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Power Quality 101 Dr. Adly Girgis APPA 2005 Customer Connections Conference October 2005 Introduction ¾ The objective of the electric utility is to deliver sinusoidal voltage at fairly constant magnitude and frequency throughout their system. ¾ If loads are linear, both the voltage and current waveforms will be sinusoidal at a fairly constant magnitude and frequency. ¾ Typical examples of linear loads include motors, heaters and incandescent lamps. Voltage Current Voltage and Current Waveforms for Linear Loads ¾ The presence of non-linear and electronic loads distort this pure sinusoidal waveform. ¾ Typical examples of non-linear loads include rectifiers (power supplies, UPS units, discharge lighting), adjustable speed motor drives, DC motor drives and arcing equipment. Voltage and Current Waveforms for Non-Linear Loads Voltage Non-Linear Load Current ¾ The current drawn by non-linear loads is not sinusoidal but it is periodic, means that the current wave looks the same from cycle to cycle. ¾ Periodic waveforms can be described as a series of sinusoidal wave forms that have been summed together. ¾ The sinusoidal components are integer multiples of the fundamental where the fundamental, in the united states, is 60 Hz. ¾ The only way to measure a voltage or current that contains harmonics is to use a true RMS reading meter. ¾ If an averaging meter is used, which is most common type, the error can be significant. Harmonic Sine Wave 60 Hz Fundamental 180 Hz (3RD Harmonic) Total Seen By Instruments Waveform with Symmetrical Harmonic Component Harmonics distort the sinusoidal waveform and falls under power quality issue. Harmonic Sine Wave 60 Hz Fundamental 300 Hz(5th Harmonic) 180 Hz(3rd Harmonic) Total Seen by Instrument Waveform with 3rd and 5th Harmonic Component Main Sources of Harmonics ¾ Power Electronics, Electric Arc Furnaces, Fluorescent Lamps, Electrical Machines and Transformers. ¾ The increasing use of power electronic devices for the control of power apparatus and systems has been the reason for the greater concern about waveform distortion in recent times. ¾ The most common power electronic load is the single phase rectifier, used to power most modern office and domestic appliances. ¾ The terms rectification and inversion are used for power transfers from AC to DC or DC to AC respectively. Transformer Magnetization Nonlinearities Flux (Φ) Voltage (V) Normal Ideal Excitation Current Transformer Inrush Current Inrush Current Wave & Excitation Saturation Curve Discharge-Type Lighting ¾ Luminous discharge lighting is highly nonlinear and gives rise to considerable odd ordered harmonic currents. This effect is clearly illustrated 0.6 Current (A) ¾ 0.4 0.2 0 -0.2 -0.4 2 4 6 8 10 12 14 16 20 22 Time (ms) Single Phase Rectification ¾ DC Power Supplies z Many commercial and domestic appliances require direct current for their operation. I V C + - TV Load Current ¾ TV Receivers Time Current Waveform generated by a 23 Inch TV Set ¾ Microwave Oven: 6 Current Waveform Because of 900 W Microwave Oven Current (A) 4 2 0 -2 -4 2 4 6 8 10 12 Time (ms) 14 16 20 22 Three Phase Current Source Conversion DC to DC Regulator The Basic One Line Diagram Load A B C Neutral Current Contains No Fundamental, but Third Harmonic is 300% of Phase Current A Balanced Three Phase System ¾ In summary, Harmonics are due to: z z z Ripples in the voltage waveform of rotating machines, due to variations in air gap reluctance over machine pole pitch, flux distortion in synchronous machines, nonlinearity in the operation. Transformer saturation. magnetizing current, core Network nonlinearities from loads such as rectifiers, inverters, arc furnaces, welders, voltage controllers, frequency converters. z z z z Load nonlinearities High voltage dc power conversion, transmission and power exchange. Interconnection of non conventional energy generation sources such as wind, solar, geothermal etc. with distribution systems. Active and Passive VAR compensators. ¾ Harmonic currents can produce a number of problems, namely: z z z z z z z Equipment heating Equipment malfunction Equipment failure Communications interference Fuse and breaker mis operation Process problems Conductor heating Capacitor Switching of Normal Operating Conditions I ¾ Benefits: z z z P.F. Improvement Loss Reduction Voltage Improvement Load Φn Φ0 ILD V V I Ic Φn < Φ 0 PFn > PF0 Improved PF I < ILD I2Rf < I2LDRf Reduced Losses ¾ The process of capacitor switching is done frequently to improve power factor and voltage regulation. z z Time of Day control Voltage Control Capacitors Switching Concerns ¾ Harmonic Resonance ¾ Voltage Rise ¾ Transients A STUDY CASE HARMONIC DISTORTION WITH CAPACITOR CORRECTION Zsj (h) I(h) I Zcj (h) RESULTS Capacitor switching in this case caused z z z z An increase in current RMS value An increase in apparent power Reduction in power factor Increase in total harmonic distortion Solution – Replace capacitor with a filter. Capacitor Switching Transients other line L1 L2 C1 L1 C2 C1 L2 C2 Voltage Flicker Phenomena ¾ ¾ ¾ Voltage flicker refers to a fluctuation in the magnitude of the supply voltage envelope, created by large non-stationary loads. These large industrial loads draw high irregular currents which produce voltage fluctuation problems for power systems. If commercial or residential loads are electrically close to such loads, customers may experience z z z z Uncomfortable light flickering Television picture distortion Computer error and memory loss Misoperation of industrial devices. Typical Voltage Flicker Disturbance Arc Furnace Operations ¾ Arc furnace often represent the single largest customer on an electric utility supply system. ¾ From the power quality point of view, electric arc furnace loads can result in serious electrical disturbances on a power system. ¾ This is due to the characteristics of the electric arc phenomena. ¾ Arc furnaces represent non-linear, asymmetric loads with a rapidly