As heat treating facilities strive for energy efficiency and reliability, investing in power improvements can move a company toward sustainable operations. In this Controls Corner installment, Brian K. Turner of RoMan Manufacturing, Inc. compares real power factor and displacement power factor in the efficiency and electrical performance of vacuum furnaces.
This informative piece was first released in Heat Treat Today’s February 2025 Air/Atmosphere Furnace Systems print edition.
To read the article in Spanish, click here.
In the context of vacuum furnaces, real power factor and displacement power factor are key concepts related to the efficiency and electrical performance of the furnace’s power supply and load. Here’s a comparison:
1. Real Power Factor (PF)
Definition: Real power factor is the ratio of real power (active power, P, measured in watts) to apparent power (S, measured in volt-amperes). It considers both the phase displacement and harmonic distortion.
Relevance to Vacuum Furnaces:
- Vacuum furnaces, especially those using induction heating, often generate nonlinear loads due to the operation of power electronics.
- Nonlinear loads introduce harmonics, which distort the current waveform, reducing the real power factor.
- A low real power factor indicates inefficiency, as the system draws more apparent power for a given amount of real power.
2. Displacement Power Factor (DPF)
Definition: Displacement power factor is the cosine of the angle (ϕ) between the fundamental components of voltage and current waveforms. It ignores harmonic distortion and considers only the phase displacement caused by inductive or capacitive loads.
Relevance to Vacuum Furnaces
- In vacuum furnaces, the inductive nature of components (e.g., transformers and inductive loads) causes a lagging power factor, which is reflected in the DPF.
- A poor displacement power factor (e.g., heavily lagging) means the system has significant reactive power demands, affecting the sizing of transformers and power distribution equipment.
The above waveforms illustrate the difference between displacement power factor (DPF) and real power factor (PF) as they relate to current and voltage:
Top Chart: DPF — Ideal Conditions
- The green sinusoidal waveform represents the current in an ideal displacement power factor scenario, where only phase displacement (ϕ) exists between the voltage (blue curve) and current.
- The waveforms are clean and sinusoidal, indicating no harmonic distortion.
Bottom Chart: PF — With Harmonic Distortion
- The red waveform represents the current with added harmonic distortion, typical in systems with nonlinear loads, like vacuum furnaces.
- This distortion causes the real power factor to drop compared to the displacement power factor, even if the fundamental phase relationship is the same.
Effects on Transformer and Utility Transformer Sizing
Increased Apparent Power Demand
- A lower real power factor (due to harmonics) means the transformer must handle higher apparent power (S), even if the real power (P) is unchanged.
- This can necessitate larger transformers, increasing capital costs.
Thermal Stress
- Harmonics lead to additional losses (eddy currents and hysteresis), causing transformers to overheat and reducing their efficiency and lifespan.
Voltage Regulation Issues
- Harmonics distort the voltage waveform, which can affect sensitive equipment and require transformers with tighter voltage regulation capabilities.
Utility Penalties
- Utilities often impose penalties for low real power factor, incentivizing users to improve power quality through harmonic filters or power factor correction.
Conclusion
Addressing power factor in vacuum furnaces is crucial for improving efficiency and reducing operational costs. As heat treating facilities strive for energy efficiency and reliability, investing in these improvements is a step toward sustainable operations.
About the Author:
Sales Applications Engineer
RoMan Manufacturing, Inc.
Brian K. Turner has been with RoMan Manufacturing, Inc., for more than 12 years. Most of that time has been spent managing the R&D Lab. In recent years, he has taken on the role as applications engineer, working with customers and their applications.
For more information: Contact Brian at bturner@romanmfg.com.
