chapter 5 load balancing of low-voltage...

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CHAPTER 5

LOAD BALANCING OF LOW-VOLTAGE DISTRIBUTION

NETWORK BY HEURISTIC METHODOLOGY

5.1 INTRODUCTION

The reduction of energy losses in the distribution of low voltage

distribution network has been achieved by using fuzzy logic based load

balancing in chapter 4. Though it is effective, further optimization by

reducing neutral current in the LV network is attempted and explained in this

chapter. This work presents load balancing using the heuristic methodology.

The main task of this investigation is how unbalance due to uneven

distribution of single phase loads at the secondary side of the distribution

network can be minimized further, as compared with fuzzy logic based load

balancing.

The unequal distribution of loads between the three phases of the

supply system determines the flow of unbalanced currents that produce

unbalanced voltage drops on the electric lines. This increase in neutral current

due to unbalance produces more line losses. Neutral flow will be less on a

system that has been phase balanced. The savings from reduced neutral flow

may range anywhere from thousands to millions of rupees in wasted fuel

costs, depending on the scale of distribution system and the imbalances that

exist. Hence this method analyzes the propagation of unbalance in LV

distribution network resulting in increase of neutral current.

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The suggested heuristic method reduces unbalance resulting in

decrease of neutral current value and ultimately reducing the losses of LV

network. Low voltage distribution systems need phase specific approach with

the neutral conductor as the fourth wire due to unbalance. Hence, the analysis

becomes more difficult than that of transmission systems which can be

represented by single phase equivalent diagrams. Additively, actual load data

collection is vitally important for the design at low voltage level. It will also

give a chance to observe the basic characteristics of the load and find the

consumer factors correctly. In this study, a comprehensive approach is

presented for the determination of span-by-span current distribution along low

voltage feeders. The actual distribution transformer with its LV network is

presented in this thesis in all chapters. Hence model developed is realistic.

The simulations are performed by utilizing actual data in order to take the

diversity between consumers into account. The literature survey indicates the

following procedures.

5.2 LITERATURE SURVEY

Distribution feeder line models that can be used in power flow and

short circuit analysis of balanced and unbalanced three phase distribution

feeders have been presented by Kersting and Phillips (1994). The major

conclusion drawn from the comparative studies is that there are significant

differences in phase power losses for balanced and unbalanced operating

conditions. Modeling of unbalanced three phase distribution feeders introduce

large errors making modeling a tough task.

Nevzat et al (1994) states that accurate determination of the neutral

conductor current distribution along a low voltage feeder is vitally important

due to two perspectives. The first one is to investigate the voltage profile

along the feeder. The second one is directly related with the economic

feasibility of the system (i.e. total losses occurred on the feeder). Results

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show that the unbalance results in considerable induced voltages and currents

through the neutral conductor. The suggestion of the paper is that the neutral

conductor should be selected in the same size with the phase conductors as

current flowing through neutral is sometimes more than the base phase

current.

Tsai-Hsiang Chen and Jeng Cherng (2000) present an effective

approach to optimize the phase arrangement of the distribution transformers

connected to a primary feeder for system unbalance improvement and loss

reduction. This method is specific to Taiwan electrical utility where

distribution transformer used is asymmetrical with an open wye-open delta

connection to obtain a 3 phase 4 wire service and also does not handle

secondary LV network.

5.3 ADVENT OF THE HEURISTIC METHODOLOGY

Fuzzy logic based load balancing discussed in earlier chapter 4 takes

the overall low voltage distribution network for load balancing and it balances

R, Y and B phase’s currents in the entire network. The results are fruitful, but

it does not guarantee reduction of neutral current in each section of the

network.

Fuzzy logic based load balancing effects load transfer between poles

by reconfiguring consumers in different poles of the selected LV network.

This will balance loads in the entire network but fails to balance loads in each

section of entire LV network. The approach which will guarantee reduction of

neutral current in each section that is in each span length of the entire low

voltage distribution network will bring down line losses to greater extent. To

solve the problem arising out of unbalance current in LV network more

effectively, the heuristic method has been developed, tested and validated in

this thesis.

