Construction Electrician Apprenticeship Program E-4. Learning guide E-4

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1 Construction Electrician Apprenticeship Program Level 3 Line E: Use Test Equipment E-4 Learning guide E-4 DESCRIBE POWER QUALITY ANALYSIS

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3 Foreword The Industry Training Authority (ITA) is pleased to release this major update of learning resources to support the delivery of the BC Electrician Apprenticeship Program. It was made possible by the dedicated efforts of the Electrical Articulation Committee of BC (EAC). The EAC is a working group of electrical instructors from institutions across the province and is one of the key stakeholder groups that supports and strengthens industry training in BC. It was the driving force behind the update of the Electrician Apprenticeship Program Learning Guides, supplying the specialized expertise required to incorporate technological, procedural and industry-driven changes. The EAC plays an important role in the province s post-secondary public institutions. As discipline specialists the committee s members share information and engage in discussions of curriculum matters, particularly those affecting student mobility. ITA would also like to acknowledge the Construction Industry Training Organization (CITO), which provides direction for improving industry training in the construction sector. CITO is responsible for organizing industry and instructor representatives within BC to consult and provide changes related to the BC Construction Electrician Training Program. We are grateful to EAC for their contributions to the ongoing development of BC Construction Electrician Training Program Learning Guides (materials whose ownership and copyright are maintained by the Province of British Columbia through ITA). Industry Training Authority January 2011 Disclaimer The materials in these Learning Guides are for use by students and instructional staff and have been compiled from sources believed to be reliable and to represent best current opinions on these subjects. These manuals are intended to serve as a starting point for good practices and may not specify all minimum legal standards. No warranty, guarantee or representation is made by the British Columbia Electrical Articulation Committee, the British Columbia Industry Training Authority or the Queen s Printer of British Columbia as to the accuracy or sufficiency of the information contained in these publications. These manuals are intended to provide basic guidelines for electrical trade practices. Do not assume, therefore, that all necessary warnings and safety precautionary measures are contained in this module and that other or additional measures may not be required.

4 Acknowledgements and Copyright Copyright 2014 Industry Training Authority All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or digital, without written permission from Industry Training Authority (ITA). Reproducing passages from this publication by photographic, electrostatic, mechanical, or digital means without permission is an infringement of copyright law. The issuing/publishing body is: Crown Publications, Queen s Printer, Ministry of Citizens Services The Industry Training Authority of British Columbia would like to acknowledge the Electrical Articulation Committee and Open School BC, the Ministry of Education, as well as the following individuals and organizations for their contributions in updating the Electrician Apprenticeship Program Learning Guides: Electrical Articulation Committee (EAC) Curriculum Subcommittee Peter Poeschek (Thompson Rivers University) Ken Holland (Camosun College) Alain Lavoie (College of New Caledonia) Don Gillingham (North Island University) Jim Gamble (Okanagan College) John Todrick (University of the Fraser Valley) Ted Simmons (British Columbia Institute of Technology) Members of the Curriculum Subcommittee have assumed roles as writers, reviewers, and subject matter experts throughout the development and revision of materials for the Electrician Apprenticeship Program. Open School BC Open School BC provided project management and design expertise in updating the Electrician Apprenticeship Program print materials: Adrian Hill, Project Manager Eleanor Liddy, Director/Supervisor Beverly Carstensen, Production Technician (print layout, graphics) Christine Ramkeesoon, Graphics Media Coordinator Keith Learmonth, Editor Margaret Kernaghan, Graphic Artist Publishing Services, Queen s Printer Sherry Brown, Director of QP Publishing Services Intellectual Property Program Ilona Ugro, Copyright Officer, Ministry of Citizens Services, Province of British Columbia Copyright Permission Infrared temperature meter photograph by Hedwig Storch. Retrieved from Wikimedia Commons. Creative Commons Attribution Share Alike 3.0 Unported license. Power quality clamp-on and three-phase graphic display meter images used by permission of Fluke Corporation. To order copies of any of the Electrician Apprenticeship Program Learning Guides, please contact us: Crown Publications, Queen s Printer PO Box 9452 Stn Prov Govt 563 Superior Street 2nd Flr Victoria, BC V8W 9V7 Phone: Toll Free: Fax: crownpub@gov.bc.ca Website: Version 1 New, April Construction Electrician Apprenticeship Program: Level 3

5 LEvel 3, Learning guide E-4: DESCRIBE POWER QUALITY ANALYSIS Learning Objectives Learning Task 1: Describe power quality issues Self-Test Learning Task 2: Describe causes of power quality issues Self-Test Learning Task 3: Perform troubleshooting techniques Self-Test Learning Task 4: Use power quality analyzers Self-Test Learning Task 5: Describe corrective action to improve power quality Self-Test Answer Key Construction Electrician Apprenticeship Program: LEvel 3 5

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7 E-4 Learning Objectives Power quality refers to the electric power being delivered to an electrical load and the load s ability to function properly. Poor quality power affects different loads in different ways. Industrial and commercial electrical power systems can be dramatically and expensively affected, whereas in residential systems the effects are much less significant. There are many different types of power quality problems that can occur, and there are specific tests that electricians perform for each type. On completion of this unit, the learner will be able to: Describe various power quality issues Describe causes of these issues Describe consequences of these issues Perform troubleshooting techniques Use power quality analyzers Activities Read and study the topics of Learning Guide E-4: Describe Power Quality Analysis. Complete Self-Tests 1 through 5. Check your answers with the Answer Key provided at the end of this Learning Guide. Resources You are encouraged to obtain the following texts to provide supplemental learning information: Power Quality Measurement and Troubleshooting, Glen A. Mazur. Delmar s Standard Textbook of Electricity, Fifth Edition, Stephen L. Herman. IPT s Electrical Training Manual, Herb Putz. Power Quality, BC Hydro PowerSmart. Construction Electrician Apprenticeship Program: Level 3 7

8 BC Trades Modules We want your feedback! Please go the BC Trades Modules website to enter comments about specific section(s) that require correction or modification. All submissions will be reviewed and considered for inclusion in the next revision. SAFETY ADVISORY Be advised that references to the Workers Compensation Board of British Columbia safety regulations contained within these materials do not/may not reflect the most recent Occupational Health and Safety Regulation. The current Standards and Regulation in BC can be obtained at the following website: Please note that it is always the responsibility of any person using these materials to inform him/herself about the Occupational Health and Safety Regulation pertaining to his/her area of work. Industry Training Authority January Construction Electrician Apprenticeship Program: Level 3

9 Learning Task 1: Describe power quality issues Historically, power quality has often been referred to in terms of the effects on system reliability caused by factors such as interruptions or outages, voltage unbalance in three-phase systems, and surges and sags on the supply service side. With the operating characteristics of modern electrical loads, surveys have concluded that the great majority of PQ problems today originate from within the consumer s facility. Voltage sags or swells due to motors starting or cycling, harmonic disturbances caused by the effects of non-linear type loads or poor electrical installation practices are often the causes. Power quality In discussing power quality analysis it is important to realize there are many definitions for power quality; the IEEE Standards defines it as, The concept of powering and grounding electronic equipment in a manner that is suitable to the operation of that equipment and compatible with the premise wiring system and other connected equipment. In British Columbia the definition used by the supply authority BC Hydro is, Any deviation of electricity applied to the equipment that results in damage or malfunction of electronic equipment or other electrical devices. Ideally, the best electrical source supply would be a sinusoidal voltage waveform with a constant amplitude and a constant frequency. The electrical characteristics of the system, such as the impedance of the supply system, phenomena such as transients and outages, as well the electrical operating characteristics of certain types of loads, mean the reality is often quite different. Electrical equipment connected to a power system is designed and manufactured to operate at the nominal voltages and currents specified in the manufacturer s nameplate data. Most equipment has a built-in tolerance of from 10% to +5% of its nominal voltage. Generally, the effects of overvoltage are more damaging than those of undervoltage, because of the stress on the insulation and the heating effect caused by the increased current. In order to provide standardization, recommended voltage variation limits at service entrance points are specified by the electrical distributor or local utility. For voltages between 1000 V and 50,000 V, the maximum variation permitted is typically ±6% at the service entrance. These voltage ranges exclude fault and temporary heavy load conditions. PCC (Point Common Coupling/Connection) Power quality is often found to be best at the service entrance or PCC (connection to utility) and deteriorates as you move downstream through the distribution system. That s because more than 50% of the time, the facility s own loads are causing the problems. Another fact is that the vast majority of power quality problems are actually related to installation techniques causing wiring and grounding problems! Construction Electrician Apprenticeship Program: LEvel 3 9

