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Maximum Loss Reduction by Optimal Placement of Capacitors on a Distribution System B.V.Vibhute, Dr. H.P. Inamdar, and S.A. Deokar

Abstract -- This paper presents an implementation of a Novel Approach in radial distribution system for cost of loss reduction on an 11 KV distribution system consisting of 37 buses and 35 transmission lines. The study is carried out incorporating an appropriate load distribution model. This approach identifies an optimal location (node) of the capacitor by sequential comparison of line flows with previous ones followed by determination of size of the capacitor for maximum loss reduction by taking the voltage magnitude and currents at that particular node. The installation of capacitor indicated the reduction in total system losses and there is overall improvement in voltage profile of the system. A study has been carried out on the 11 KV distribution system. The objective of reducing the losses and improvement in voltage profile has been successfully achieved. After installation of capacitor, the system can save a total energy of 682.8 KWH per day, which is very substantial. Index Terms – Capacitor, Energy, Reactive Power, System loss, Voltage Profile.

and energy losses and to maintain the voltage profile within the acceptable limits. The amount of compensation provided is very much linked to the placement of capacitors in the distribution system, which is essentially determination of the location, size, number and type of capacitors to be placed in the system. The capacitor placement problem is a well research topic that has been addressed by many authors in the past. All approaches differ from each other by way of their problem formulation and problem solution methods employed. The paper proposes a method of minimizing the cost of loss associated with the reactive component of branch currents by placing optimal capacitors at proper locations. The method first finds the location of the capacitors in a sequential manner. Once the location is determined, the capacitor size at each location is determined through optimizing the reduction in the cost of losses. II. PROBLEM FORMULATION

I. INTRODUCTION HE I2R loss reduction in distribution systems is very essential to improve the overall efficiency of power system. The I2R losses can be separated into two parts based on the active and reactive components of the branch current. Capacitors have been very commonly used to provide reactive power compensation in distribution system. The amount of compensation provided is very much linked to the placement of capacitors in distribution feeders as it reduces power and energy losses, increases the available capacity of the feeders, and improves the feeder voltage profile. These capacitors also reduces the lagging component current, increases the power factor of generators, improves regulation and more importantly increases the savings and hence reduces the cost of power to consumers. Capacitors provide reactive power compensation in distribution systems. They are provided to minimize power

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B.V.Vibhute is with the Department of Electrical Engineering, Bharati Vidyapeeth Deemed University College of Engineering, Pune, India ([email protected]) Dr. H.P. Inandar is with the Department of Electrical Engineering, Walchand College of Engineering , Sangli, India S.A. Deokar is with the Department of Electrical Engineering, All India Shri Shivaji Memorial Societies College of Engineering, Pune, India ([email protected])

0-7803-9525-5/06/$20.00 ©2006 IEEE.

In the proposed method a sequence of nodes to be compensated by the capacitors are identified. The sequence is determined by repetitive application of minimization cost of loss technique satisfying with single capacitor located at proper node. Once the sequence of nodes to be compensated are identified, the corresponding optimal capacitor size at the compensated nodes can be determined simultaneously by minimizing the cost of loss saving equation with respect to the capacitor currents. Following sections describes the procedure for placement of capacitor. III. METHODOLOGY With the help of line flows and bus voltages and powers obtained from the load flow result, the branch current is calculated from the formula.

I ik = where Iik Pik Qik Vi

= = = =

Pik − jQik Vi

--- ------------(I)

Current through branch (ik). Total real power flow in the branch (ik). Total reactive power flow in the branch (ik). Voltage at node (i).

Total power loss

The loss saving S is the difference between equation (1) and (2) is given by

n

TPL = ¦ I ik2 Rik ik =1

S = TPLr–TPLrcom

where Rik = Resistance of branch (ik). n = Total number of branches. The branch current has two components: active (Ia) and reactive (If). The total loss associated with the active and reactive components of branch current can be written as, n

TPLa = ¦ I a2(ik ) Rik ik =1

n

ik =1

ik =1

The loss TPLa associated with the active component of branch current cannot be minimized For a single – source radial network because all active power must be supplied by the source at the root bus. However, supplying part of the reactive power demands locally, the loss TPLr associated with the reactive components of branch currents can minimized.

