Industrial Power Quality: Diagnose Before You Buy
A desk companion for the operator deciding whether to buy power quality protection. It covers how to read the warning signs, how to find where a disturbance starts, why grounding comes first, and how to buy only the protection that matches what you measured.
Who this is for
- ■Plant managers and facilities managers at industrial manufacturing plants dealing with unexplained equipment failures and downtime.
- ■Operations directors at healthcare facilities whose electronic equipment resets, overheats or fails early.
- ■Managers at water and wastewater treatment plants and large commercial buildings who are weighing a power conditioning or harmonic filter proposal.
- ■Anyone trying to tell whether a power problem comes from the utility or from inside their own building.
Do the problems in your own plant justify buying protective equipment, and which equipment matches which problem?
Industrial power quality is how clean and steady the electricity reaching your equipment is. The ideal is voltage that rises and falls in a smooth, steady, repeating wave. One full repeat of that wave is called a cycle. Poor power quality is any departure from that smooth wave: dips, jumps, sudden bursts, distortion or a loss of power. When the electricity reaching your machines dips, jumps or gets distorted, electronic equipment can malfunction, reset, overheat or fail early. You pay for that in downtime and replacement equipment.
Poor power quality costs a plant more today than it used to. Older electro-mechanical equipment could handle minor power quality issues with little or no effect on operations. Most plants have since replaced much of that equipment with electronic equipment: variable frequency drives, computers, chargers and inverters. Electronic equipment is far less tolerant of a dirty wave. It also draws power in uneven, rapidly changing patterns, so it creates disturbances as well as suffering from them.
The warning signs you can see from the plant floor
A PLC resetting for no reason
Trips and blown fuses
Equipment running hot
Backup power switching on
Lost or corrupted data
23%of this guide, read. The rest of it is below.
Where a power quality problem starts decides who fixes it, and most of the time it starts inside your building. Ubicquia, a company that sells power monitoring equipment, states that the majority of power quality disturbances originate inside the facility. Hartford Steam Boiler states that lightning, weather and utility operations account for only a small portion of all electrical disturbances. A large portion comes from equipment inside the building, or from neighboring businesses that share the building or sit close by. The internal sources it names include air conditioners, elevators, copiers and variable frequency drives.
Guessing at the source of a power quality problem gets expensive. If you assume the utility is the cause, you may wait on the wrong party for a fix. You may also buy protection and install it at the wrong point in your system.
MeasureA power quality survey finds where the problem starts
- 1 A power quality survey is a meter installed on your electrical system that records the power continuously while your plant runs.
- 2 The survey runs for days or weeks, because many disturbances come and go and a short test can miss them.
- 3 The survey runs during normal operations. Never during a shutdown.
- 4 Hartford Steam Boiler recommends that only electricians trained on power monitoring instruments perform it, and that surveys go to qualified power quality contractors.
Repair firstGrounding comes before any fix
Grounding is the set of conductors that connects your electrical system to earth and gives every piece of equipment the same electrical reference point. A common symptom of a grounding problem is heat on your grounding conductors or on your neutral, the wire that carries current back. An infrared survey finds that heat: it is a scan of your electrical gear with a camera that sees heat instead of light. Hartford Steam Boiler states that the power and grounding system should be the first thing addressed, for 4 benefits reasons.
Protects your people
Correct grounding is a personnel safety repair before it is anything else.Cuts neutral current
Fixing grounding reduces excessive current on the neutral conductor.Common reference
Your electronic equipment gets a common reference point to work from.Surge devices work
A surge protection device needs good grounding to divert a burst of voltage properly.A power quality survey records 5 categories core disturbances on your electrical system. Each one has a symptom you can see on the floor, a cause you can trace and a fix that matches it. The fix for one disturbance does nothing for another, which is why the survey comes before the purchase.