10 Learning Task 1 E-4 The PCC is a point in the electrical system where multiple customers or multiple electrical loads may be connected. According to IEEE-519, this should be a point that is accessible to both the utility and the customer for direct measurement. Although in many cases the PCC is considered at the metering point, service entrance or facility transformer, IEEE-519 states that within an industrial point, the PCC is the point which is accessible to both the utility and the customer for direction measurement and is also the point between the non-linear load and other loads. Symptoms Listed below are a few of the symptoms of poor power quality that are early indicators of power quality issues. 1. Overheated service and feeder conductors Harmonic frequencies that are multiples of the fundamental frequency cause a greater degree of heating in conductors. Harmonic frequencies increase skin effect, which becomes a factor. Skin effect reduces the cross-sectional diameter of the conductor and thereby reduces the ability of the conductor to carry current. Harmonic currents may result in overheating of electrical distribution system wiring, bus bars, lugs and conductor insulation, resulting in conductor failure. For typical wire sizes found in distribution systems, the resistance at the 25th harmonic may be two to four times greater than the 50/60 Hz resistance. Generally speaking, the larger the diameter of a wire, the greater the impact of the harmonic frequency will be. 2. Overheated neutral conductors and terminations In a balanced three-phase system, phase currents travel through each of the three-phase conductors and return on a common neutral. The three neutral currents will tend to cancel each other out mathematically. Triplen harmonics cancel this effect and cause the neutral currents to mathematically add together, overloading the neutral conductor by causing more current to flow in the neutral conductor than in the phase conductors. 3. Overheating of service equipment through induction heating The higher frequencies of harmonic waveforms also increase hysteresis effects and eddy currents in metallic enclosures such as electrical panels or transformer cores and may cause induction heating to occur. Panels that are designed to carry 60 Hz currents can become mechanically resonant to the magnetic fields generated by higher frequency harmonic currents. When this happens, the panel vibrates and emits a buzzing sound at the harmonic frequencies. 4. Nuisance tripping of electronic circuit breakers Nuisance tripping of electronic circuit breakers is also a problem, because unlike thermo-magnetic circuit breakers that employ a bimetallic strip, these types of breakers use solid-state trip devices that sense peak current values. Harmonic frequencies can cause the peak current values to distort, thus causing the breaker to trip prematurely. 10 Construction Electrician Apprenticeship Program: Level 3

11 Learning Task 1 E-4 5. Electric motor malfunctioning Harmonic distortion in the power supply to a motor may lead to decreased efficiency, excessive heating, vibration and reduced torque output. Voltages above the motor s rated value, as well as phase voltage imbalance, can cause increased starting current and motor heating. Reduced voltages result in increased full-load temperatures and reduced starting torques. Contactors and relays may malfunction, stopping the motor. 6. Power factor correction capacitor failure The inductance characteristic of the supply system can become resonent with system power factor correction capacitors as a result of a harmonic frequency. When resonance occurs, large currents and voltages may also occur, which can lead to overheating and premature failure. In many cases, power factor correction capacitor failure can be directly attributed to harmonic current content. High harmonic currents can act to overheat correction capacitors, causing premature failure and sometimes resulting in explosion. 7. Random equipment resets or process failures Many devices such as digital clocks and process control equipment often rely on the timing regularity of the sinusoidal waveform to maintain process timing synchronization. Heavy harmonic content can cause a error and inaccurate timekeeping, resulting in the system crashing or locking up and failure of the process. 8. Effects of voltage deviations on lighting There are three major effects of voltage deviations on lighting: Reduced lifespan Change of intensity or output (voltage flicker) Short deviations leading to lighting shutdown and long turn-on times Fluorescent lighting systems with electronic ballasts are more forgiving of voltage deviations due to the nature of the ballast circuitry. Ballasts may overheat with high applied voltage, but these lights are usually less susceptible to flicker. 9. Transformer heating and humming Commercial buildings are commonly supplied from a 120/208V transformer in a delta-wye configuration. Single-phase, non-linear loads drawing current from the building supply in a pulsed manner produce triplen harmonics, which add up in the neutral. When this neutral current reaches the transformer, it is reflected in the delta primary winding, where it causes overheating and transformer failure. Another transformer problem results from core loss and copper loss. Transformers are normally rated for a 60 Hz electrical frequency. Higher frequency harmonic currents may cause increased core loss due to eddy currents and hysteresis, resulting in more excessive heating effect. These heating effects demand that transformers be derated for harmonic loads or replaced with specially designed transformers. Construction Electrician Apprenticeship Program: Level 3 11

12 Learning Task 1 E Computer problems: crashing, locking up, memory loss, power supply failure, circuit board failure Most modern electronic office equipment is computer based. This essential equipment may be susceptible to power disturbances, causing equipment damage or malfunction. Examples of computer-based equipment that may be susceptible to power disturbances include: personal computers security systems cash registers electronic fire alarms digital clocks ovens inventory systems billing systems switching equipment memory typewriters machines CAD workstations Costs Power quality problems make their effects felt in four general areas: downtime, equipment problems, energy costs and mitigation costs. Downtime Waste. How much raw material or product do you have to throw away if a production process goes down? Restoration. How much does it cost to clean up and restart after an unplanned shutdown? Lost revenue. Both present and future revenues may be affected if reliable delivery of product to clients is affected. Equipment problems Equipment problems include: Computer failures: power supply failures, circuit board failures Damage to transformers and motors from overheating Damage to service equipment and conductors Energy costs You can reduce power usage by eliminating inefficiencies in your distribution system. Inefficiency sources include: High neutral currents due to unbalanced loads and triplen harmonics Heavily loaded transformers, especially those serving non-linear loads Motors not operating at peak efficiency due to PQ issues 12 Construction Electrician Apprenticeship Program: Level 3

13 Learning Task 1 E-4 Mitigation costs Mitigation costs include: The initial power quality analysis Rewiring of the electrical distribution system with larger conductors Improving grounding and bonding systems Replacing overheated transformers with special K-rated or harmonic mitigating transformers Installing power conditioning equipment Now do Self-Test 1 and check your answers. Construction Electrician Apprenticeship Program: Level 3 13

14 Learning Task 1 E-4 Self-Test 1 1. BC Hydro defines power quality as. 2. Most equipment has a built-in tolerance of overvoltage and undervoltage. 3. List four major power quality issues. 4. Voltage sags or swells due to and caused by the effects of non-linear type loads are often the causes of power quality issues. 5. Describe the relationship between harmonic frequencies and the ability of a conductor to carry current. 6. Higher frequency harmonic currents may cause increased core loss in transformers due to and, resulting in more excessive heating effect. 7. List the three major effects of voltage deviations on lighting. 8. Many devices such as digital clocks and process control equipment often rely on the timing regularity of the to maintain timing synchronization. 14 Construction Electrician Apprenticeship Program: Level 3

15 Learning Task 1 E-4 9. cause the neutral currents in an affected three-phase system to mathematically add together overloading the neutral conductor by causing more current to flow in the neutral conductor than the phase conductors. 10. Describe in detail the effect of non-linear loads on distribution transformers in commercial buildings. Go to the Answer Key at the end of the Learning Guide to check your answers. Construction Electrician Apprenticeship Program: Level 3 15

16 16 Construction Electrician Apprenticeship Program: Level 3

17 Learning Task 2: Describe causes of power quality issues Mysterious events are occurring in your facility: lights are flickering, computers are crashing, transformers are humming and running hot, circuit breakers trip under less than rated current, and motors aren t running properly. The cause could be anywhere from the supply authority s generators to the electrical equipment within the facility itself. Despite popular belief, studies have shown that the majority of the causes of power quality issues come from within the facility itself. Supply-side causes Our electrical distribution system is subject to a number of external influences that can cause power line disturbances. Some of the more common ones are: Lightning, wind and other weather-related conditions Vehicular accidents involving utility poles or underground equipment Digging into underground cable Tree branches Animals contacting the equipment Equipment malfunctions Vandalism Switching Lightning Disturbances to the fundamental system waveform do occur frequently in the electrical power system on the supply side. These disturbances occur whenever lightning hits a power line, power lines slap together, a tree branch falls into the power lines in a windstorm, or a power pole is hit by a vehicle and a power line falls to the ground. And they may occur during a rain- or windstorm when a substantial amount of dust is stirred up, covering and contaminating the surface of the line insulators. When the distribution system equipment supplying the consumer is involved in a fault, the voltage level will fluctuate outside the normal ranges. Lightning strikes are a well-known high-energy transient with a very short duration. Surge arrestors and all similar devices are designed to contain and control the damaging effects of the more distant and less severe disturbances. The supply authority installs lightning/surge arrestors on the system to protect selected distribution system equipment from severe overvoltage and damage. Construction Electrician Apprenticeship Program: LEvel 3 17