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5.4 HEURISTIC METHOD LOAD BALANCING OF LV

NETWORK

Types of load conditions, load combinations and prediction of

unbalance currents in LV network have been discussed earlier elaborately in

the chapter 2 and chapter 4. For the different combination of loads described

consumers are shifted pole-wise so that all the individual poles of the

distribution transformer remains balanced after the process. By this approach,

the neutral current in all sections of LV distribution network gets reduced.

The flow chart explaining the procedure to shift consumers is shown in

Figure 5.1.

All load combinations and load conditions considered for overall

LV network has been adopted for each and every pole of the LV network in

which consumers (node) are connected. The objective of the switching logic

is to minimize neutral current. The difference between optimum current and

phase current is calculated. Each consumer’s current is compared with the

“difference value” and single consumer matching the difference value is

tabulated. Similar exercise is done for sum of currents of two consumers

taken at a time and three consumers taken at a time and results are tabulated.

The sum of currents of consumers which almost matches the “difference

value” is found out. The suggestion is given by consumer shifting logic to

shift those consumers from overloaded phase to under loaded phase. The

same logic is adopted for all the poles with connected consumers of entire LV

distribution network. The entire logic has been developed in c-program.

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Figure 5.1(a) Flow chart for Consumer Shifting Technique

F

Start

Read the consumer details from the excel file

and save them in the structure consumer

Find the number of poles, total number of

consumers and no. of consumers in each pole

For a pole, find IR, IY and IB ,

sum of currents in R, Y, B phase respectively

IR= IY = IB ? Pole is balanced

Iopt= (IR +IY + IB)/3

Find

r = IR – Iopt

y = IY – Iopt

b = IB – Iopt

Stop

A

YES

NO

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Figure 5.1(b) Flow chart for Consumer Shifting Technique

A

Check r, y, and b. If one of them is positive and

one is negative, set case = 1. Assign

corresponding phases as posphase and negphase.

If two phases are positive and one is negative,

set case = 2. Assign corresponding phases as

posphase, posphase1 and negphase.

If one phase is positive and two are negative,

set case = 3. Assign corresponding phases

as posphase, negphase and negphase1.

Is case=1? B

= posvalue

Find min1 = min [ | (∆ – current of

any consumer) | ]

C

YES

NO

∆

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Figure 5.1(c) Flow chart for Consumer Shifting Technique

YES

YES

C

Find min2 = min [ | ( ∆ – sum of currents

of any two consumers) | ]

Find min3 = min [ | ( ∆– sum of currents

of any three consumers) | ]

Find min (min1, min2, min3)

If there is no such consumer, print

“Cannot shift from posphase to

negphase”

Is

case=2D B NO

= posvalue

1∆ = posvalue1

E

∆

Shift the corresponding consumer(s) from

posphase to negphase

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Figure 5.1(d) Flow chart for Consumer Shifting Technique

E

Repeat steps of case = 1

for ∆ and 1∆

Is

case=3? D

∆= (negvalue) 1∆ = (negvalue1)

Repeat steps of case = 1 ∆ for 1∆

Find IR, IY and IB

sum of currents in R, Y, B phase after

balancing

Are all poles

considered?

Stop

F

Inconsistent Data

Stop YES

NO

YES

NO

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5.5 RECONFIGURATION USING HEURISTIC

METHODOLOGY

Three transformers have been examined for unbalanced condition of

LV network and overall balanced (between sections, between poles) condition

of LV network and results are studied in chapter 4. For analyzing with

heuristic method, two numbers of distribution transformers, Urban DT2 and

Urban DT3 are taken for study. Load balancing is effected within sections

taking into consideration all sections in the LV network. Based on the

analysis, the results obtained in simulation software by reconfiguring the

consumers (nodes) of Urban DT2 and Urban DT3 so as to balance the system

is presented in this section.

5.6 CASE STUDY 1: RECONFIGURATION OF URBAN DT2

The schematic diagram, low voltage distribution album (LV album)

and load analysis by distribution simulation package of urban DT 2 has been

already presented in the section 4.6. It contains twenty poles and the

consumers connected in different phases of each pole. It caters to the needs of

103 consumers with 96 single phase consumers connected in different phases

R, Y, B and 7 three phase consumers with balanced loads. The inputs to the

c-program are the single phase consumers for balancing suggestion. The three

phase consumers are industrial consumers whose loads are already balanced.