=

¦ (2 D

ik

ik =1

Rik − ¦ ( I r ( ik ) + D(ik ) I c ) 2 Rik ik =1

I r (ik ) I c + Dik I c2 ) Rik

The capacitor current Ic that provides maximum loss saving can be obtained from Ÿ δS/δIc=0

ªn º − 2 «¦ ( Dik I r (ik ) + Dik I c ) Rik » = 0 ¬ik =1 ¼ Thus the capacitor current form loss saving is given by

Ic =

.

n

2 r ( ik )

n

n

TPLr = ¦ I r2(ik ) Rik

¦ (I

=

− ¦ I r (ik ) Rik ik∈α

¦α R

ik ∈

----- (II)

ik

The corresponding capacitor size is

Qc = Vm I c

-----(III)

Where Qc = Capacitor size in KVAR Vm = Voltage magnitude of bus ‘m’ in volts Ic = Capacitor current in amps. The corresponding Susceptance is Fig. 1. Loss minimization using capacitor.

Let a capacitor be placed at bus ‘q’ and ‘α’ be a set of branches connected between the source and capacitor is placed and capacitor bus. A section of single line diagram is shown in Fig 1. If the capacitor is placed at ‘bus8’(q=8) the set α consists of branches a, b, c, f. Similarly when capacitor is placed at ‘bus 6’ (q=6) the set α consists of branches a, b, e. The capacitor draws a reactive current IC and for a radial network it changes only the reactive component of current of branch set α. The current of other branches (∉α) is unaffected by the capacitor. Thus the new reactive current th I rnew ( ik ) of the (ik) branch is given by,

I rnew ( ik ) = I r ( ik ) + D( ik ) I c where Dik = 1 ; if branch ik ∈ α = 0 , otherwise. Here Ir(ik) is the reactive current of the (ik)th branch in the original system obtained from the load flow solution. The loss TPLrcom associated with the reactive component of branch current in the compensated system (when the capacitor is connected) can be written as n

TPLcom = ¦ ( I r (ik ) + D(ik ) I c ) 2 Rik r ik =1

S = Ic

Vm

---------------------------(IV)

The proposed technique can also be repeatedly employed to further optimising saving of cost of energy by identifying sequence of buses to be compensated for further loss reduction by optimal placement of capacitor. IV. ALGORITHM Step 1 : Variable declaration. Step 2 : Opening of input and output file. Step 3 : Conversion of polar form of bus voltage to corresponding rectangular form. Step 4 : The branch current is calculated using (I) with the help of line flows. Step 5 :The resistance of each line is read from the input file. In order to find capacitor current. Step 6 :The destination is fixed as bus number ‘2’. The source count is taken as ‘37’. From the line flows, the From bus Of the 37th bus is compared with the bus of the previous branch line flow, if both are same, the branch is taken else it is left and is compared with the previous line.The process is repeated till the destination i.e bus ‘2’ is reached. Step 7:After finding the path, the capacitor current is calculated using the formula (II).

Step 8 :The capacitor size is found by the formula (III). Step 9 :The susceptance for the corresponding Q value is calculated by formula (IV). Step10 : Now the source count is decremented till it reaches bus number 2. Then the whole process is repeated from step 6. V. CASE STUDY & RESEARCH The technique proposed is tested on 11 KV distribution system. There are about 37 buses, 35 transmission lines and 28 load centres. The data regarding, line and transformers are collected and are converted into per unit values to feed to a load flow program. Load flow study of the base case system is carried out using Mipower package. The result shows a system loss of 10.179% and voltage drop of 2.1 KV. This tells about the scope for improvement in the distribution system. With the help of the proposed technique loss reduction is maximum when a capacitor is placed at 22nd bus. After installation, the load flow result indicate that the system loss is reduced from 10.179 to 8.127 % and there is an overall improvement in the voltage profile of the system

