How Does Three-Phase Power Quality Analyzer Factories Work?

By Randy Barnett

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The use of a three-phase power quality analyzer can be intimidating for those not familiar with power quality and the instrument. Learn the basics and then practice!

If the only power quality problems were created by single-phase nonlinear loads such as copy machines and printers, we might think the world of power quality measurement was a lot simpler. However, in the world we live in today, whether you're conducting power quality surveys or troubleshooting electrical system issues, you need a three-phase power quality analyzer. Setting up a power quality analyzer with five voltage leads and four amp clamps, and then selecting from various screens that that offer well over a dozen different parameters to measure and record, can all be intimidating. However, three-phase power quality analyzers such as the Fluke 435, as powerful as they are, are simple to use once you understand the basics of operation.

Monitoring three-phase power quality is a must. Whether you troubleshoot mysterious electrical problems or provide additional services to a client, it is three-phase power that is provided to commercial and industrial customers and three-phase power that is distributed throughout a facility.

Installing a three-phase analyzer

Unless you're troubleshooting a specific problem, a good place to start with a general power quality survey is the point of common coupling (PCC). The PCC is the point at which the electric utility and the customer interface occurs. For practical purposes, the PCC is the customer side of the utility revenue meter. Power quality analyzers should be used at a safe location downstream of the main disconnect and installed following all safe work practices.

The Fluke 435 power quality analyzer configuration screen indicates the appropriate analyzer lead to connect to certain specific conductors in the distribution system.

Before installing the three-phase analyzer, select the distribution system configuration on the instrument "setup" screen. The Fluke 435 offers ten different configurations. The three-phase Wye is most commonly used in commercial and industrial applications with voltages of 480Y/277 or 208Y/120. To avoid confusion when connecting leads, use the colored lead markers to match voltage and clamp leads to the color depicted on the analyzer configuration screen.

Always connect the ground lead first for safety, then the remaining voltage and current leads. Press "Scope" to check for proper connections and look for the proper rotation, verifying all leads are connected properly.

The Menu screen provides an overview of the many functions available on the power quality analyzer. Select the appropriate screen to begin monitoring parameters.

Measuring and analyzing data

Begin measuring and analyzing data by pressing Menu to select and set up the desired parameters to be analyzed. The Volts/Amps/Hertz screen is good place to start and to get the overall picture of system conditions. An important value is the Crest Factor (CF) indicated. CF is the ratio of peak voltage to RMS voltage. The amount the CF drops below 1.4 indicates the extent of flattening of the sine wave peaks. Sine waves that tend to flatten out do not allow the capacitors in power supplies to charge to their maximum value (these capacitors are designed to charge to the peak voltage). Capacitors not fully charged could result in problems, from computer lockups to spurious alarms on electronic equipment. Conversely, if the CF rises above 1.4 this indicates another type of distortion, and if peak voltage rises too high, it can cause component break down. It is important to note that an RMS multimeter would continue to read satisfactory values, while the CF has deviated away from the nominal 1.4 of the pure voltage sine wave to cause equipment problems. For this and other similar reasons, DMMs cannot be used to troubleshoot power quality problems.

Selecting Dips and Swells on the Fluke 435 menu will allow the user to view and record voltage variations over time. Sags (referred to as "dips" in the European standards) and swells are fairly common power disturbances. Sags and swells are short-duration voltage variations either down (sag) or up (swell) in the distribution system. Sags can result in improper operation of electronic equipment, motors tripping off the line, and even cause relays to chatter or drop out. Over a period of time swells can damage insulation and cause failure of electronic components.

Nonlinear loads, such as variable frequency drives (VFDs) and uninterruptible power supply (UPS) systems produce harmonic voltages and currents. Harmonic currents are integer multiple frequencies of the fundamental frequency (60 Hz). For example, the third harmonic is voltage and current that flows at 3 x 60 Hz, or 180 Hz. The fifth harmonic would be current at 300 Hz. Harmonic currents distort the fundamental (60 Hz) sine wave, causing improper operation of electronic equipment. The total harmonic distortion (THD) is the sum of the distortions created by harmonics and represents the magnitude of the total distortion. At 5 percent voltage THD the operation of loads may be affected. THD can be easily read on the power quality analyzer.

