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A Presentation on A Comparative Study of Short Term Flicker Severity Due to Electric Arc Furnace OperationAuthors : Pertha Protim Dutta Abul Hasan FahadDr. Abdul Hasib Chowdhury December 22, 2014

Salient Features Developing a comparative approach to observe flicker in the power system under several Operating Conditions

Voltage FlickerFlicker Cyclic Non cyclicSinusoidal variation of RMS voltage consideredRandom variation in voltage involved Effect of Voltage flicker quantified by Flicker Severity Indices

Short Term Flicker Severity Pst denotes the severity limit that should not be exceeded in order not to create malaise for an observer.

Calculated with the data of instantaneous flicker at every 10 minutes interval

Standard value depends on the base voltage of the bus

Allowable PstBus voltage level1.0132 KV0.8230 KV

Estimation of PstFor single EAF operation : From statistical evaluation of s(t) Direct approximation (Thumb rule) :In occurrence of sinusoidal fluctuation of system voltage short term flicker severity approximated directly from instantaneous flicker sensation by

Where Smax is the maximum value of s(t).

Estimation of PstFor multiple EAF operation : Cumulative Pst at PCC calculated by

Where , n= summation factor having range between [1,4]and Pst,i denotes flicker due to individual EAF operation Determining Summation factor , n :In parallel operation of identical EAFs (having same rating and modulation parameter), the summation factor can be determined directly using

Where, m = number of furnaces ln(Pst cum) = cumulative flicker severity ln(Pst ind ) = flicker severity for single EAF

Modulation Parameter Required to model the continuous change of arc length in each arcing cycle

To simulate the sinusoidal flicker phenomenon amplitude modulation index , m is chosen as the parameter

For stochastic (non sinusoidal ) flicker modeling the noise power ,P is selected as the modulation parameter.

Pst vs. EAF RatingsFor a fixed m and modulation frequency Pst increases with furnace ratings Both cyclic and non cyclic flicker shows similar trendsResults from the fact that EAF with higher power rating draws much higher current during Arc Extinction

EAF Ratings vs. Modulation Index

For keeping Pst under acceptable limit modulation parameter (m,P) must be reduced if EAF rating is higherSimulation reveals that same decisions can be drawn for parallel operation of EAFs

Effect of Pst on Modulation Frequency Value of Pst has been plotted with corresponding modulation frequency 6, 8.8 ,10 HzMaximum value occurs at f = 8.8 HzSo the rate of change of arc length should not be around that value.

Effect on Pst Due To Multiple EAF Operation

Severity of Sinusoidal Flicker

MW Rating of EAF-2 > EAF-1 chosen Summation factor n for parallel EAF operation found 1.94, 1.468 and 1.54, respectively Indicating that cumulative flicker level at PCC is more severe when two identical EAFs of smaller ratings are operated simultaneously.

Effect on Pst Due To Multiple EAF Operation

Severity of non cyclic Flicker

Simulated using maximum allowable noise power for the selected power rating Parallel operation causes objectionable flicker at PCC even though it is tolerable for standalone action

Summation factor n not fixed as cyclic flicker phenomenon

Variation of Modulation index in Parallel EAFs

Observed only for parallel EAF operation of identical power ratings Pst value at PCC remains approximately same if the summation of m of each furnace is constant This factor may be vital in installation of multiple EAFs in a region

Validitation of Thumb Rule Simulation ensures the validity of the thumb rule , for all cases of sinusoidal flicker sensation. Applicable both for single and multiple EAF operation of any ratings

Comparison of Pst Ratio in EAF OperationPst Ratio =Pst due to parallel EAF operation Pst due to single EAF operation Pst Ratio have been plotted with increasing modulation parameter both for cyclic and non cyclic flicker phenomena.

Comparison of Pst Ratio in EAF Operation contd. Simulation shows that at lower value of this parameter voltage flicker due to parallel operation of EAFs becomes prominent.

In case of sinusoidal flicker Pst ratio becomes less sensitive to variation of m at higher modulation indices. Non Cyclic flicker may not follow such trend

Potential Decisions Relative variation of arc length to be decreased for higher ratings of EAF for reliable operation Individual modulation indices have little effects on allowable Pst in sinusoidal flicker if the summation fulfils the condition.Comparison between cyclic and non-cyclic flicker : The former is more threatening to power system than the other. For non cyclic flicker no thumb rule is exactly satisfied.May be useful both for EAF operators and Power System Authority

List of ReferencesAngelo Baggini, Handbook of Power Quality, New York, USA: Wiley, April 2008. S. R. Mendis, M. T. Bishop, A. V. Do, D. M. Boyd, Investigation of transmission system voltage flicker due to multiple ac and dc arc furnaces, IEEE Trans. On Power Del., vol.10, no.1, Jan. 1995.IEC Standard 61000-4-15 (Edition 1.1, 2003-02): Electromagnetic Compatibility(EMC)Part4 Testing and Measurement TechniquesSection15 Flickermeter: Functional and Design Specifications.G. C. Montanari, M. Loggin, A. Cavallin, L. Pitti, D. Zaninelli, ARC-furnace model for the study of flicker Compensation in electrical networks, IEEE Transactions on Power Delivery, vol. 9, no. 4, Oct. 1994. M. Maksi, I. Papi, Network Flicker Levels due to Simultaneous Operation of Two Arc Furnaces, Proc. of 14th International Conference on Harmonics and Quality of Power (ICHQP, 2010), pp. 1-5, Bergamo, Italy, 26-29 Sept. 2010 IEEE PES 01TP151, "Tutorial on voltage fluctuations and lamp flicker in electric power systems", 2001.S. Varadan, E.B. Makram, Adly A. Gigris, A new time domain voltage source model for an arc furnace using EMTP, IEEE Trans. On Power Del., vol 11, no. 3,pp.165-1690, July 1996 M. Islam, A.H. Chowdhury, Comparison of dynamic resistance arc furnace models for flicker study, 7th International Conference on Electrical and Computer Engineering , December 2012, Dhaka, Bangladesh