varying demand for reactive power. ¾ In the power supply, there are generally strong power quality impacts appearing as fluctuations, harmonics and unbalances of the voltage. ¾ An arc furnace installation consists of a refractory lined shell which holds the scrap metal charge. Movable Arms Electrodes Water Cooled Leads Scrap Charge Furnace Transformer ¾ Due to the random motion of the arc and the resulting change in the arc length, the random demand in power demand produces irregular fluctuations in current. ¾ These current fluctuations produce the voltage drop across the furnace transformer leads to a voltage flicker. ¾ The arc furnace load will vary from a complete open-circuit to a full three phase short-circuit several times during the melting process. Voltage Flicker Limitation ¾ At higher levels of flicker magnitude variation for a given frequency, the lamp flicker became annoying and objectionable. ¾ This led to the establishment of a tolerance threshold or borderline of objection. ¾ From the electric utility’s point of view, the tolerance threshold may be used to aid in the design and operation of a power system while minimizing the possibility of flicker complaints from its customers. At higher frequencies of voltage fluctuation above 1 hertz, there is little difference between a perceptible flicker and an objectionable flicker. 8 7 6 5 4 3 2 1 0 10 0 10 1 0. 1 Objectionable Visible 0. 00 01 0. 00 1 0. 01 Percent Voltage Change ¾ Frequency of Voltage Fluctuation (Hz) Faults in Power Systems Looks Like a Snake !! Time for a nap? Example: Fault Condition (A-G) F Va Area of voltage variation during fault “A-G Fault Vc Vb Industrial Park F I1 Feeder 1 S Feeder 2 P Recloser I1 S Distribution Substation P Sources of Continuing Education and Professional Development ¾ IEEE Tutorials Conferences. in ¾ Coming Conferences: General and Regional Power Systems Conference 2006 Advanced Metering, Protection, Control, Communication and Distributed Resources March 14-17, 2006 Clemson, SC, USA http://www.ces.clemson.edu/powsys2006 Preliminary Technical Program ¾ Panel Discussions: z z z z z Distribution automation advancements to improve system reliability and power quality. BPL past, present and future technology and applications. Advanced Metering Technology. Power Quality Issues in Metering and Relays. Cyber Security for SCADA and Protection Systems. ¾ Technical Paper Session: z z z z z ¾ Innovation in Distribution System Protection. State Estimation, Load Shedding and Restoration. Substation and Line Protection. Innovation in SCADA and Communication Systems I & II. Distribution System Operation, Automation and Reliability. Tutorials: z z All Tutorials are offered at no additional cost, but advanced registration is required. A – Power System Protection and Automation Innovation – Ed Schweitzer, Schweitzer Engineering Laboratories (Full Day) z z z ¾ B – State of the art in Power Systems Communications, Control and Protection – Mark Adamiak, GE (Full Day) C – Cyber Security best practices in the context of NERC – CIP Regulations – Jason Stamp, Sandia National Laboratories (Full Day) D – Distribution Automation – John McDonald, President of PES (Half Day) Important Dates: z z January 15, 2006 ÆPP Presentation and Advanced Registration March 14-17, 2006 Æ Pre-Conference Tutorials and Conference More Information ¾ For updated information, hotel reservation and registration visit the conference website http://www.ces.clemson.edu/powsys2006 or Contact the Conference Chair Dr. Adly Girgis [email protected] 864-656-1053 864-656-5936 ONE DAY TUTORIAL March 14, 2006 Clemson, SC IEEE Power Engineering Society Power System Basics for Non-Engineering Professionals Course Description This one-day course is intended to give non-engineering professionals a better understanding of electric power systems planning, operations and regulatory frameworks. Basic electrical terminology and concepts are explained in simple to understand terms with regard to design, construction, operations and maintenance of power plants substations and transmission and distribution lines. Basic electrical safety concepts are included. ¾ Who Should Attend? z Regulatory Affairs, Legislators, Commission Staff Professionals, z Power Brokers, Power Marketers, Consumer Groups and related organizations, z Policy Makers, Public Affairs Administrators, Legal Councils, Media Communications Staff Experts, z Energy Agency Leaders, Business Executives, Education Institution Board Members, z Utility Management, or anyone interested in learning about electric power systems. ¾ Benefits of Attending ¾ Participants gain more insight into the concerns of engineers, the demands of regulators and consumer groups and a perspective of how these factors play a major role in the operation of today’s electric power systems. This course will help participants become more productive and proactive in professional situations. ¾ ¾ ¾ Course Outline ; ; ¾ Introduction and Brief History Fundamentals of Electric Power Discussion of how natural recourses such as coal, gas, water, solar, wind, etc. are converted into useable electrical energy. Generation and Transmission The operation of generation plants, substations and transmission lines are explained plus how these systems work together to efficiently transport electrical power long distances. Distribution and Utilization Power delivery to residential, commercial and industrial customers is explained including emergency backup generators. Power System Protection Design concepts of power system protective relaying and coordination are explained for local and interconnected systems. Power System Operation How electric power systems are monitored, controlled and operated under normal and abnormal conditions, including the use of telecommunications channels are included in this course. Interconnection and Regulation The benefits of interconnected power systems and regulatory requirements of electric power systems are discussed. ; ¾ ; ¾ ; ¾ ; ¾ ; ¾