IDEAL Test and Measurement THE BASICS OF POWER QUALITY

Transcription

1 IDEAL Test and Measurement THE BASICS OF POWER QUALITY

2 Table of Contents What is Power Quality? 2 Power Quality: An Introduction The Basics of Power Quality is a convenient guide to understanding the essential aspects of monitoring and troubleshooting power quality. Its easy-to-read format provides you with a reference point on how to deal with the three key issues that make up power quality: power factor, harmonics and disturbances. Just like our complete line of power quality testers and meters, this guide represents the IDEAL Test & Measurement commitment to helping the professional electrician. IDEAL. The way every job should be. D Sources of Poor Power Quality 3 Power Factor 4 Harmonics 8 Disturbances 12 IDEAL Power Clamps 14 IDEAL SureTest Circuit Analyzer 16 IDEAL Power Analyzer 18 Technical Definitions 20 Power Clamp Features & Ordering 22 SureTest Features & Ordering 23 Technical Support Toll Free Power Analyzer Features & Ordering 24 1

3 What Is Power Quality? The concept of power quality has often been misunderstood and oversimplified. But in this day and age of sophisticated electronics, monitoring power quality has become too important to ignore. The widespread use of high-tech devices has complicated every aspect of electrical power. Not only are these devices more sensitive to the effects of power quality, but they can also impact it negatively. Poor power quality can result in lost productivity, lost and corrupt data, damaged equipment and poor power efficiency. When added up, U.S. companies waste an estimated $26 billion on electrical power-related issues each year.* Power Quality is a broad term used to describe the measurement of electrical power performance. It can be broken down into three key areas. Each will be discussed in the following pages. THREE KEY ASPECTS OF POWER QUALITY Power Factor Harmonics Disturbances *Electrical Contractor Magazine, Surveying Power Quality Options, March Sources of Poor Power Quality Power Quality problems can be tracked to three origins - supply, internal distribution and internal loads. Supply This is the initial source of power from the utility company such as the main transformer of a commercial building. It s where power coming into the facility can be monitored. Internal Distribution 80% of all power quality problems occur in a company s A facility s incoming power is typically monitored at the main transformer, referred to as the supply. distribution and grounding systems. Corroded connections, defective conduit, defective electrical devices, improper wiring and improper grounding are just some of the obstacles to be dealt with. Internal Loads Everything from variable speed drives and high-tech devices to unsophisticated loads such as heaters and lights contribute to the quality of electrical power in a circuit. Internal loads can cause poor power factor, harmonics and disturbances. Industrial machines containing variable speed drives can cause a variety of costly power quality problems. 2 3

4 Power Factor Power Factor is the ratio of true power to apparent power in a circuit, or in other words, a circuit s level of power efficiency. It is expressed as a ratio by using the equation below. Voltage Power Factor In-Phase PF = Power Factor = W VA Watts Volts x Amps To determine power factor, divide true power (watts) by apparent power (volt amps). If true power and apparent power were equal, the result would be a power ratio of Current The most common reason to measure power factor is to determine the amount of power in a commercial or industrial environment that is supplied but not utilized. When the power factor ratio is 1.00 it means that every watt of power arriving from the utility company is put to use. But unfortunately, motors and electronic equipment apply a load to the circuit which can result in out-of-phase power. (See illustration on next page) Voltage Power Factor Out-of-Phase Current A power factor of less than 0.90 is considered poor. It means that a considerable amount of incoming power is being used inefficiently. To make matters worse, utility companies apply a penalty charge when power factor drops to low levels. Maintaining a healthy power factor is an important part of maximizing power efficiency. When power is in-phase, voltage and current travel congruently, meaning they reach maximum height and zero simultaneously. A large motor load can cause current to lag behind voltage. This lagging effect, or phase shift, can cause a poor power factor. 4 5

5 Troubleshooting Power Factor In nearly all cases, it is more cost-efficient to take steps toward improving power factor than it is to live with excessive utility charges. While the effects of power factor cannot necessarily be eliminated, they can be minimized if properly diagnosed. Identify the Problem The first step in resolving a power factor issue is to identify the origin and extent of the problem with a power clamp or power analyzer. A healthy power factor is in the mid to upper 0.90s. As mentioned earlier, a poor power factor usually results from a motor causing a phase-shift. Once the power factor is determined and the motors are identified, correcting the problem is a fairly simple process. Large motors make industrial operations especially susceptible to a poor power factor. A power clamp, such as the IDEAL pictured above, is the best way to monitor a circuit s power factor. With a single reading directly at the transformer, a power clamp can measure true power, apparent power and power factor. Implement a Solution The most common means of correcting a low power factor is to compensate the circuit with additional components. Most often, this compensation comes in the form of capacitor banks. While capacitor banks are a permanent solution, it is wise to continue monitoring the circuit for any new problems. 6 7