Total cost of capacitor = 345 * 220 * 4 = Rs. 3,03,600 VI. CONCLUSION The objective of reducing the losses and improvement in voltage profile has been successfully achieved studying 11 KV distribution system. After installation of capacitor, the system can save a total energy of 862.8 KW per day, which is very substantial. The repeated simulation results could be used to develop a Neural Network Model which can accurately predict the location and size of capacitor for any load conditions which gives a great promise for practical implementation of the proposed technique. The proposed method was tested on a 11 KV distribution system and promising results were obtained. VII. REFERENCES [1]

[2]

TABLE I POWER SAVING WITH CAPACIOR AND WITHOUT CAPACITOR [3]

Power Without placing capacitor

Power With the capacitor placed at 33rd bus

Difference in Active Power

Full load

0.2600

0.177

0.083

Half – Load

0.0559

0.0405

0.0154

Loading

The load period per day is aassumed as Full-load = 6 hrs Half –load = 12 hrs The cost of 1 KVAR of capacitor = Rs. 225 The cost of 1 KWH of energy = Rs. 2.5 Table I. presents computation results of active power with and without capacitor placement. Energy Saving per day: F.L. = 0.083 * 6 * 103 = 498 KWH H.L = 0.0154 * 12 * 103 = 184.8 KWH --------------------------Total savings per day = 682.8 KWH --------------------------Total cost of energy saved per day = 682.8 * 365 * 2.5 = Rs. 6,23,055. A capacitor bank consisting of 4 capacitors each of 340 KVAR is installed at 22nd bus. The capacitor bank is switched on / off according to the loading condition.

[4]

[5]

[6] [7]

S.I.Wamoto and Y.Tamura (1981), “A load flow calculation method for ill-conditioned power system”, IEEE Trans. on Power Apparatus and Systems, Volume100, pp.1736-1740. D. Rajicic and Y.Tamura (1988), “A modification to fast decoupled power flow for networks with high R/X Ratio”, IEEE Trans. on Power Systems, Volume 3, pp. 341- 348. [3] W.H.Kersting and D.L.Mendive (1796), “An application of ladder networks theory to the solution of three phase radial load flow problem”, IEEE PES winter meeting, New York, paper A76 044-8. Aoki K, Kuwabara H, Satoh t, Kanezashi M (1988), “An efficient algorithm for load balancing of transformers and feeders”. IEEE Trans Power Deliv, Volume 3 (issue 4), pp.1865-1872. Aoki k, Ichimori T, Kanezashi M. (1985), “Normal state optimal load allocation in distribution systems”. IEEE Trans Power Deliv, Volume 3 (issue 1), pp. 147-155. S.Sivanagaraju, M.S.Giridhar, E.Jagadeesh Babu and Y. Srikath (2004), “A novel load flow technique for radial distribution system”,Proc. of National Power System Conference (NPSC-2004), IIT, Chennai, India, pp. 140- 144. D.M. Tagare, Reactive Power Management, McGraw-Hill, 2000. Rani and Vijaya, “Distribution system loss reduction by capacitors”,Proc. of National Conference on Emerging Trends in Engineering(2000), Husur.

VIII. BIOGRAPHIES B.V. Vibhute received the B.E. Degree in Electrical from Shivaji University in 1993, M.E. Degree in Electrical Power System from Pune University in 2002 and perusing Ph.D. Degree under Bharati Vidyapeeth Deemed University, Pune. Presently working as Assistant Professor at Bharati Vidyapeeth Deemed University College of Engineering, Pune. His research interests are electricity sector deregulation and ancillary service pricing and management. Dr. H.P. Inamdar received the B.Sc. Degree from Pune University in 1961,B.E. Degree in Electrical and Mechanical from Shivaji University in 1964 and 1965 respectively, M.E. Degree in Electrical from Shivaji University in 1975 and Ph.D. Degree in H.V. Engineering from Indian Institute of Science, Banglore in 1985. Presently working as Professor at Walchand College of Engineering, Sangli. S.A. Deokar is perusing M.E. Degree in Electrical Power System from Pune University and Presently working as Lecturer at All India Shri Shivaji Memorial Societies College of Engineering, Pune. His research interests are modeling and design of hybrid renewable energy system and energy conservation.