Distributed Generator For Loss Minimization Biology Essay

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Distribution systems, whether they are radial type systems found in rural or suburban areas, or network type systems found in urban areas are generally designed to operate without any generation on the distribution system or at customer loads. The introduction of generation sources on the distribution system can significantly impact the flow of power and voltage conditions at customers and utility equipment. These impacts may manifest themselves either positively or negatively depending on the distribution system operating characteristics and the DG characteristics. Positive impacts are generally called "system support benefits," and include:

Loss reduction

Improved utility system reliability

Voltage support and improved power quality

Transmission and distribution capacity release

Deferments of new or upgraded TBD infrastructure

Improved utility system reliability

Achieving the above benefits is in practice much more difficult than is often realized. The DG sources must be reliable, dispatchable, of the proper size and at the proper locations. They must also meet various other operating criteria. Since many DGs will not be utility owned or will be variable energy sources such as solar and wind, there is no guarantee that these conditions will be satisfied and that the full system support benefits will be realized. In fact, power system operations may be adversely impacted by the introduction of DG if certain minimum standards for control, installation and placement are not maintained. This chapter will address how to achieve equipment deferments or T&D capacity release with DG; that is a comprehensive topic in itself that is best dealt with in a separate paper. Rather, this paper is focusing on the voltage quality, loss reduction and reliability factors associated with DG. For DG to have a positive benefit in these areas, it must at least be suitably "coordinated" with the system operating philosophy and feeder design. This means addressing issues related to voltage regulation, voltage flicker, harmonic distortion, islanding, grounding compatibility, over current protection, capacity limits, reliability and other factors. The larger the aggregate DG capacity on a circuit relative to the feeder capacity and demand, the more critical is this "coordination" with these factors.

Distributed Generation [DG] [104] is any small-scale electrical power generation technology that provides electric power at or near the load site. It is either interconnected to the distribution system or directly to the customer's facilities, or both. The Distributed Power Coalition of America (DPCA) research indicates that distributed power has the potential to capture up to 20% of all new generating capacity, or 35 Giga Watts (GW), over the next two decades. Recent development in small generation technologies has drawn attention of the utilities to bring in change in the distribution system infrastructure for adapting Distributed Generation (DG) .Employment of DG technologies make it more likely that electricity supply system may depend on DG systems that are operated in deregulated environment to achieve a variety of benefits. As DG systems generate power locally to fulfill customer demands, appropriate size and placement of DG can drastically reduce power losses in the system. DG inclusion also defers generation, transmission and distribution upgrades, improves supply quality, reliability and reduces green house effects.

While most works have been done on DG placement in radial balanced distribution systems, very little research has been done on DG placement and sizing in unbalanced radial distribution systems. Cheng and Shirmohammadi [41] proposed PV nodes for three phase unbalanced system. Noel Schulz and Sarika Khushalani [118] developed three phase unbalanced power flow algorithm with the choice of modeling DG (single and multiple) as PQ or PV node. Chen et.al [24] proposed different mathematical modeling of DG and transformers.

In this chapter, voltage sensitive nodes are first identified by penetrating DG with 20% of the total feeder loading, at each node and the node with least voltage index after placing DG will be picked as the best location for the DG placement. The sizing method is formulated as a constrained optimization problem adapted from a reactive power compensation sizing algorithm. Variational Algorithm is used to find the optimal size of the DG with the standard size of the DGs. The objective function formulated is to minimize the system losses satisfying the voltage and power limits.

7.2 Mathematical Formulation for DG Model

The DG can be treated as PV or PQ model in the unbalanced radial distribution system (URDS). The PV model represents a DG which delivers power at a specific terminal voltage; while PQ model DG delivers power irrespective of the node voltage. The latter DG model representation is adopted here. Such source is modeled as a negative load delivering real and reactive power to the unbalanced distribution system.

The objective function of the present work is to,

(7.1)

subjected to

Voltage constraint

Voltage magnitude at each node must lie with their permissible ranges to maintain power quality.

(7.2)

Current constraint

Current magnitude of each branch (feeder, laterals, and switches) must lie with their permissible ranges.

(7.3)

Power source limit constraint

The total loads of a certain partial network can not exceed the capacity limit of the corresponding power source.