6 Harmonics Widespread use of electronic equipment in today s commercial and industrial environments has made harmonics an important but complex power quality issue. Fundamental Sine Wave 2nd Harmonic 60Hz Sine Wave With Harmonics 3rd Harmonic Most simple electric devices like motors and incandescent lighting are linear loads, which means AC impedance is constant regardless of the applied voltage. In this case, the fundamental AC sine wave, pictured below, is unaffected. 60Hz Sine Wave Notice that the fundamental frequency requires twice as long as the second harmonic and three times as long as the third harmonic to complete a single waveform. Harmonic Distortion In the United States, the fundamental frequency of electricity is 60Hz. This illustration shows one cycle of that frequency. On the other hand, non-linear loads such as personal computers and copy machines strip off AC power and convert it to DC power. This process adds harmonics to the fundamental frequency. By definition, a harmonic is a frequency which is an integer of the fundamental 60Hz wave. For example, the second harmonic of the fundamental frequency is 120Hz, the third harmonic is 180Hz and so on. The addition of harmonics to a system results in distortion to the voltage and current waveforms. The impact to the electrical system depends on the total amount of distortion present and on which harmonic the distortion is located. 8 Total harmonic distortion (THD) is the percentage of distortion to the fundamental frequency. As a general rule, THD should not exceed 5% of voltage or 20% of current. Harmonic Factorization Breaking down the total harmonic distortion into individual harmonics is an analysis called harmonic factorization. Typically, only the odd-numbered harmonics are analyzed. They are created by non-linear loads and have the greatest impact on an electrical system. The two most important categories for commercial and industrial settings are the zero sequence, or triplen harmonics (3rd, 9th, 15th, etc.) and the negative sequence harmonics (5th, 11th, 17th, etc.) The triplen harmonics are most commonly found in commercial settings and are caused by computers and other electronic office equipment. Negative sequence harmonics are commonly found in industrial environments and are caused by variable speed drives and other electronic equipment. 9

7 Commercial Environments In the 3-phase, 4-wire electrical system commonly found in commercial buildings, current flows through each phase conductor and returns in a common neutral conductor. In a balanced system, the neutral currents from each phase will mathematically cancel each other out. Any imbalance in phase current will return on the neutral at the fundamental frequency (60Hz). As this return current is typically small, it is generally not considered a problem. The characteristics of the triplen harmonics (3rd, 9th, 15th, etc.) disrupt this balance. Rather than canceling each other out on the neutral, the triplen harmonics from all three phases are mathematically added together in the neutral conductor. This can result in a higher than expected current which can cause excessive heat in the neutral conductor and transformer. Troubleshooting Harmonics Preventing harmonics from causing damage to electrical circuits and expensive equipment can be a difficult task. To effectively troubleshoot the problem, the total harmonic distortion and harmonic factorization should be analyzed. Knowing the amount and characteristics of the harmonics will aid in identifying a solution. The IDEAL Power Analyzer can collect data concerning harmonic distortion as well as power quality issues like disturbances. Industrial Environments The electrical loads within an industrial plant can be greatly affected by the negative sequence harmonics (5th, 11th, 17th, etc.). These harmonics counteract the energy created by the electrical power system. For example, in a motor the negative sequence harmonics will try to force the motor to turn in a reverse direction. The impact to the rotation of the motor depends on the magnitude of the current harmonics. A level of 20% distortion on the fifth harmonic means 20% of the energy is working against the motor. This has a serious impact both to the torque produced by the motor and the heat given off. This affects both production being run on the machine and the life of the motor. In our commercial example, harmonics are not usually removed. Removal of harmonics requires the use of filters or devices that minimize the effects on the circuit, and these are not always cost-efficient solutions. The alternative to removing harmonics is to minimize the effect they have on the system. Oversizing the neutral conductor or derating the existing transformers are possible solutions for a 3-phase, 4-wire system affected by triplen harmonics. While derating a motor is possible, it is more common to use snubbers or filters to reduce the effects of harmonics in an industrial facility