Though there are twenty poles, the c-program displays number of poles with

single phase consumers.

The snap shots of the consumer shifting program output for Urban

DT2 are shown below. The transformer profile of Urban DT2 is shown in

Figure 5.2(a). Figure 5.2(b) to Figure 5.2(j) display the status of the

consumers in poles before and after balancing.

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Figure 5.2(a) Urban DT2 Profile

Out of 20 poles in the LV network, the consumers are connected in

13 poles. 7 numbers of three phase consumers are connected in 4 poles and 96

numbers of single phase consumers are connected in 9 poles. Unbalance is

created due to the presence of 96 service connection single phase consumers

in 9 poles. The total number of consumers connected in each pole is as shown

in Figure 5.2(a), Urban DT2. By heuristic approach, balancing is suggested in

all 9 poles as shown in below figures (Figure 5.2(b) to Figure 5.2(j)) by

displaying service connection numbers of consumers to be shifted between

phases in each pole.

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Figure 5.2(b) Urban DT2 – Pole 5

Figure 5.2(c) Urban DT2 – Pole 6

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Figure 5.2(d) Urban DT2 – Pole 7

Figure 5.2(e) Urban DT2 – Pole 8

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Figure 5.2(f) Urban DT2 – Pole 9

Figure 5.2(g) Urban DT2 – Pole 10

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Figure 5.2(h) Urban DT2 – Pole 11

Figure 5.2(i) Urban DT2 – Pole 16

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Figure 5.2(j) Urban DT2 – Pole 18

5.6.1 CYMDIST Load flow Report

The transformer networks are simulated for load flow under

unbalanced and pole-wise balanced conditions. The load flow report of

unbalanced Urban DT2 is reproduced in Table 5.1 and Table 5.2 shows the

report for pole-wise balanced Urban DT2. From the tables it is observed that

neutral current gets reduced in each node (pole) in pole balanced transformer.

This is due to reconfiguration of consumers effected pole-wise, that is, within

section, all phase currents are balanced thereby reducing the neutral current.

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Table 5.1 CYMDIST Load flow Report of Unbalanced Urban DT2

Equipment No Real Power

(kW)

Voltage

(V)

IA

(A)

IB

(A)

IC

(A)

IN

(A)

3910 28.43 242.53 21.3 90.8 24.2 68.07

3908 23.62 244.53 112 0 0 112.3

3906 11.02 246.17 18.8 17 16.3 2.16

3904 10.65 247.83 17.8 16.4 15.8 1.74

3902 5.66 258.67 8.98 8.37 8.09 0.788

3900 22.63 259.00 35.8 33.4 32.3 3.124

3898 14.63 257.74 0 66 0 65.99

3896 4.35 258.30 0 19.6 0 19.57

3894 10.41 251.65 47.9 0 0 47.89

3892 28.79 251.02 0 133 0 132.85

3890 12.36 251.32 0 57.2 57.19

3888 12.27 251.29 0 56.8 56.78

3886 12.16 251.95 0 0 56.1 56.12

Table 5.2 CYMDIST Load flow Report of Pole-Balanced Urban DT2

Equipment

No

Real Power

(kW)

Voltage

(V)

IA

(A)

IB

(A)

IC

(A)

IN

(A)

3910 28.20 242.53 44.89 44.35 45.96 1.42

3908 24.97 244.53 39.91 39.6 39.21 0.61

3906 11.14 246.17 17.41 17.51 17.7 0.26

3904 10.74 247.83 16.7 16.78 16.93 0.20

3902 5.73 258.67 8.59 8.54 8.61 0.06

3900 22.81 259.00 33.94 34.09 34.37 0.38

3898 14.64 257.74 21.61 22.34 22.12 0.65

3896 4.68 258.30 6.97 8.11 5.98 1.85

3894 10.61 252.65 16.24 16.08 16.53 0.40

3892 28.72 252.82 45.81 42.15 44.14 3.17

3890 10.31 252.92 9.96 16.13 21.32 9.85

3888 12.54 252.87 18.91 18.34 20.41 1.85

3886 12.04 252.95 18.52 18.17 18.67 0.44

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5.6.2 Line Loss Report

Simulation result of urban DT2 with unbalanced and pole-balanced

configuration is tabulated in Table 5.3 and Table 5.4, respectively.