(7.4)

(7.5)

Distributed Generator losses constraint

The distributed generator active losses of the network can not exceed the total active power line losses of the network.

(7.6)

Distributed Generator power constraint

Limit on total power generated by DG subject to a penetration level of 20% (i.e. it must not exceed 20% of feeder load).

(7.7)

(7.8)

7.3 Basis for Location of DG Placement

The placement of DG is chosen at such a place which gives the best voltage profile of the unbalanced radial distribution network. This could be done by injecting 20% of the DG at each node and calculating the voltage index by using eqn. (7.9). The node with least voltage index is selected as the best location for DG placement.

Voltage index () is defined as

(7.9)

Where is voltage at qth node and n is is the number of nodes.

The voltage index is calculated for unbalanced system analysis with 20% DG penetration. Though per-phase analysis gives better voltage indices as compared to unbalanced analysis, they may not be representing the actual conditions.

7.4 DG Size

In this section determination of the amount of standard DG that can be added at the identified nodes without loss increase and operational constraints violation is presented. Given information is on the available distributed generation and assuming no expected load growth in the region of interest. Variational algorithm is used to deal with this optimization problem. The size of the DG is changed in ''small'' steps as per the standard available size and power loss in each step is calculated using URDS load flow. The losses obtained are compared with the losses obtained in previous step. The size is changed in steps till there is no change in reduction of losses

7.5 Algorithm for DG Placement and Sizing

Step 1: Run the base case URDS load flow.

Step 2: Find the voltage index at each node (i.e. one at a time) using eqn. (7.9) by penetrating 20% DG value at respective node and rank the sensitivities of all nodes in ascending order to form priority list.

Step 3: Select the bus with lowest priority and place DG at that bus.

Step 4: Change the size of DG in ''small'' steps and calculate power loss for each by running URDS load flow.

Step 5: Store the size of DG that gives minimum loss.

Step 6: Compare the loss with the previous solution. If loss is less than previous solution, store this new solution and discard previous solution.

Step 7: Repeat Step 4 to Step 6 for all buses in the priority list.

Step 8: End

Simulation Results and Analysis

Case Study I : 25 - Bus URDS

The proposed algorithm is tested on 4.16 kV, 25-bus unbalanced radial distribution system shown in Fig. 7.1. The line and load data are given at Appendix D in Table D1 and line impedance is shown in Table D2.

Fig. 7.1 Single line diagram of 25-bus URDS

Fig. 7.2 shows the voltage index values of the 25-bus URDS to place the DG at suitable place. From the voltage sensitivity analysis, optimal placement of the DG is at bus 13 and size of the DG from the variation algorithm has been placed with 6 kW at 0.85 lagging power factor.

Fig. 7.2 Voltage Index for 25-bus URDS

Fig. 7.3 Voltage magnitude variation in all the phases for base case and after DG placement for 25 bus URDS

Table 7.1 Voltage profile for 25-bus URDS after DG placement

Bus No

Phase a

Phase b

Phase c

|Va| p.u.

Va

deg.

|Vb| p.u.

Vb

deg.

|Vc| p.u.

Vc

deg.

