power qualily....................................

power qualily

1. Introduction to Power Quality

2. There are four major reasons for the increased concern of power quality: 1. A newer-generation of load equipment, with microprocessor-based controls which are increasingly sensitive to power quality variations than in the past. 2. The increasing emphasis on overall power system efficiency to reduce costs which has resulted in continued growth in the application of devices such as variable speed drives (VFD ), programmable logic controls (PLC) and power factor correction to reduce losses and improve production. 3. End users have an increased awareness of power quality issues . Utility customers are becoming better informed about such issues such as interruptions, sags, and switching transients . 4. Many things are now interconnected in a network. Integrated processes mean that the failure of any component has much more important consequences .

3.   There are many misunderstandings regarding the causes of power quality problems . The charts below show the results of one survey conducted by the Georgia Power in which both utility personnel and customers were polled about what causes power quality problems . While surveys of other market sectors might indicate different splits between the categories, these charts clearly illustrate one common theme that arises repeatedly in such surveys: The utility’s and customers perspectives are often much different. While both tend to blame about two-thirds of the events on natural phenomena (e.g., lightning), customers, much more frequently than utility personnel, think that the utility is at fault. What Causes Power Quality issues?  

4. What is Power Quality? There can be completely different definitions for power quality, depending on your frame of reference. For example : A utility may define power quality as reliability and show statistics demonstrating that there system is 99.98 % reliable. A criteria established by regulatory agencies. “An assumption”. An equipment manufacturer may define power quality as those characteristics of the power supply that enable their equipment to work properly and/or within their performance specifications. Power quality is ultimately a consumer-driven issue, and the end user’s point of reference takes precedence .

5. What is a power quality problem? Any power problem manifested in voltage, current, or frequency deviations that result in failure or misoperation of customer equipment. Some common symptoms are: Unexplained equipment trips or shutdowns. Occasional equipment damage or component failures. Erratic control of process performance. System crashes and equipment failures Random lockups and data errors. Power system component overheating These problems can be complicated

6. Power Quality Power Quality issues cause businesses problems. Equipment downtime resulting in loss of productivity Material waste, idle people & equipment. System crashes and equipment failures Lost orders and good will, Lost customers and profits Lost transactions and orders not being processed Revenue and accounting problems Overtime required to make up for lost work time Customer and/or management dissatisfaction.

7. Ideal Voltage Waveforms Single Phase Ideal power quality for the source of energy to an electrical load.

8. Ideal Waveforms Three (3) Phase

9. Ideal & Non-ideal Waveforms

10. Linear & Nonlinear Loads When voltages are applied to electrical loads, the load currents will have frequency and amplitudes dependent on the impedance or other characteristics of the load. A linear load is one where voltage (a sine wave) is applied across a constant resistance resulting in sinusoidal load current (another sine wave). A nonlinear load is one where voltage (a sine wave) is applied across a changing impedance resulting in distorted load current (distorted waveform). The load current with distorted waveforms can produce distortion of the voltage in the supply system , which is an indication of poor power quality. Devices that are converting alternating current (AC) to direct current (DC), is the most common nonlinear load found in electrical systems. It is used in equipment that ranges from 100-W personal computers to 10,000-kW adjustable speed drives.

11. Sources of Power Quality Problems Utility Sources Lightning Power Factor Correction Equipment Faults Switching Internal Sources Individual Loads – Lighting, Elevators, Coolers, HVAC Uninterruptable Power Supplies (UPS) Variable Frequency Drives (VFD) Battery Chargers Large Motors During Start up Electronic Dimming Systems Electronic Ballasts/Drivers Arc Welders, other Arc Devices Medial Equipment, e.g. MRI’s and X-Ray Equipment Office Equipment and Computers Wiring

12. The Definition of Power Quality General: “ Any power problem manifested in voltage, current, or frequency deviations that result in failure or mis operation of customer equipment” IEEE: “ P ower quality is the concept of powering and grounding sensitive electronic equipment in a manner that is suitable for the equipment's operation ” IEC : Power Quality or Electromagnetic compatibility (EMC) is defined as: "the ability of an equipment or system to function satisfactorily in its electromagnetic (EM) environment (immunity) without introducing intolerable electromagnetic disturbances to anything in that environment (emission)“. Standard Handbook of Electrical Engineers: Good power quality, however, is not easy to define because what is good power to a refrigerator may not be good enough for today’s personal computers and other sensitive loads. For example, a short outage would not noticeably affect motors, lights, etc. but could cause a major nuisance to digital clocks, computers, etc.

13. Power Quality Terms Some ambiguous terms: Blackout/Brownout Bump Power Surge Clean Power Surge Outage Blink Dirty Power Spike/Wink Raw Power Glitch IEEE Defined power quality disturbances : Transients Interruptions Sag/Undervoltage Swell/Overvoltage Waveform distortion Voltage Fluctuations Frequency Variations

14. Examples of Poor Power Quality Impulse & Oscillatory Transients: are a brief, unidirectional (impulse) and bidirectional (Oscillatory) variation in voltage, current or both on a power line. The most common causes: I mpulsive transients is lightning strikes, poor grounding, electrostatic discharge (ESD), switching inductive loads, or switching in power distribution system. Oscillatory transients can occur due to the switching of power factor correction capacitors, or etc. These occur when you turn off an inductive or capacitive load, such as a motor or capacitor bank. The #1 reason out of 13 for motor failures. Potential effects: Loss or corruption of data, possible damage, system halts.