Harmonic currents, created by nonlinear loads such as VFDs and UPS systems, can create excessive distortion (THD) of the 60 Hz sine wave and cause overheating of conductors and equipment. Isolate sources of harmonics using the Fluke 435 Power Quality Analyzer.

The prevalence of certain harmonic frequencies may cause the overheating of neutral conductors, reverse torque and overheating in motors. The normal cycling of nonlinear loads will vary the frequency and magnitude of harmonic currents in the distribution system. By selecting the Harmonics function from the menu screen, you can view the harmonic frequencies and amplitudes present.

As utility costs increase, power and energy usage in facilities is of more and more concern. Power factor penalties can be significant - ranging into the tens of thousands of dollars per month for even a mid-size manufacturing facility. Power factor is a ratio of the true power being consumed in a facility (kW) to the apparent power (kVA) delivered by the utility. If too much apparent power is being delivered compared to the amount being used to do work, utility power factor penalties can result. By selecting Power and Energy from the menu screen, you can readily read power factor. Large motor loads causing power factor problems can be isolated and power factor correction capacitors installed - often totally eliminating power factor penalty charges.

Commercial and industrial customers may also pay peak demand charges. Peak demand is the maximum amount of kW used over a fifteen- or thirty-minute period. Utilities size their equipment to meet this demand and typically charge for kW usage based on peak demand values. With the power quality analyzer, kW, kVA and kVAR (reactive load) can all be monitored and, then, intelligent energy management decisions made.

Flicker is a perceived, unsteady wavering of light output due to voltage variations. Flicker is measured as both short term and long term values. Too much flicker means human discomfort and possible utility penalty charges. Selecting the Flicker screen from the menu while troubleshooting power quality problems can help isolate the cause of flicker such as, welders, arc-furnaces or cycloconverter generators.

Unbalanced voltages in a three-phase system occur when there is unequal loading between the three phases. Placing too many single-phase loads on one particular phase will result in a lower voltage on that phase as compared to the other two. Voltages to three phase motors will now be unbalanced. Variable frequency drives may produce increased harmonics and drive output can be affected. Voltage Unbalance is measured using the Unbalance screen and should not exceed 2 percent without corrective action taken.

Transients are very short duration changes in voltage typically occurring for only a fraction of a sine wave, but can create undesired effects. While a lightning strike may be considered the most severe transient, other causes such as the operation of large loads or capacitor banks also create problems. Failure of electronic equipment is one of the gravest issues caused by transients. Because of their very nature transients can only be captured and measured with specialized monitoring equipment. The Fluke 435 Transients function records voltage levels thus monitoring for transient conditions.

Inrush currents for motors when they are started may run from five to seven times (or more) of their normal full load current ratings. These large currents can cause significant voltage sags in the distribution system creating the problems mentioned earlier inherent with these sags. With the Inrush function of the Fluke 435 inrush current values can be measured over time as motors cycle on and off.

Utilities may use their power distribution system to carry higher frequency signals to switch appliances on and off (ripple control). Selecting Mains Signaling from the menu allows the Fluke 435 to capture when these signals occur, to aid in troubleshooting suspected signaling problems.

Selecting the Logger function from the Fluke 435 menu allows logging of several system parameters including voltage, amperage, energy and crest factor variances caused by harmonic distortion. The ability to download data collected over time and then to be able to compare that information to operation of plant equipment, such as large motors and nonlinear loads, can help in troubleshooting and identifying the source of power quality issues.

