**1. Introduction**

234 Power Quality Harmonics Analysis and Real Measurements Data

[32] Rana Abdul Jabbar Khan, "Power Quality and On-line Harmonics Monitoring in Power

[33] Juan C. Meza, Abdul H. Samra, "A New Technique to Reduce Line-Current Harmonics

[34] Serge B. G. Trochain "Compensation of harmonic currents generated by Computers utilizing an innovative active harmonic conditioner", *MGE UPS Systems*, 2000.

Generated by a Three-phase Bridge Rectifier", *IEEE Proceedings of Southeastcon '98*,

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pp: 354-359, 24-26 April 1998.

The increased problems in power networks impose to identify the sources of power quality deterioration. The most important parameters which affect power quality are harmonics, voltage instability and reactive power burden (Arrillaga et al., 2000). They cause low system efficiency, poor power factor, cause disturbance to other consumers and interference in the nearly communication networks (Lattarulo, 2007; De la Rosa, 2006; Muzi, 2008).

In induction melting is noticed mainly the efficiency, high heating rate and the reduced oxidation level of the processed material, the improved work conditions and the possibility of an accurate control of the technological processes (Rudnev et al., 2002).

Induction heating equipments do not introduce dust and noise emissions in operation, but cause power quality problems in the electric power system (Nuns et al., 1993).

Induction-melt furnaces supplies by medium frequency converters generate fixed and variable frequency harmonics. Both current and voltage-fed inverters generate harmonics back into power lines in the process of rectifying AC to DC (EPRI, 1999).

Harmonics flowing in the network causing additional losses and decreasing the equipments lifetime. Also, the harmonics can interfere with control, communication or protection equipments (Arrillaga et al., 2000; George & Agarwal, 2008).

In addition to the harmonics that are normally expected from different pulse rectifiers, large furnaces operating at a few hundred hertz can generate interharmonics (EPRI, 1999). Interharmonics can overload power system capacitors, introduce noise into transformers, cause lights to flicker, instigate UPS alarms, and trip adjustable-speed drives.

High-frequency systems, which operate at greater than 3 kHz are relatively small and limited to special applications. Electromagnetic pollution produced by the operation of these equipments is small.

The induction furnaces supplied at line frequency (50 Hz) are of high capacity and represent great power consumers.

Being single-phase loads, these furnaces introduce unbalances that lead to the increasing of power and active energy losses in the network. In case of channel furnaces it was found the presence of harmonics in the current absorbed from the power supply network. These harmonics can be determined by the non-sinusoidal supply voltages or the load's nonlinearity, owed to the saturation of the magnetic circuit (Nuns et al., 1993).

This chapter presents a study about power quality problems introduced by the operation of line frequency coreless induction furnaces. The specialty literature does not offer detailed information regarding the harmonic distortion in the case of these furnaces.

Power Quality Problems Generated by Line Frequency Coreless Induction Furnaces 237

Fig. 1. Electric scheme of the analyzed furnace
