Considering Voltage Variation at Distribution Level: A Proposal Dr. - - PowerPoint PPT Presentation

Electricity Tariff for a Retail Market Considering Voltage Variation at Distribution Level: A Proposal

• Dr. Pankaj Mishra

Assistant Professor Department of Electrical & Electronics Engineering BIT, Mesra Off – Campus Deoghar

Contents

• Why such tariff ?
• The technicality involved.
• The Proposal.

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Why Such Tariff ?

• Restructuring:

– DISCOMs are now independent players. – Competition in retail electricity market.

• Introduction of intermittent energy sources in Micro Grid:

– Fast fluctuations in output from wind, and/or solar energy disrupt the hourly load-following and – balance between total electric supply and demand

• On going expansion of distribution network.

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Contd.

• Changing lifestyle– Temperature dependent

Loads:

– Use of air conditioner and heating equipments

• Power Quality Issues:

– Prolonged voltage sag may cause voltage collapse in the system – Voltage fluctuation, sag and harmonics affect the working of various house hold and office electrical equipments and devices.

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The Technicality Involved

• Voltage instability is load driven phenomenon.
• Reactive power is strongly coupled with voltage

stability.

• Real power loading may also result in voltage

instability.

• Losses in the system exaggerate the problem of

voltage dip.

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Contd.

Voltage stability is the ability of a power system to maintain steady voltages after a disturbance. Must maintain or restore equilibrium between connected load, and load supply from the power system. Instability is progressive fall or rise of voltages at some buses. (IEEE/CIGRE)

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Contd.

Typical reasons of voltage collapse are:

– Outage of large generating units near load centers

• Results in reactive power mismatch
• Some lines may be heavily loaded so as to carry sufficient reactive

power to problematic parts of the grid.

– Outage of transmission line: This increases the reactive power requirement in the system. – Outage of static compensators – The tap changing operation of transformer.

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Contd.

• The mathematical equation showing the dependency
• f the voltage on the reactive power in simplified

form, is expressed as:

Where, R = resistance of line; X = reactance of the line; P = real power drawn; Q = reactive power drawn; and V = voltage at load point

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Contd.

• The change in series reactive loss increases sharply with

any drop in transmission voltage.

• P-V and V – Q curves illustrating the voltage instability

points.

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Contd.

• How summer affects the voltage stability:

– Increase in temperature during summer increases the use of air conditioning system [1]. – The traditional air conditioner aggravates the voltage sag condition by drawing more real and reactive power during voltage dip thus resulting in voltage collapse [3]. – Increased loss in the system adds to the ambient temperature resulting in insulation failures.

• Some facts:

– The low voltage problem of Patna in summer 2015. (Source: Local

newspaper)

– The power cuts & low voltage problem of Chennai during peak summer of

• 2016. (Source: Local newspaper)

– During the period 2007-08 to 2016-17 the consumption of electricity increased by 7.82%. Wherein more than 50% consumption arises from non – industrial sector. (As per Energy Statics 2018 Central Statistics Office Ministry

• f Statistics and Programme Implementation Government of India)

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The Proposal

• Applicable at distribution level.
• Will levy charges on retailers for not maintaining appropriate

reactive power.

• The charges will vary as per prevailing voltage level.
• The price corresponding to each voltage level is to be decided by

the system operator.

• The variation in voltage level over a specified period is

determined using statistical method.

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Contd.

Index of Voltage Deviation:

• The standard deviation (SD) can be calculated for the predefined

time period.

• As the system operator tries to keep the voltage at nominal value

and allow the variation of ±10%, thus any deviation from these limits will be clearly indicated by the high value of standard deviation.

• Hence, for each time period along with voltage value the standard

deviation and the mean is to be recorded by the operator.

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Contd.

The Pricing:

• Pricing structure for distribution level voltage monitoring can

be similar to that of pricing for unscheduled interchange in ABT for bulk power transfer.

• For voltage dip of more than 10%, the value of standard

deviation in the time period will be very high.

• And for slight variation in voltage values, the value of SD will

be near to 1.

• Thus, starting with normal values near to one the price will

increase with increasing value of SD.

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Contd.

Example showing the SD values for summer & winter season:

Station: Bawana-220 kV

Date Voltage Date Voltage

10-06-18 211 10-11-18 223 11-06-18 209 11-11-18 224 12-06-18 208 12-11-18 225 13-06-18 209 13-11-18 223 14-06-18 209 14-11-18 222 15-06-18 210 15-11-18 222 16-06-18 200 16-11-18 222 17-06-18 211 17-11-18 221 18-06-18 210 18-11-18 222 19-06-18 210 19-11-18 225 20-06-18 210 20-11-18 221 Standard Deviation: 3.060006

1.420627

Mean : 208.8182

222.7273

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Conclusion

• A regular monitoring and correction of the voltage at distribution system

is equally important as that of frequency at power grid level.

• As the voltage of the distribution network is uniform at all distributor

nodes, so a standard deviation can be used as an index for monitoring of the voltage of all nodes.

• Defining a tariff including voltage deviation is a need of the time,

because the residential and commercial load has now a remarkable contribution in the inductive loading of the system, especially in the summer or extreme temperature condition.

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References

• C.H. Lin, C. S. Chen, M. S. Kang, T.T. Ku, J.S. Huang, Z.S. Chiou, and C.W.

Huang, “Temperature Effect to Distribution Feeder Load Profiles and Losses”, 2006 International Conference on Power System Technology 1-4244-0111- 9/06/$20.00c2006 IEEE.

• Bei Wu, Yan Zhang, Minjiang Chen, “The Effects of Air Conditioner Load on

Voltage Stability of Urban Power System”, Proceedings of the 6th WSEAS International Conference on Power Systems, Lisbon, Portugal, September 22- 24, 2006.

• Katsuyuki Tomiyama John P. Daniel Satoru Ihara, “Modeling Air Conditioner

Load for Power System Studies”, IEEE Transactions on Power Systems, Vol. 13, No. 2, May 1998.

• S. Chakrabarti, “Notes on Power System Voltage Stability”, Dept. of EE, IIT,
• Kanpur. http://home.iitk.ac.in/~saikatc/EE632_files/VS_SC.pdf.
• https://www.delhisldc.org/Voltageprofile.aspx.

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THANK YOU

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