The harmonic voltages applied to capacitors cause the flow of currents proportional to the frequency of the harmonics. These currents cause additional losses.
The active power transmitted to a load is a function of the fundamental component I1 of the current.
When the current drawn by the load contains harmonics, the rms value of the current, Ir.m.s, is greater than the fundamental I1.
The harmonic voltages (order h) supplied to asynchronous machines cause the flow of currents in the rotor with frequencies higher than 50 Hz that are the origin of additional losses.
Harmonic currents flowing in transformers cause an increase in the “copper” losses due to the Joule effect and increased “iron” losses due to eddy currents. The harmonic voltages are responsible for “iron” losses due to hysteresis.
It is generally considered that losses in windings increase as the square of the THDi and that core losses increase linearly with the THDu.
In Utility distribution transformers, where distortion levels are limited, losses increase between 10 and 15%.
The simultaneous use of capacitive and inductive devices in distribution networks may result in parallel or series resonance.
The origin of the resonance is the very high or very low impedance values at the busbar level, at different frequencies. The variations in impedance modify the current and voltage in the distribution network.
Distortion of the supply voltage can disturb the operation of sensitive devices:
Harmonics cause disturbances in control circuits (low current levels). The level of distortion depends on the distance that the power and control cables run in parallel, the distance between the cables and the frequency of the harmonics.
An electric overload occurs when too much current passes through electric wires. The wires heat and can melt, with the risk of starting a fire.
Generators supplying non-linear loads must be derated due to the additional losses caused by harmonic currents.
The level of derating is approximately 10% for a generator where the overall load is made up of 30% of non-linear loads. It is therefore necessary to oversize the generator, in order to supply the same active power to loads.
The current drawn by computer systems has a very high crest factor. A UPS sized taking into account exclusively the r.m.s. current may not be capable of supplying the necessary peak current and may be overloaded.
Harmonics cause additional losses (Joule effect) in conductors and equipment.
The presence of harmonic currents can require a higher subscribed power level and consequently higher costs. What is more, Utilities will be increasingly inclined to charge customers for major sources of harmonics.
When the level of distortion THDu of the supply voltage reaches 10%, the duration of service life of equipment is significantly reduced. The reduction has been estimated at:
To maintain the service lives corresponding to the rated load, equipment must be oversized.
Circuit-breakers in the installation are subjected to current peaks caused by harmonics. These current peaks may cause nuisance tripping of old technology units, with the resulting production losses, as well as the costs corresponding to the time required to start the installation up again.
YTPQC Active Harmonic Filter has a advanced modular design. Usually YTPQC-AHF consists of one or several AHF modules and an optional touched LCD Human Machine Interface. Each AHF module is an independent harmonic filtering system, and users can change the harmonic filtering system rating by adding or removing AHF modules.
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