Non-linear loads, particularly in industrial and commercial settings, are significant contributors to electrical power quality issues. A prime example of a non-linear load is the Switch-Mode Power Supply (SMPS), which is prevalent in most digital electronic equipment today. Unlike linear loads, non-linear loads draw current in a non-sinusoidal manner, leading to the generation of harmonic currents.
The SMPS, by drawing current in pulsed forms rather than a smooth, continuous flow, generates harmonic currents that distort the voltage waveform. This distortion becomes particularly problematic when high densities use SMPS units, as they can significantly contribute to voltage distortion across the power system.
Figure 8-1 illustrates this phenomenon, where the pulsed current consumption of a single-phase SMPS results in voltage distortion, commonly referred to as voltage flat-topping. This occurs because current is drawn primarily at the peak of the voltage waveform to charge the smoothing capacitor.
As a result, the voltage drop occurs only at the waveform's peak because of system impedance, leading to a flattened voltage peak. Such distortion can reduce the DC bus voltage of the SMPS, compromise its power disturbance ride-through capability, and increase both current draw and I²R losses.
At YT Electric, we understand the challenges posed by non-linear loads and the importance of maintaining power quality. Our Low-Voltage Active Power Filters and Static Var Generators (SVGs) are designed to address these issues directly by mitigating the harmful effects of harmonic currents and voltage distortion.
Our Low-Voltage Active Power Filters are engineered to actively monitor and filter out harmonic currents generated by non-linear loads like SMPS. By injecting equal but opposite currents to cancel out the harmonics, these filters ensure that your power system remains clean and stable, reducing the risks associated with voltage flat-topping and other forms of distortion.
Key Benefits:
Our Static Var Generators are designed to provide dynamic reactive power compensation, which is crucial for maintaining voltage stability in systems with fluctuating loads. SVGs quickly respond to changes in load conditions, supplying or absorbing reactive power as needed to maintain optimal voltage levels.
Key Benefits:
To better understand the impact of non-linear loads like SMPS, it's essential to analyze the behavior of harmonic currents as they flow through the distribution system's various impedances. According to Fourier analysis, the 2-pulse current drawn by the SMPS rectifier comprises a fundamental frequency component along with all odd harmonics (3rd, 5th, 7th, 9th, 11th, etc.).
When modeling the distribution system, each SMPS can be seen as a generator of harmonic currents. These harmonic currents, when injected into the power system, interact with the system impedance, leading to voltage drops at corresponding harmonic frequencies. This relationship is governed by Ohm’s Law (Vh = Ih x Zh), where:
Figure 8-2 highlights how system impedance relates to the voltage and current distortion components within a typical power system. By applying Parseval’s Theorem, we can calculate the RMS value of voltage or current distortion, which is essential for determining Total Harmonic Distortion (THD).
THD is a critical metric in analyzing power quality. It’s typically expressed as a percentage of the fundamental component's value. For voltage total harmonic distortion (Vthd), the formula is:
Similarly, current total harmonic distortion (Ithd) is calculated as:
Voltage distortion is influenced by both system impedance and the amount of harmonic current within the system. Higher system impedance, often caused by factors like long cable runs, high-impedance transformers, or weak power sources such as diesel generators, results in greater voltage distortion.
In Figure 8-2, we observe that voltage distortion peaks at the loads themselves. This occurs because the harmonic currents face the full system impedance at this point, which includes cables, transformers, and sources. A common misconception is that low voltage distortion at the service entrance implies minimal distortion at the loads, but this is not necessarily the case. Keeping system impedances low when managing non-linear loads is crucial to mitigate voltage distortion.
To effectively reduce voltage distortion, two approaches are recommended:
Understanding the relationship between non-linear loads, harmonic currents, and voltage distortion is essential for maintaining power quality in modern electrical systems. By incorporating YT Electric's Low-Voltage Active Power Filters and Static Var Generators, you can significantly reduce the adverse effects of voltage distortion, ensuring a stable and reliable power supply even in environments with high densities of non-linear loads.
If you have any inquiries or questions, feel free to contact us: sales@yt-electric.com
Subscribe to us to enjoy event prices and get some of the best prices.