18 learning task 2 E-4 Due to their limited energy absorption capabilities, surge arrestors are unable to limit the effects of a close-in lightning strike. Even when employing all possible protective measures, a direct strike to the electrical system will almost always result in some damage. The magnitude and duration of a fault-inspired disturbance for the consumer are determined by factors such as the customer s electrical distance from the fault, the nature of the fault, and what corrective action was required to clear the fault. While lightning/surge arrestors protect the supply authority s equipment the consumers should not plan on the supply authority s arrestors protecting their equipment from lightning or other voltage transients. Capacitor banks The supply authority tries to maximize the efficiency of power transfer lines by maintaining a power factor close to unity. The application of capacitor banks has become a common method to offset added reactive loads and to improve voltage regulation on heavily loaded transmission and distribution systems. It is common for these capacitor banks to be switched frequently to prevent overcorrection as the system loads and voltage schedule vary during the day. 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 to minimize the electrical system losses. Switching of capacitor banks causes high frequency, voltage and current transients that may cause nuisance tripping of adjustable-speed drives, computer network problems and customer equipment damage or failure. These transients cause insulation stress on equipment and cable insulation, shortening their life. Typically, the disturbance created by the switching of capacitors is a ringing of the voltage waveform for less than a cycle (Figure 2). The ringing often creates multiple zero crossings during one cycle. The voltage transient often can exceed +150% of the steady-state voltage. Figure 1 Capacitor switching transients 18 ConstruCtion ElECtriCian apprenticeship program: level 3

19 Learning Task 2 E-4 A steady-state voltage rise will also occur when the capacitors are first connected to the lines as the capacitor s plates become fully charged. The steady-state voltage will rise when the capacitor closes and may exceed the normal steady-state voltage limits for up to 2 minutes, until a voltage regulator compensates for the changed voltage. The voltage sag when the capacitor opens may also exceed the normal steady-state voltage limits until a voltage regulator compensates for the changed voltage. Line switching The switching of both transmission and distribution lines is required to: perform maintenance on the utility system provide for the economic operation of the system prevent the overloading of heavily loaded lines restore service in the event of a power outage Line switching is done almost continually throughout the system. A voltage transient can be created by line switching but is usually less severe than capacitor switching. Line switching usually does not create noticeable problems to the customer. Interruptions A momentary disruption is one in which there is a decrease in voltage to 0 volts on one or more power lines lasting from 1/120th of a second (one-half cycle) to 3 seconds. This is due mainly to the tripping and automatic resetting of protection devices on a faulty section of the network caused by insulation failure, lightning or insulator flashover. A temporary interruption is one in which a decrease to 0 volts on one or more power lines occurs and lasts for more than 3 seconds but less than 1 minute. The time gap between when an interruption occurs and when a standby power supply such as a generator takes over would be considered this type of interruption. These types can also occur when debris such as branches or trees fall across power lines, especially during storms, or when large birds or animals accidently cause a short circuit or fault across two or more power lines, resulting in tripped utility circuit breakers. A sustained interruption is one in which a decrease to 0 volts occurs on all power lines for a period of more than 1 minute. Lightning strikes, storms, fires and motor vehicle accidents can cause damage not just to power lines but to equipment as well, which can result in sustained interruptions. A planned interruption to allow for upgrades or replacement of equipment, or for regular maintenance to be performed would also be considered a sustained interruption. This situation is called a blackout. These interruptions invariably cause loss of information and malfunction of microprocessorcontrolled data processing equipment. ASDs, PCs, and PLCs are sensitive to these faults and may malfunction or stop unless the installation has circuitry to protect the process from these faults. Other types of power quality issues, while not causing actual power interruptions, can create power fluctuation problems as defined below. Construction Electrician Apprenticeship Program: Level 3 19

20 learning task 2 E-4 undervoltages The term brownout has been commonly used to describe this problem, but largely this has been replaced by the term undervoltage. Electric utilities try to maintain voltage levels delivered to customers at ±5%. However, factors like weather, high demand and others can cause the utility voltage to fall within a ±10% range. Even under ideal conditions, most customers will see a drop in utility voltage levels over the course of the day as demand begins to increase around 8 a.m. and peaks around 3 or 4 p.m. Distribution system characteristics can also contribute to chronically lowvoltage situations. For example, customers at the end of a long line may be subject to a permanent voltage drop due to line losses on top of the utility voltage variations. The symptoms of undervoltage can range from none to daily equipment malfunction or premature equipment failure. Undervoltage may occur when new equipment is installed or the electrical system is otherwise changed and the new combined load increases the line drop. Besides the obvious malfunction of sensitive electronic equipment, persistent undervoltage can cause excess wear on some electrical equipment like motors, as they will tend to run overly hot if the voltage is low. Typical causes of system undervoltage are: Overloaded customer wiring Loose or corroded connections Unbalanced phase loading conditions Faulty wiring Overloaded distribution system Figure 2 Undervoltage waveform Sag A voltage sag is not a complete interruption of power; it is a temporary drop below 90% of the nominal system voltage level for a period of 0.5 cycles to 1 minute s time. Voltage sags are probably the most significant power quality problem facing industrial customers today, and they can be a significant problem for large commercial customers as well. For voltage sags and momentary outages, the system effects may be the same: Information technology equipment failure VFD/ASD malfunctions resulting in a process failure Nuisance tripping of contactors and electromechanical relays 20 ConstruCtion ElECtriCian apprenticeship program: level 3

21 Motor overloads tripping; motors running hot, or reduced life of motors and driven equipment; blinking, dimming or flickering of lights; digital clocks failing to keep proper time or flashing Common causes of sags include starting large loads and remote fault clearing performed by utility equipment. The starting of large motors inside an industrial facility can result in significant voltage drop (sag). A motor can draw six or more times its normal running current while starting. Creating a large and sudden electrical load such as this will likely cause a significant voltage drop to the rest of the circuit it resides on. Solutions to large starting loads include alternative power starting sources that do not load the rest of the electrical infrastructure at motor start-up, such as reduced-voltage starters, with either autotransformer, or star-delta configurations. A solid-state type of soft starter is also available and is effective at reducing the voltage sag at motor start-up. Most recently, adjustable-speed drives (ASDs), which vary the speed of a motor in accordance with the load (along with other uses), have been used to control the industrial process more efficiently and economically. ASDs offer the additional benefit of addressing the problem of large motor start-ups. Some of the same techniques that are used to mitigate interruptions can be utilized to address voltage sags: UPS equipment, motor generators and system design techniques. However, sometimes the damage being caused by sags is not apparent until the results are seen over time (damaged equipment, data corruption, errors in industrial processing). Figure 3 Voltage sag waveform Overvoltage Technically speaking, an overvoltage condition is when the system voltage exceeds the nominal voltage by 10% for a period of more than 1 minute. Chronic high voltage is most often attributable to excessive correction for voltage drop on the utility transmission and distribution system. To correct for voltage drops, the utility employs onload tap changing voltage regulators and line drop compensating voltage regulators to boost or buck the voltage. Customers nearest to an OLTC or LDC can experience overvoltage as the utility tries to overcome conductor voltage drop for those customers at the far end of the line. ConstruCtion ElECtriCian apprenticeship program: level 3 21

22 learning task 2 E-4 Figure 4 Overvoltage waveform Another common cause of overvoltage problems is local transformers that have been set to boost voltage to offset reduced voltage levels. This most often occurs at facilities with heavy loads at the end of distribution lines. When the heavy loads are operating, a normal voltage level is maintained, but when the loads are shut off, the voltage levels shoot up. Operating an electrical device above the specified voltage level range can lead to problems such as malfunction, shutdown, overheating, premature failure, etc. Some of the more common symptoms of overvoltage are: Electronics and other electrical equipment runs hotter than normal and fails prematurely. Equipment shuts down due to overvoltage protection. Unexplained malfunctions. voltage swell Also referred to as a surge, a voltage swell is defined as an increase in the voltage level to 110 to 180% of nominal, at the power frequency for durations of one-half cycle to 1 minute. The term momentary overvoltage is used as a synonym for the term swell. Figure 5 Voltage swell waveform Like voltage sags, voltage swells are usually associated with system fault conditions but they are much less common. This is particularly true for ungrounded or floating delta systems, where the sudden change in ground reference results in a voltage rise on the ungrounded phases. In the case of a voltage swell due to a single line-to-ground (SLG) fault on the system, the result is a temporary voltage rise on the unfaulted phases that lasts for the duration of the fault. Voltage swells can also be caused by the de-energization of a very large load. 22 ConstruCtion ElECtriCian apprenticeship program: level 3

