Nicole George is the product manager, pumping variable frequency drives, industrial controls division, Eaton. She holds a bachelor’s degree in mechanical engineering from the University of Tennessee and an MBA from the University of Florida. For more information, visit www.eaton.com.
In today’s business environment, expectations are only getting higher. Managers are increasingly concerned with operational efficiency. This includes minimizing costs, capital expenses and unplanned downtime. Rocketing prices have also caused the industry to take a closer look at energy consumption and make adjustments to help keep these costs and corresponding expenses at a minimum. Here are some common questions about harmonics and explanations about preventing wasted energy and costs by controlling harmonics.
Q: What are harmonics?
A: Harmonics are distorted electrical waveforms that introduce inefficiencies into the electrical system. They produce wasteful heat and can cause plant issues and fees from local power utilities. Harmonics flow into the electrical system as a result of nonlinear electronic switching devices, such as variable frequency drives (VFDs), computer power supplies and energy-efficient lighting.
Q: What are some problems that can occur with harmonic distortion?
A: Systems with heavy motor, VFD and lighting loads need to be aware of the problems that harmonics can cause. These include: increased electrical usage, increased wear and tear on motors or equipment, higher maintenance cost, power quality problems upstream and downstream of the load, and utility penalties for creating problems for the power grid.
Q: What are some benefits of better awareness of electrical inefficiencies like harmonics?
A: Benefits can include controlled capital expenses, IEEE-519 compliance, increased uptime and profits, added value to facilities and reduced energy expenses.
Q: What is IEEE-519?
A: The Institute of Electrical and Electronics Engineers (IEEE) established the IEEE-519 guideline written from the point of view of electrical utilities. This guideline establishes the level at which electrical energy is determined “clean.”
Q: Why is low harmonic technology used?
A: Applications that require multiple VFDs typically produce a higher level of harmonic distortion due to the intrinsic nature of VFD technology. Low-harmonic drives are used in these applications to limit the amount of harmonic distortion and improve
Q: What are the costs associated with harmonics?
A: Depending on the electrical power system, there are a lot of places where harmonics can cause inefficiencies. In a manufacturing setting, unmanaged harmonics can increase motor temperatures by 10 degrees to maintain output. This can reduce the life of a motor by 50 percent. Distribution transformers can lose a full +1 percent of efficiency when carrying 100 percent harmonic current, and motors lose 0.1 percent efficiency with each 1 percent of harmonic voltage distortion. These losses can cause a dramatic decrease in the life span of fan and pump motors due to extra heating in the motor stator.
In a hospital setting, a large heating, ventilation and air conditioning (HVAC) system with a 500-horsepower fan and pump load, running at 5 percent voltage distortion instead of 1 percent, can cost $15,000 per year at 10 cents per kilowatt hour (kWh). This is in addition to the costs of the reduced life span of the motors caused by the heating effects of the harmonic currents.
Q: Which markets do low harmonic drive solutions serve?
A: The most common market segments served are water and wastewater, building services, commercial HVAC and manufacturing conveyors.
Q: What are the different types of low harmonic solutions?
A: Inductive motors mitigate higher-order harmonics by providing high-input impedance that limits high-frequency currents. The 12-pulse converters consist of two parallel six-pulse converters fed by parallel isolation transformer paths, phase shifted 30 degrees, which mitigates fifth and seventh order harmonics. Passive filter technology provides high-input impedance for higher-order harmonics and a shunt-tuned reactor and capacitor to mitigate fifth and seventh harmonics.
Active harmonic correction filters actively measure and inject equal and opposite harmonics into the system, canceling most harmonic currents below the 49th harmonic.
Active front-end drives have insulated gate bipolar transistors (IGBT)—front-end technology that pulls relatively linear power from the line and uses an L-C-L (inductor-capacitor-inductor) filter to mitigate the IGBT switching noise.
The 18-pulse converters consist of three parallel six-pulse converters fed by a single-phase shifting autotransformer, phase shifted 20 degrees to cancel all harmonics below the 17th. Input impedance mitigates higher-order harmonics as well.
Q: What problems could higher-frequency harmonic currents cause when they flow through the power system in addition to communication errors, overheating and hardware damage?
A: Problems include, but are not limited to: overheating of electrical distribution equipment, cables, transformers, standby generators, etc.; high voltages and circulating currents caused by harmonic resonance; high neutral currents that generate heat and waste energy; equipment malfunctions due to excessive voltage distortion; increased internal energy losses in connected equipment, causing component failure and shortened life span; false tripping of branch circuit breakers; metering errors and fires in wiring and distribution systems.