Disturbance What you see What causes it The matching fix Voltage transient (surge) Corrupted data, malfunctions, damaged equipment, interrupted processes, failed surge devices Switching-type loads; a high-energy burst shorter than a single cycle Surge protection devices in zones, supplementing built-in protection Harmonic distortion Excess heat, failing equipment, malfunctioning computer controls, lost data, a hot neutral Nonlinear loads: elevators, heating and cooling, rectifiers, welders, variable frequency drives A harmonic filter designed to the distortion your survey measured Voltage sag or swell PLC resets, a robotic line that stops, random malfunctions nobody can explain Utility system events, and large loads in your own plant starting or stopping A fast voltage regulator, protected PLC control power, or a motor generator Voltage imbalance Three-phase equipment running erratically, not running, or failing Single-leg loads spread unevenly across the legs, poor connections, blown fuses Rebalance loads and repair connections: maintenance work, early in the plan Interruption Frequent switching to backup power, electronics damaged after an outage A significant or complete loss of voltage, momentary or sustained A UPS sized to the criticality of the load, with maintained batteries Sags and swellsVoltage sags arrive more often than you think
How often voltage sags arrive, and what they cost nationally66sags/yearAverage sags per industrial facility per year60$ billion/yearAnnual cost to U.S. businessesAn average industrial facility sees a sag more than once a week, and the national bill lands in downtime, equipment wear and lost production.A study by EPRI, the Electric Power Research Institute, as cited by Rockwell Automation and reported by Ubicquia, found that industrial facilities experience an average of 66 sags/year voltage sags a year, and put the cost to U.S. businesses at 60 $ billion/year a year in downtime, equipment wear and lost productivity. That is more than one sag a week. If even one of your lines resets its PLC on each of those sags, you are restarting that line more than once a week. A sag or swell lasts from 0.5 cycles up to several seconds. Pushed slightly outside its design envelope, equipment malfunctions at random. Pushed far outside, it will not run and can fail early. The damage depends on how long the event lasts, how deep it goes and when it lands in your process.
The ANSI voltage-range standard, current version 2,020, sets the range your utility should hold your everyday voltage within: roughly 5% above or below the rated voltage on your equipment nameplate. That standard does not govern sags lasting a fraction of a second. For those, what counts is how much of a dip your own equipment can ride through, and the survey compares that against each recorded event. Often the cheaper fix for sags is protecting only the control power that feeds the PLC, the small supply of electricity that runs the controller itself.
HarmonicsHow a bent wave turns into a hot wire
Harmonic distortion is a bending of the smooth voltage wave's shape, caused by machines that draw current in short gulps instead of a smooth wave. Those gulps add extra current that repeats at multiples of the normal 60 Hz rhythm. That extra current does no useful work, but it still heats wires, motors and transformers. On the neutral wire, some of it piles up instead of canceling out, which is why the neutral runs hot. Your survey reports this as total harmonic distortion, a percentage that says how far the wave has bent from the clean shape. Higher means worse. If you put in variable frequency drives to save energy, that equipment belongs in this part of your plan.
IEEE, the Institute of Electrical and Electronics Engineers, publishes a recommended practice on harmonic distortion, current version 2,022. That guideline is a recommended practice and carries no force of law. It applies at the point where your service connects to the utility, and does not apply at each machine. It sets the most total harmonic distortion you should put back onto the utility's lines, and the allowed percentage depends on the size of your service. Hitachi Energy names utility penalties for breaking grid code, the utility's technical rules for connecting to its system, as one cost of poor power quality. Whether your utility charges that kind of penalty depends on your utility and your state's rules, so check your own tariff.
Power quality protection helps when your survey has identified the disturbance causing your failures, you have estimated what it costs and the equipment matches that disturbance. Protection can hurt when you buy it in general. Each of the beliefs below sends capital to equipment that never addresses the actual problem.
What operators assume What actually happens The utility is causing our problems. Most disturbances start inside the facility. Assume the utility and you wait on the wrong party for a fix. Our machines have built-in surge protection. Built-in protection is often an inexpensive varistor that may or may not be enough. Hartford Steam Boiler recommends supplementing it with field-installed devices. Any harmonic filter will fix our harmonics. A harmonic filter that was not designed to your measured distortion may not suppress it. A UPS means our critical loads are covered. A UPS with poorly maintained batteries can become the point of failure itself. Protect the whole facility to be safe. In many commercial and light industrial businesses only a few loads are harmed. The survey finds those few, and protecting them at the point of use can cost far less. Vendor claimsCheck who wrote the numbers
Much of the published material on power quality comes from companies that sell power quality equipment and services. The EPRI voltage sag cost figure reaches you through 2 companies before it reaches you from EPRI. Ubicquia states that fixed power quality meters often take 2 weeks to produce analysis, and that its own transformer monitoring samples 130 samples/cycle. That is the seller describing its own product. Treat it as a vendor claim until you can test it.
The order you buy power quality protection in is where you save money. The sequence below runs 6 steps, and the purchase is the last of them. The payback on any fix depends on what the problem costs you today, which is why you estimate that cost before you price the fix.