1

1.0000

0.00

1.0000

-120.00

1.0000

120.00

2

0.9760

-0.43

0.9767

-120.30

0.9801

119.47

3

0.9691

-0.56

0.9701

-120.41

0.9745

119.31

4

0.9657

-0.62

0.9669

-120.46

0.9721

119.24

5

0.9646

-0.62

0.9659

-120.46

0.9711

119.23

6

0.9665

-0.40

0.9670

-120.24

0.9711

119.48

7

0.9590

-0.37

0.9595

-120.18

0.9639

119.49

8

0.9644

-0.39

0.9650

-120.23

0.9693

119.47

9

0.9585

-0.35

0.9588

-120.15

0.9634

119.51

10

0.9595

-0.32

0.9593

-120.13

0.9640

119.53

11

0.9607

-0.31

0.9603

-120.12

0.9650

119.55

12

0.9597

-0.31

0.9591

-120.11

0.9640

119.55

13

0.9640

-0.30

0.9634

-120.11

0.9682

119.56

14

0.9532

-0.37

0.9538

-120.15

0.9581

119.47

15

0.9510

-0.37

0.9517

-120.14

0.9562

119.47

16

0.9580

-0.37

0.9585

-120.18

0.9629

119.48

17

0.9520

-0.37

0.9527

-120.15

0.9568

119.48

18

0.9632

-0.56

0.9643

-120.39

0.9690

119.30

19

0.9584

-0.55

0.9601

-120.38

0.9647

119.31

20

0.9608

-0.56

0.9620

-120.38

0.9667

119.30

21

0.9597

-0.55

0.9606

-120.38

0.9653

119.31

22

0.9578

-0.55

0.9582

-120.37

0.9633

119.32

23

0.9624

-0.62

0.9640

-120.46

0.9695

119.23

24

0.9604

-0.62

0.9622

-120.46

0.9678

119.23

25

0.9580

-0.62

0.9604

-120.46

0.9659

119.23

Fig. 7.3 shows the voltage variation of the 25 bus URDS for base case as well as after the DG placement. Table 4.4 and Table 7.1 are given the voltage and voltage angles for the base case and after DG placement. From Table 4.4 and Table 7.1, it has been observed that the minimum voltages in phases a, b & c are improved from 0.9284, 0.9284 and 0.9366 p.u without DG placement to 0.9510, 0.9517, 0.9562 p.u with DG placement respectively. Hence improvement has been observed in the minimum voltage and voltage profile of the system in all the phases after DG placement.

Fig. 7.4 Real power losses in all the phases for base case and after DG placement for 25 bus URDS

The total real power losses of the 25 bus URDS system is improved in phases a, b & c from 52.82, 55.44 and 41.86 kW to 31.48, 32.86 and 24.67 kW respectively. Fig. 7.4 shows the variation of the real power losses in the each branch of the phases a, b & c for the before and after the DG placement respectively. The total reactive power losses of the system are improved in phases a, b & c from 58.29, 53.30 and 55.69 kVAr to 36.44, 31.12 and 34.93 kVAr respectively. Table 4.5 and Table 7.2 shows the 25 bus URDS power flows before and after DG Placement.

Table 7.2 Power flows for 25-bus URDS after DG Placement

Bus From

Bus To

Phase a

Phase b

Phase c

P

(kW)

Q (kVAr)

P

(kW)

Q

(kVAr)

P

(kW)

Q

(kVAr)

1

2

889.78

695.19

901.16

700.88

892.97

701.68

2

3

511.56

382.10

516.50

378.28

510.01

377.37

2

6

361.92

289.96

367.29

301.58

371.53

302.21

3

4

246.60

186.61

246.39

178.32

231.03

166.20

3

18

227.22

166.59

227.27

166.49

232.12

175.60

4

5

40.04

30.03

40.04

30.03

40.04

30.03

4

23

155.89

115.65

145.71

102.48

140.62

100.46

6

7

278.13

227.23

278.23

236.94

293.02

244.43

6

8

40.09

30.06

40.09

30.06

40.08

30.06

7

9

10.81

29.31

15.73

39.25

10.73

34.26

7

14

225.03

166.26

220.04

166.11

240.02

178.36

7

16

40.04

30.03

40.05

30.03

40.04

30.03

9

10

-49.21

-15.70

-34.30

-0.77

-39.29

-0.75

10

11

-84.26

-40.73

-74.32

-30.79

-84.31

-32.77

11

12

50.05

35.03

60.08

45.05

50.05

40.04

11

13

-179.40

-107.84

-169.47

-100.88

-174.44

-102.87

14

15

133.60

100.22

133.61

100.20

133.56

100.21

14

17

40.05

30.04

35.04

25.03

45.06

32.04

18

20

95.40

70.29

90.32

65.21

95.34

72.25

18

21

90.44

65.30

95.54

70.36

95.49

72.34

20

19

60.15

45.11

50.10

35.07

50.11

40.07

21

22

50.10

35.07

60.15

45.11

50.11

40.08

23

24

95.35

70.25

95.27

62.18

90.25

65.18

24

25

60.15

45.11

50.09

30.06

50.10

35.07

Table 7.3 Summary of Test Results for 25 bus URDS for DG placement

Before DG Placement

After DG Placement

Description

Phase a

Phase b

Phase c

Phase a

Phase b

Phase c

Distributed generator placed node and size of DG

13

-

-

-

215 kW

at 0.85 p.f

215 kW

at 0.85 p.f

215 kW

at 0.85 p.f

Minimum Voltage

0.9284

0.9284

0.9366

0.9510

0.9517

0.9562

Voltage regulation (%)