23 learning task 2 E-4 Although the effects of a sag are more noticeable, the effects of a voltage swell are often more destructive. It may cause breakdown of components on the power supplies of the equipment, though it may be a gradual, accumulative effect. It can cause control problems and hardware failure in the equipment due to overheating that could eventually result in shutdown. Also, electronics and other sensitive equipment are prone to damage due to voltage swell. voltage fluctuations A voltage fluctuation is a systematic variation of the voltage waveform or a series of random voltage changes of small dimensions, namely 95 to 105% of nominal at a low frequency, generally below 25 Hz. Any load exhibiting significant current variations can cause voltage fluctuations. Arc furnaces are the most common cause of voltage fluctuation on the transmission and distribution system. One symptom of this problem is flickering of incandescent lamps. Removing the offending load, relocating the sensitive equipment or installing power line conditioning or UPS devices are methods to resolve this problem. Figure 6 Voltage fluctuations waveform Transients Often the most damaging type of power disturbance on the supply side, transients are classified as either impulsive or oscillatory transients. Impulsive Impulsive transients are sudden peak events that raise the voltage and/or current levels in the system to very high levels. These types of events can be categorized further by the speed at which they occur (fast, medium and slow). Impulsive transients can be very fast events with durations in the nanosecond range. The impulsive transient is what is often referred to as a surge or a spike. Other terms, such as bump, glitch, power surge, and swell have also been used to describe impulsive transients. The primary causes of impulsive transient disturbances include lightning, poor grounding, the switching of inductive loads, utility fault clearing and electrostatic discharge (ESD). Of these causes, lightning is probably the most damaging. The results can range from the loss or corruption of data in computer and process control systems to physical damage of equipment. ConstruCtion ElECtriCian apprenticeship program: level 3 23

24 learning task 2 E-4 Figure 7 Impulse transients Oscillatory An oscillatory transient is a sudden change in the amplitude of the system s waveforms, either the voltage, the current or both, without a change in 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. These transients occur when you turn off an inductive or capacitive load, such as a motor or capacitor bank. When a motor is stopped, as it slows down and comes to rest it acts as a generator, producing electricity and sending it back into the electrical distribution system. A long electrical distribution system can act like an oscillator when power is switched on or off, because all circuits have some inherent inductance and distributed capacitance. The most recognized problem associated with capacitor switching and its oscillatory transient is the tripping of adjustable speed drives (ASDs). The relatively slow transient causes a rise in the DC link voltage (the voltage that controls the activation of the ASD), which causes the drive to trip off-line with an indication of overvoltage. A common solution to capacitor tripping is the installation of line reactors or chokes that dampen the oscillatory transient to a manageable level. These reactors can be installed ahead of the drive or on the DC link and are available as a standard feature or as an option on most ASDs. Figure 8 Oscillatory transients 24 ConstruCtion ElECtriCian apprenticeship program: level 3

25 learning task 2 E-4 DC offset Direct current (DC) can be induced into an AC distribution system, often due to failure of rectifiers within the many AC-to-DC conversion technologies that have proliferated in modern equipment. DC can traverse the AC power system and add unwanted current to devices already operating at their rated level. Overheating and saturation of transformers can be the result of circulating DC currents. When a transformer saturates, it not only gets hot but also is unable to deliver full power to the load, and the subsequent waveform distortion can create further instability in electronic load equipment. Figure 9 DC offset The solution to DC offset problems is to replace the faulty equipment that is the source of the problem. Having very modular, user replaceable equipment can greatly increase the ease of resolving DC offset problems caused by faulty equipment, with less cost than may usually be needed for specialized repair labour. Electrical noise Noise is produced on electrical systems anytime intentional or unintentional arcing occurs within that system Anytime a set of electrical contacts opens or a ground fault occurs, it results in arcing, which produces noise on the system. The larger the amount of current being interrupted, the larger and longer the arc and the more noise is produced. Contacts inside circuit breakers, contactors, relays, starters and switches will bounce extremely quickly before completely closing, which can create excessive noise and cause problems for very sensitive equipment. Distant lightning strikes, switching power supplies, electronic circuits, poor brush contacts on motors, improper grounding and bonding and utility switching are just some examples of electrical noise sources. Figure 10 Electrical noise waveform ConstruCtion ElECtriCian apprenticeship program: level 3 25

26 learning task 2 E-4 Frequency fluctuations A change in frequency stability, frequency fluctuation results from generator or small cogeneration sites being loaded and unloaded. This occurs due to a change of effective power balance between supply and consumption, or an excessive increase or decrease of the load. Frequency fluctuations can exist if local power generation has poor speed regulation or as a result of faults in the system. Varying rotation speeds of synchronous generators, the most common type of generator used in utility power systems, may be the cause of frequency fluctuations. Frequency fluctuations can cause erratic operation, data loss, system crashes and equipment damage. Figure 11 Frequency fluctuation waveform notching Notching is a periodic voltage disturbance caused by electronic devices such as variable speed drives, light dimmers and arc welders under normal operation. This problem could be described as a transient impulse problem, but because the notches are periodic over each half cycle, notching is considered a waveform distortion problem. The usual consequences of notching are system halts, data loss and data transmission problems. One solution to notching is to move the load away from the equipment causing the problem (if possible). UPSs and filter equipment are also viable solutions to notching if equipment cannot be relocated. Figure 12 Notching waveform Common internal causes of poor power quality Although power quality within a facility may be affected by disturbances on the supply side, studies have shown that most power quality issues arise from the consumer s side of the PCC. With the increased use of non-linear loads, harmonic disturbances have become a major source of power quality disturbances. As we add more of those types of loads, it is essential that installation practices keep pace with and reflect the requirements of these types of loads. The following are some of the causes of poor power quality found within the consumer s facility. 26 ConstruCtion ElECtriCian apprenticeship program: level 3

27 learning task 2 E-4 Harmonics A major cause of power quality issues is harmonic distortion. Sometimes referred to as harmonics, which can be misleading, harmonic distortion is an overall distortion to the voltage and current sine waves and is a consequence of the use of electronic, non-linear loads. It is estimated that as many as 60% of all electrical devices operate with non-linear current draw. Figure 13 Harmonic distortion waveform A harmonic may be defined as a multiple of the fundamental frequency of 60 Hz. Harmonics are referred to by the harmonic number. The second harmonic would be two times the fundamental, or 120 Hz. The third would be three times the fundamental, or 180 Hz, and so on. Non-linear loading equipment generates harmonic frequencies. The non-linear nature of a device load draws current waveforms that do not follow the voltage waveform. Electronic equipment is a good example. While this broad category encompasses many different types of equipment, most of these devices have one characteristic in common: They rely on an internal DC power source for their operation. non-linear loads In non-linear type loads the DC power requirements are supplied by rectifying the input AC into DC with an internal diode-capacitor type rectifier similar to the circuit shown in Figure 14. The equipment s DC requirements are fed from the capacitor section, but the capacitor only draws current from the source in a short pulse during the peak of the sine wave as the capacitor charges to the peak of line voltage. The result of this action, aside from improved efficiency, is that highfrequency harmonics are created and as a result the current waveform becomes distorted. The harmonics are superimposed onto the fundamental 60 Hz frequency by the diode-capacitor input section, which rectifies the AC signal into DC. The circuit draws current from the line only during the peaks of the voltage waveform, thereby charging a capacitor to the peak of line voltage. The equipment DC requirements are fed from this capacitor, and as a result the current waveform becomes distorted. Voltage A B C D 1 D 2 D 3 D 4 D 5 D 6 Current Time Figure 14 Diode capacitor rectification ConstruCtion ElECtriCian apprenticeship program: level 3 27

