CHAPTER 7 DESIGN FOR DISTRIBUTION FACILITIES- 7-6 - Study on Rural Energy Supply with Utilization of Renewable Energy Manual for Micro-hydro power Developmen t Chapter 7 7.4 Pole Standard

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Study on Rural Energy Supply with Utilization of Renewable Energy in Rural Areas in the Republic of Indonesia Manual for Micro-hydro power Development

Chapter 7

CHAPTER 7 DESIGN FOR DISTRIBUTION FACILITIES 7.1 Idea of Electricity

Electricity is similar to Water.

Hydropower potential is proportional to Height (m) of water and Volume of flow (m3/s).

Similary, electric power potential is proportional to Voltage (V) and Ampere.

E (V)

I (A)

P (W) = E (V) * I (A)

H (m) Q (m3/s)

Turbine P (W) = 9.8* Q(m3/s) * H (m)

T

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Chapter 7

Thick pipe enables easier to flow, because thicker pipe offers less resistance.

Important Notice The given items are only basic concepts after section 7.2. When you design a distribution line in detail, it is recommendable to consult materials such as PLN.

< Q (m3/s) Q (m3/s)

Pipe

I (A) I (A)

Conductor

<

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Chapter 7

7.2 Selection of Distribution Route Locations of supporting structures should be selected at places where (a) Access and maintenance are easy (b) Soil condition is firm and stable (c) No trouble is expected in land acquisition (d) There is no problem concerning distance from buildings and trees, etc (e) Distribution route is shortest (f) If poles are set around steep slopes or at the bottom of cliffs, take into account the follow pictures: Because landslides may take place at the site, route the solid line.

Avoid erecting a pole at the bottom of a cliff. (f) Height of conductor from ground should be more than 4 m.

Low voltage: more than 4 m 20kW: more than 6.5 m

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Chapter 7

Deficiency of height



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Chapter 7

7.3 Distribution Facilities Supporting structures are included such as follows:

(a) Pole (d) Protection (b) Guy wire (e) Distribution transformer (c) Conductors and cables (f) House connection

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Chapter 7

7.4 Pole Standard poles for overhead lines are classified as shown in Table 7.4.1: Priority of use shall be on locally manufactured concrete poles. For concrete poles, manufacture of longer and stronger poles will be preferred to widen the scope of use. To improve workability in construction and maintenance, design the poles to enable fixing of step bolts.

Table 7.4.1 Application of Supporting Structures Supporting structures Application Concrete poles Generally applied Wooden poles (including bamboo poles)

Applied to areas where access of heavy machines is difficult

Steel poles Applied to areas where access of heavy machines is difficult (standard is attached to Ref. 7-1)

Concrete pole Wooden pole Steel pole

7.4.1 Span Length of Poles The span length between distribution line supports is to be determined taking into account the following:

Recommended span 50 m; Maximum 80 m, for areas outside settlements, areas for rice fields, and open spaces; Maximum 50 m, for areas of population settlement.

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Chapter 7

7.4.2 Allowable Minimum Clearance of Conductors and Environment The minimum clearances of conductors above ground will be designed with the following criteria:

Conductor height above ground

20 kV Low Voltage

Road crossing 6.5 m 4.0 m Along road 6.0 m 4.0 m

Other places 6.0 m 4.0 m

Vertical clearance between 20 kV bare conductor and LV insulated

conductor 0.8 m

Clearance between phases of 20 kV bare conductors 0.8 m

Vertical clearance between 20kV bare conductors 1.0 m

Clearance between LV insulated conductors 0.2 m

7.4.3 Height of Poles The height of pole is to be determined taking into account the following factors: (a) Necessary height of the feeder conductors above the ground can be secured under the largest sag. (b) Necessary clearance between the feeder conductors and buildings, other electrical wires or trees can be secured (clearance under maximum sag should be examined). The recommended height of the supporting structures is as follows:

Table 7.4.2 Recommended height of Supporting Structures Voltage Recommended Support Length 20 kV 9 m

Low Voltage 7 m (a) The recommended minimum pole setting depth is one sixth of pole length. For example,

Pole setting depth = Pole length 9m×1/6 = 1.5 m (b) If soil condition is not stable, the root of pole should be reinforced firmly. Refer to the following pictures.

