Most industrial facilities in today’s marketplace have a high percentage of non-linear loads. As a result, these loads add harmonic currents to the power system, resulting in harmonic distortions in voltage. So, what does this mean? How are non-linear loads affecting your facility? In short, problems arise as components heat up, ultimately causing malfunctions to occur. But let’s break it down a bit.
Linear Loads vs. Non-linear Loads
A linear load is an electrical load where the sinusoidal relationship between current and voltage waveforms. At any time, the current is proportional to the voltage (as when in a steady state of operation).
Linear loads Examples:
- Motors
- Capacitors
- Transformers
A load becomes non-linear when its impedance varies with the applied voltage throughout the cycle waveform. Moreover, the changing impedance means that the non-linear load current draw will not be sinusoidal. These non-sinusoidal currents contain harmonics that interact with and distort the voltage of power distribution system equipment and loads connected to them.
Non-linear load Examples:
- Computers
- Lighting
- Adjustable Speed Drives
- Rectifiers
Harmonic Effects
A distortion to voltage and current sine waves is known as Harmonics. Distortion can negatively impact motors, computers, transformers, and conductors. Due to this low power factor, the harmonic contribution from the non-linear loads results in voltage drops across the power system. Further, increased harmonics results in power factor loss, lower voltages in power systems, adverse effects on machinery performance, and higher operating costs.
To offset the cost increase brought about by a low power factor, industrial facilities use power factor correcting capacitor banks. However, this application is not without its disadvantages. Increasing harmonics generate multiples of 60hz sine waves. These multiples add to the base wave and form second (120hz), third (180hz) harmonics, and so on. Many pieces of equipment are susceptible to harmonic interference, resulting in early failures and reduced performance.
Various non-linear load types can generate harmonics, such as induction furnaces, AC and DC adjustable motor drives, electronic lighting, switch-mode power supplies, and renewable energy sources. Yet, some facilities may not experience adverse effects. Even so, as harmonics increase, equipment issues will begin to arise.
Here are a few examples of potentially harmful harmonic effects
- Overheating of transformers
- Induction motors and neutral conductors
- Malfunctioning of electronic microprocessor equipment
- Power factor correcting capacitors failing
- Operations of breakers
- Fuses and relays failing
- Magnetic fields increase around transformers and switchgear
Harmonics may interfere with communications equipment, meters, and generators as well. Furthermore, harmonics can enter or exit a facility from the electric utility grid.
Several techniques (or combinations techniques) can minimize harmonic effects. K-Factor transformers, for example, are more capable of withstanding harmful harmonic effects while not reducing them. Similarly, HMTs (Harmonic Mitigating Transformance ) and phase shift transformers reduce harmonics. Another option is to use either active or passive harmonic filters with capacitors to shunt or block harmonics from entering the system. Even so, designing electrical systems not to produce harmonics remains the most efficient solution.
Get in Tune
Take action to identify and manage harmonics in your facility. Monitoring your power quality, measuring electrical loads and supply allows you to pinpoint where problems exist in real-time. Identifying harmonics is also possible through the use of harmonic measurement equipment. When you know where harmonics exist, you can mitigate their source. Prevent problems before they arise. Let APT customize the right solution to fit your business’s needs.
Nick Skarvelis, APT Field Service Electrician