The order of operations for power quality protectionRepair and diagnosis come before any purchase, so the money goes only to protection that matches a measured problem. - 1 Fix your power distribution and grounding system.
- 2 Walk the plant with your electrician. Note the equipment installed, how much electronic equipment is concentrated in one place, any welders, power factor correction capacitors or variable frequency drives, heat discoloration on electrical gear, control or communication wiring running close to power wiring, the condition of the grounding, and whether surge protection is installed on power and data lines.
- 3 Commission a power quality survey from a qualified power quality contractor, running for days or weeks during normal operations.
- 4 Identify which disturbances are causing your actual failures.
- 5 Estimate what those failures cost you, because that number sets your budget.
- 6 Buy protection targeted at the specific machines being harmed.
Hartford Steam Boiler notes that in many commercial and light industrial businesses, only a few loads are harmed by poor power quality. The survey finds those few loads. Your contractor may also raise isolation transformers, which filter high-frequency electrical noise and give sensitive equipment its own local ground reference. The same rule applies: buy one when the survey shows the problem it fixes.
TransientsSurge protection belongs in zones
Zone oneService entrance
Where power enters your building.Zone twoDistribution panels
The panels that feed equipment around the plant.Zone threePoint of use
Right at the machine, supplementing any built-in varistor.For the vendorQuestions that expose a weak proposal
- 1 Which disturbance did you measure, and on which machines?
- 2 How long did the survey run, and was the plant running normally?
- 3 Was the grounding checked and corrected first?
- 4 Was the harmonic filter designed to the distortion measured in our survey?
- 5 What does the problem cost us today, and how was that number built?
This weekWhat you do this week
- 1 Pull your maintenance log and mark every unexplained breaker trip, blown fuse, PLC reset, hot piece of equipment and switch to backup power.
- 2 Write down what each of those events cost you in downtime and repairs.
- 3 Ask your electrician for an infrared survey of your grounding conductors and neutrals.
- 4 Walk the plant with your electrician using the walk-through checklist above.
- 5 Get a quote for a power quality survey from a qualified contractor that runs for days or weeks during normal production.
- Decision matrix
When power quality protection is worth buying
✓ Worth acting on when- Your maintenance log shows unexplained trips, blown fuses, PLC resets or hot equipment.
- A survey run for days or weeks during normal production has identified the disturbance causing the failures.
- You have put a dollar figure on what those failures cost you today.
- The protection you are pricing matches the measured disturbance on the specific machines it harms.
✗ Hold off when- Grounding and distribution have not been checked and corrected.
- No survey has run, or it ran for a short window or during a shutdown.
- The proposal covers the whole facility and names no specific machines.
- The vendor cannot say which disturbance was measured or what it costs you.
- The harmonic filter was not designed to distortion measured in your plant.
Questions for your morning huddle- How many unexplained breaker trips, blown fuses and PLC resets did we log in the last 12 months, and what did each one cost us?
- When did we last check our grounding, and has anyone run an infrared survey of our grounding conductors and neutrals?
- For our engineer: has a power quality survey ever run on our system for days or weeks during normal production, and how does our measured total harmonic distortion compare with the IEEE harmonic limit at our connection point?
- Does our current surge protection cover the service entrance, the distribution panels and the point of use, or are we relying on what is built into the machines?
The one thing to rememberFix the grounding and measure before you buy. Then buy only the protection that matches the disturbance you measured, on the machines it is actually harming.
This week, pull your maintenance log, mark every unexplained trip, blown fuse, PLC reset and switch to backup power, write down what each cost, and ask your electrician for an infrared survey of your grounding conductors and neutrals.
Know if the numbers actually pencil out before you sign anything.
A written second opinion on the project in front of you, whether that is a rate change, new equipment, or a renewable installation.
- 01A short call, to figure out quickly whether we can actually be helpful. If we can't, we'll say so on the spot.
- 02We pull the data, your bills, your rate structure, vendor proposals, project specs.
- 03You get the verdict in writing: whether the payback will materialize, and the opportunities or risks nobody has raised.