8 Disturbances The term disturbances is actually used to describe any kind of fluctuation in power. The most common types of disturbances are sags, swells, overvoltages, undervoltages, transients and outages. Sags, Undervoltages and Outages Sags are momentary decreases in voltage. This decrease is typically 80% of the normal voltage with a duration between 0.5 seconds and one minute. A decrease in voltage lasting longer than a period of one minute is called an undervoltage and a complete loss of power is called an outage. Sags occur when there is a momentary loss of available electricity due to the starting of heavy loads such as a motor or heavy machinery. Swells and Overvoltages Swells are the opposite of sags. They are momentary increases involtage up to 120% of normal with a duration between 0.5 seconds and one minute. This surge of energy may occur when a motor or heavy machinery is shut down abruptly. An increase in voltage lasting longer than a period of one minute is called an overvoltage. 12 Sags & Swells Though they are caused by different factors, sags and swells often follow each other as the system attempts to compensate. This further increases their potential to cause damage. Transients Transients are short-duration, high-amplitude pulses superimposed on a normal voltage waveform. They can vary widely from twice the normal voltage to several thousand volts and last from less than a microsecond up to a few hundredths of a second. Transients are caused by a rapid release of energy stored in an inductive or capacitive source in the electrical system, or from an external source such as lightning. Transient Voltage While the duration of transients is unnoticeable to a human observer, their effect on power quality is still considerable. A single lightning strike can result in a transient large enough to destroy electronic devices. Troubleshooting Disturbances Disturbances may require a certain degree of monitoring in order to properly diagnose. The nature of disturbances in industrial settings is often systematic but infrequent. By tracking a circuit over an extended period of time with the IDEAL Power Analyzer, data can be saved and analyzed later on a computer. This makes disturbances easier to pinpoint. Unlike harmonics, reoccurring disturbances are often fairly easy to eliminate once they ve been properly identified. For example, devices like surge protectors are a simple way to protect against transients. 13

9 IDEAL 800 Series Power Clamps When testing power quality on high-voltage circuits, a heavy-duty power clamp can help ensure accuracy and safety. The 800 Series Power Clamps are True RMS clamps capable of measuring 2000A AC and DC currents for commercial and industrial jobs. They are designed to measure true power, apparent power, reactive power and power factor in a single reading, bypassing the need for manual calculations. Another key feature of these clamps is their ability to measure both single-phase and three-phase circuits. Built to be rugged and versatile, the 800 Series is a necessity for commercial and industrial power quality jobs. 2000A AC/DC current capability Power measurements Data hold True RMS An easy-to-read dual display is a useful feature for viewing measurements like: power factor and kw, volts and amps, or frequency and volts. Calculates readings for both threephase, three-wire and three-phase, four-wire circuits Large, easy-to-read dual display See page 22 for features and ordering information

10 Circuit/Harmonics Analyzer In the past, measuring total harmonic distortion (THD) was a task for bulky and expensive equipment, but the SureTest Circuit Analyzer has changed that. The SureTest is designed to troubleshoot an electrical distribution system, analyzing both common circuit and power quality problems. It is the first handheld circuit analyzer capable of applying a full 15-amp load without causing interruption to equipment on the circuit. It identifies and locates loose connections, bad splices or receptacles, loose ground connections and high-resistance grounds. The SureTest model ST-1THD is specifically designed for commercial and industrial environments where electronic lighting and electronic equipment are present. The SureTest captures True RMS measurements, analyzes power measurements such as watts and power factor, and measures harmonic distortion to the 31st harmonic. Large, easy-to-read LED display Retractable ground prong Comfortable, ergonomic design Easy, one-button operation The SureTest Circuit Analyzer is used for a multitude of power quality measurements including total harmonic distortion (THD). See page 23 for features and ordering information

11 IDEAL Power Analyzer There are a number of instruments designed for in-depth examination of commercial and industrial power quality issues like harmonics and disturbances. What sets the IDEAL Power Analyzer apart from the rest is its versatility and ease-of-use. 1 MB of memory enables the saving of parameters and allows for long periods of testing. Information can then be downloaded to a computer for analysis. The Power Analyzer contains five base programs which comprehensively test every power quality issue discussed in this guide. The PowerVision analysis software creates a variety of tables and graphs to make in-depth analysis of power quality problems easier. It all adds up to the most complete, versatile and easy-to-use power quality tool anywhere. Easy-to-use push button operation Lightweight, portable design 1 MB memory Large, easy-to-use LCD display The versatility of the IDEAL Power Analyzer enables four testing programs to run simultaneously for extended durations of time. Comes standard with a full range of accessories for complete analysis See pages for features and ordering information