Reducing energy costs

Power quality analyzers such as the Fluke 435 are powerful measuring and recording tools that can not only diagnose and isolate unique electrical distribution system problems, but can help reduce energy costs as well. Payback times for the investment in such equipment and associated training can be infinitesimally small when downtime or equipment damage is considered. The key is finding a power quality analyzer that measures and records needed data, is easy to set up and use, and then provides for downloading and analysis of that data. For those already performing power quality surveys, or those anxious to learn the fundamentals of power quality - what to measure, what to look for and how - the Fluke 435 fits the bill.

This guide covers the basic theory and applications of power quality monitoring and analysis. Photo: TestGuy.

There are several ways in which electric power can be of poor quality. Improper wiring, incorrect grounding, and unbalanced loads are just a few examples of conditions that can produce electrical noise through a system and compromise power quality.

There is no such thing as perfect power quality in the real world. Service interruptions, equipment malfunctions, and excess power consumption are all common symptoms of poor power quality.

To minimize the risk of lost production and damage to electrical equipment, power quality analysis is employed to monitor a system for problems, identify the cause, and initiate corrective action. After collecting system data in the field, a power quality engineer will search for unusual events and determine the appropriate power conditioning equipment or other steps needed to resolve the issue.

Contents

Ideal Power Conditions

It is important that power serving electrical loads is &#;clean,&#; meaning voltage and current waveforms are relatively in phase, free of distortion, and balanced between each other. Low-quality power can increase utility bills and cause damage to critical power equipment, resulting in higher production costs and a greater chance of downtime.

An &#;ideal&#; three-phase power system has the following characteristics:

• The current is in phase with the voltage for each phase. Power Factor = 1.
• The phase voltage and currents are exactly 120 degrees apart and all equal to each other. No unbalance.
• The voltage and current sine waves are not distorted or interrupted in any way.
• The source impedance is zero, so that events at the load don&#;t affect the source voltage.
• The actual frequency is equal to the nominal frequency.

In an ideal 3-phase system, voltage and current waveforms are relatively in phase, free of distortion, and balanced between each other. Photo: Wikimedia.

No power system is &#;ideal&#; in the real world, but understanding these characteristics can help identify non-ideal power features of real systems. There is some acceptable range of deviation from the &#;ideal&#; for each application, which can be defined as &#;acceptable power.&#;

In the United States, acceptable limits for service voltage and utilization voltage are defined in ANSI C84.1. Power quality monitoring is employed to ensure that an electrical power system is operating within acceptable limits and to capture waveform distortion and other anomalies that may cause power interruptions or other system phenomena.

Power Interruptions

The most simple type of power quality problem occurs when power delivered to an electrical load goes away; this is called a &#;power interruption.&#; The different types of power interruptions are classified according to their duration.

• A momentary interruption is a complete loss of voltage on one or more phase conductors for a time period between 0.5 cycles and 3 seconds.

• A temporary interruption is a complete loss of voltage on one or more phase conductors for a time period between 3 seconds and 1 minute.

• A sustained interruption is a complete loss of voltage on one or more phase conductors for more than 1 minute.

A power interruption occurs when power delivered to an electrical load goes away. Photo: TestGuy.

Power interruptions are caused by many different sources, such as lightning strikes, utility switching operations, physical damage to power lines, and human error. A momentary power interruption could have serious or even dangerous results depending on the connected load, such as microprocessor-based or hospital equipment.

Undervoltage, Overvoltage, Sags, Swells

The second type of power quality problem occurs when the voltage at the load drops below a minimum rated voltage or climbs above a maximum rated voltage for some period of time. Depending on how long these conditions last, they may be referred to as undervoltage or overvoltage, and sags or swells.

• An undervoltage occurs when the RMS voltage drops below 90% of the nominal RMS voltage and stays at that level for more than one minute. The term &#;brownout&#; often refers to an intentional or unintentional drop in voltage in an electrical power supply system.

• An overvoltage is an event where the RMS voltage rises above 110% of the nominal RMS voltage and stays there for more than one minute.

