Table of Contents. Introduction. About the Power System. Issues and Strategies. Other Helpful Information

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2 Table of Contents Introduction The importance of power quality to customers and a summary of the material to be found in this booklet About the Power System The different levels of the power system grid, including characteristics and voltage levels of each Transmission System Sub-Transmission System Distribution System SCE Supply Voltages Issues and Strategies Information on different types of power quality conditions and recommendations for how customers can minimize the adverse affects from such conditions Voltage Sags Transients Voltage Imbalance Harmonics Other Helpful Information List of power quality standards and terms Power Quality Handbook

3 Introduction Power Quality:Why Do We Care? A t Southern California Edison (SCE), we care about the reliability, consistency, and quality of power supply more than ever. The reason is straightforward. People are using more and more sophisticated electronic controls in their business equipment, most of which are sensitive to voltage variations. Fluctuations in power supply such as momentary voltage sags or transients can cause problems with electronic business equipment like never before. It s not practical to eliminate every power quality disturbance there are many variables outside the control of both the utility and the customer. There are things, however, that can be done. The best approach to maintaining consistent, high quality power is to prevent problems from ever developing. That s something Edison and its customers can work on together. Power Quality: It Takes Two Southern California Edison understands that consistent power supply is of utmost concern to our customers. It s our priority to oversee and assure the quality of the power we deliver, in every area within our control. We do this first by adhering to regulated standards and requirements. Most power quality problems are the result of incompatibilities between customer equipment and the electrical system it s connected to. SCE is committed to minimizing power quality disturbances at the system level. It is the responsibility of the customer to maintain power quality at the facility level. SCE power quality specialists are always available to assist customers with their power quality questions and to help diagnose power quality-related problems within their facilities. We hope this document is one way SCE can make power quality a part of your operation. How This Information Will Help The information in this document is intended to help your selection of equipment so that it will be compatible with electric supply systems, and to identify possible remedial measures for existing power quality problems. We will cover: Rules applicable portions of Rule 2 the tariff authorized by the California Public Utilities Commission (CPUC) outlining voltage and current requirements to which both SCE and the customer must adhere; Electrical Levels levels at which a customer s electrical system and equipment should be able to operate without malfunction or damage; Potential Problems descriptions of power quality conditions which occur in the normal operation of an electrical distribution system and the problems that these conditions may present for customers; and Solutions measures which the customer may take to minimize the problems caused by some power quality conditions. 2 Questions? Call PowerCo or pwrqlity@sce.com

4 About the Power System The transmission and sub-transmission electric system is an interconnected grid of different voltage networks designed to automatically isolate problems and minimize the number of customers who are affected during a disturbance. A transmission level problem may be felt in many states, while a distribution problem is likely to be isolated to a street or several homes. Where a problem occurs on an electrical system often determines whether you re affected by an interruption lasting just a moment or several hours, as repairs are completed. Having a basic understanding of transmission systems and voltage levels helps to identify different kinds of power disturbances, and understand where they occur, how long it takes to repair them, and how to mitigate any detrimental effects. The following section provides a summary of the power transmission systems and supply voltages. Transmission System The SCE transmission system is part of a large grid of interconnected power systems throughout the western United States. The Western Systems Coordinating Council (WSCC) provides standards for participants on this grid system. Purpose: To move large amounts of bulk electrical power over long distances. Design Elements Designed to assure that failure of a single component or path does not result in a blackout or catastrophic power failure. In order for a power system to operate properly, the balance between electric load and generation must be re-established after it is disturbed by a fault or system component outage. Voltage Level Typically, 500 kv and 220 kv. Customers are not typically served directly from the transmission system. Drawback Disturbances in one part of this large interconnected grid can sometimes affect the power system in Southern California, even if the disturbance originates far away. A recent example of this occurrence was the August 1996 blackout in Southern California and throughout the western U.S., which was caused by multiple line outages in Oregon. Some Recent Changes to the Transmission System The Independent System Operator (ISO) In early 1998, operation of the electric transmission in California was transferred from the utilities. The Independent System Operator (ISO) a non-profit, independent, entity now controls the flow of electricity throughout California, including SCE s transmission system. The ISO is regulated by a board responsible to the state of California and is completely independent of the utilities. It does not own any of the transmission lines or equipment, but directs their use in a manner similar to how an aircraft control tower directs aircraft and airways. Because power quality is based on the wires attached to customer equipment, the ISO does not have a direct impact on the power quality customers receive. However, the ISO does control the flow of electricity into SCE s transmission system and how power is delivered to a customer s business. It may therefore become necessary for SCE to coordinate problemsolving activities with the ISO on behalf of its customers. The California Power Exchange (PX) Like the ISO, the California Power Exchange (PX) was created by California legislation as a non-profit, independent entity and is regulated by a board responsible to the state of California. Where the ISO oversees physical operation of transmission lines, the PX oversees transactions that are financial, such as the sale and purchase of electric power contracts. The PX works with the ISO and with utilities, but it s entirely independent from them. 3 Power Quality Handbook

