demands a large amount of current, then suddenly stops demanding it, there will be a dip or spike in the voltage due to the inductances in the power supply line). Variations in the wave shape – usually described as harmonics at lower frequencies (usually less than 3 kHz) and described as Common Mode Distortion or Interharmonics at higher frequencies. Waveform The oscillation of voltage and current ideally follows the form of a sine or cosine function, however it can alter due to imperfections in the generators or loads. Typically, generators cause voltage distortions and loads cause current distortions. These distortions occur as oscillations more rapid than the nominal frequency, and are referred to as harmonics. The relative contribution of harmonics to the distortion of the ideal waveform is called total harmonic distortion (THD). Low harmonic content in a waveform is ideal because harmonics can cause vibrations, buzzing, equipment distortions, and losses and overheating in transformers. Each of these power quality problems has a different cause. Some problems are a result of the shared infrastructure. For example, a fault on the network may cause a dip that will affect some customers; the higher the level of the fault, the greater the number affected. A problem on one customer’s site may cause a transient that affects all other customers on the same subsystem. Problems, such as harmonics, arise within the customer’s own installation and may propagate onto the network and affect other customers. Harmonic problems can be dealt with by a combination of good design practice and well proven reduction equipment. Power conditioning Power conditioning is modifying the power to improve its quality. An uninterruptible power supply (UPS) can be used to switch off of mains power if there is a transient (temporary) condition on the line. However, cheaper UPS units create poor-quality power themselves, akin to imposing a higher-frequency and lower-amplitude square wave atop the sine wave. High-quality UPS units utilize a double conversion topology which breaks down incoming AC power into DC, charges the batteries, then remanufactures an AC sine wave. This remanufactured sine wave is of higher quality than the original AC power feed. A dynamic voltage regulator (DVR) and static synchronous series compensator (SSSC) are utilized for series voltage-sag compensation. A surge protector or simple capacitor or varistor can protect against most overvoltage conditions, while a lightning arrester protects against severe spikes. Electronic filters can remove harmonics. Smart