Ongoing testing and monitoring tools help determine waste caused by harmonics and unbalance, and prevent work stoppages.
From Fluke Corp.
Productivity is the key to survival in today’s globally competitive environment. When you think about the basic inputs to production — time, labor and materials — optimization usually isn’t an option. You have 24 hours per day, labor is costly, and you don’t have much choice in materials. Thus, every company must use automation to gain more output from the same inputs, or perish.
So, we rely on automation, which in turn relies on clean power. Power quality problems can cause processes and equipment to malfunction or shut down. The consequences can range from excessive energy costs to complete work stoppage. Obviously, power quality is critical.
The interdependence of various systems adds layers of complexity to power quality issues. Your computers are fine, but the network is down, so nobody can book a flight or file an expense report. The process is operating correctly, but the HVAC has shut down and production must stop. Mission-critical systems exist throughout the facility and throughout the enterprise — power quality problems can bring any one of these to a grinding halt at any time. And that will usually be the worst possible time.
Power Quality Problems
Where do power quality problems come from? Most originate inside the facility. They may be due to problems with:
- Installation — improper grounding, improper routing or undersized distribution.
- Operation — equipment operated outside of design parameters.
- Mitigation — improper shielding or lack of power factor correction.
- Maintenance — deteriorated cable insulation or grounding connections.
Even perfectly installed and maintained equipment in a perfectly designed facility can introduce power quality problems as it ages.
Using instruments that measure power quality issues generated by harmonics and unbalance can help determine waste. Those instruments then can quantify the cost of that waste based on the unit cost of power from the utility.
Power quality problems also can originate from outside the facility. We live with the threat of unpredictable outages, voltage sags and power surges. How do you quantify the cost?
Measure Power Quality Costs
Power quality problems make their effects felt in three general areas: downtime, equipment problems and energy costs.
Downtime. To quantify system downtime costs, you need to know two things:
- The revenue per hour your system produces.
- Your production costs.
Also consider the business process. Is it a continuous, fully utilized process (such as a refinery)? Must your product be consumed when produced (such as a power plant)? Can customers switch instantly to an alternative if the product is not available (such as a credit card)? If the answer to any of these questions is yes, then lost revenue is difficult or impossible to recover.
Are you an OEM producer? If you can’t make timely deliveries, your customer may switch to a source that can.
Equipment problems. Exact costs are hard to quantify because you are dealing with many variables. Did that motor really fail from excess harmonics, or was there some other cause? Is Line Three producing scrap because variations in the power supply are causing variations in machine performance?
To get the correct answers, you should:
- Troubleshoot the root cause.
- Determine the actual costs.
Energy costs. To reduce your power bill, record consumption patterns and adjust the system and load timing to reduce one or more of the following:
- Actual power (kWh) usage.
- Power factor penalties.
- A peak demand charge structure.
Until now, capturing energy waste costs caused by power quality issues was a task for more experienced engineers. Waste costs could be calculated only by serious number crunching, as a direct measurement of the waste and monetization wasn’t possible. In modern products with patented algorithms, waste resulting from common power quality issues such as harmonics and unbalance can be measured directly. By inputting the cost of energy into the instrument, the cost is calculated directly.
Reduce Power Usage and Associated Expenses
You can reduce power usage by eliminating inefficiencies in your distribution system. Inefficiency sources include:
- High neutral currents from unbalanced loads and triplen harmonics.
- Heavily loaded transformers, especially those serving non-linear loads.
- Old motors, old drives, and other motor-related issues.
- Highly distorted power, which may cause excessive heating in the power system.
You can avoid power factor penalties by correcting for power factor. Generally, this involves installing correction capacitors. But first correct for distortion on the system — capacitors can present low impedance to harmonics, and installing inappropriate power factor (PF) correction can result in resonance or burned out capacitors. Consult a power quality engineer before correcting PF if harmonics are present.
You can reduce peak demand charges by managing peak loading. Unfortunately, many people overlook a major component of this cost — the effect of poor power quality on peak power usage — and thus underestimate their overpayments.
To determine the real costs of peak loading, identify the following:
- “Normal” power usage.
- “Clean power” power usage.
- Peak loading charge structure.
By eliminating the power quality problems, you reduce the size of the peak demands and the base from which they start.
By using load management, you control when specific equipment operates and thus how the loads “stack on top of each other.” For example, your building might average 515 kWh and your peak load pegs at 650 kWh. However, if you add load management to move some loads around so that fewer loads stack on top of each other at once, your new peak load rarely will go beyond 595 kWh.
Save Money with Power Quality
You’ve tallied up the costs of poor power quality. Now you need to know how to get rid of those costs. The following steps will get you there:
- Examine design. Determine how your system can support your processes best and what infrastructure you need to prevent failure. Verify circuit capacity before installing new equipment. Re-check critical equipment after configuration changes.
- Comply with standards. For example, examine your grounding system for compliance with IEEE-142. Examine your power distribution system for compliance with IEEE-141.
- Examine power protection. This includes lightning protection, transient voltage surge suppressor (TVSS) and surge suppression. Are these properly specified and installed?
- Get baseline test data on all loads. This is the key to predictive maintenance, and it allows you to spot emerging problems.
- Question mitigation. Mitigating power quality problems includes correction (such as grounding repair) and coping (such as K-rated transformers). Consider power conditioning and backup power.
- Review maintenance practices. Are you testing and then following up with corrective actions? Conduct periodic surveys at critical points — for example, check neutral-to-ground voltage and ground current on feeders and critical branch circuits. Conduct infrared surveys of distribution equipment. Determine root causes of failures, so you know how to prevent recurrences.
- Use monitoring. Can you see voltage distortions before they overheat motors? Can you track transients? If you don’t have power monitoring installed, you probably won’t see a problem coming — but you will see the downtime it causes.
At this point, you need to determine the costs of prevention and remediation and then compare those to the costs of poor power quality. This comparison will allow you to justify the investment needed to fix the power quality problems. Because this should be an ongoing effort, do your own power quality testing and monitoring using the right tools rather than outsourcing. It’s surprisingly affordable and typically will cost less than downtime.
Fluke Corp. is a participating Encompass™ Product Partner in the Rockwell Automation PartnerNetwork™. Based in Everett, Washington, Fluke Corp. manufactures, distributes and services electronic test tools.
The Journal From Rockwell Automation and Our PartnerNetwork™ is published by Putman Media, Inc.