5 California s investor-owned utilities are required to sell and buy electricity solely through the PX, but private parties are not. The PX can be compared to a travel agent that sells airline tickets. The ticket sold has no direct relationship to how long a plane waits on the runway, for instance. In the same sense, making deals with various energy providers (through the PX) has no physical effect on any existing power quality or reliability problems for customers. Sub-Transmission System SCE has many sub-transmission systems, each serving a different geographical area. Purpose: To supply areas of approximately 100,000 electricity customers. Design Elements Typically, designed to ensure that the loss of a single component or circuit does not cause a blackout (power interruption). Designed to isolate faults to lessen the impact on individual customers. Voltage Level Typically, 66 kv, or 115 kv. Typically, customers over 10 megawatts are served from 66 kv or 115 kv. Distribution System The distribution system is the largest and most expensive electrical system in terms of capital investment. It s what most customers see from their homes or businesses. Purpose: To establish radial circuts serving approximately 1,000 customers each. Design Elements Traditionally, these are designed as radial systems. Failure in a system can cause all customers on the distribution system to lose electric power. SCE operates its radial systems with back-up ties to isolate faulted sections and to minimize duration of customer outages. Voltage Level Typical primary voltage: 4.16 kv, 12 kv, 16.5 kv or 33 kv Service voltage (Rule 2 voltages): Single phase V, 120/240 V, 240/480 V Three phase - 120/208 V, 277/480 V Large customers can be served at the primary voltages, or at the service voltages indicated. SCE Supply Voltages As is the case with any electric utility s power supply, the voltage on SCE s system varies throughout the day. The voltage at the service delivery point is referred to as service voltage. Under normal load conditions, SCE is required to maintain its secondary service voltage levels to within 5% of the nominal values shown in Table 1. This table applies to customers who are served at less than 600 volts. The Rule 2 tariff outlining voltage requirements, however, does provide exceptions to these voltage limits. Exceptions may be granted when the voltage variations: Arise from the temporary action of the elements; Are infrequent, momentary fluctuations of a short duration; Arise from service interruptions; Arise from temporary separation of parts of the system from the main system; and Are from causes beyond the control of SCE. Correct voltage is an essential part of power quality which requires information-sharing and coordination between the customer and SCE. SCE supplies nominal service voltages at the following levels: Single-phase: 120 V, 120/240 V, 240 V, 240/480 V and, depending on location, 2400 V, 12 kv, 16.5 kv, 33 kv. Three-phase: 120/208 V, 240 V, 277/480 V, 2400 V, 4160 V and, depending on location, 4800 V, 6900 V, 12 kv, 14.4/24.9 kv, 13.8 kv, 16.5 kv or 33 kv. 4 Questions? Call PowerCo or pwrqlity@sce.com

6 About the Power System Table 1 Steady State Voltage Limits Customers Served at Less Than 600 Volts Utilization Voltage Maximum Service Voltage Residential and Two-Wire and Minimum Commercial Agricultural and Multi-Wire Voltage to Distribution Industrial Service Voltage All Services Circuits Distribution Circuits Power Quality Handbook