12 Technical Definitions D Ampere - A unit of measure for the rate of current flow. Measured in Amps. Apparent Power - Applied voltage multiplied by current.this is the power utilized by a load or electrical system. Measured in Voltamperes (VA). Frequency - The number of cycles per second that a wave form repeats itself. Measured in Hertz (Hz). Harmonics - A frequency that is an integer (multiple) of the fundamental frequency caused by electronic equipment. Harmonics cause distortion to the voltage and current waveforms. Harmonic Factorization - Analysis where the total harmonic distortion is broken down into the individual harmonics. Linear Loads - A load where the load impedance is constant. The relationship between the voltage and current drawn from the circuit are proportional. Examples of linear loads are motors and incandescent lighting. Negative Sequence Harmonics - Odd-numbered harmonics with a phase sequence opposite to the fundamental frequency (5th, 11th, 17th, etc.). They have a reversal effect on motors within an industrial facility. Non-Linear Loads - A load where the load impedance is not constant. The relationship between the voltage and current is unique to the type of load, resulting in harmonics on the circuit. Examples of non-linear loads are computers and variable speed machines. Odd-Numbered Harmonics - Odd-numbered integer of the fundamental frequency (60Hz). The 3rd harmonic of the fundamental frequency is 180Hz, the 5th is 300Hz, etc. Oddnumbered harmonics are typically created by non-linear loads. Outage - The total loss of AC power for greater that one minute. Outages typically last from 15 minutes to a few hours. Power Factor - The ratio of true power (watts) to the apparent power (voltamperes). It is an indication of the efficiency of an electrical system. Power Quality - A broad term used to describe the measurement of electrical power performance. Sag - A reduction in AC voltage up to 20% below nominal level lasting for a duration from one half cycle up to a few seconds. Swell - An increase in AC voltage up to 20% above nominal level lasting for a duration from one half cycle up to a few seconds. Transient - A release of positive or negative energy creating a disturbance within a single cycle of the AC waveform. Total Harmonic Distortion (THD) - The percentage of distortion to the fundamental frequency caused by harmonics within the electrical system. Triplen Harmonics - see zero sequence harmonics. True Power - The power extended when one ampere of current flows through a resistance of one ohm. Measured in Watts. Voltage - A unit of measure of the electrical pressure in an electrical system. Measured in Volts. Voltamperes - Applied voltage multiplied by current. This is the power utilized by a load or electrical system. Watt - Often referred to as true power. It is the power expended when one ampere of current flows through a resistance of one ohm. Zero Sequence Harmonics - Also called triplen harmonics, these are concurrent in direction with the fundamental frequency (3rd, 9th, 15th, etc.). They produce an amplitude that is triple any one phase when they combine on the neutral of a 3-phase, 4-wire electrical system

13 IDEAL 800 Series Power Clamps Common Features 2000A AC/DC current capability True RMS Kilowatts Data hold Auto ranging DC current zero function Oveload protection Lifetime limited warranty A AC/DC current capability kva kvar Power factor Frequency Dual display Memory recall IDEAL SureTest Circuit Analyzer Common Features Identify and locate high resistance connections, bad splices/receptacles, high resistance grounds Verify proper wiring and GFCI operation Test voltage drop under actual 15A load Test line voltage (ST-1THD) True RMS Power factor Harmonics Event recording Ground impedance Load on branch Dedicated circuits Isolated grounds False grounds AAC current capability 2500ADC current capability Temperature Analog output (current ranges) Relative mode Min/max Audible continuity Description Cat. No. 800 Series Power Clamp Series Power Clamp Description Cat. No. ST-1 Circuit Analyzer ST-1P+ Circuit Analyzer ST-1D Circuit Analyzer (120VAC) ST-1THD Circuit/Harmonics Analyzer ST-1THDC Circuit/Harmonics Analyzer for use with Amp Clamp ST-1THDC Circuit/Harmonics Analyzer Kit, Clamp Adapter Included Ground Continuity Adapter Isolated Ground Adapter Extension Cord Carrying Case Amp Clamp Adapter

14 IDEAL Power Analyzer Features Single- or three-phase measurements True RMS Data logging (1MB memory) Auto ranging Min/max/avg Energy and Harmonics Program PowerVision Software Optional programs: Disturbances Check-Meter Fast-Check Lightweight, portable design Easy-to-use push-button operation Password protected on-screen setup 160 x 160 pixel LCD RS-232 interface Customized data collection Real-time clock Programmable triggerpoints and start/stop time Auto display shutoff Rechargeable Ni-Cad battery Intelligent battery charging system Standard Equipment RS232 Interface/ Power Supply 1000AAC Clamp Adapters Power Analyzer Test Leads with Alligator Clips Power Measurements Kilowatts (kw) Voltamperes (VA) Inductive reactive power (kvarl) Capacitive reactive power (kvarc) Power factor (PF) Frequency (Hz) Kilowatt hours (kwh) Reactive power per hour (kvarhl, kvarhc) Harmonics Measurements Total harmonic distortion (%THD) Harmonic factorization to 51st harmonic 24 Description Cat. No. 800 Series Power Analyzer Disturbances Program Check-Meter Program Fast-Check Program /200AAC Clamp Adapter AAC Clamp Adapter

15 Test & Measurement IDEAL INDUSTRIES, INC. Technical Hotline Toll Free Becker Place, Sycamore, IL in U.S.A. Ajax, Ontario, L1S 2E1, Canada in Canada Warrington, Cheshire WA5 5TN, England No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any storage and retrieval system, without written permission. Form No. P 2110 Rev. 12/00 Printed in U.S.A IDEAL INDUSTRIES, INC.