER QUALITYSubmitted in partial fulfillment of the requirementsFor the award of the degreeBACHELOR OF TECHNOLOGYINELECTRICALS AND ELECTRONICS ENGINEERING BY G.MOUNIKA REDDY (08PR1A0221) Under guidance of Mr.UPENDAER RAO Associate.Professor

Department of Electrical and Electronics Engineering

(Affiliated to JNTU University, Hyderabad)-2012

ELECTRICAL POWER QUALITYA SEMINOR REPORT

Mohabath Nagar, Near Maheshwaram X Road, On Srisailam Highway, R.R.Dist-501359. A.P. INDIAPhone: +918414 200111 Email: aryabhata.its@gmail.com www.aryabhata.its.ac.in(June-2012)

CERTIFICATE

This is to certify that the technical seminar report entitled... that is being submitted by Mr./Ms..in partial fulfillment for the award of the Degree of Bachelor of Technology in to the Jawaharlal Nehru Technological University is a record of bonafide work carried out by him/her under my guidance and supervision. The results embodied in this technical seminar report have not been submitted to any other University or Institute for the award of any degree or diploma.

Date:

Seminar Incharge Internal Guide

Head of Department Project Coordinator

ACKNOWLEDGEMENT

The satisfaction and euphoria that accompany the successful completion of any task would be incomplete without the mentioning of the people whose constant guidance and encouragement made it possible. I take pleasure in presenting before you, my seminar report, which is result of studied blend of both research and knowledge.I express our earnest gratitude to my internal guide, Associate Professor Mr. UPENDAR RAO Department of EEE, for his constant support, encouragement and guidance. I am grateful for her cooperation and her valuable suggestions. Also I sincerely thank to our project coordinator and HOD Mr. A. Nagaraju M.Tech for their encouragement for through out this work.

G.MOUNIKA (08PR1A0221)

INDEX CONTENTS PAGE NO.1. ABSTRACT 12. POWER QUALITY DEFECTS 23. POWER CONDTIONING 3 4. POWER QUALITY DEFECTS4 5. VOLTAGE DISTURBANCES 5 6. CAPACITORS SWITCHING 6 7. SYSTEM FAULTS 7 8. TRANSIENTS 8 9. SURGES 9 10. POWER QUALITY EVENTS 10 11.POWER QUALITY PROBLEMS 1112.IMPROVEMENT OF POWER QUALITY 12

13.CONCLUSION 13

ABSTRACT

Power quality is simply the interaction of electrical power with electrical equipment. Power qualityis the set of limits of electrical properties that allowselectrical systemsto function in their intended manner without significant loss of performance or life. The term is used to describeelectric powerthat drives anelectrical loadand the load's ability to function properly with that electric power. Without the proper power, an electrical device (or load) may malfunction, fail prematurely or not operate at all. There are many ways in which electric power can be of poor quality and many more causes of such poor quality power.Theelectric power industrycompriseselectricity generation(AC power),electric power transmissionand ultimatelyelectricity distributionto anelectricity meterlocated at the premises of the end user of the electric power. Theelectricitythen moves through the wiring system of the end user until it reaches the load. The complexity of the system to move electric energy from the point of production to the point of consumption combined with variations in weather, generation, demand and other factors provide many opportunities for the quality of supply to be compromised.While "power quality" is a convenient term for many, it is the quality of thevoltagerather than power orelectric currentthat is actually described by the term. Power is simply the flow of energy and the current demanded by a load is largely uncontrollable.