Undervoltage and overvoltage occur when voltage at the load drops below a minimum rated voltage or climbs above a maximum rated voltage for longer than a minute. Photo: TestGuy.

• Sags occur when the RMS voltage decreases between 10% and 90% for a duration of a half-cycle to one minute. In a 60Hz power system, a complete sine wave lasts approximately 16 milliseconds, and a half cycle is approximately 8 milliseconds.

• Swells are defined as an increase in the rms voltage to over 110% for a duration of a half-cycle to one minute.

Sags and Swells occur on the power system when voltage drops below or exceeds nominal voltage for a short duration. Photo: TestGuy.

Reductions in voltage and sags usually occur when the RMS current to the load increases significantly. There are three categories of sags and swells, depending on their duration:

• 0.5 cycles to 30 cycles: Instantaneous
• 30 cycles to 3 seconds: Momentary
• 3 seconds to 1 minute: Temporary
• 1 minute+: Sustained Undervoltage or Overvoltage

Flicker, Transients and Noise

Repetitive voltage reductions in lighting circuits can be detected by the human eye, a phenomenon known as &#;flicker.&#; The term flicker refers to a very specific problem related to the human perception of light produced by incandescent light bulbs, not necessarily general voltage fluctuations.

Some common sources of flicker include: Arc welders, Electric boilers, Industrial motors, Lasers, Photocopying machines, Saw mills, and X-ray machines.

Flicker, transients, and noise examples. Photo: Various Sources.

Transients occur when spikes are superimposed on a voltage or current sine wave, ranging in amplitude from just a few volts to several thousand volts. Lightning and utility switching typically cause high-energy impulsive transients of short duration, while electronic devices, VFDs, and switching inductive loads typically cause low-energy transients continuously.

• Impulsive Transients last anywhere from 50 nanoseconds to >1 milliseconds
• Oscillatory transients last anywhere from 0.3 milliseconds to 5 microseconds

Noise refers to unwanted, high-frequency oscillations that are superimposed on an alternating voltage or current sine wave. This phenomenon is usually intensified by improper grounding and is capable of disrupting electronic devices such as computers and programmable controllers.

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Power Factor, Unbalance and Harmonics

Electrical loads are often composed of more than just pure resistance; the combination of resistance and reactance in an AC system is called impedance. Reactance comes in two forms: inductive and capacitive, neither of which contributes to &#;useful&#; work on the power system.

Power Factor is a way to characterize how much electrical power goes toward producing useful work such as light, heating, or machinery. A low power factor means a large amount of energy is being lost in the system in the form of wasted heat, which generally equates to higher energy bills and equipment degradation.

Three types of power - true, reactive, and apparent - relate to one another in trigonometric form. Photo: TestGuy.

Motors, solenoids, and pumps typically have impedances that are combinations of resistance and inductive reactance, which vary with the mechanical load on the machine. Capacitors have impedances that are combinations of a typically small resistance and a larger capacitive reactance component.

When reactance is present in an AC system, the voltage and current sine waves will shift out of phase from each other. Voltage leads current with inductive reactance, and current leads voltage with capacitive reactance; the two cancel each other out.

When reactance is present in an AC system, the voltage and current sine waves will shift out of phase from each other. Photo: Georgia State University.

Low power factor tends to occur in industrial facilities that contain a large number of motors or other inductive loads. Utility companies typically charge large industrial and commercial customers a higher rate for low power factor.

Unbalance occurs in three-phase power systems when single-phase loads (lighting, office equipment, etc.) do not draw the same amount of current on each phase, resulting in greater stress on the neutral conductor. An ideal condition occurs when the loads are balanced, meaning that the voltage and current phases are exactly 120 degrees apart from each other, although the currents might not be in-phase with the voltages.

Unbalance occurs in three-phase power systems when single phase loads do not draw the same amount of current on each phase. Photo: Sonel.

