Abstract
A numerical investigation on the harmonic disturbances in low-voltage cables feeding large LED loads is reported. A frequency domain analysis on several commercially-available LEDs was performed to investigate the signature of the harmonic current injected into the power system. Four-core cables and four single-core cable arrangements (three phases and neutral) of small, medium, and large conductor cross sections, with the neutral conductor cross section approximately equal to the half of the phase conductors, were examined. The cables were modelled by using electromagnetic finite-element analysis software. High harmonic power losses (up to 2.5 times the value corresponding to an undistorted current of the same rms value of the first harmonic of the LED current) were found. A generalized ampacity model was employed for re-rating the cables. It was found that the cross section of the neutral conductor plays an important role in the derating of the cable ampacity due to the presence of a high-level of triplen harmonics in the distorted current. The ampacity of the cables should be derated by about 40 %, almost independent of the conductor cross sections. The calculation have shown that an incoming widespread use of LED lamps in lighting could create significant additional harmonic losses in the supplying low-voltage lines, and thus more severely harmonic emission limits should be defined for LED lamps.
Highlights
IntroductionWith the technological advancement in semiconductors, light-emitting diode (LED) lamps are becoming in a promising lighting technology due to its superior energyefficiency and longer life-time compared to most of the conventional light sources [1,2]
With the technological advancement in semiconductors, light-emitting diode (LED) lamps are becoming in a promising lighting technology due to its superior energyefficiency and longer life-time compared to most of the conventional light sources [1,2].In general lighting applications, a compact ac/dc converter [3,4] should be used to supply dc current to LEDs, which introduce nonlinearity to the system
This work investigates the harmonic disturbances in low-voltage installations having the neutral cross section approximately equal to half of the phase conductors when used for feeding large LED lighting loads
Summary
With the technological advancement in semiconductors, light-emitting diode (LED) lamps are becoming in a promising lighting technology due to its superior energyefficiency and longer life-time compared to most of the conventional light sources [1,2]. The magnetic field generated by harmonic currents flowing in the conductor induces on the conductor itself eddy currents, which modify the current distribution displacing it toward the periphery; this “skin effect” phenomenon increases the value of the resistance (as compared to the dc resistance) in proportion to the root of the harmonic frequency, increasing the conductor power losses [6,7]. This work investigates the harmonic disturbances in low-voltage installations having the neutral cross section approximately equal to half of the phase conductors when used for feeding large LED lighting loads. The cables were modelled by using the QuickField Lite, which is a commercially available electromagnetic finite-element analysis software manufactured by Tera Analysis Ltd
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