IntroductionThe quality of electrical power may be described as a set of values of parameters, such as: Continuity of service Variation in voltage magnitude (see below) Transient voltages and currents Harmonic content in the waveforms for AC powerIt is often useful to think of power quality as a compatibility problem: is the equipment connected to the grid compatible with the events on the grid, and is the power delivered by the grid, including the events, compatible with the equipment that is connected? Compatibility problems always have at least two solutions: in this case, either clean up the power, or make the equipment tougher.The tolerance of data-processing equipment to voltage variations is often characterized by the CBEMA curve, which give the duration and magnitude of voltage variations that can be tolerated.[1]Ideally, AC voltage is supplied by a utility as sinusoidal having an amplitude and frequency given by national standards (in the case of mains) or system specifications (in the case of a power feed not directly attached to the mains) with an impedance of zero ohms at all frequencies

Power conditioningPower conditioning is modifying the power to improve its quality.An uninterruptible power supply can be used to switch off of mains power if there is a transient (temporary) condition on the line. However, cheaper UPS units create poor-quality power themselves, akin to imposing a higher-frequency and lower-amplitude square wave atop the sine wave. High-quality UPS units utilize a double conversion topology which breaks down incoming AC power into DC, charges the batteries, then remanufactures an AC sine wave. This remanufactured sine wave is of higher quality than the original AC power feed.[2]A surge protector or simple capacitor or varistor can protect against most overvoltage conditions, while a lightning arrestor protects against severe spikes.Electronic filters can remove harmonics

Power Quality Defects:Power quality problems have many names and descriptions. They are Harmonics Voltage Disturbances Transients Blackouts SurgesHarmonics:Harmonicsare electric voltages and currents that appear on theelectric powersystem as a result of certain kinds of electric loads. Harmonicfrequencies in the power grid are a frequent cause ofpower qualityproblems.In a normalalternating currentpower system, thevoltagevariessinusoidalat a specific frequency, usually 50 or 60hertz. When alinear electrical load is connected to the system, it draws a sinusoidal current at the same frequency as the voltage (though usually not inphase with the voltage).When a non-linear load, such as arectifier, is connected to the system, it draws a current that is not necessarily sinusoidal. The current waveform can become quite complex, depending on the type of load and its interaction with other components of the system. Regardless of how complex the current waveform becomes, as described throughFourier seriesanalysis, it is possible to decompose it into a series of simple sinusoids, which start at the power systemfundamental frequencyand occur at integer multiples of the fundamental frequency.One of the major effects ofpower system harmonicsis to increase the current in the system. This is particularly the case for the third harmonic, which causes a sharp increase in thezero sequencecurrent, and therefore increases the current in theneutralconductor. This effect can require special consideration in the design of an electric system to serve non-linear loads.[1]In addition to the increased line current, different pieces of electrical equipment can suffer effects from harmonics on the power system.

Voltage Disturbances:Voltage disturbances are the most common PQ problem causing effect ranging from minor annoyance through equipment failure to the shutdown of complete production processes. The economic impact can be very large and can threaten the economic viability of a business. The frequency of occurrence and the magnitude of a voltage disturbance are dependent on the cause of the disturbance. Some events are fairly predictable, such as capacitor bank or line switching. Other events, such as line faults, are more probable during certain adverse weather conditions. In the following sections, we will discuss the expected frequency of various types of disturbances, their characteristics, and a few sample voltage waveforms.

Capacitor Switching

Capacitors are installed on the utilitys electrical system to provide reactive power for the customers motor loads, and to provide voltage support on the system. Because the need for vars (volt-amperes reactive) varies over time, some of the capacitors must be switched in and out to follow the reactive load requirements. Some capacitors are switched multiple times a day, some are switched daily, some are switched seasonally, and some are always kept closed. The switching is required to maintain system voltage within reasonable limits, and also minimize the electrical system losses. Any needed vars, which are not produced by capacitors, must be produced by generation, which is usually very distant from the load.Typically, the disturbance created by the switching of capacitors is a ringing of the voltage waveform lasting one cycle or less. The ringing often creates multiple zero crossings during one cycle.

Power factor correction capacitors. Switching these can create high-voltage transients, steady-state voltage shifts, and multiple zero crossings of the voltage waveform. These can also cause high voltage under light load conditions by driving the facility into a leading power factor condition. In addition, capacitors can resonate with other equipment such as ASDs. This can usually be avoided by using low-distortion (12 pulse) drives or through careful sizing of capacitors prior to installation.

Computer equipment. These have solid-state switching power supplies, which can cause a significant amount of current distortion. A large office setting can have very high levels of third harmonic current distortion. The third harmonic and all other tripled harmonics are additive in their distortion. These can also cause very high neutral currents to flow, even if the load is balanced between all three phases. It is possible for the neutral current to be much larger than the phase current in office buildings.