7.16

7.16

6.34

4.90

4.83

4.38

Improvement of Voltage regulation (%)

-

-

-

31.56

32.54

30.91

Active Power Loss (kW)

52.82

55.44

41.86

31.48

32.86

24.67

Total Active Power Loss reduction (%)

-

-

-

40.40

40.73

41.07

Reactive Power Loss (kVAr)

58.29

53.30

55.69

36.44

33.12

34.93

Total Reactive Power Loss reduction (%)

-

-

-

37.49

37.86

37.28

Total Demand (kW)

1126.12

1138.74

1125.16

1104.78

1116.16

1107.97

Total Released Demand (kW)

-

-

-

21.34

22.58

17.19

Total Reactive Power Demand (kVAr)

850.29

854.30

855.69

828.44

834.12

834.93

Total Released Reactive Power Demand (kVAr)

-

-

-

21.85

20.18

20.76

Total Feeder Capacity (kVA)

1411.09

1423.57

1413.60

1380.88

1393.40

1387.34

Total Released Feeder Capacity (kVA)

-

-

-

30.54

30.28

26.87

Table 7.3 has been shown the summary of test results obtained before and after DG placement for 25 bus URDS.

7.6.2 Case Study II : 37-bus IEEE URDS

The problem of placement and sizing of the capacitors banks has been solved for the unbalanced IEEE 37-bus test system shown in Fig. 7.5 [127] where the original voltage regulator has been removed; the IEEE 37-bus test system is an actual unbalanced distribution system located in California.

Fig. 7.5 Single line diagram of IEEE 37-bus URDS

The nominal voltage level of the test network is 4.8 kV with three-wire delta operation. All the line segments are underground. All loads are spot loads and consist of constant PQ and loading is very unbalanced. The line and load data, line impedance, line charging admittances, substation and transformer data are given at Appendix D in Tables D3, D4, D5 and D6 respectively.

Fig. 7.6 Voltage Index for 37-bus IEEE URDS

From the voltage sensitivity analysis, it is observed that node 722 is the best location for DG placement. Voltage index graph for IEEE 37-bus is shown in fig. 7.6. From the graph it has been observed that node 722 shows the minimum voltage index, hence the best location for DG placement. The DG size from the variational algorithm at 722 is 495 kW at 0.85 lagging power factor.

Table 7.4 Voltage profile of base case and after capacitor placement for IEEE 37bus URDS

Bus No.

Base case

After Capacitor placement

Phase a

Phase b

Phase c

Phase a

Phase b

Phase c

|Va| p.u.

Va

deg.

|Vb| p.u.

Vb

deg.

|Vc| p.u.

Vc

deg.

|Va| p.u.

Va

deg.

|Vb| p.u.

Vb

deg.

|Vc| p.u.

Vc

deg.

