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Electronic devices such as computers and variable frequency drives cause power system harmonics, resulting in distorted voltages and negative effects on system performance. Non-linear loads produce harmonic current, causing equipment to operate erratically and power system inefficiencies. Engineers use various methods to reduce harmonics, including efficient designs and isolation transformers.
Power system harmonics are the by-products of electronic devices that occur when certain types are connected to power systems. Devices such as uninterruptible power supplies, personal computers, and variable frequency drives create power system harmonics when they draw energy in short pulses rather than uniformly. The effects of these harmonics cause distorted voltages and problems that negatively affect system performance.
Electric power sources aim to deliver sinusoidal voltages in a coherent manner. When non-linear loads or any device that uses solid-state switching power supplies to transform alternating current into direct current are connected to a power source, power system harmonics occur. A linear load has a direct current relationship where power is proportional to voltage with both waves having the same shape. Incandescent lamps, motors and heaters are some examples of linear loads.
Loads that produce harmonic current are non-linear, where the current and voltage waveforms differ from each other in shape. When such a load absorbs energy, harmonic voltages are generated by the impedance within the system. Ferromagnetic devices, discharge lighting units and arc devices are some examples of non-linear loads. The effects of power system harmonics can be quite severe depending on the magnitude of the voltage distortion.
In many ways, its effect is comparable to how stress negatively affects the human body. High levels of harmonic distortion can cause equipment to operate erratically, power system inefficiencies, and even crashes. The entire utility distribution system and all connected devices can be affected to varying degrees in various ways. For example, power system harmonics can shorten the life of capacitors or cause them to fail or break. Components may trip, explode, or fail for no discernible cause.
Harmonic voltage distortions cause unstable operation of generators and overheating of windings in transformers. Devices such as phones and computers may fail intermittently or exhibit interference. Users could end up with excessive electric bills due to utility meters recording power measurements incorrectly.
Engineers use many methods to reduce power system harmonics, ranging from more efficient designs to using isolation and delta-delta transformers. With improved design, harmonics can be reduced by limiting non-linear loads to a certain percentage of a transformer’s capacity. Delta-delta transformers shift phase relationships using various techniques, which are also beneficial. Isolation transformers attempt to solve the problem by stepping up and stepping down the system voltage to match.
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