28 Learning Task 2 E-4 Classification of harmonics Each harmonic has a name, frequency and sequence (Figure 15). Sequence refers to phasor rotation. In an induction motor, a positive sequence harmonic will generate a magnetic field that rotates in the same direction as the fundamental. A negative sequence harmonic will generate a magnetic field that rotates in the reverse direction. Name F 2nd 3rd 4th 5th 6th 7th 8th 9th Frequency Sequence Positive Negative 0 Positive Negative 0 Positive Negative 0 Rotation Forward Reverse Zero Forward Reverse Zero Forward Reverse Zero Figure 15 Harmonic reference table Positive sequence harmonics Positive sequence harmonics such as the 1st, 4th, 7th, 10th and 13th orders rotate in the same sequence as the fundamental, frequency. Typically, these types of harmonics cause overheating of transformer windings and supply conductors. If the facility has a standby generator, then the generator windings will also overheat from these harmonics, especially if the generator is feeding data processing equipment. Negative sequence harmonics Negative sequence harmonics such as the 2nd, 5th, 8th, 11th and 14th orders rotate in the opposite sequence as the fundamental, creating a negative sequence current. When distorted voltage containing the 5th or 11th harmonic is applied to a three-phase motor, it will attempt to drive the motor in reverse, creating a negative torque on the rotor. In order to overcome this negative torque, the motor must draw additional fundamental current. This increase in current, in turn, can cause overheating and/or the tripping of overcurrent protection devices. Older 6-step adjustable speed drives are a major source of the 5th, 7th and 11th harmonics. 12- step drives are significantly more expensive, and through their design are able to eliminate the 5th and 7th but are a source of the 11th and 13th harmonics. Triplen harmonics Triplen harmonics, also called zero sequence harmonics, are neither negative nor positive sequence. Three-phase, four-wire systems are prone to overheating of neutral conductors caused by triplen harmonics, mostly of the third order. These harmonics are all multiples of three (3rd, 9th, 15th etc.). Switching power supplies used by personal computers and electronic ballasts are the largest source of harmonic currents in large offices and institutions. Harmonics in the electric power system combine with the fundamental frequency to create distortion. 28 Construction Electrician Apprenticeship Program: Level 3

29 Learning Task 2 E-4 3rd 180 Hz Fundamental 60 Hz Distorted resultant waveform Figures 16a and 16b Effect of a harmonic frequency on the fundamental waveform Phase voltage imbalance Phase voltage imbalance is most often seen as a result of single-phase motors installed on a threephase circuit. Voltage imbalance that exceeds 2% is detrimental to reliable long-term three-phase motor operation and tends to generate unwanted heat in motors. This, in turn, results in wasted energy, insulation breakdown and improper/inefficient motor operation. Under the NEMA limits, a motor should not be operated with a voltage imbalance at or above 5%. During a fault on a phase of a distribution system, the electrical system voltage sags on the faulted phases due to the line drops on the conductors resulting from the extremely high current flows. Under extreme conditions the electrical characteristics of the circuit may cause the electrical system voltage on the faulted phases to fall to zero volts. The unfaulted phases may rise in voltage due to the increased ground and neutral current flow. This disturbance lasts from 30 milliseconds to a few seconds, after which protective equipment operates to clear the fault. This equipment consists of circuit breakers, fuses, protective relays or similar equipment. Phase current imbalance Imbalanced currents often arise when single-phase loads are employed unevenly on a three-phase distribution system. When the imbalance approaches 10%, the following problems may surface in an electrical distribution system: Circulating currents Excessive current in neutral conductor Increased neutral-to-ground voltage Overheating of motors (insulation breakdown) Reduced motor efficiency Motor bearings failures Increased maintenance of equipment and machinery Wasted energy / higher electric bills Loose electrical connections Electrical connections may become loose over a period of time due to vibration and the heating cooling cycle caused by the ebb and flow of current in the conductors. Aluminum conductors, which are commonly used on services and other larger systems, loosen over time due to the physical properties of aluminum. Aluminum warms up under a heavy electrical load and expands. It then flows out from under a tight connector because of its softness. As the conductor cools, it becomes loose in the connector. Construction Electrician Apprenticeship Program: Level 3 29

30 Learning Task 2 E-4 Scheduled infrared or thermographic inspections and a preventive maintenance program involving periodic tightening of connections can often solve many problems. Faulty installation practices Common violations involve undersized feeder or service conductors or electrical equipment, improper grounding of the neutral wire, or ground loops with the neutral connected to ground in multiple locations. This gives low voltage, ground currents or high neutral-to-ground voltages. Large motor start-ups At start-up, which may take from 2 seconds to a minute, a motor appears to the system as a large load due to the inrush current, possibly causing voltage disturbances such as sags or dips. The effects from these may be reduced by starting the offending motors during non-critical periods, not turning them off as often and thus not having to start them as often, installing reducedvoltage starters, or starting them with a low-distortion variable speed drive. Variable speed drives These are also known as variable frequency drives (VFD) or adjustable speed drives (ASD). They create current harmonics and thus distort the voltage waveform. Voltage distortion caused by the drive can interfere with the proper operation of the drive or other equipment within a facility. Excessive current distortion from drives can lead to overheating of the utility transformer and premature failure. Figure 17 Current spikes from VFD Electric arc welders These create very high levels of electrical noise. Some options for mitigation include serving the welder from a dedicated circuit from the main panel, having an oversized distribution transformer serve the building, or serving the sensitive equipment affected by the disturbance with an on-line UPS. Power factor correction capacitors Switching these can create high-voltage transients, cause large voltage swells and sags and cause large disruptions of the voltage waveform. If left energized these can also cause overvoltage under light load conditions by driving the facility into a leading power factor condition. In addition, harmonic frequencies may cause resonance between the inductive nature of the system and the capacitor, causing an increase in harmonic current. 30 Construction Electrician Apprenticeship Program: Level 3

31 Learning Task 2 E-4 Computer equipment These have non-linear 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. Copy machine/fax/laser printer These are notorious for interfering with other office equipment by introducing harmonic distortion and highly fluctuating loads. Placing these on a separate circuit from the main panel is usually sufficient to solve the problem. Electronic ballasts Electronic ballasts and compact fluorescent lamps create small amounts of harmonic current individually, but when considered as a whole may cause large harmonic currents. Medical imaging machines/x-ray machines When operating, these have a high current draw, with a high current distortion. They should be served from their own dedicated circuit. CT scanners or MRI equipment These have a very high and distorted current draw when operating, similar to the X-ray machine; however, the operating cycles are longer and the load is greater. These should be served from their own dedicated circuit. Sometimes the only way to properly serve these is to install a dedicated utility distribution transformer. Now do Self-Test 2 and check your answers. Construction Electrician Apprenticeship Program: Level 3 31

32 Learning Task 2 E-4 Self-Test 2 1. Describe the factors that affect the magnitude and duration of a fault-inspired disturbance for the consumer. 2. If there are large VFD loads, capacitor banks must be tuned to the system by using a in series with the capacitor bank. 3. Why are some capacitors switched multiple times a day, while some are switched daily, some are switched seasonally and some are always kept closed? 4. are probably the most significant power quality problem facing industrial customers today, and they can be a significant problem for large commercial customers as well. 5. Typically, sequence types of harmonics cause overheating of transformer windings and supply conductors. 6. Phase voltage imbalance is most often seen as a result of 32 Construction Electrician Apprenticeship Program: Level 3

33 Learning Task 2 E-4 7. Notching is a periodic voltage disturbance caused by electronic devices, such as, and under normal operation. 8. Describe what occurs when a distorted voltage containing the 5th or 11th harmonic is applied to a three-phase motor. 9. Describe three options for mitigation of the high level of electrical noise on the system from a welding shop. 10. Describe what occurs during a fault on a phase of a distribution system. Go to the Answer Key at the end of the Learning Guide to check your answers. Construction Electrician Apprenticeship Program: Level 3 33