. Laser printers Their interference is similar to that which is created by copy machines. When operating they have a high current draw, with a high current distortion.

X-ray machines. These have a very high and distorted current draw when operating. These should be served from their own dedicated circuit.

System FaultsElectrical system faults are the most troublesome to the majority of customers. They occur whenever lightning hits the line, power lines slap together from excessive wind, or whenever a power line falls to the ground, such as when a power pole is hit by a vehicle. They occur whenever tree branches fall into the power lines, such as during a wind storm; and they occur during a rain storm when a substantial amount of dust is stirred up, thus compromising the effectiveness of the line insulators. The clearing of these faults is necessary to prevent catastrophic damage to the electrical system, and to ensure public safety. The word fault indicates either a short circuit condition, or an abnormal open wire condition. The magnitude and duration of a fault inspired disturbance are determined by the customers electrical distance to the fault, the amount of electrical support available between the customer and the fault, the nature of the fault, and what corrective action was required to clear the fault. Typical Voltage and Current Waveforms during a FaultTransients:A temporary component of current and voltage in an electric circuit which has been disturbed. Atransientevent is a short-lived burst of energy in a system caused by a sudden change of state. The source of the transient energy may be an internal event or a nearby event. The energy then couples to other parts of the system, typically appearing as a short burst of oscillation.

Surges:Electrical surges are sudden, brief rises in voltage and/or current to a connected load. They may originate inside or outside any home or business. Standard household equipment operating at 120 volts can be damaged by surges of 500 volts or greater.Indoors, they're generally caused by major equipment, such as your air conditioner or refrigerator, switching on or off. Outdoors, they can be caused by incidents involving electric lines, neighbors using heavy power equipment or power equipment failures. Lightning most often causes them during seasonal electrical storms.

Without some type of surge protection, excess voltage goes into your appliances or anything plugged in and can cause damage. You may not notice damage at the time a surge occurred, however, over time it will shorten the life of your appliances.

Power Quality EventsPower quality problems have many names and descriptions. Surges, spikes, transients, blackouts, noise, are some common descriptions given, but what do they mean? This section delves into defining power quality issues and terminology.Power quality issues can be divided into short duration, long duration, and continuous categories. The computer industry has developed a qualification standard to categorize power quality events. The most common standard is the CBEMA curve (Computer Business Equipment Manufacturing Association). Other standards include ANSI and ITIC. Figure 1 is an example of the CBEMA curve for site. The various power quality events are plotted on the curve based on time and magnitude. Any event outside the curve would be a suspect power problem.

What can cause power quality problems?We have found that the majority of power quality problems are related to issues within a facility as opposed to the utility. Based on over 20 years of field experience, we have found that 90% of power quality problems are caused within the site. Typical problems include grounding and bonding problems, code violations and internally generated power disturbances. Other internal issues include powering different equipment from the same power source. Lets take an example of a laser printer and a personal computer. Most of us would not think twice about plugging the laser printer into the same power strip that runs the PC. We are more concerned about the software and communication compatibility than the power capability; however, some laser printers can generate neutral-ground voltage swells and line-neutral voltage sags every minute or so. The long term effect to the PC may be power supply failure. We have to be careful in how technology is installed and wired

IMPROVEMENT OF POWER QUALITY: Improvement of the power quality in the utility grid can be obtained by connecting damping power-electronic devices. Regarding the increased presence of converter-based distributed generation units in the power system, an active front end for distributed generation units is extended with a mitigating function. However, in order to encourage the connection of mitigating devices to the power system, damping behaviour should be financially rewarded. In this paper, the financial benefits of connecting a damping distributed generation unit to the present power system are verified

CONCLUSION:This centers objective must be towards work with industry to improve the quality and reliability of the electricity supply to industrial, commercial and domestic users. Power supply should be quality so that the customers dont face any problems. Power supplied should be free of harmonics, surges, voltage disturbances and transients. The power supplied reduces the cost of generation and supply if it is quality.