15. Examples of Poor Power Quality Interruption: is defined as a reduction in line-voltage or current to less than 10% of the nominal, not exceeding 60 seconds in length. The most common causes: power grid damage, lightning strikes, animals, trees, vehicle accidents, destructive weather, equipment failure, or circuit breaker tripping. Momentary 30 cycles – 3 seconds Temporary 3 seconds – 1 minute Sustained > 1 minute Potential effects : loss of data, system damage and /or shutdown

16. Examples of Poor Power Quality Voltage Sag/Undervoltage: a brief decrease in the rms line voltage of 10 to 90% of nominal line voltage. The most Common causes: The starting of large induction motors and/or the -initial starting of large air conditioning systems. Instantaneous 0.5 – 30 cycles Momentary 30 cycles – 3 seconds Temporary 3 seconds – 1 minute Potential effects: System halts, loss of data, system damage and /or shutdown

17. Examples of Poor Power Quality Voltage Swell/Overvoltage: is the converse to the swag. A swell is a brief increase in rms line-voltage of 110 to 180% of nominal line voltage. The common causes: are line faults and incorrect tap settings in tap changers in substations due to reduction of loads. Instantaneous 0.5 – 30 cycles Momentary 30 cycles – 3 seconds Temporary 3 seconds – 1 minute Potential effects: Nuisance tripping, equipment damage/reduced life

18. Examples of Poor Power Quality Voltage distortion – defined as a steady-state deviation from an ideal sine wave of power frequency principally characterized by the spectral content of the deviation. There are five (5) primary waveform distortions: DC offset, Notching, Harmonics, Inter-harmonics, and Noise The #3 reason out of 13 for motor failures. DC Offset Notching

19. Examples of Poor Power Quality Voltage Distortion (Cont.) Harmonics: the corruption of the fundamental sine wave at frequencies that are multiples of the fundamental frequency (50 Hz.). This is due to nonlinear characteristics of devices and loads on the power system. Symptoms include: overheated transformers, neutrals conductors, and other electrical equipment as well as circuit breaker & nuisance tripping

20. Examples of Poor Power Quality Voltage Distortions (Cont.) Total Harmonic Distortion (THD) is the sum of the contributing harmonics . Harmonic distortion is a normal consequence of a power system supplying electronic loads such as computers, electronic ballast/drivers, adjustable speed drives, and other control systems. Symptoms include: High current to flow in neutral conductors Motors and transformers to run hot, shortening their lives Increased susceptibility to voltage sags/undervoltage Reduced efficiency of transformers Audible noise Harmonics are a mathematical way of describing distortion to a voltage or current waveform.

21. Examples of Poor Power Quality Voltage imbalance: is a variation in the amplitudes of three-phase voltages, relative to one another. This can be caused by different loads on the phases, resulting in different voltage drops through the phase-line impedances. The #2 reason out of 13 for motor failures.

22. Examples of Poor Power Quality Voltage Imbalance (Cont.) In a balanced three (3) phase system, the phase voltages should be equal or very close to equal . Imbalance is the measurement of the inequality of the phase voltages. Voltage imbalance can cause three (3) phase motors and other 3 phase loads to experience poor performance or premature failure because of the following: Mechanical stresses in motors due to lower than normal torque output. Higher than normal current in motors and 3 phase rectifiers. Imbalance current will flow in neutral conductors in 3 phase wye systems.

23. Power Quality standards International Electrotechnical Commission ------ IEC European Committee for Electrotechnical Standardization (CENELEC) --- EN

24. Power Quality Standards IEEE Standards 519 and 1159 Standards are needed so all end users (industrial, commercial, and residential) and transmission and distribution suppliers (the utilities) speak the same language when discussing power-quality issues. Standards also define recommended limits for events that degrade power quality. IEEE Standards are publications that provide acceptable design practices as well as a common language. IEEE Standard 519: Recommended Practice and Requirements for Harmonic Control in Electrical Power Systems . Establishes goals for the design of electrical systems that include both linear and nonlinear loads. IEEE Standard 519 is twofold. The utility has the responsibility to produce good quality voltage sine waves. The end user customers have the responsibility to limit the harmonic currents their circuits draw from the line. IEEE Standard 1159 : Recommended Practice for Monitoring Electric Power Quality . Covers the monitoring of electrical characteristics of single-phase and polyphase (three-phase) AC power systems.

25. Computer Business Equipment Manufacturers Association

26. Information Technology Industry Council

27. IEEE 519 -2022

28. EN50160

29. EN50160

30. EN50160

31. Medium Voltage levels

32. High Voltage levels

33. Constant power supply Filters Static var compensators Thyristor based static switch Energy storage system Flexible ac transmission system Transformers Connection PQ problem mitigation Techniques

34. EMC (Electro Magnetic Compatibility) “The ability of equipment or a system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in that environment”

35. IEC EMC Standards Immunity Requirements IEC-61000-4-1 Normal performance within the specification limits. Temporary degradation or loss of function which is self-recoverable. Temporary degradation or loss of function which requires operator intervention or system reset. Degradation or loss of function which is not recoverable due to damage of equipment, components or software, or loss of data

36. Emission Standards Harmonic currents - IEC 61000-3-2, IEC 61000-3-6 Voltage fluctuations - IEC 61000-3-3, IEC 61000-3-5, IEC 61000-3-7

37. Electromagnetic Environment Compatibility levels Voltage characteristics Planning levels

38. Assignment -1 Explain the classification of power quality issues Explain the various terms that are used in power quality Define power quality. Explain the reasons for increased concerned in power quality Explain briefly about international standards for power quality Explain the CBEMA curve