34 34 Construction Electrician Apprenticeship Program: Level 3

35 Learning Task 3: Perform troubleshooting techniques It s tough to diagnose PQ problems without having a working knowledge of the site being investigated. To assist in the analysis, the initial part of this process should be the gathering of all technical information available including: Design drawings and specifications document Equipment manufacturer s installation and operations manuals As-built drawings Utility bills to determine demand charges and power factor penalties Data from preventive maintenance program documentation To conduct a proper power quality analysis it is necessary to gather as much pertinent information as is possible about the electrical distribution service. The next step is to develop an accurate, up-to-date one-line drawing of the installation s electrical distribution system. The one-line will identify the incoming supply service equipment, the size and type of the transformers, the size and length of the distribution conductors and branch feeders, the panels they feed and the types of loads they serve. When documenting the building loads, identifying whether the load being served by each panel and transformer is a non-linear or linear type will also be extremely valuable later in analyzing and evaluating the electrical characteristics at any point in the system. The more complete your documentation, the easier it will be to identify and target areas and equipment that might affect the power quality of the facility. The third step is to gather as much information about specific problems as is possible. As with any other type of troubleshooting, the root source of power quality issues can be determined by using a systematic approach to isolate and identify problems. When you gather information in order to investigate and analyze a complex electrical system, it is important to approach the task in an organized manner. Develop and document a procedure and process that will provide a framework. Keep detailed notes of your findings and keep gathered information organized and readily available by using a troubleshooting checklist. This will help you be efficient and professional by ensuring that no steps are missed. It will also greatly assist with reporting, ordering of material, follow-up and maintenance. As you build the documentation, it may be necessary to do a walkthrough of the building to observe the system and loads during all phases of operation, start-up, partial and full operation and shutdown. With the electrical operating characteristics of loads such as variable fan motors, solid-state controls, welding machines and certain types of fluorescent lighting, if they are present in a facility it s likely that further investigation will determine harmonics are also present. Construction Electrician Apprenticeship Program: LEvel 3 35

36 Learning Task 3 E-4 Harmonics are always present when there are non-linear loads, so they are easier to identify than other issues such as transients, spikes and sags, which appear randomly. For these types of problems, it is necessary to start by interviewing any affected personnel to establish: Which loads are affected When they are affected How often they are affected How long are they affected What else is occurring at that time For example, if there is a printer, plotter or copier in close proximity, it may be causing excessive noise in the circuit. Large HVAC loads or compressors starting can cause flicker, sags and other issues. Try to establish a pattern to see if the start-up of these devices corresponds to the issue in question. Different troubleshooting checklists are recommended for determining load problems, distribution problems, transformer and main service equipment problems. The checklist should contain information about: Problems reported Types of loads Problem patterns Problem history Possible problems Measurements taken Recommended course of action Troubleshooting a system problem should start at the service entrance and work through the service and distribution system toward the loads. Troubleshooting load problems should start at the loads, since that is where most power quality problems will appear, and work progressively back through various components toward the main service. Locate the power transformers supplying the non-linear loads you have identified and check for excessive heating or humming. Both are symptoms of harmonic disturbances. Also make sure the cooling paths are unobstructed. Depending on the accuracy and amount of information required for analysis, there are various measurement and testing devices that may be used to evaluate and analyze the power quality of a facility s electrical supply and installation. These may range from the average responding and true RMS meters to single-phase clamp-on power quality analyzers or three-phase power quality loggers or recorders. Hand-held oscilloscopes, infrared thermometers and thermographic cameras may also be used to assist. While these are all portable field testing devices, there may be cabinetstyle power analyzers installed in a facility that may also be employed. These are permanently installed devices and usually form part of the service equipment metering hardware, though they can also form part of an MCC or be an integral part of a VFD for an individual motor. 36 Construction Electrician Apprenticeship Program: Level 3

37 Learning Task 3 E-4 It is important to communicate details of testing procedures and schedules with all affected personnel prior to beginning any testing. If circuits are to be de-energized, this could cause the loss of important data or production time, so a coordinated approach with the client is strongly advised so that they are able to accommodate any disruptions to normal service. The client must be given ample opportunity to back up any data beforehand. Since testing will often need to be conducted on energized equipment, personal safety is of paramount importance, and all persons performing the testing must be trained and adhere to all applicable safe work practices such as those identified in CSA Z462 Workplace Electrical Safety and CSA Z460 Control of Hazardous Energy. Before beginning any tests: Complete a job hazard analysis (JHA) to identify the various tasks and their associated hazards and to determine control methods to minimize these hazards. Check for arc flash hazards and ensure that appropriate personal protective equipment (PPE) such as head protection, eye protection, hearing protection, foot protection, insulating gloves, and flame-proof coveralls are utilized as required. Always refer to the test equipment s user manual to know its proper operating procedures, safety precautions and limitations, particularly when high voltages and high currents are present. Check all test leads for appropriate CAT rating and for insulation damage. Use only meters and test equipment that have the appropriate CAT rating. Ensure there are no atmospheric hazards present such as flammable dust or vapours. Test meters on a known source first to ensure proper operation. Ensure the function switch and range selector are in their correct positions and leads are in their correct jacks. Start with the highest range when measuring unknown values. Never assume that a circuit is de-energized. Always check to see if voltage is present before proceeding with other tests. Ensure that any DMM used for power quality purposes is listed as a true RMS meter; otherwise it will not be able to accurately measure values of non-linear loads. True RMS meters measure non-linear loads that draw power in pulses, such as PCs, copiers, printers and motor drives. Construction Electrician Apprenticeship Program: Level 3 37

38 Learning Task 3 E-4 A simple way for an electrician to determine whether there are harmonic disturbances present in an electrical system without sophisticated equipment such as a three-phase power quality analyzer is to compare voltages using a digital multimeter with a peak hold or crest factor feature. The crest factor of a waveform is the ratio of the peak value to the RMS value. For a pure sine wave, the crest factor is A crest factor other than indicates the presence of harmonics. In typical single-phase cases, the greater the difference from 1.414, the higher the harmonic content is. With voltage harmonics present, the typical crest factor is below 1.414, or a flat top waveform results. For single-phase current harmonic disturbances, the crest factor is typically much higher than Voltage waveforms can be higher than 1.41 from transients or other issues, or they could be lower than 1.41 if the tops of their waveforms are flat. High current peaks can cause current waveforms to have a crest factor of greater than The greater the deviation from the ideal crest factor of a circuit, the more distorted the waveform will be. Some DMMs and most power quality analyzers have a crest factor (CF) function. If yours does not, measure the true RMS value of the voltage, and then multiply this value by to get the theoretical peak value. Using the peak-capture feature, a measured voltage peak that s significantly higher than the crest factor of indicates the presence of harmonics. Many non-linear loads will cause these peaks to be reduced or clipped, especially if the source impedance is high. To verify voltage clipping due to harmonics: 1. Measure the actual peak value using the peak-capture feature. 2. Compare the actual value to the theoretical value. If they re significantly different, the waveform is distorted and contains harmonics. The ratio of the peak voltage to the RMS voltage is called crest factor and is an indicator of waveform distortion. This value should also be measured to indicate the purity of the waveform. A pure sinusoidal waveform would have a crest factor of Another method of determining the existence of harmonic problems uses two current checks, one with an average ammeter and the second with a true RMS ammeter. In the example in Figure 1, the average ammeter indicates a value of 12.2 amps while the true RMS ammeter indicates a value of 18.4 amps. We use these values to calculate a ratio by dividing the average value by the true RMS value as shown below. 38 Construction Electrician Apprenticeship Program: Level 3

39 Learning Task 3 E-4 Ratio = Average ammeter value True RMS ammeter value Ratio = 12.2 A 18.4 A Ratio = Average ammeter indicates a value of 12.2 amps. True RMS ammeter indicates a value of 18.4 amps. Figure 1 Determining harmonic concerns using two ammeters A ratio of 1 indicates no harmonic distortion while a ratio of 0.5 would indicate extreme harmonic distortion. This method does not define the sequence of the harmonic distortion but it does indicate the presence of harmonic distortion. These readings indicate a significant harmonic distortion that would require more analysis to get a clearer definition of the sequence of the harmonic distortion. Three-phase current waveforms often exhibit a double hump waveform; therefore the crest factor comparison method should not be applied to three-phase load current. After you ve determined that harmonics are present, a power quality analyzer should be used to conduct a more in depth analysis of the disturbances present. If these tests indicate harmonics are present, the following tests should be performed using a digital multimeter on a distribution panelboard and the results recorded on the checklist. Measure the voltages: Line-to-line feeder voltages between line bus Line-to-neutral voltages between neutral bus and line bus Line-to-ground voltages between ground bus and line bus Neutral-to-ground voltage between neutral bus and ground bus Voltage drop across closed circuit breakers to give an indication of contact pitting Construction Electrician Apprenticeship Program: Level 3 39