Table 5.3 CYMDIST Summary Report of Unbalanced Urban DT2

Summary kW kVAR kVA PF(%)

Total Generation 211.29 126.94 246.49 85.72

Load read (Non-adjusted) 199.7 96.72 221.89 90

Load used (Adjusted) 196.98 95.39 218.86 90

Total Loads 196.98 95.39 218.86 90

Line Losses 14.31 33.94 36.83 38.85

Cable Losses 0 0 0 0

Transformer Losses 0 0 0 0

Total Losses 14.31 33.94 36.83 38.85

Power loss in unbalanced Urban DT3 is found to be 14.31kW. After

pole-balancing of the network, the power loss is found to be 8.36kW. A

reduction of 41.6% is obtained.

Table 5.4 Cymdist Summary Report of Pole wise Balanced Urban DT2

Summary kW kVAR kVA PF (%)



Load used (Adjusted) 197.14 95.46 219 90

Total Loads 197.14 95.46 219 90

Line Losses 8.36 13.51 15.89 22.61



Total Losses 8.36 13.51 15.89 22.61

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The total power delivered from the transformer is 211.29 kW and

the total loss is 14.31 kW which is 6.77% of total power. After load balancing

the loss is arrived as 8.36kW, which is 4.0% of total power and there is

significant reduction of power loss up to 2.77%. If a condition is presumed in

which the transformer is operated with 211.29 kW of total power for the

period of 10 hours in a day then the energy delivered would be 2112.9 kWhr.

Loss reduction of 2.72% is equivalent to 58 units which is saving

met out from load balancing. An average cost of `3.20 is adopted to compute

the saving per transformer. The saving per transformer is 58*3.20=185 and

for one year 365*185= `67525 is arrived at. For 1,92,000 distribution

transformers in one electrical utility, the total saving per year will be

67525*1,92,000=12964.8 million rupees/annum.

5.7 CASE STUDY 2: RECONFIGURATION OF URBAN DT3

The schematic diagram, low voltage distribution album (LV album)

and load analysis by distribution simulation package of Urban DT 3 has been

already presented in the section 4.7. It contains fourteen poles and the

consumers connected in different phases of each pole. It caters to the needs of

83 single phase consumers connected in different phases R, Y, B in 7 poles

and 6 three phase consumers with balanced loads in 2 poles. The result of

consumer shifting logic is tabulated in Table 5.5.

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Table 5.5 Profile of Urban DT3 before and after Balancing

Optimum

Current

(A)

IR IY IB Iopt Sc NO I (A) From To IR IY IB

421 12 B R

645 10 B R

1089 10 B R

1100 8 B Y

1598 8 B Y

1198 8 B Y

1264 7 R B

126 12 R Y

927 11 R B

236 11 R B

649 10 R Y

946 12 R Y

820 6 Y R

895 4 Y B

1011 3 B R

1123 8 B R

1231 9 B Y

718 10 Y R

896 12 Y R

876 9 Y B

562 10 B R

1225 10 B R

124 9 B R

856 10 B Y

1162 10 B Y

1048 9 B Y

R,Y 29 29 30

22 23 22

7 14 0 0 88 29.33 B

5 13911B11330

41 40 43

R,Y09

35 50 39 41.33 Y R,B

R,BY22.3313540

22.3300

6

6773

10

4 8

18 18

B,YR 23 22 22

6 11 19 R B,Y 21

77 78134 77.33 B R,Y53

6

Pole

NoS.No

1 774 45

2 40

Phase ChangeAfter Balancing

Current in Amps

Over

Loaded

Phase

Under

Loaded

Phase

Before Balancing

Current in Amps

Consumers to be

Shifted

5.7.1 CYMDIST Load flow Report

The transformer network is simulated for load flow under

unbalanced and pole-wise balanced conditions. The load flow reports of

unbalanced and pole-wise balanced Urban DT3 are tabulated in Table 5.6

(reproduced from Table 4.8) and Table 5.7, respectively. From the tables, it is

observed that neutral current gets reduced in each node (pole) in pole –

balanced load flow report compared to unbalanced load flow report.

