Power quality made simpler
Understanding power quality (PQ) is a challenge for many companies, but using a management process can help users realize where “dirty” power is coming from and help mitigate the effects for a more energy-efficient company.
Power quality (PQ) is a big deal for most owners and facility managers looking to improve energy efficiency. Many have already addressed the low-hanging fruit. Generators and uninterruptible power supply (UPS) systems protect against loss of power or voltage deviations. Surge suppression devices protect against spikes. Capacitor banks address poor power factor. However, there is more work to be done.
A study conducted by the European Copper Institute in 2012 found 40% of unplanned outages are caused by PQ disturbances. The same study also concluded that 4% of lost annual revenue can be attributed to PQ issues.
According to a May 2017 Research & Markets report, "The global power quality equipment market is valued at $29.74 billion in 2017 and is expected to grow…from 2017 to 2022, reaching $40.8 billion." Anyone who manages a facility or electrical distribution system won’t find these facts surprising. Several factors have increased attention to PQ:
- An aging electrical infrastructure
- The proliferation of renewables and distributed generation
- The unintended consequences of energy efficiency.
"Dirty" power puts a company’s equipment and facility at risk every day. It reduces capacity, shortens asset life expectancy, and can result in downtime with significant impact to the company’s bottom line. "Dirty" power is the silent killer within a facility’s electrical distribution system.
The challenge most facility owners are faced with is a lack of actionable information regarding PQ. Though the number of PQ analyzers, monitors, and meters have increased in the past two decades, for the typical facility manager or engineer, PQ is complicated and intimidating. However, in the hands of a PQ expert, the data from these tools can become meaningful and useful.
What is power quality?
In an ideal three-phase power system, voltages are at a nominal magnitude, at nominal frequency, and perfectly balanced with a perfect sinusoidal waveform. Any disturbance of one of four parameters-magnitude, frequency, waveform, and symmetry-is classified as a PQ problem.
Many different PQ disturbances can have a negative impact on the electrical system and equipment. Common disturbances that impact PQ include—but aren’t limited to—interruptions, sags, undervoltage, harmonics, and frequency variations.
For having such a large potential to seriously devastate an industrial infrastructure, PQ events are largely untracked and undetected.
Most owners are familiar with the consequences: plant downtime, premature equipment failure, utility bill surcharges, reduced electrical capacity, and impact to facility communications. When it comes to identifying and quantifying the causes however, most owners do not have the tools and systems to manage PQ in their facilities.
PQ events will increase in frequency. An aging infrastructure means higher risk of disruptions. Renewable energy helps lower the cost of energy, but brings intermittency and grid stiffness challenges. Energy conservation measures such as variable speed drives and LED lights introduce harmonics that result in excessive heat, lost capacity, and surcharges.
A simple PQ management process, depicted in Figure 1, can help companies stop "dirty" power from happening within facilities. This process has three steps that companies and managers need to take in order to make the process successful.
Step 1: Measure PQ, place meters
PQ first needs to be measured in order to understand the process. Selecting the correct meter is important. Understanding what will be measured is even more important.
Since PQ meters generally cost more than basic power and energy meters, users need to be place the meters strategically. For example, if disturbances originate externally and internally to your facility, place PQ meters with disturbance direction capability on the main service feeds.
Users also need to determine which types of disturbances are "system" versus "isolated" in nature. For example, if the concern is about voltage total harmonic distortion instead of current total harmonic distortion, the metering approach will differ.
Gaining a better understanding of the types of disturbances happening in a facility will help regarding PQ meter selection and placement decisions. If a company does not have existing meters, one option is to engage a PQ professional for a PQ assessment using portable meters and analyzers.
A PQ assessment will allow the user to categorize disturbance types based on economic impact. In general, voltage dips and transients are the disturbances that cause the highest economic impact. This information will come in handy when asked to justify the investment to mitigate PQ risk.
Level 3 PQ meters are basic power and energy meters that provide harmonics measurements. Level 3 meters should be installed on feeders and branch circuits deep within an electrical distribution system. Level 2 meters, mid-range PQ meters, typically add waveform capture with sag/swell detection, disturbance direction, and limited PQ compliance reporting (EN50160 and IEC61000-4-30). Level 2 meters can be installed at primary medium or low voltage distribution switchgear.
The most advanced PQ meters, Level 1, should be installed on service mains as well as other equipment associated with power delivery, such as generator switchgear. Level 1 meters have full PQ compliance reporting, can detect transients, impulsive disruptions, and flicker, and have comprehensive harmonics analysis capabilities.
It also is important to understand what thresholds to use when measuring the different types of disruptions. IEEE 1159 is an industry standard that defines a set of recommended practices for monitoring electric PQ (see Table 1).
Step 2: Understand, interpret PQ measurements
The second step in the PQ management process is to understand and interpret PQ measurements. Analysis includes the interpretation of recorded data and evaluation of PQ’s impact on electrical installation and equipment. Analysis can be performed regularly (for example, once per month) or ad hoc (when there is a problem caused by a potential PQ disturbance).
Experienced professionals usually perform analysis with specific competencies in PQ, electric installation, and equipment. They are capable of correlating PQ disturbances with equipment damage, malfunction, or electrical installation downtime.
Because facility managers and engineers are not always PQ experts, they may have difficulties interpreting and benefitting from PQ data.
The current trend is to embed analysis and expertise capabilities into PQ monitoring systems. Such systems provide meaningful dashboards and appropriate widgets to analyze PQ problems. A good system will pre-process PQ data, scrub it, categorize it, normalize it, and present it in an actionable, easy-to-interpret manner.
A facility manager can view PQ metrics on a high-level PQ dashboard and gain valuable insight into important trends within a facility. A good electrical power management system will incorporate PQ dashboards just as it would energy dashboards for managing energy efficiency in your facility.
For short-term PQ disturbances or events such as voltage sags, swells, transients, and interruptions, using statistical widgets, pie charts, or counters is recommended. Relevant information will include the number of events for a given timeframe, and a breakdown by type of event, origin (downstream or upstream), and estimated impact (likely impact or no impact).
This type of information can help electrical engineers evaluate the operating conditions of the electrical installation and detect if a PQ problem is at the origin of a power outage or equipment failure.
Some dashboards simplify PQ analysis by associating green-yellow-red color code indicators to each PQ disruption type. Using this dashboard, a user can see areas of concern, then drill down to more detailed information to perform root cause analysis.
A good system also should address the cost aspects of PQ, estimating losses due to poor PQ. Putting a price tag on PQ issues makes it easier to perform the cost-benefit analysis, and facilitates return-on-investment evaluations of PQ monitoring systems.
Step 3: Act on the information provided
After analyzing the PQ events in your facility and understanding the potential costs they may have, facility managers and engineers are in a much better position to develop a PQ plan. This plan may be an investment in PQ mitigation equipment, electrical system design and architecture modifications, settings modifications, selection of equipment that is less sensitive to PQ events, and/or discussions with the electric utility about the quality of electrical service delivery. Once a prioritized plan has been developed, the user will want to measure and interpret the results of the PQ mitigation strategy using the same process depicted in Figure 1.
Some examples of PQ corrective equipment are given in Table 2 below:
Identify, prioritize, eliminate
PQ events happen every day in a facility. They are the silent killer within an electrical distribution system. Owners, facility managers, and engineers no longer should be intimidated by the complex nature of PQ. Today’s advanced meters, combined with easy-to-use software systems and the iterative process presented within, provide a simple methodology for identifying, prioritizing, and eliminating PQ in a facility.
Allan Evora is founder of Affinity Energy. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, email@example.com.
Standard view: Some standards related to power quality
- EN50160 — Voltage Characteristics in Public Distribution Systems
- IEC 61000-4-30: Testing and Measurement Techniques — Power Quality Measurement Methods
- IEEE 1159-2009 — IEEE Recommended Practice for Monitoring Electric Power Quality
About the author
Allan Evora is a Certified Measurement & Verification Professional (CMVP). He established Affinity Energy in 2002 and the company is certified as a Schneider Electric Critical Power EcoXpert.
"Power Quality Equipment Market – Global Forecast to 2022," Research and Markets, May 2017
Affinity Energy is a CSIA member.