7 V A oltage Sags Issues & Strategies ny interconnected power system (as described in the previous section) will normally experience momentary voltage sags, swells, and other fluctuations. A voltage sag is defined as a partial reduction in root mean squared (RMS) voltage that usually lasts from 0.5 to 30 cycles. Although a short duration voltage sag generally does not cause problems for incandescent lights and small motors, it can be long enough to cause interruptions on computers and other sensitive electronic equipment. Causes of Voltage Sags A common cause of voltage sags is power system faults events which cause circuit interruptions. On the utility s system, faults occur most often when the integrity of a utility s power system has been interrupted by wind, lightning, an airplane, car or animal. Power lines broken by trees falling during a storm, or short-circuited by kites or metal balloons, and many other occurrences may also cause a voltage sag. A large portion of fault causes are unforeseen and beyond control; however, many customers experience voltage sags that they create. For instance, sags can occur when customers start large motors or other electric loads. The magnitude of a voltage sag that originates on the utility s system is related to the customer s location relative to the fault. The closer a customer is to the point where a fault occurs, the greater the voltage sag experienced. If the fault occurs at a substation, the magnitude of the sag is equal on all of the circuits on that particular system. Clearing a Voltage Sag The duration of a voltage sag caused by a fault is the period of time between when a fault occurs and when the electric utility s protection system clears the fault. This period of time is referred to as the fault clearing time. In most cases, normal operation of the utility s protection system will result in several voltage sags in succession. Typical fault clearing times for the SCE electrical system at the distribution, subtransmission and transmission levels are listed on the table below. Table 2 SCE Typical Clearing Times Includes Circuit Breaker Operating Time Type of Circuit Voltage (kv) Standard Standard Clearing Time Clearing (seconds) Time (cycles) Distribution Distribution Distribution Distribution Subtransmission Subtransmission Transmission Transmission Note: The values listed in Table 2 represent typical clearing times. Longer clearing times may occur for ground and/or high impedance fault conditions. Customer utilization equipment should be designed and constructed to ride through voltage sags of durations based on table shown above. 6 Questions? Call PowerCo or pwrqlity@sce.com

8 Problems Caused by Voltage Sags Certain devices and equipment are sensitive to voltage sags and may not function properly when they occur. Such fluctuations in voltage usually do not cause complete equipment failure nor will they damage electronic equipment. Some devices that are sensitive to voltage sags are as follows: Variable-Frequency Drives (VFD) or Adjustable- Speed Drives (ASD); Personal computers; Programmable logic controllers (PLC); Large motors and motor controls; and High-Intensity Discharge (HID) lighting systems (metal halide, low and high pressure sodium, mercury vapor, metallic sodium, etc.). Because voltage sags are mostly due to unforeseen and uncontrollable events, the number of voltage sags experienced in the power system varies from year to year. Several industry studies conducted in the last decade provide insight on the number of voltage sags at particular magnitudes and durations that may occur annually. Data from one study are presented in Figure 1 below. This figure only gives averages across North America and cannot be expected to specifically characterize events on SCE s system. Figure per Year 743 per Year 244 per Year 0-16 per Year ITIC* 244 per Year 0-6 per Year per Year ANSI C Steady - State Voltage Range per Year 0-10 per Year EVENT DURATION (SECONDS) Voltage Magnitude (pu) * Information Technology Industry Council. 7 Power Quality Handbook

9 Recommended Ways to Avoid Problems with Sags There are ways customers can mitigate the potential problems associated with voltage sags in their facilities. Some of those methods are listed below. Customers are also encouraged to consult qualified power quality professionals when designing and/or making decisions regarding electrical systems and equipment. Most cities and counties regulate wiring design and construction. Professional engineers can be helpful in assuring designs meet all requirements. Use Proper Grounding Practices In maintaining power quality, there is no element more essential than grounding. Incorrect grounding can cause personal computers and other equipment to malfunction and can even increase dangers for electric shock. Use Proper Wiring Practices Close attention to proper wiring practices must be part of any voltage sag solution. Improper wiring can result in the lumping of internal loads that should not be on a common panel. If, for example, an elevator motor is on the same panel as the lights, the lights may blink every time someone calls for the elevator. Watch for Voltage Ride-Through Options Customers considering the purchase of equipment should investigate voltage sag ride-through options offered by manufacturers. Purchase Equipment Which Can Withstand Voltage Sags The customer may want to create a specification describing the voltage sag magnitude and duration that the equipment must be able to withstand. In preparing such specifications, it may be helpful to consider the Information Technology Industry Council (ITIC) curve (see Figure 1), which describes the desired performance of common office equipment. Use Voltage Sag Mitigation Equipment Customers experiencing equipment misoperation caused by voltage sags may benefit from installing one or more of the devices listed on Table 3. SCE recommends customers work with qualified power professionals to implement solutions that best address their needs. Table 3 SAG MITIGATION EQUIPMENT Equipment Uninterruptible Power Supply (UPS) Ride-Through Capacitors Rotary Uninterruptible Power Source Ferroresonant/Constant Voltage Transformer How It Works When utility power fluctuates or is lost, the UPS transfers its load to a battery system to maintain load system operations. A UPS can be sized to maintain power to equipment for up to 15 minutes or longer, depending upon battery size. A series of capacitors maintain electric charge and when utility power is lost, they provide a few seconds of ride-through voltage to control the system and maintain load. In the event of a sag or swell, this provides complete generation isolation for a load.the UPS is coupled to a DC motor driven by batteries, providing both power conditioning and ride-through protection. This provides ride-through using transformer core saturation. When the transformer core is loaded (saturated), it will have enough stored energy to ride-through momentary dips in voltage. 8 Questions? Call PowerCo or pwrqlity@sce.com