40 Learning Task 3 E-4 Check for % voltage unbalance. To do this, add all three line voltages together and divide by 3 to determine the average voltage. Divide each phase voltage deviation by the average voltage and multiply by 100. A tolerance of 1% is acceptable. Measure the currents: Feeder currents in all three phases Feeder neutral current Branch circuit neutral and line currents Check for % current unbalance. To do this, add all three line currents and divide by 3 to obtain the average line current. Divide each phase current deviation by the average current and multiply by 100. Current unbalances should not exceed 10%. Measure and record the transformer secondary currents in each phase and in the neutral (if used). Compare the kva delivered to the load against the nameplate rating. If harmonic currents are present, the former can overheat even if the kva delivered is less than the nameplate rating. Use the k-factor measurement from a power quality analyzer to determine whether de-rating or transformer replacement is appropriate. Measure the frequency of the neutral current. 180 Hz would be a typical reading for a neutral current consisting of mostly third harmonic. Check the current and voltages at subpanels that feed loads. With the system energized, measure the current in each branch neutral and compare the measured value to the rated capacity for the wire size used. Check the neutral bus bar and feeder connections for heating or discoloration. Look, listen, touch and smell for signs of excessive heating or any other extraordinary conditions while you are conducting and recording measurements. A non-contact infrared thermometer is useful for detecting excessive overheating on bus bars and connections or terminations. Neutral overloading in receptacle branch circuits can sometimes be detected by measuring the neutral-to-ground voltage at the receptacle. Measure the voltage when the loads are on. Two volts or less is about normal. Higher voltages can indicate trouble, depending on the length of the run, quality of connections, etc. Hand-held oscilloscope These sophisticated oscilloscopes are very useful in viewing the waveform or waveforms under test and their relationship in time. They typically come with up to four separate colour-coded input probes with insulated BNC connectors for safety. Each voltage lead has its own reference ground lead. Each input will show a different waveform, all of which can be shown simultaneously on the graphic display screen. The scope can be programmed to show either live or captured waveforms, and can also record events. They will also have a USB port or optical output port and adapter cable so that information can be exported to a laptop for more in-depth analysis, and for use with report writing. 40 Construction Electrician Apprenticeship Program: Level 3

41 Learning Task 3 E-4 Their graphic screen can also display values just like a DMM, when the display parameters are set to meter mode. Using the standard leads, they can be used to measure resistance and voltage, and with auxiliary leads they can be used to measure current and temperature. Instructions vary greatly between brands and models. It is important to become familiar with the user s manual for the device you are using. Infrared thermometer These non-contact devices are a quick way of determining specific hotspots in a panelboard, splitter, disconnect switch or transformer. Hotspots can be caused by such things as loose connections and corrosion at lugs, on busses, fuseholders, or line and load connections of circuit breakers. To use it, aim its laser light at a point inside the equipment where no wiring is located to establish the ambient temperature. The temperature at that point will be displayed on the graphic screen and will become the reference temperature. Next, aim the laser light at a wiring connection point and compare to the reference temperature. The difference in temperature between this point and the reference point is the amount of heat being produced at that connection point. Check temperatures at all connection points and compare to the reference temperature. Any unusually high temperature readings will be a good indication of areas that need attention during the next routine maintenance. Some DMMs have a separate non-contact temperature probe that functions in much the same way. Insurance underwriters often require a full thermographic imaging study as part of an annual preventive maintenance program for large facilities. Figure 2 Infrared temperature meter Construction Electrician Apprenticeship Program: Level 3 41

42 Learning Task 3 E-4 Power Quality Troubleshooting Checklist Load Problems Problem Observed or Reported: o Overloads Tripping o Computer Hardware Problems o Erratic Operation o Shortened Life o Other Load Type: o Computer o Printer/Copier o PLC o Drive o Modem o Other Problem Pattern: Day(s) of week: o Continuous o Random o Monday o Tuesday o Wednesday o Thursday o Friday o Saturday o Sunday Time(s): o Continuous o Random o Always Same Time o Morning o Afternoon o Evening o Night Problem or Load History: Has problem been observed or reported before? o No o Yes Was any action taken? o No o Yes Are other loads affected? o No o Yes Are nonlinear loads in area, or on same circuit? o No o Yes Has there been any recent work or changes made to system lately? o No o Yes Possible Problem(s): o Operator Error o Power Interruptions o Sags or Undervoltage o Swells or Overvoltage o Harmonics o Transients or Noise o Improper Wiring/Grounding o Undersized Load o Undersized System o Improperly-sized Protection Devices o Other Measurements Taken at Load: Line Voltage V, Neutral-to-Ground Voltage V, Current A, Power W, VA, VAR, Power Factor PF, DPF, Voltage THD, Current THD, K Factor, Other Waveform Shape: Voltage Waveform: o Sinusoidal o Non-Sinusoidal o Flat-topped o Other Current Waveform: o Sinusoidal o Non-Sinusoidal o Pulsed o Other Measurements Taken at Load (Over Time): Normal Voltage V, Lowest Sag V at (Time), Highest Swell V at (Time) Highest Inrush Current A at (Time) Number of transients recorded over a time period of at a level of % above normal Possible Problem Solution(s): o UPS o K-Rated Transformer o Isolation Transformer o Zig-Zag Transformer o Line Voltage Regulator o Serge Suppressor o Power Conditioner o Proper Wiring and Grounding o Harmonic Filter o Derate Load o Proper Fuses/CBs/Monitors o Other 42 Construction Electrician Apprenticeship Program: Level 3

43 Learning Task 3 E-4 Power Quality Troubleshooting Checklist Building Distribution Problems Problem Observed or Reported: o CBs Tripping o Conduit Overheating o Overheated Neutrals o Electrical Shocks o Damaged Equipment o Humming/Buzzing Noise o Other Load Type: o 1φ o 3φY o 3φ o Fuses o CBs o Voltage(s) V o Amperage Rating A o Other Problem Pattern: Day(s) of week: o Continuous o Random o Monday o Tuesday o Wednesday o Thursday o Friday o Saturday o Sunday Time(s): o Continuous o Random o Always Same Time o Morning o Afternoon o Evening o Night Problem or Distribution History: Has problem been observed or reported before? o No o Yes Was any corrective action taken? o No o Yes Are other parts of system affected? o No o Yes Are nonlinear loads in area, or on same circuit? o No o Yes Has there been any recent work or changes made to system lately? o No Are large power loads being switched ON/OFF? o No o Yes Is panel properly grounded? o No o Yes o Yes Possible Problem(s): o Conductors Undersized (Hot) o Neutral Conductors Shared/Undersized o High Number of Nonlinear Loads o Voltage/Current Unbalance o Harmonics o System Undersized o Improper Wiring/Grounding o Other Measurements Taken: Taken at panel Located at Voltage V, Current A, Power W, VA, VAR, Power Factor PF, DPF Voltage THD, Current THD, K Factor, Other Waveform Shape: Voltage Waveform: o Sinusoidal o Non-Sinusoidal o Flat-topped o Other Current Waveform: o Sinusoidal o Non-Sinusoidal o Pulsed o Other Measurements Taken at Load (Over Time): Normal Voltage V, Lowest Sag V at (Time), Highest Swell V at (Time) Number of transients recorded over a time period of at a level of % above normal Possible Problem Solution(s): o Oversize Neutrals o Run Separate Neutrals o Additional Transformer o Separate Loads o Harmonic Filter o Proper Wiring and Grounding o Proper Fuses/CBs/Monitors o Additional Subpanel o Surge Suppressor o Power Factor Correction Capacitors o Other Construction Electrician Apprenticeship Program: Level 3 43