799

1.0000

0.00

1.0000

-120.00

1.0000

120.00

1.0000

0.00

1.0000

-120.00

1.0000

120.00

701

0.9878

-0.66

0.9894

-120.27

0.9812

119.70

0.9989

-0.60

0.9968

-120.18

0.9873

119.80

702

0.9808

-1.17

0.9825

-120.37

0.9722

119.54

1.0003

-1.06

0.9959

-120.21

0.9817

119.74

703

0.9720

-1.62

0.9779

-120.48

0.9652

119.44

0.9980

-1.46

0.9958

-120.28

0.9768

119.70

730

0.9658

-1.93

0.9736

-120.40

0.9593

119.42

0.9973

-1.77

0.9952

-120.22

0.9720

119.69

709

0.9636

-2.02

0.9720

-120.39

0.9581

119.42

0.9970

-1.86

0.9949

-120.21

0.9711

119.69

708

0.9600

-2.17

0.9705

-120.38

0.9559

119.43

0.9961

-2.00

0.9954

-120.20

0.9695

119.70

733

0.9558

-2.32

0.9715

-120.38

0.9535

119.49

0.9929

-2.15

0.9967

-120.20

0.9667

119.76

734

0.9505

-2.56

0.9727

-120.35

0.9490

119.57

0.9891

-2.38

0.9985

-120.17

0.9614

119.83

737

0.9437

-2.71

0.9746

-120.40

0.9471

119.67

0.9834

-2.53

1.0005

-120.22

0.9590

119.93

738

0.9418

-2.80

0.9754

-120.39

0.9454

119.71

0.9820

-2.61

1.0014

-120.21

0.9571

119.96

711

0.9421

-2.87

0.9758

-120.34

0.9432

119.71

0.9825

-2.68

1.0020

-120.16

0.9548

119.96

741

0.9422

-2.89

0.9760

-120.32

0.9425

119.71

0.9827

-2.70

1.0022

-120.15

0.9540

119.96

713

0.9805

-1.28

0.9797

-120.31

0.9703

119.50

1.0027

-1.17

0.9953

-120.16

0.9807

119.70

704

0.9797

-1.39

0.9752

-120.26

0.9694

119.44

1.0057

-1.28

0.9939

-120.12

0.9811

119.64

720

0.9816

-1.47

0.9685

-120.14

0.9672

119.29

1.0127

-1.37

0.9915

-120.03

0.9815

119.52

706

0.9819

-1.47

0.9674

-120.14

0.9674

119.28

1.0131

-1.37

0.9906

-120.02

0.9816

119.50

725

0.9820

-1.48

0.9667

-120.13

0.9675

119.27

1.0133

-1.37

0.9899

-120.01

Contd . . .0.9816

119.49

705

0.9811

-1.24

0.9807

-120.31

0.9704

119.53

1.0010

-1.12

0.9943

-120.16

0.9796

119.73

742

0.9812

-1.23

0.9791

-120.30

0.9707

119.51

1.0012

-1.12

0.9928

-120.15

0.9798

119.71

727

0.9703

-1.69

0.9777

-120.47

0.9642

119.46

0.9968

-1.53

0.9957

-120.27

0.9755

119.72

744

0.9690

-1.74

0.9776

-120.47

0.9641

119.48

0.9959

-1.57

0.9958

-120.28

0.9752

119.74

729

0.9682

-1.75

0.9777

-120.48

0.9642

119.49

0.9953

-1.59

0.9959

-120.28

0.9752

119.75

775

0.9636

-2.02

0.9720

-120.39

0.9581

119.42

0.9970

-1.86

0.9949

-120.21

0.9711

119.69

731

0.9640

-2.01

0.9699

-120.38

0.9584

119.38

0.9976

-1.85

0.9930

-120.20

0.9712

119.65

732

1.0000

0.00

1.0000

-120.00

1.0000

120.00

1.0000

0.00

1.0000

-120.00

1.0000

120.00

710

0.9510

-2.69

0.9717

-120.27

0.9464

119.56

0.9903

-2.50

0.9978

-120.11

0.9583

119.83

735

0.9511

-2.72

0.9719

-120.26

0.9453

119.57

0.9905

-2.53

0.9979

-120.09

0.9572

119.84

740

0.9422

-2.90

0.9760

-120.32

0.9421

119.71

0.9828

-2.71

1.0022

-120.15

0.9536

119.97

714

0.9792

-1.40

0.9752

-120.26

0.9695

119.44

1.0053

-1.29

0.9939

-120.12

0.9811

119.65

718

0.9764

-1.44

0.9756

-120.28

0.9699

119.48

1.0030

-1.33

0.9944

-120.15

0.9813

119.68

707

0.9832

-1.53

0.9580

-120.01

0.9675

119.16

1.0226

-1.52

0.9888

-120.01

0.9881

119.31

722

0.9833

-1.53

0.9569

-119.99

0.9675

119.15

1.0238

-1.53

0.9887

-120.01

0.9889

119.29

724

0.9834

-1.58

0.9559

-119.97

0.9678

119.14

1.0234

-1.57

0.9870

-119.98

0.9880

119.29

728

0.9686

-1.75

0.9772

-120.46

0.9637

119.48

0.9957

-1.59

0.9954

-120.27

0.9747

119.74

736

0.9514

-2.78

0.9683

-120.22

0.9469

119.52

0.9916

-2.60

0.9948

-120.05

0.9582

119.79

712

0.9813

-1.28

0.9809

-120.29

0.9691

119.54

1.0014

-1.16

0.9946

-120.14

0.9782

119.73

Table 7.5 Power flows of base case and after capacitor placement for IEEE 37-bus URDS