A balanced three-phase 4-wire wye system will have zero current on the neutral wire. The amount of current on the neutral wire in an unbalanced system will increase as the imbalance increases, which could result in overheating and the risk of fire.

Motors being driven by unbalanced voltages will result in a small motor torque working in the opposite direction from the motor rotation, a phenomenon known as counter-torque. When this condition occurs, part of the energy delivered to the motor will work against itself.

Harmonics are a type of waveform distortion that occurs in circuits containing semiconductor-based electronics such as LED lighting, switching power supplies, electronic ballasts, computers, robotics, test equipment, etc. These &#;non-linear&#; loads impose higher frequency sine waves on the system, resulting in more power lost in the form of wasted heat.

The excess heat produced by harmonics can have detrimental effects on a power system. Transformers are especially susceptible to damage caused by harmonics due to stray &#;eddy currents,&#; which circulate in the iron core and produce excess heat.

Harmonics are identified by their frequency in multiples of the &#;fundamental&#; or main frequency. Photo: Researchgate.

Harmonics are identified by their frequency in multiples of the &#;fundamental&#; or main frequency (60Hz in the United States). For example, the third harmonic in a 60 Hz system would be 180 Hz (60×3 = 180), and the 5th harmonic would be 300 Hz (60 x 5 = 300).

The magnitude of each harmonic frequency can be measured using power quality meters and is generally displayed in the form of a harmonic spectrum. Total harmonic distortion (THD) and total demand distortion (TDD) are sometimes used with power quality meters to simplify harmonic distortion as a single measurement rather than an entire spectrum.

How Power Quality is Measured

Several types of instruments are available for power quality measurement, each serving their own unique purpose. Power quality analyzers are the most commonly used tools to observe real-time readings and also collect data at high speeds for downloading to computers for analysis, as opposed to a power recorder or &#;data logger,&#; which is mainly used for simple voltage and current measurements.

Related: Test Equipment 101: The Basics of Electrical Testing

Oftentimes, power interruptions are unpredictable and of short duration, which can only be captured using a power quality meter (PQM) installed over a period of days, weeks, or months. Each phase in the system has a voltage probe and current sensor applied to monitor the magnitude and polarity of each channel over the specified period.

Several types of instruments are available for power quality measurement, each serving their own unique purpose. Photo: Fluke Corporation.

The place where the PQM is connected is called the measurement plane; everything to the right of the plane is considered part of the load, and everything to its left is considered the source. The measurement plane can be any point within the power system, not necessarily at the incoming service.

A cycle is the time that the waveform takes to travel from the zero line up to its positive peak, back down to its negative peak, and then back to zero. Power quality meters can be extremely high-speed devices designed to capture events down to the sub-cycle level.

In an ideal 60Hz system, one cycle takes 16.7 milliseconds, or 0. seconds. This is called the period of the wave, and is represented by the letter T. Frequency is equal to the inverse of the period, f = 1/0. = 60Hz.

Power Quality Analyzer Connection Example. Photo: Fluke Corporation.

The type of meter to install will depend on the data to be captured. For example, a simple ampere load evaluation or utility bill audit would require a far less sophisticated meter than trying to pinpoint the cause of a nuisance trip or other power interruption.

The most important factor to consider when performing power quality analysis is safety. Oftentimes, meters are applied live with equipment in service, which can be an extremely dangerous task. This type of work should only be performed by qualified personnel while observing all appropriate safety precautions. A local power outage at the monitoring location is always the safest way to install and remove a power quality meter.

The most important factor to consider when performing power quality analysis is safety. Photo: Fluke Corporation.

Power Quality Reports

A power quality meter can plot the voltage and current waveforms as functions of time; this is called an oscillogram. Data can be extracted from the power quality recorder and analyzed to determine the overall condition of the power system using various time plots and tables.

The actual data analysis is usually performed by an electrical engineer, who will generate a report that provides a summary of the various power conditions, a list of events that occurred during the analysis, and any corrective action or recommendations that should be considered.

