Harmonics can significantly impact power systems, leading to transformer failures, motor burnouts, nuisance tripping of circuit breakers, and overheating of neutral conductors and other components in a power distribution network. This overheating can be severe enough to cause electrical fires.
Nonlinear loads, which draw current in pulses, cause harmonics by distorting the waveform. These harmonics are a major source of power quality problems, resulting in the overheating of circuit components. To mitigate harmonics in power distribution systems, harmonic mitigating transformers are often used.
When harmonics are present, they distort voltage and current waveforms on the lines. Analyzing these distorted waveforms is necessary to identify the type and amount of harmonics. Higher-order harmonics combine with the fundamental frequency to create a resultant waveform, which can be measured by a power quality analyzer. Fourier analysis, particularly the Fourier transform, is used to analyze these waveforms.
The Fourier Transform
The Fourier transform is essential for analyzing the resultant waveform to determine the harmonics present. It converts a time-based waveform into frequency-based information, breaking down a periodic waveform into a series of sine waves that can be added together to reproduce the original waveform. This method helps identify the frequency and magnitude of harmonics present on the lines, as indicated by the power quality analyzer.
[Figure 1: Fourier analysis decomposes a distorted wave into its component harmonics. Image courtesy of SALICRU]
Combining Waveforms
Waveforms from different loads combine at points where two or more wires join, such as the windings of a transformer or a common bus feeding multiple transformers. When sine waveforms combine, they sum up, and the resultant waveform equals the sum of individual values. If one waveform is positive and the other is negative but equal in value, they cancel each other out. For instance, if two current waveforms are exactly out of phase, one being +10 A and the other -10 A, the resultant current at that instant is 0.
Jean Baptiste Joseph Fourier developed the concept behind Fourier analysis, transforming time-varying signals with harmonics into their frequency components.
When two current waveforms are out of phase but do not exactly cancel, the resultant waveform will have a non-zero value. For example, a Switched-Mode Power Supply (SMPS) draws current in pulses, separated from each other. If one waveform is shifted by 60° relative to the other and they are added, the resultant has two peaks for each peak of the original waveform. This type of shift and recombination happens in transformers with standard delta-wye or wye-zigzag windings, leading to the cancellation of triplen harmonics.
[Figure 2: Waveforms add together at a wiring junction, with a 60° phase shift canceling triplen harmonics.]
Combining the waveform created by a delta-wye or a wye-zigzag transformer with two other appropriately phase-shifted waveforms creates a new waveform that cancels the 5th, 7th, 17th, and 19th harmonics in addition to the triplen harmonics. This additional phase shift can be achieved with delta-zigzag transformers in parallel with wye-zigzag or delta-wye transformers, visible at the power busbar upstream of the transformer pair.
[Figure 3: Further waveform shifts cancel higher-order harmonics.]
However, if the load on a transformer changes, the waveforms become unbalanced and do not cancel. Although additional phase shifts can be designed to eliminate more harmonics, the benefits are minimal. The transformer bank would need modifications with every load change, which is impractical as loads can vary frequently, such as when computers are turned on or off, or the load on a variable-speed motor drive changes.
Practical Solutions for Harmonics
To practically manage harmonics in power systems, using active harmonic filters (AHF) can be an effective solution. Unlike passive filters, AHFs can adapt to changes in the system and provide real-time filtering of harmonic distortions. They work by injecting currents that cancel out the harmonic components, ensuring a clean power supply.
Furthermore, regular monitoring and maintenance of the power system are crucial. Using power quality analyzers helps in continuously assessing the harmonic levels and identifying potential issues before they cause significant damage. By combining advanced technologies like AHFs with proactive system management, harmonics can be effectively controlled, ensuring the reliability and efficiency of power distribution systems.
An Active Harmonic Filter (AHF) is an essential component in modern power systems, especially in industrial and commercial settings. YT Electric's Active Harmonic Filter is an advanced power quality solution designed to eliminate harmonics and reactive power in the power system, thereby improving power quality, reducing equipment wear, and lowering maintenance costs.
Harmonic Suppression: The Active Harmonic Filter can detect and suppress harmonic currents in real-time. Harmonics are produced by non-linear loads such as variable frequency drives, rectifiers, and computer equipment. These harmonics can cause overheating, reduced efficiency, and shortened lifespan of electrical equipment.
Reactive Power Compensation: In addition to harmonic suppression, YT Electric's Active Harmonic Filter also provides reactive power compensation. This means it can dynamically adjust to the power system's needs, providing or absorbing reactive power as required. This improves the power factor, reduces energy losses, and enhances the overall efficiency of the power system.
Improved Power Quality: By mitigating harmonics and compensating reactive power, the AHF enhances the overall power quality. This results in smoother operation of sensitive electronic equipment, fewer disruptions, and extended equipment life. Improved power quality also means compliance with stringent international standards and regulations, making YT Electric's AHF a reliable choice for global markets.
Scalability and Flexibility: YT Electric's AHF is designed to be scalable and flexible, catering to various power ratings and configurations. Whether for small commercial buildings or large industrial plants, the AHF can be customized to meet specific needs, ensuring optimal performance.
Easy Integration and Maintenance: The AHF is engineered for easy integration into existing power systems with minimal disruption. Its user-friendly interface and advanced diagnostics make monitoring and maintenance straightforward, reducing downtime and operational costs.
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