Bus

From

Bus To

Base Case

After Capacitor Placement

Phase a

Phase b

Phase c

Phase a

Phase b

Phase c

P

(kW)

Q

(kVAr)

P

(kW)

Q

(kVAr)

P

(kW)

Q

(kVAr)

P

(kW)

Q

(kVAr)

P

(kW)

Q

(kVAr)

P

(kW)

Q

(kVAr)

799

701

964.09

1129.30

1554.00

1130.80

1198.90

1552.50

409.37

428.71

98.10

517.70

642.97

511.29

701

702

791.90

645.61

1392.4

895.51

826.79

1216.80

274.69

489.11

82.83

362.87

313.33

286.43

702

703

521.25

410.87

690.46

531.81

471.17

581.96

324.62

197.69

43.76

191.77

236.02

197.31

703

730

387.58

349.82

549.54

419.96

382.77

494.64

196.92

159.75

37.77

146.78

159.18

143.21

730

709

378.12

255.53

543.44

421.86

296.22

453.90

197.28

152.79

37.21

147.06

81.37

89.31

709

708

377.84

280.68

436.18

394.45

288.92

365.52

195.78

126.69

29.32

53.57

81.96

88.83

702

705

101.52

85.60

228.71

153.77

99.35

216.64

10.07

53.60

8.15

93.48

77.08

53.57

702

713

166.34

147.75

467.57

204.76

251.04

412.55

55.76

234.27

28.87

78.36

0.46

32.55

703

727

132.08

60.64

138.74

110.48

86.51

85.81

128.20

32.69

3.57

46.23

77.87

51.73

709

731

0.16

25.21

106.67

27.17

6.91

88.19

1.65

25.54

7.72

93.55

0.50

0.30

709

775

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

708

733

375.24

323.38

196.06

337.27

257.32

164.43

352.45

48.74

9.22

43.15

230.88

163.16

708

707

2.11

42.73

239.43

57.03

31.14

200.98

156.56

174.23

19.61

10.73

148.60

74.73

733

734

289.73

291.41

180.53

247.69

257.12

164.57

268.76

12.07

8.45

43.65

230.77

162.49

734

737

277.78

216.75

74.89

264.67

127.22

60.19

261.11

89.36

2.64

1.50

115.12

81.12

734

710

8.35

34.11

97.51

12.24

87.54

83.45

5.74

66.28

4.98

45.72

75.64

54.66

737

738

137.26

156.84

55.90

113.16

127.14

60.46

125.11

18.42

1.72

0.98

115.54

80.63

738

711

11.14

106.06

36.44

21.65

127.09

60.68

3.99

42.89

1.00

0.57

Contd . . .115.92

80.15

711

741

2.918

36.38

11.278

6.72

42.00

20.87

1.25

13.34

0.36

0.20

38.93

26.03

711

740

8.19

69.86

25.16

14.72

85.02

39.95

2.74

29.02

0.14

0.08

77.17

53.66

713

704

157.87

63.06

454.87

211.86

165.48

372.50

56.04

220.03

28.14

78.73

76.48

20.72

704

714

102.06

13.31

83.76

91.38

1.61

21.60

102.75

9.26

2.53

22.74

0.77

0.45

704

720

10.66

21.25

312.29

60.19

118.91

285.73

158.59

210.18

24.46

56.52

74.64

21.78

720

707

2.11

42.97

240.42

56.98

31.07

201.93

161.12

175.36

19.57

10.62

150.68

75.17

720

706

0.01

18.38

57.56

11.54

2.31

43.95

0.91

19.07

3.70

46.42

0.89

0.53

706

725

0.01

18.08

57.54

11.84

2.302

44.21

0.87

18.21

2.98

46.79

0.19

0.11

705

742

8.01

16.09

102.94

38.76

6.99

88.35

8.63

15.94

7.60

93.67

0.22

0.13

705

712

93.42

101.86

125.41

115.08

92.06

128.36

1.48

37.16

0.17

0.10

77.59

53.06

727

744

129.04

32.24

120.46

121.24

44.46

64.95

126.94

11.04

3.16

46.47

38.71

25.97

744

725

44.99

35.49

75.37

50.24

44.45

65.18

42.73

11.83

2.51

46.83

39.31

25.61

744

729

42.00

2.08

22.96

35.28

0.00

0.073

42.08

0.09

0.20

0.11

0.19

0.11

710

735

8.32

70.99

24.24

14.21

85.02

39.95

2.47

28.05

0.14

0.08

