• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Electrical Engineering News and Products

Electronics Engineering Resources, Articles, Forums, Tear Down Videos and Technical Electronics How-To's

  • Products / Components
    • Analog ICs
    • Connectors
    • Microcontrollers
    • Power Electronics
    • Sensors
    • Test and Measurement
    • Wire / Cable
  • Applications
    • Automotive/Transportation
    • Industrial
    • IoT
    • Medical
    • Telecommunications
    • Wearables
    • Wireless
  • Resources
    • DesignFast
    • Digital Issues
    • Engineering Week
    • Oscilloscope Product Finder
    • Podcasts
    • Webinars / Digital Events
    • White Papers
    • Women in Engineering
  • Videos
    • Teschler’s Teardown Videos
    • EE Videos and Interviews
  • Learning Center
    • EE Classrooms
    • Design Guides
      • WiFi & the IOT Design Guide
      • Microcontrollers Design Guide
      • State of the Art Inductors Design Guide
    • FAQs
    • Ebooks / Tech Tips
  • EE Forums
    • EDABoard.com
    • Electro-Tech-Online.com
  • 5G

The many measurements of power quality

June 21, 2022 By Lee Teschler

There’s a confusing variety of ways to quantify power consumption. Make sure you understand what your favorite power metric means.

To most engineers, the concept of power quality pertains to characteristics of the ac line feeding grid energy to equipment in a facility. But variations of the “power quality” term now can refer not just to the ac line but also to properties of devices connected to the ac mains. Thus it may be useful to review the basics of power quality and some of its newer interpretations.

First consider an “ideal” three-phase power system. Here the current is in phase with the voltage for each phase, the phase voltage and currents are exactly 120° apart and all equal to each other, the voltage and current sine waves are not distorted the source impedance is zero, so events at the load don’t affect the source voltage, and the actual frequency is equal to the nominal frequency.

Of course, no real-world power system is ideal. There is an acceptable range of deviation. In the U.S. ANSI C84.1 defines the acceptable limits for service voltage and utilization voltage. Power Factor is one of the properties it defines. A power factor of one is ideal, meaning ac voltage and current sinewaves are exactly in phase with one another. Capacitive and inductive impedances tend to cause power factors less than one. Motors, solenoids and pumps typically have impedances containing inductive reactance, which vary with their mechanical load. Capacitors have impedances that are combinations of a typically small resistance and larger capacitive reactance component.

Reactance present in ac systems shifts the voltage and current sine waves out of phase from each other. Voltage leads current with inductive reactance and current leads voltage with capacitive reactance. Low power factor tends to arise in industrial facilities containing numerous motors or other inductive loads. Electric utilities typically charge large industrial and commercial customers a higher rate for low power factor loads.

Unbalance arises in three-phase power systems when single phase loads (lighting, office equipment, etc.) draw unequal amounts of current on each phase. This kind of load causes greater stress on the neutral conductor. Ideally loads are balanced, meaning the voltage and current phases are exactly 120° apart from each other, though the currents might not be in-phase with the voltages. A balanced three-phase four-wire wye system will have zero current on the neutral wire. The amount of current on the neutral wire in an unbalanced system rises with the unbalance, potentially causing overheating and a risk of fire.

Motors driven by unbalanced voltages generate a phenomena known as counter-torque where a small motor torque works in the opposite direction from the motor rotation. Thus part of the energy delivered to the motor works against itself.

Harmonics are a form of waveform distortion arising in circuits containing non-linear loads primarily characterized by switching power supplies. These non-linear loads may impose higher frequency sine waves on the ac input, causing a power lose in the form of wasted heat. The excess heat produced by harmonics can be detrimental to a power system. Transformers are especially susceptible to damage caused by harmonic eddy currents which circulate in the iron core and produce excess heat.

Harmonics are multiples of the main frequency, 60 Hz in the U.S. For example, the third harmonic in a 60 Hz system is 180 Hz and the fifth harmonic is 300 Hz. Power quality meters can display the magnitude of each harmonic frequency. They may also read out total harmonic distortion (THD) and total demand distortion (TDD) to provide a single harmonic distortion measurement rather than an entire spectrum.

PQR

The widespread use of power quality metrics has given rise to more specialized but similar measurements often aimed at individual ac loads or ac-powered appliances. One

The point of the PQR measurement devised by 3DFS is to make real-time corrections in power consumption as in this example.

such measurement is the power quality rating or PQR, a metric created by N.C.-based engineering firm 3DFS. An electrical network with a PQR of 28% utilizes 28% of the energy consumed as electricity and the remaining 72% as heat or vibration somewhere in the electrical network.

equation

3DFS defines its PQR metric for each of the three phases and factors in both THD and phase lag/lead (cos ℘) between voltage and current.