10 Issues & Strategies Transients Transients are fast changes (measured in milliseconds) in system voltage or currents that are characterized by peak magnitude, frequency, and rate of rise. Transients are momentary disturbances rather than steady-state variations such as harmonic distortion or voltage imbalance, and can originate on a customer s system or on the utility s system. Causes and Extent of Transients Transients are usually caused by lightning strikes, static electricity, circuit switching, or capacitor switching. On SCE s system, capacitor switching switching on capacitor banks to support distribution voltages can occur multiple times a day. Typically, SCE s capacitors are switched on early in the morning and switched off in the evening, but they may be switched at any time. A capacitor switching transient ordinarily lasts less than 1 cycle of the power system frequency. Switching on a capacitor will typically result in a steady-state voltage rise of 1% to 3%. Problems Caused by Transients Certain devices and equipment are sensitive to transients and may not function properly when they occur, although such conditions do not generally cause complete equipment failure. Some devices that are sensitive to transients are as follows: Variable-frequency drives (VFD), or Adjustable-speed drives (ASD); Personal computers; Phone systems; Televisions; and Point-of-sale terminals. Recommended Ways to Avoid Problems with Transients There are a number of ways customers can limit problems with transients in their facilities. It s best to start by selecting equipment that can withstand transients, and by using proper wiring/grounding practices. As for any electrical design, we recommend customers seek professional help from qualified electrical professionals. Here are some devices that can help mitigate problems from transients: Surge Arrestor Equipment There are several devices that protect equipment from transient overvoltage by limiting the maximum voltage impulse. These include: Surge Arrestors Metal Oxide Varistor (MOV) Transient Voltage Surge Suppressors (TVSS); and Isolation Transformers. Layered Defenses Using multiple TVSSs will increase protection to equipment due to transient overvoltage. In addition to having a TVSS at the service entrance, one should be installed at each device (TV, computer, etc.). Utilize a TVSS that has a UL 1449 listing. Service entrance TVSSs should be installed in the service panel, not the meter socket. 9 Power Quality Handbook

11 Voltage Imbalance A Issues & Strategies voltage imbalance is a long-term, steady-state problem caused by unbalanced phase loading conditions such as large single phase loads, defective transformers, or a ground fault in ungrounded or resistive grounded systems. Problems Caused by Voltage Imbalance Voltage imbalances only affect three-phase applications. Problems in such applications occur because some motors are designed to tolerate only very small voltage imbalances. Voltage imbalances can cause premature failure of motors and transformers due to overheating and can cause electronic equipment to malfunction. Recommended Ways to Mitigate Problems with Voltage Imbalance SCE designs and operates its electrical system in an attempt to limit the maximum voltage imbalance to 3% when measured at the electric utility revenue meter under no-load conditions, as recommended by ANSI C Voltage Ratings for Power Systems and Equipment. However, SCE cannot guarantee the voltage imbalance will not temporarily exceed this level because of unusual operating conditions or the nature of the load in a certain area. Based on NEMA MG the following formula should be used to determine utility and customer voltage imbalance. Percent Voltage = 100 X Imbalance Maximum Voltage Deviation From Average Voltage Average Voltage Example: With voltages of 220, 215 and 210, the average is 215, the maximum deviation from the average is 5, and the percent imbalance = 100 x 5/215 = 2.3 percent The following recommendations are offered to help customers mitigate the adverse effects of voltage imbalances in the power system. Purchase Equipment That Can Withstand Voltage Imbalance When selecting motor sizes, provide a margin for voltage imbalance to avoid overheating and consequent damage to the motor. Follow Voltage Imbalance Recommendations Generally, most electrical equipment can be derated to operate under relatively large voltage imbalance conditions. This may, however, result in a cost increase to the end-user. 10 Questions? Call PowerCo or pwrqlity@sce.com

12 Harmonics Cause and Control of Harmonics In most cases, harmonics are generated by customerowned equipment. When customers introduce harmonics into the power system, they can cause power quality problems for themselves and for other utility customers. Typical equipment that creates harmonics includes personal computers, HID lighting, electronic ballasts and variable-frequency drives. In the United States, the presently accepted standard governing harmonics is IEEE IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems. This standard takes a systems approach by considering harmonic current and voltage distortion limits only at the point of interface between the customer and the electric utility. Responsibility for controlling harmonics is twofold: The customer is responsible for limiting harmonic currents which interfere with the power system; and The utility is responsible for maintaining the quality of the voltage waveform. Problems Caused by Harmonics The adverse effects of harmonic currents and voltages on various types of power system equipment are summarized in Table 4. Recommended Ways to Mitigate Problems with Harmonics With the increased use of personal computers, variable-frequency drives, highly efficient T-8 and HID lighting systems, harmonics will continue to be a major power quality concern in the years to come. Unfortunately, there exists no equipment designed to tolerate harmonics. It is the responsibility of the Issues & Strategies E lectrical power systems in the United States are designed to operate at a frequency of 60 Hz. However, some equipment that customers connect to the power system generates currents and voltages at frequencies other than 60 Hz. These currents and voltages are known as harmonics or waveform distortion and can interfere with the functioning of other equipment. engineer to design a system that will minimize harmonics. The following are guidelines to creating a tuned electrical system within facilities to mitigate the effects of harmonics. Design Wiring Systems Properly Make sure wiring and conductor sizing within the facility meet the requirements for harmonic loads. This could require design in excess of the National Electric Code. Assure Proper Isolated Grounding Install sensitive equipment correctly. Install isolated ground receptacles consistent with FIPS 94 grounding practices and use the National Electrical Code as a guideline. Use IEEE Emerald and Green books for grounding principles. Design and Install An Appropriate Distribution System Use a qualified electrical engineer to design the facility s internal distribution system and assure the system meets all the requirements for an isolated ground system. This requires design in excess of National Electric Codes. Use K-Factor Transformers Transformers serving harmonic loads need to be designed to withstand the additional heating caused by harmonic currents. Use transformers with adequate K- factor ratings. Consult with your transformer supplier. Harmonic Filters Filters are available to isolate problem areas. Consult filter manufacturer specifications for correct filter applications. IMPORTANT. The installation of a code-compliant system will not reduce or remove fire hazards. Owner should require the design engineer to address fire concerns at the time of design. 11 Power Quality Handbook

13 TABLE 4 PROBLEMS ASSOCIATED WITH HARMONICS Type of Equipment Motors and Generators Impact Increased heating Higher audible noise Mechanical oscillations due to mechanical resonance Pulsating or reduced torque Transformers Power Cables Capacitors Electronic Equipment Metering Switchgear & Relaying Telephone Systems Increased heating and some vibrations.transformers are especially sensitive to harmonics. An appropriate transformer K-factor should be specified to account for skin effects and eddy currents. Increased heating and possible insulation failure if there is system resonance. Increased heating and dielectric stresses Increased voltage and corona stress (if there is resonance) Capacitor failure (if harmonics are excessive or resonance occurs) Possible malfunction due to harmonic distortion. Possible errors due to harmonic distortion. Increased heating and relay malfunctions. Interference of harmonic frequencies with telephone audio frequencies. 12 Questions? Call PowerCo or pwrqlity@sce.com