Data can be extracted from the power quality recorder and analyzed to determine the overall condition of the power system using specialized computer software. Photo: Dranetz BMI Dranview

Power Quality Meters are capable of calculating a large number of power measurements at extremely high speeds. These measurements may include minimum, average, and maximum values for parameters such as:

• current and voltage RMS
• phase relationship between waveforms
• power factor and frequency
• active power (kW), reactive power (kVAr), apparent power (kVA)
• active energy (kWh), reactive energy (kVArh) and apparent energy (kVAh)
• harmonic spectrum, THD, TDD

Power Quality Meters are capable of calculating a large number of power measurements at extremely high speeds. Photo: Fluke PowerLog.

Techniques for Improving Power Quality

Depending on the results of the power quality analysis, a number of recommendations can be made to improve the quality of an electrical power system. Some of the common solutions found in power quality reports are briefly described below.

1. Voltage stabilizers (or regulators) may be used to provide precise voltage regulation to protect equipment from overvoltage, undervoltage, sags and swells.

2. Electronic equipment should be protected from transients with surge suppressors or surge protection devices, such as SPDs or transient voltage surge suppression devices &#; TVSS. Surge suppressors may be installed at the service entrance panels, distribution panels and/or individual loads to protect sensitive electronic equipment.

Electronic equipment should be protected from transients with surge suppressors. Photo: Square D.

3. Snubber circuits can be used on inductive loads to suppress the transient that naturally occurs when de-energizing the load. Typical snubber circuits use a resistor-capacitor (RC) circuit, a metal oxide varistor (MOV) or a diode.

4. Noise problems can be addressed by using line filters, isolation transformers, and line conditioners. Line filters are also called electromagnetic interference (EMI) filters or radio frequency interference (RFI) filters. They should be installed at branch panels or at any sensitive electronic load such as computers and medical equipment.

5. Low power factor can be corrected with the use of capacitor banks to cancel out inductive loads. The banks may be placed at each inductive load, or they may be installed upstream to protect a group of motors, or a single compensation system may be installed at the origin of the installation. In every case, the capacitor banks correct the power factor upstream of the bank, but not downstream.

6. Unloaded synchronous motors can be used to continuously correct a system&#;s power factor by adjusting the excitation of the synchronous motor&#;s field. The motor can be made to behave like a variable capacitor, a device referred to as a synchronous condenser.

125MVA synchronous condenser at Templestowe substation in Melbourne, Victoria, Australia. Photo: Wikimedia.

7. Unbalance can be corrected by redistributing single-phase loads onto different circuits to minimize the maximum unbalance over some period, such as a full week. Power quality meters are used to monitor current draw on all three phases and the neutral wire for several days or weeks at a time.

8. Harmonic filters can be used to attenuate harmonic distortion to acceptable levels. Each stage of a harmonic filter is composed of capacitors, inductors, and resistors designed to attenuate a specific harmonic frequency.

Power Quality Standards

There are a number of industry standards available that address the correct procedures and methods for performing a power quality analysis. These standards should be reviewed to help better understand the science behind monitoring and correcting power quality:

• ANSI C84.1 - American National Standard for Electric Power Systems and Equipment&#;Voltage Ratings (60 Hz)
• IEC - IEC standards on Electromagnetic compatibility
• IEEE 519 - IEEE Recommended Practice and Requirements for Harmonic Control in Electric Power Systems
• IEEE - IEEE Recommended Practice for Monitoring Electric Power Quality
• IEEE - IEEE Guide for Identifying and Improving Voltage Quality in Power Systems
• IEEE - IEEE Trial-Use Recommended Practice for Voltage Sag and Short Interruption Ride-Through Testing for End-Use Electrical Equipment Rated Less than V
• IEEE - IEEE Recommended Practices for Modulating Current in High-Brightness LEDs for Mitigating Health Risks to Viewers

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