In a nutshell, 3DFS claims ordinary power quality measurements are incomplete because they typically are calculated by some combination of harmonic distortion and reactive power. The problem, says 3DFS, is that this measurement typically doesn’t consider whether there are imbalances across phases. PQR is meant to be a more informing metric that includes such conditions. The point of this exercise is to correct for harmonics and reactive power while simultaneously balancing the phases as power flows in real time. This is something 3DFS claims it can do via something it calls a software-defined power controller.

bijou

Though any device can theoretically get PQS, Bijou is targeting smaller power-consuming devices, enforcing a 2.4 kW or 2.4 kVA upper limit.

To complicate matters somewhat, there is a similar sounding metric called a power quality score, PQS. This one comes from Bijou Electronics in New York. Rather than being a metric for power consumption in a facility, PQS is aimed at individual power consuming appliances. Bijou sees PQS as potentially an energy efficiency benchmark for any device that gets plugged into the power grid. PQS is a combined metric containing power factor, efficiency or efficacy, and THD. PQS is a single number rating of power quality at each device setting or at several load settings, typically 0, 0.1, 10, 25,50, 75, and 100% load for a power supply or power adapter. Bijou has published PQS results for a number of consumer devices and typically gives results at three points, idle, average, and max PQS. Bijou defines PQS as having a value from 0 to 200—it says the reason for going to 200 rather than something smaller is to provide more detail when comparing products. This helps find differences between various power consuming devices of similar types which may bunch up if made with the same basic topology.

Though any device can theoretically get PQS, Bijou is targeting smaller power-consuming devices, enforcing a 2.4 kW or 2.4 kVA upper limit. Bijou tests consumer devices and assigns a PQS score and publishes the results online. As of this writing, the firm has published results for products that include various light bulb technologies, fans, power adapters, transformers, humidifiers, power supply modules, display monitors, and even an electric blanket.

You may also like:


  • Now out: The new Test & Measurement Handbook

  • Why I’m divided on “Right to Repair”
DesignFast Banner version: 12cf851b

Filed Under: FAQ, Featured, Test and Measurement Tips Tagged With: FAQ

Primary Sidebar

EE Training Center Classrooms

EE Classrooms

Featured Resources

  • EE World Online Learning Center
  • CUI Devices – CUI Insights Blog
  • EE Classroom: Power Delivery
  • EE Classroom: Building Automation
  • EE Classroom: Aerospace & Defense
  • EE Classroom: Grid Infrastructure
Search Millions of Parts from Thousands of Suppliers.

Search Now!
design fast globle

R&D World Podcasts

R&D 100 Episode 7
See More >

Current Digital Issue

Our second 5G Handbook is now available

Featuring 15 articles, the 2022 5G Handbook looks at private networks, timing, connectivity, latency, mmWaves, test, and other topics.

Digital Edition Back Issues

Sponsored Content

Positioning in 5G NR – A look at the technology and related test aspects

Radar, NFC, UV Sensors, and Weather Kits are Some of the New RAKwireless Products for IoT

5G Connectors: Enabling the global 5G vision

Control EMI with I-PEX ZenShield™ Connectors

Speed-up time-to-tapeout with the Aprisa digital place-and-route system and Solido Characterization Suite

Siemens Analogue IC Design Simulation Flow

More Sponsored Content >>

RSS Current EDABoard.com discussions

  • Using LTspice to check Current sense transformer reset?
  • Plotting E_theta and E_phi using the fields calculator in HFSS
  • SRF04 module measure distance
  • Motherboard - worst case scenario
  • Will Wifi throughput be affected by RSSI (attenuation) in my setup?

RSS Current Electro-Tech-Online.com Discussions

  • Are Cross-wind compensation and Road crown compensation functions inputs to LKA function?
  • Interfacing ZMOD4410 with Arduino UNO
  • Help diagnosing a coffee maker PCB
  • Capacitor to eliminate speaker hum
  • Identify a circuit.

Oscilloscopes Product Finder

Footer

EE World Online

EE WORLD ONLINE NETWORK

  • 5G Technology World
  • Analog IC Tips
  • Battery Power Tips
  • Connector Tips
  • DesignFast
  • EDABoard Forums
  • Electro-Tech-Online Forums
  • Engineer's Garage
  • Microcontroller Tips
  • Power Electronic Tips
  • Sensor Tips
  • Test and Measurement Tips
  • Wire & Cable Tips

EE WORLD ONLINE

  • Subscribe to our newsletter
  • Lee's teardown videos
  • Advertise with us
  • Contact us
  • About Us
Follow us on TwitterAdd us on FacebookConnect with us on LinkedIn Follow us on YouTube Add us on Instagram

Copyright © 2022 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy