Detect and Reduce Harmonics, Distortion, and Noise in Your Power Systems

Following the webcast "Power Systems: How to Detect and Reduce Harmonics, Distortion, and Noise," many attendees raised thoughtful questions about optimizing their power systems. This article addresses a few key points discussed during the session and provides some insights into mitigating harmonics and improving system performance at your facility. 

Measuring Power Quality Effectively 

The duration and methodology of a power quality study depend on the goals of the evaluation. A single point load reading provides a snapshot of system performance, while extended monitoring helps capture trends during normal operation. A comprehensive 30-day study can align with NEC 220.87(1) requirements and validate system behavior over time. However, practical factors like sample rates and storage capacity must be considered when planning long-term measurements. To gain meaningful insights, monitoring should span several production days to identify trends in harmonics, loading, and other key measurements. 

Mitigating Harmonics in Operating Facilities 

Mitigating harmonics in an operational plant is challenging but achievable with the right strategies. Solutions include: 

• Line Reactors and Active Harmonic Filters: These can address specific problem areas with minimal downtime. 
• Isolation Transformers and Higher-Pulse Drives: While effective, these solutions often require more downtime and additional space for implementation. 

Strategic planning ensures that harmonic mitigation efforts can be incorporated efficiently, even in fully operational facilities. A thorough evaluation of plant operations and power requirements helps identify the corrective actions that are most appropriate for your facility. 

Enhancing Power Quality with UPS Systems 

UPS (Uninterruptible Power Supply) units are excellent tools for improving power resilience and voltage regulation. While UPS units can introduce harmonics due to their non-linear nature, many manufacturers design systems to limit this effect. Often, a UPS output is cleaner than the input, especially in environments with high harmonic content. Choosing a UPS with published harmonic data ensures alignment with system needs and minimizes unintended disruptions. 

Understanding the Point of Common Coupling (PCC) 

The PCC is critical in harmonic evaluations. IEEE 519 defines it as the point in a power system where service could be provided to other users. Typically, this point is the high-voltage side of a service transformer. It also serves as the transition point between utility and customer ownership, clarifying inspection jurisdictions and aiding in system evaluations. Understanding the PCC’s location is vital for assessing harmonic impact and determining responsibilities among stakeholders. 

Managing Harmonics from VFDs 

Variable Frequency Drives (VFDs) contribute to harmonics on both line and load sides. Strategies for mitigation include: 

• Line Reactors and DC Link Chokes: To manage line-side harmonics. 
• Proper Cable Selection and Inverter-Duty Motors: To address load-side harmonics. 
• Active-Front-End Technologies: For advanced harmonic control on the line side. 

Employing these measures ensures that both sides of the VFD are managed, minimizing disruptions to the broader power system. 

Accessing Harmonic Data for Equipment 

Manufacturers often provide harmonic data for individual components like VFDs and UPS units. For complex systems, modeling significant non-linear components together using power system software can approximate harmonic performance. For example, combining data from multiple VFDs and power supplies can simulate the harmonic impact of an entire industrial panel, enabling better planning and mitigation. 

Insulation Recommendations for VFD Wiring 

Standard THHN wiring is insufficient for the motor branch circuits of VFDs due to its vulnerability to harmonics and transients. Thermoset insulation types like XHHW offer better resilience, especially when paired with ferrous conduits. High-quality VFD cables, which provide enhanced insulation and shielding, are ideal for mitigating noise and voltage spikes. Ensuring proper cable selection not only prolongs equipment life but also reduces maintenance costs over time. 

Addressing Harmonics at Higher Voltages 

Harmonics affect the entire power system, not just utilization levels. High-voltage systems will carry the harmonics that translate from the secondary to primary transformers, impacting distribution-level performance. Systemic harmonic mitigation is essential for robust power quality, particularly in facilities with extensive high-voltage operations. Ignoring harmonics at this level can lead to inefficiencies and increased energy costs. 

Identifying Significant Motors 

Motors with substantial contributions to system harmonics warrant targeted solutions such as higher-pulse or active-front-end drives. For systems with numerous smaller drives, centralized harmonic correction is often more cost effective and space efficient. Evaluating motor size, frequency of use, and system demands helps prioritize harmonic mitigation efforts for maximum impact. 

The Impact of Conductor Length on Harmonics 

Long motor branch circuits exacerbate voltage spikes due to Pulse-Width-Modulated (PWM) outputs from VFDs. Reflective wave phenomena can occur with circuit lengths over 100 feet. Proper motor and cable selection, along with output filters, mitigate these issues effectively. Additionally, consulting manufacturer data for specific distance recommendations ensures compliance and optimal performance. 

Determining When to Invest in Power Quality Improvements 

IEEE 519 guidelines provide a benchmark for evaluating system harmonic content. While plants with systemic harmonic issues often exceed these guidelines, even compliant systems can have localized problems requiring attention. Best practices in installation, coupled with active harmonic management, ensure optimal power quality and system reliability. Facilities should consider power quality improvements whenever harmonic content impacts operational efficiency or equipment longevity. 

Improving power systems requires a balance of strategic measurement, targeted solutions, and adherence to best practices. Proactively addressing harmonics, distortion, and noise can enhance operational efficiency and resilience at your facility. Whether through detailed evaluations, equipment upgrades, or system-level corrections, investing in power quality pays dividends in reliability and performance. For more information or assistance with your power system challenges, contact the Interstates team.