44 Learning Task 3 E-4 Power Quality Troubleshooting Checklist FACILITY TRANSFORMER AND MAIN SERVICE EQUIPMENT PROBLEMS Problem Observed or Reported: o CBs Tripping/Fuses Blowing o Conduit Overheating o Overheated Neutrals o Electrical Shocks o Damaged Equipment o Other Distribution Type: o 1φ o 3φY o 3φ o Fuses o CBs o Voltage(s) V o Amperage Rating A o Other Problem Pattern: Day(s) of week: o Continuous o Random o Monday o Tuesday o Wednesday o Thursday o Friday o Saturday o Sunday Time(s): o Continuous o Random o Always Same Time Problem or Distribution History: Has problem been observed or reported before? o No o Yes Was any corrective action taken? o No o Yes Are other parts of system affected? o No o Yes Have additional loads been added to system? o No o Yes Has there been any recent work or changes made to system lately? o No Are large power loads being switched ON/OFF? o No o Yes ls main service panel properly grounded? o No o Yes Are any subpanels grounded? o No o Yes Has there been a recent lightning storm? o No o Yes Has there been a recent utility feeder outage? o No o Yes o Morning o Afternoon o Evening o Night Possible Problem(s): o Conductors Undersized (Hot) o Neutral Conductors Shared/Undersized o High Number of Nonlinear Loads o Voltage/Current Unbalance o Harmonics o System Undersized o Improper Wiring/Grounding o Other Measurements Taken: Taken at panel Located at Voltage V, Current A, Power W, VA, VAR, Power Factor PF, DPF Voltage THD, Current THD, K Factor, Other Waveform Shape: Voltage Waveform: o Sinusoidal o Non-Sinusoidal o Flat-topped o Other Current Waveform: o Sinusoidal o Non-Sinusoidal o Pulsed o Other Measurements Taken at Load (Over Time): Normal Voltage V, Lowest Sag V, Highest Swell V Number of transients recorded over a time period of at a level of % above normal Possible Problem Solution(s): o Oversize Neutrals o Run Separate Neutrals o Additional Transformer o Harmonic Filter o Change to K-Rated Transformer o Separate Loads o Add Subpanel o Proper Wiring and Grounding o Proper Fuses/CBs/Monitors o Power Factor Correction Capacitors o Change Transformer Size o Surge Suppressor o Other o Yes Now do Self-Test 3 and check your answers. 44 Construction Electrician Apprenticeship Program: Level 3

45 Learning Task 3 E-4 Self-Test 3 1. Explain the purpose of a one-line drawing. 2. Describe the distribution system features that should be found on a one-line diagram. 3. List the essential documentation that should be gathered prior to starting a power quality analysis. 4. Describe the normal flow of troubleshooting when it appears to be a system problem. Construction Electrician Apprenticeship Program: Level 3 45

46 Learning Task 3 E-4 5. What important process is required before any physical test measurements are conducted? 6. List the appropriate personal protective equipment (PPE) to be used when switching hazardous energy sources. 7. Provide a detailed explanation of the term crest factor. 8. Thoroughly describe a simple way for an electrician to determine whether there are harmonic disturbances present in an electrical system without sophisticated equipment such as a threephase power quality analyzer. 46 Construction Electrician Apprenticeship Program: Level 3

47 Learning Task 3 E-4 9. Describe how to analyze the system for neutral current overloading. 10. Describe an organized three-step approach to troubleshooting power quality issues. Go to the Answer Key at the end of the Learning Guide to check your answers. Construction Electrician Apprenticeship Program: Level 3 47

48 48 Construction Electrician Apprenticeship Program: Level 3

49 Learning Task 4: Use power quality analyzers Power quality measurement is a fairly new and rapidly evolving and expanding field of electrical technology. The new IEC Class-A standard takes the guesswork out of selecting a power quality instrument. This standard defines the measurement methods for each parameter to obtain reliable, repeatable and comparable results. In addition, the accuracy, bandwidth and minimum set of parameters are all clearly defined. Standardization of power quality measurement is relatively new. The Class-A standard describes the power quality measurement methods and defines the accuracy, bandwidth, range, time synchronization (for example by GPS) and minimum set of measurement parameters including: Power frequency Supply voltage magnitude Flicker Harmonics and interharmonics Dips and swells Interruptions Supply voltage unbalance Rapid voltage changes Advanced power quality issues such as harmonic disturbances require in-depth analysis using samples taken at specified intervals over a period of time with very specialized test equipment referred to as power quality loggers and power quality recorders. Dedicated power quality analysis instruments fall into two basic categories: power quality clamp-on meters and power quality logger/recorders. Power quality clamp-on Power quality analyzers may be hand-held clamp-on style meters that go far beyond simply monitoring voltage or current. Power measurements watts, VA, VAR, volts, amps, frequency and power factor are the essential electrical characteristics of any system analysis. A handheld clamp -on power quality analyzer is typically capable of measuring these electrical characteristics in both single-phase and balanced three-phase power systems. Power quality clamp-ons have the ability to measure both peak in-rush currents of loads as well as measuring the peak voltage on the circuit. They can be used to identify issues such as phase unbalance, transients, harmonics, power interruptions, voltage problems, noise and power factor on both single and three-phase systems. Power quality clamp-on meters offer the ease of use, portability, and flexibility needed to solve most problems in commercial, industrial and residential settings. With this kind of tool, you can make everyday voltage and current measurements; evaluate harmonics, power and in-rush current, view waveforms; and log measurements. Construction Electrician Apprenticeship Program: LEvel 3 49

50 Learning Task 4 E-4 The LCD screen gives several options for viewing data. Data can also be displayed digitally. These are instantaneous values and will change in real time as the system changes. Another option is a bar graph screen that shows the measured parameters in instantaneous bar graphs that also change in real time. A third option is the waveform screen, which shows a graphic instantaneous representation of voltage and current waveforms like an oscilloscope. Included is a phasor diagram function showing the phasors and their angular relationship for the test system. This option also has a zoom feature, which allows any waveform to be closely analyzed. Figure 1 Power quality clamp-on Reproduced with permission, Fluke Corporation Figure 2 shows the current and voltage waveform being displayed on the waveform screen , 09:00 Waveform 60.1Hz 5 ms/ div A +1.0A -1.0A V +12V -12V Figure 2 Power quality clamp-on LCD screen Power quality clamp-ons will measure the total harmonic distortion, once the clamp meter is in harmonics mode shown in Figure 3a for voltage and Figure 3b for current. It s a simple matter to view the THD and to evaluate the individual harmonics, up to the 40th, using a bar graph. All of the same information is available for current as well. 50 Construction Electrician Apprenticeship Program: Level 3

51 Learning Task 4 E , 09:00 Harmonic V THD H 0.0 Hz 3.9 % V 3.8 % Vac , 09:00 Harmonic A Aac H 0.0 Hz 0.9 % A % THD V 3 A 30 % H % Figure 3a Harmonic voltage disturbances Figure 3b Harmonic current disturbances Many power quality clamp-on meters today also offer limited data logging capability with an external power supply, and allow the data collected to be downloaded via a USB port or memory card for a more in-depth analysis. Power quality logger Loggers are the basic tools for creating energy usage profiles used in monitoring and targeting. You can also use a power quality logger to validate voltage quality and look for general trends in the power quality. There are many times when the only way to troubleshoot a problem is to capture and analyze data over an extended period of time. For these advanced troubleshooting scenarios, energy loggers are invaluable, and they are much more affordable and easier to use than a more complex power recorder. Power quality recorder When it is necessary to capture comprehensive details on user-selected parameters over a long period of time or to catch fast acting transients, a power quality recorder is more suitable than power quality loggers. The power quality recorder is used for making detailed disturbance analysis and quality-of-service compliance testing in accordance with the Class-A standard. Typically a minimum 2 GB data memory enables simultaneous recording of all parameters for extended periods up to three months. Other important considerations, such as an uninterrupted power supply, mean important events are captured even during outages. With this type of tool, the data collected is subsequently analyzed using software programs to carry out data analysis and to generate reports. Construction Electrician Apprenticeship Program: Level 3 51

52 Learning Task 4 E-4 Figure 4 Three-phase graphic display meter; AC current measurement Reproduced with permission, Fluke Corporation All data can be exported to a laptop or PC for more in-depth analysis and report writing. The recorder s memory (typically 2GB or larger) makes it capable of storing a substantial amount of data. Power quality recorders have a triggering function, which allows the parameters to be set so that only minimum and/or maximum programmed values will trigger the data logger, saving memory space and simplifying the sorting-out of data. Multiple memory files allow for the storage of information about various jobs at the same time. If the equipment being measured uses current or voltage transformers (CTs or PTs), the transformer ratios must be entered into the analyzer during set-up. This will allow the user to directly connect the recorder leads to the CT or PT output terminals, and the actual values of voltage and current will then register on the display. The analyzer also comes with current leads with built in CTs, much like a hook-on ammeter, that are large enough to fit around most bus bars. When these leads are used, the device will use its auto detect feature and display the proportionate current values. Should any instrument adjustments need to be made, pressing the menu key and opening the set-up screen provides a menu of possible changes. Such adjustments include changing the specific type of probes being used, the harmonic values to be measured, the date and time, and other basic parameters. Select the volts/amps/hertz function and both voltage and current waveforms appear on the screen with frequency and crest factor displayed as well. AMPS/VOLTS/HERTZ 2.2 CF 4.90 A 10A V 1.41 CF 60.9 Hz 100V 0 BACK FORWARD SCROLL Figure 5 Power quality analyzer waveform display 52 Construction Electrician Apprenticeship Program: Level 3