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Table 5.6 CYMDIST Load flow Report of Unbalanced Urban DT3

Equipment

No

Real

Power

(kW)

Voltage

(V)

IA

(A)

IB

(A)

IC

(A)

IN

(A)

3884 24.03 234.45 35.12 50.58 36.32 14.90

3883 11.80 237.70 40.33 6.76 11.99 31.28

3881 13.48 238.41 67.30 0.00 0.00 67.30

3878 48.74 239.33 45.02 53.99 143.45 94.27

3876 17.97 242.31 0.00 0.00 88.28 88.28

3874 20.07 243.46 32.88 33.73 31.53 1.92

3868 14.25 248.06 0.00 54.76 13.61 49.38

3866 7.07 248.43 0.00 0.00 33.86 33.86

3871 23.67 248.58 37.88 36.76 38.74 1.72

Table 5.7 CYMDIST Load flow Report of Pole wise Balanced Urban DT3

Equipment

No

Real

Power

(kW)

Voltage

(V)

IA

(A)

IB

(A)

IC

(A)

IN

(A)

3884 25.47 242.5 41.12 40.58 43.32 2.51

3883 12.09 244.5 21.33 18.76 18.75 2.58

3881 14.49 246.2 23.01 23.92 23.14 0.85

3878 48.84 247.8 77.31 78.56 78.76 1.36

3876 19.33 258.7 29.5 29.82 29.63 0.28

3874 21.35 259 32.88 33.73 31.53 1.92

3868 14.52 257.7 22.4 22.71 21.96 0.65

3866 7.41 258.3 11.53 9.41 13.21 3.30

3871 24.06 252.7 37.88 36.76 38.74 1.72

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5.7.2 Line Loss Report

Simulation result of Urban DT3 with unbalanced and pole-balanced

configuration is tabulated in Table 5.8 and Table 5.9, respectively.

Table 5.8 CYMDIST Summary Report of Unbalanced Urban DT3

Summary kW kVAR kVA PF(%)




Total Loads 181.07 88.81 203.73 90

Line Losses 7.13 41.16 41.78 17.06



Total Losses 7.13 41.16 41.78 17.06

Table 5.9 CYMDIST Summary Report of Balanced Urban DT3

Summary kW kVAR kVA PF (%)




Total Loads 187.56 90.85 208.42 90

Line Losses 4.11 35.75 35.99 11.41



Total Losses 4.11 35.75 35.99 11.41

The power loss in unbalanced Urban DT3 is found to be 7.13kW.

After pole-balancing of the network, the power loss is found to be 4.11kW. A

reduction of 42.3% is obtained. The total power delivered from the

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transformer is 192.33 kW and the total loss is 7.13 kW which is 3.7% of total

power. After load balancing the loss is arrived as 4.11kW, which is 2.1% of

total power and there is reduction of power loss up to 1.6%. If a condition is

presumed in which the transformer is operated with 192.33 kW of total power

for the period of 10 hours in a day then the unit delivered would be

1923.3 kWhr.

The loss reduction of 1.6% is 31 units which is saving met out from

load balancing. The average cost of Rs.3.20 is adopted to compute the saving

per transformer. The saving per transformer for one year 365*99= `36135 is

arrived at. For 1,92,000 distribution transformers in one electrical utility the

total saving per year will be 36135*1,92,000 = 6937.9 million rupees/annum.

In this thesis, a complete off-line package has been designed by

using heuristic methodology. The proposed load balancing technique

effectively meets the criteria to minimize energy loss which has been proved

by CYMDIST simulation. On an average, 41% power loss reduction is

accomplished in the case studies undertaken. Significant reduction in energy

losses and hence a huge savings in cost is ascertained by the aforesaid

approach.

Both the distribution transformers taken as case study belong to

urban area. Hence they represent worst-case study for the proof of the

method. If rural area or semi-urban area distribution transformer is load

balanced using heuristic method, the result will be very much beneficial to

electrical utility due to the presence of lengthy distribution lines in LV

network and scattered consumers.

chapter 5 load balancing of low-voltage...

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