14 Other Helpful Information We hope the information provided in this booklet will help every customer to choose equipment and design electrical systems for their facilities wisely. At SCE, we want customers to have as much information as possible on power quality. We welcome inquiries regarding power quality and encourage customers to call POWERCO ( ) with their questions. They may also refer to published power quality guidelines listed below. Table 5 Listing of Existing Power Quality Guidelines United States Organization Standard Title/Scope ANSI/IEEE 141 Industrial Electric Power Systems ANSI/IEEE 142 Industrial & Commercial Power System Grounding ANSI/IEEE 241 Commercial Electric Power Systems ANSI/IEEE 242 Industrial & Commercial Power System Protection ANSI/IEEE 399 Industrial & Commercial Power System Analysis ANSI/IEEE 446 Industrial & Commercial Power System Emergency Power ANSI/IEEE 493 Industrial & Commercial Power System Reliability ANSI/IEEE 518 Control of Noise in Electronic Controls ANSI/IEEE 519 Harmonics in Power Systems ANSI/IEEE 602 Industrial & Commercial Power Systems in Health Facilities ANSI/IEEE 739 Energy Conservation in Industrial Power Systems ANSI/IEEE 929 Interconnection Practices for Photovoltaic Systems ANSI/IEEE 1001 Interfacing Dispersed Storage and Generation ANSI/IEEE 1035 Test Procedures for Interconnecting Static Power Converters ANSI/IEEE 1050 Grounding of Power Station Instrumentation & Control ANSI C62 Guides & Guidelines on Surge Protection ANSI C84.1 Voltage Ratings for Power Systems & Equipment ANSI C37 Guides and Standards for Relaying & Overcurrent Protection ANSI C Transformer Derating for Supplying Nonlinear Loads IEEE P487 Wire Line Communication Protection in Power Stations IEEE 1100 Power and Grounding Sensitive Equipment IEEE P1159 Monitoring and Definition of Electric Power Quality IEEE P1250 Guide on Equipment Sensitive to Momentary Voltage Disturbance IEEE P1346 Guide on Compatibility for ASDs and Process Controllers NEMA UPS Uninterruptible Power Supply Specification NEMA 70 National Electric Code NEMA 75 Protection of Electronic Computer Data Processing Equipment NEMA 78 Lightning Protection Code for Buildings NIST 94 Electric Power for ADP Installations NIST SP678 Overview of Power Quality and Sensitive Electric Equipment UL 1449 Standards for Safety of Transient Voltage Surge Suppressors 13 Power Quality Handbook

15 Terms and Definitions That May Help Many terms, definitions and acronyms have been developed to describe power quality conditions. In order to standardize terms used to describe power quality and ease communication between people working on power quality, IEEE , IEEE Recommended Practice on Monitoring Power Quality, lists standard terms and definitions. These values are provided below to help define the power quality categories. They are not intended to characterize conditions present on the SCE electrical system. Table 6 Categories and Typical Characteristics of Power Systems IEEE Typical Typical Voltage Categories Description Duration Magnitude 1.0 Transients 1.1 Impulsive Nanosecond (ns) 5 ns rise <50 ns Microsecond (µs) 1 µs rise 50 ns - 1ms Millisecond (ms) 0.1 ms rise >1 ms 1.2 Oscillatory Low Frequency <5 khz ms 0-4 per unit Medium Frequency khz 20 µs 0-8 per unit High Frequency MHz 5 µs 0-4 per unit 2.0 Short Duration Variations 2.1 Instantaneous Sag cycles per unit Swell cycles per unit 2.2 Momentary Interruption 0.5 cycles <0.1 per unit Sag 30 cycles per unit Swell 30 cycles per unit 2.3 Temporary Interruption 3 s - 1 minute <0.1 per unit Sag 3 s - 1 minute per unit Swell 3 s - 1 minute per unit 3.0 Long Duration Variations 3.1 Interruption, sustained >1 minute 0.0 per unit 3.2 Undervoltages >1 minute per unit 3.3 Overvoltages >1 minute per unit 4.0 Voltage Imbalance Steady State % 14 Questions? Call PowerCo or pwrqlity@sce.com

16 Please Give Us Your Feedback We d like to know how well this handbook served your needs. Please take a few moments to complete the brief survey below, then drop it in the mail. Thanks for helping us make this a better information resource. Please describe yourself. Occupation/Title: Consulting Engineer Architect Electrician Facility Engineer Maintenance Production Design Engineer Manager Other: Type of Business: Consulting/Contract Manufacturing Process Retail Commercial Institution Government Other What is your general level of understanding regarding electrical power systems and power quality? Please mark your level on the scale below Very little Thorough knowledge of the field or no understanding Please rate the handbook s content on the scales below Too Too advanced elementary Not detailed Too detailed enough Are there any topics that you d like to see added to the handbook? Do you have any other comments about the handbook? Return address printed on other side

17 (FOLD HERE) Southern California Edison Power Quality Department 7951 Redwood Avenue Fontana, CA 92236

18 For additional information, please contact us at: Southern California Edison Power Quality Department 7951 Redwood Avenue Fontana, CA POWERCO