For having such a large potential to seriously devastate industrial infrastructure, power quality events are largely untracked.
By: Allan Evora
Most power quality issues are hidden from normal utility bills and plant information systems, but their consequences include plant downtime, reduced capacity, production waste, premature equipment failure, utility penalties, and significant financial impact.
In recent years, electric utilities’ ability to deliver reliable clean power has become increasingly more difficult. In their rush to meet renewable energy portfolio standards, solar and wind farms have created serious grid stability challenges. This strain on utilities, in combination with the increase in electronic equipment used in industrial facilities means power quality events are only increasing.
For many, power quality monitoring is intimidating. The perceived complexity of detecting, analyzing, and solving power quality issues like sags, swells, transients, harmonics, and power factor means it isn’t generally isn’t part of a normal plant information system.
But as the sole party responsible for protecting their own equipment, owners can’t afford to sweep power quality under the rug any longer. They must understand the four major power quality issues in order to mitigate costs and improve process reliability.
Voltage sags are defined as a deviation in which voltage is lower than nominal voltage for multiple cycles. Nominal voltage is the designated voltage provided by the electric utility or the voltage provided by a transformer within your facility.
A swell is the opposite of a sag. It’s a deviation in which the voltage on electrical distribution exceeds the nominal voltage over multiple cycles.
Causes of sags include a short circuit, overload, or the starting of large motors. A swell can happen when a large load is turned off. Utility grid operations, damaged voltage regulators, wiring issues, or even a solar farm ramping up and d
own on a cloudy day are other potential causes of sags and swells.
In terms of their affect to a plant, a sag runs the risk of shutting down equipment (especially industrial computers and PLCs). Both sags and swells could result in breakers tripping or transfer schemes sequencing, depending on the design of the electrical system.
For monitoring purposes, we typically recommend sag thresholds be set at 90% of nominal voltage and swell thresholds be set at 110% of nominal voltage. These thresholds are also recommended within IEEE Standard 1159, which is an industry standard covering power quality monitoring.
One of the most damaging voltage disturbances is a transient (or spike). Similar to the swell, a transient is a condition in which the voltage on the electrical system is higher than the expected voltage. The distinguishing characteristic of a transient is the duration. A transient typically occurs with the electrical cycle, which means it's duration is less than 1/60th of a second.
Transients have the potential to damage equipment with power supplies, especially computers, instruments, and control devices. Transients also spell doom to industrial facilities that produce the memory and processors in these equipment (e.g., semi-conductor manufacturers). Over time, repeated transients will cause equipment to fail prematurely.
The source of a transient can be both internal or external to your facility. For example:
- utility switching on the grid
- lightning strike
- neighboring industrial plant turning on high current arc welders
- equipment within your facility cycling on or off
- motors within your facility turned on without sequencing in stages
While the IEEE 1159 standard recommends a threshold of 2X the phase peak voltage, we typically recommend setting your power quality meter to detect transients at 125% of the nominal voltage.
We also recommend owners plot each sag/swell or transient event on an ITIC curve (formerly known as CBEMA). After you plot your event magnitude and duration, you can determine if the event may have been impactful to sensitive equipment in your facility.
Harmonics (aka noisy/dirty electricity) are distortions to voltage and current sign waves. If equipment in an industrial facility operates by altering sign wave behavior between AC and DC, it will cause harmonic distortion.
This equipment includes variable speed drives, furnaces, light ballasts, and DC power supplies in computers/other electronic equipment.
According to the IEEE 1159 standard, voltage harmonic distortion should be kept under 4% to avoid problems with extremely sensitive equipment like lighting and computers. Harmonic distortion issues are one of the higher probability reasons of downtime and why equipment fails to properly operate.
High harmonic content in a system has the potential to cause nuisance tripping, and increase heat in conductors and motor windings. Harmonics also reduce your power capacity.
Power factor (PF) is the ratio of real power to apparent power. When voltages and currents within a power system are in phase, the power factor is considered to be unity or 1 and the load is purely resistive. If the current lags the voltage, inductive loads are present. When the current leads the voltage, capacitive loads are present.
Most industrial plants will have a lagging power factor within their facility. This is due to the motors, pumps, and fans prevalent in most industrial settings.
It’s important to pay attention to power factor because, like harmonics, it can reduce capacity within your facility.
In some parts of the country, electric utilities penalize customers based on low power factor. This does not just apply to industrial customers, but can also apply to large consumers of electricity like hospitals or universities.
Remember, the utility generates apparent power or KVA, and if capacity on the electric grid is in short supply they will probably charge you for both the real and reactive component. In the past, I have seen 0.85 lagging power factor as a common threshold for additional utility charges.
Stay tuned for part 2: Detecting Power Quality Events in Industrial Facilities and part 3: Mitigating Power Quality Issues in Industrial Facilities
Allan D. Evora is a leading expert in control systems integration and president of Affinity Energy with over 20 years of industry experience working in every capacity of the power automation project life cycle. With a background at Boeing Company and General Electric, Allan made the decision to establish Affinity Energy in 2002. Allan is an alumnus of Syracuse University with a B.S. in Aerospace Engineering, graduate of the NC State Energy Management program, and qualified as a Certified Measurement & Verification Professional (CMVP).
Throughout his career, Allan has demonstrated his passion for providing solutions. In 1990, he developed FIRST (Fast InfraRed Signature Technique), a preliminary design software tool used to rapidly assess rotary craft infrared signatures. In 2008, Allan was the driving force behind the development of Affinity Energy's Utilitrend; a commercially available, cloud-based utility resource trending, tracking, and reporting software.
Allan has been instrumental on large scale integration projects for utilities, universities, airports, financial institutions, medical campus utility plants, and manufacturing corporations, and has worked with SCADA systems since the early ‘90s. A passion for data acquisition, specialty networks, and custom software drives him to incorporate openness, simplicity, and integrity into every design in which he is involved.