HARMONICS IN ROTATING MACHINES AND ARC FURNACE BASICS AND TUTORIALS

HARMONICS IN ROTATING MACHINES
The distribution of the armature windings and the presence of slots in the machines cause spatial harmonics in them. These in turn produce time harmonics in the induced voltages, which appear at the terminals.

Most of the power station generators are wye-connected. In such machines, triplen harmonic voltages do not appear in line-to-line voltages. Also, triplen harmonics can be eliminated even in phase-to-neutral voltages by using two-third pitch winding.

Usually, the most significant harmonics to be minimized by the use of fractional pitch windings are the fifth and seventh. Higher harmonics than the ninth are so small that they require little attention except in rare cases.

HARMONICS IN ARC FURNACE LOADS
Voltage flicker is caused by arc furnace loads at the point of common coupling. For steel making, arc furnaces of the rating 100 MW and above are used.

Usually, a melting cycle can be divided into three distinct steps—drilling period, melting period, and reheating period. The full voltage is applied during the melting period, and the time required for melting is rather large compared with other steps.

Due to uneven arc length, the bus voltage fluctuates continuously during the melting cycle. For large arc furnaces, reactive voltage controllers such as SVCs are required to keep the voltage within the specified limits.

REFERENCES/ ADDITIONAL READING
1. Kimbark, E.W., Direct Current Transmission (1971). Vol. 1, John Wiley, New York.
2. Schlabbach, J., Blume, D., and Stephanblome, T. (2001). Voltage Quality in Electrical
Power Systems, IEE, London.
3. Mahmoud, Aly A. (1984). Power System Harmonics: An Assessment. IEEE Tutorial
Course Text, EHO221-2-PWR, 1–9.
4. Arrillaga, J., Bradley, J.D., and Bodger, P. (1985). Power System Harmonics, John
Wiley, Chichester, U.K.
5. Arrillaga, J. and Watson, N.R. (2003). Power System Harmonics, John Wiley,
Chichester, U.K.
6. Adamson, C. and Hingorani, N.G. (1960) High Voltage Direct Current Power Transmission,
Chapter 3, Garraway, London.
7. Dugan, R.C., McGranaghan, M.G., and Beaty, H.W., (1996). Electrical Power Systems
Quality, McGraw-Hill, New York.
8. Feature Article: “Reducing the Safety Hazard of Switchers,” Electronics Australia,
February 1990, 124–125.