Get a Blueprint at blueprint.tac-nrg.com Free for Indiana-based operations spending five figures or more a month on electricity. No obligation. You keep the write-up either way. how to tell if a power problem is from the utility or inside our building
Run a power quality survey: a meter installed on your electrical system that records power continuously for days or weeks while the plant runs normally, never during a shutdown. Hartford Steam Boiler, an equipment insurer, states that lightning, weather and utility operations account for only a small portion of electrical disturbances. Ubicquia, a monitoring vendor, states that most originate inside the facility. The survey data settles whose problem it is, and the fix starts once that question is answered.
is it worth installing a harmonic filter
A harmonic filter is worth buying only after a power quality survey has measured your total harmonic distortion and you have estimated what that distortion costs you in heat, failed equipment and downtime. The filter should be designed to suppress the specific distortion the survey measured. A filter bought before the survey is a guess, and a filter not designed to your measured distortion may not suppress it.
do I need surge protection if my equipment has it built in
Usually yes. Built-in surge protection in machines is often an inexpensive component called a varistor, which may or may not be enough. Hartford Steam Boiler recommends supplementing it with field-installed surge protection devices in 3 zones: the service entrance, the distribution panels and the point of use at the machine. Fix grounding first, because a surge protection device on poor grounding may not work properly.
how long should a power quality survey run
A power quality survey should run for days or weeks during normal production. Many disturbances come and go, and a short test can miss them. A survey run during a shutdown records a plant that is not doing what it normally does. Hartford Steam Boiler recommends that only electricians trained on power monitoring instruments perform it, and that surveys go to qualified power quality contractors.
how much do voltage sags cost a manufacturing plant
A study by EPRI, the Electric Power Research Institute, as cited by Rockwell Automation and reported by Ubicquia, found that industrial facilities average 66 sags/year voltage sags a year, and put the cost to U.S. businesses at 60 $ billion/year a year in downtime, equipment wear and lost productivity. That is a national figure. Your plant's number is what each restart and repair costs you, times how often your lines trip, which is why you pull your maintenance log before you price a fix.
does the IEEE harmonic distortion limit apply at every machine
No. The IEEE recommended practice on harmonic distortion, current version 2,022, is a recommended practice without force of law, and it applies at the point where your service connects to the utility. It sets the most total harmonic distortion you should put back onto the utility's lines, and the allowed percentage depends on the size of your service. Ask your engineer for the limit at your connection point next to your survey's measured percentage. Whether your utility penalizes you for exceeding it depends on your utility and your state's rules, so check your tariff.
how much do voltage sags cost a manufacturing plant
A study by EPRI, the Electric Power Research Institute, as cited by Rockwell Automation and reported by Ubicquia, found that industrial facilities average 66 sags/year voltage sags a year, and put the cost to U.S. businesses at 60 $ billion/year a year in downtime, equipment wear and lost productivity. That is a national figure. Your plant's number is what each restart and repair costs you, times how often your lines trip, which is why you pull your maintenance log before you price a fix.
does the IEEE harmonic distortion limit apply at every machine
No. The IEEE recommended practice on harmonic distortion, current version 2,022, is a recommended practice without force of law, and it applies at the point where your service connects to the utility. It sets the most total harmonic distortion you should put back onto the utility's lines, and the allowed percentage depends on the size of your service. Ask your engineer for the limit at your connection point next to your survey's measured percentage. Whether your utility penalizes you for exceeding it depends on your utility and your state's rules, so check your tariff.
- Power quality
- How close the electricity reaching your equipment comes to the ideal: voltage that rises and falls in a smooth, steady, repeating wave. Poor power quality is any departure from that wave.
- Voltage sag and swell
- A drop (sag) or rise (swell) in voltage lasting from 0.5 cycles up to several seconds, caused by utility events or large loads in your plant starting and stopping.
- Voltage transient
- Also called a surge. A sudden, high-energy burst in voltage that typically lasts less than 1 cycle, caused by equipment that switches its power on and off.
- Harmonic distortion
- A bending of the smooth wave's shape in voltage and current, caused by nonlinear loads. The extra current does no useful work but heats wires, motors, transformers and the neutral.
- Total harmonic distortion
- The percentage a power quality survey reports for how far the wave has bent from its clean shape. Higher means worse.
- Nonlinear load
- Equipment that switches its power draw on and off momentarily instead of drawing power smoothly, such as variable frequency drives, rectifiers, welders, elevators and heating and cooling equipment.
- Grounding
- The set of conductors that connects your electrical system to earth and gives every piece of equipment the same electrical reference point. It is the first thing to fix.
- Surge protection device
- Equipment that gives a burst of voltage an easy path to ground so the energy goes there instead of into your machines. Installed in zones from the service entrance to the point of use.
- Power quality survey
- A meter installed on your electrical system that records power continuously for days or weeks during normal operations, never during a shutdown, to find which disturbances are present and where.