The word “harmonics” is a broad term and is used in many different industries. Unfortunately, certain electrical problems are incorrectly blamed on harmonics. These harmonics should not be confused with radio frequency interference (RFI), which occurs at much higher frequencies than harmonics. Power line harmonics are lowfrequency, thus they do not interfere with wireless LAN signals, cellphones, FM or AM radios, or any equipment that is specifically sensitive to high-frequency noise.
Harmonics are caused by non-linear loads. Nonlinear loads do not draw current sinusoidally from the utility. Examples of non-linear loads include VFDs, EC motors, LED lighting, photocopiers,computers, uninterruptible power supplies, televisions, and the majority of electronics that include a power supply. The most significant causes of harmonics in the building are typically non-linear, three-phase power, and the more power there is, the bigger the harmonic currents in the network will be. The next section reviews the electrical
characteristics of a VFD. This is to illustrate an example of a non-linear load. The most popular VFD design works by taking a three-phase AC line input voltage and rectifying the voltage through diodes. This turns the voltage into a smooth DC voltage across a bank of capacitors. The VFD then converts the DC back into an AC waveform for the motor in order to control the speed, torque and direction of the motor. The non-linear current is created by the three-phase AC-to-DC rectification. Problems caused by harmonic distortion High levels of harmonic distortion in a facility can create a wide range of problems. Some of the problems that may be encountered are:
• Premature failure and reduced lifespan of devices often occurs when overheating is present, such as: – Overheating of transformers, cables, circuit breakers and fuses
– Overheating of motors that are powered directly across the line
• Nuisance trips of breakers and fuses due to the added heat and harmonic loading
• Unstable operation of backup generators
• Unstable operation of sensitive electronics that require a pure sinusoidal AC waveform
• Flickering lights
There are many ways to mitigate harmonics and there is no”one size fits all”solution. Noker Electric is a professional supplier of active harmonic filter and static var generator .If any question about harmonic, please contact Noker Electric, we will offer you a solution for you.
Post time: Aug-28-2023