77.42

53.30

710

736

0.01

36.36

73.21

2.48

2.41

43.93

3.29

36.85

3.60

46.50

0.84

0.49

714

718

85.04

8.86

35.13

77.95

0.00

0.13

84.72

12.47

0.37

0.21

0.36

0.21

707

724

0.00

34.22

71.295

3.71

2.19

44.18

1.86

34.58

3.36

46.65

0.52

0.32

707

722

2.08

8.45

168.44

53.38

28.35

157.86

164.14

142.03

15.43

35.64

150.72

75.88

Table 7.4 is given the voltage and voltage angles for the base case and after DG placement. From Table 7.4, it has been observed that the minimum voltages in phases a, b & c are improved from 0.9418, 0.9559 and 0.9421 p.u. without DG placement to 0.9820, 0.9870, 0.9536 p.u with DG placement respectively. Hence improvement has been observed in the minimum voltage and voltage profile of the system in all the phases after DG placement.

The total real power losses of the IEEE 37 bus URDS system is improved in phases a, b & c from 31.56, 23.67 and 30.44 kW to 25.44, 2.63 and 22.96 kW respectively. The total reactive power losses of the system are improved in phases a, b & c from 24.01, 22.32 and 29.19 kVAr to 22.87, 2.17 and 10.30 kVAr respectively. Table 7.5 shows the IEEE 37 bus URDS power flows before and after DG Placement. Table 7.6 shows the summary of test results before and after DG placement.

Table 7.6 Summary of test results for 37 bus IEEE URDS for DG placement

Description

Before DG Placement

After DG Placement

Phase a

Phase b

Phase c

Phase a

Phase b

Phase c

Distributed generator placed bus and size of DG

722

-

-

-

165 kW

At 0.85 p.f

165 kW

at 0.85 p.f

165 kW

at 0.85 p.f

Minimum Voltage

0.9418

0.9559

0.9425

0.9814

0.9863

0.9534

Voltage regulation (%)

5.03

4.12

5.55

1.87

1.37

4.70

Improvement of Voltage regulation (%)

-

-

-

62.82

66.74

15.45

Active Power Loss (kW)

31.56

23.67

30.44

25.44

2.63

22.96

Total Active Power Loss reduction (%)

-

-

-

19.39

88.89

24.57

Reactive Power Loss (kVAr)

24.01

22.32

29.19

22.87

2.17

10.30

Total Reactive Power Loss reduction (%)

-

-

-

4.75

90.27

64.71

Total Demand (kW)

885.56

789.67

1163.4

879.44

768.63

1155.92

Total Released Demand (kW)

-

-

-

6.12

21.04

7.48

Total Reactive Power Demand (kVAr)

442.01

397.32

521.81

441.87

377.17

502.92

Total Released Reactive Power Demand (kVAr)

-

-

-

1.14

20.15

18.89

Total Feeder Capacity (kVA)

989.74

883.99

1275.1

983.53

854.86

1254.78

Total Released Feeder Capacity (kVA)

-

-

-

6.21

29.13

20.32

6.7 Conclusions

In this work, a new methodology has been presented for solving the best location and sizing of DG problem in unbalanced radial distribution systems through Voltage Index Analysis and Variational Algorithm with the standard sizes of DG. The effectiveness of the algorithm has been demonstrated and tested. The sizing of DG has been obtained with an objective function of reducing power losses. The proposed methodology was successfully applied to IEEE 25 node and IEEE 37 node URDS test feeders and found successful in reducing total active power losses in 25 node URDS and in 37 node URDS. Thus the proposed method has been observed as efficient for solving DG placement and sizing in unbalanced radial distribution systems.

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