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Chapter 7

7.4.4 Size of Poles Size of pole is to be determined taking into account the moment on pole by wind load. The following table shows the relation between size and height of poles each cable size in case of square shape. Concrete: 210 kgf/cm2 Reinforcement: SR235, allowable stress is 1400 kgf/cm2, 19 mm2 D0 = size of square on side of pole Pole span: 50 m Cable size:70mm2

Length

of pole

Height

of pole

Maximum

moment by

pole

Maximum

moment by

cable

Sum of

moment

D0

(cm)

Reinforcement

19mm2（pcs） d (cm)

7 m 5.8 m 204 898 1103 20 8 4 for LV

9 m 7.5 m 388 1155 1543 23 8 4 for 20kV

Cable size:35mm2

Length

of pole

Height

of pole

Maximum

moment by

pole

Maximum

moment by

cable

Sum of

moment

D0 Reinforcement


7 m 5.8 m 184 583 767 18 8 4 for LV

9 m 7.5 m 338 750 1088 20 8 4 for 20kV

Cable size: 16mm2

Length

of pole

Height

of pole

Maximum

moment by

pole

Maximum

moment by

cable

Sum of

moment

D0 Reinforcement


7 m 5.8 m 174 519 693 17 8 4 for LV

9 m 7.5 m 338 668 1005 20 8 4 for 20kV

D0

Reinforcement

d

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Chapter 7

7.5 Guy wire Guy wire should be installed to balance the pole. Kinds of load to supporting structures are (a) vertical load, (b) longitudinal load, and (c) lateral load. (a) Vertical load Pole weight, cable weight, vertical load of wire tension load, etc. (b) Longitudinal load Wind pressure to pole, imbalanced load from difference of span length (c) Lateral load Wind pressure to cable, component of lateral load of wire tension, etc. The place where guy wire should be constructed is as follows: -End of distribution line -Distribution lines bend in an elbow-shape. It is possible to omit guy wire if the angle is less than 5 degrees. -To reinforce straight distribution line against wind pressure

Tension

(a)

(c) (b)

wind pressure

wind pressure

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Chapter 7

- In undulated area, if necessary, guy wire shall be installed.

Use of stay wire for 20 kV pole 9 m – 200 daN (substructure) (Guy wire angle with surface = 60 degree)

Bend Angle Conductor size 10 < β < 45 45 < β < 75 75 < β < 90

AAAC – 25 m m2 AAAC – 35 m m2 AAAC – 50 m m2 AAAC – 70 mm2

Type I Type I Type I Type I

Type I Type I Type II Type II

Type I Type II Type II Type II

Use of stay wire for 20 kV pole 9 m – 200 daN (semi-substructure)

(Guy wire angle with surface = 60 degree) Bend Angle Conductor size

5 < β < 10 10 < β < 30 30 < β < 60 60 < β < 75 75 < β < 90 AAAC – 25 mm2 AAAC – 35 mm2 AAAC – 50 mm2 AAAC – 70 mm2


Type I Type II Type II Type II

Type II Type II Type II Type III

Type II Type II Type III Type III

Type II Type III Type III Type III

Use of stay wire for 20 kV pole 7 m – 100 daN

(Guy wire angle with surface = 60 degree) Bend Angle Conductor size 5 < β < 10 10 < β < 60 60 < β < 90

2 x 25 + 1 x 25 mm2 3 x 25 + 1 x 25 mm2 2 x 35 + 1 x 25 mm2 3 x 35 + 1 x 25 mm2 2 x 50 + 1 x 35 mm2 3 x 50 + 1 x 35 mm2 2 x 70 + 1 x 50 mm2 3 x 70 + 1 x 50 mm2

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Type I Type I Type I Type I Type I Type I Type I Type I

Type I Type I Type I Type I Type I Type I Type II Type II

Type I : Guy wire diameter = 5 mm Type II : Guy wire diameter = 9 mm Type III : Guy wire diameter = 2 x 9 mm

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Chapter 7

H = Depth of buried part of stay rod h = Length of remaining stay rod

above stay rod α= Angle between stay and surface

(horizontal)

Use of stay rod, stay block and depth of burial for each stay - classification Stay rod material: U24 – 24daN/mm2

α=60° Classification of stay

L Length of rod

(m)

D Diameter (mm) H (cm) h (cm)

Stay block

L (Light) 2.1 12 155 55x55x15 M (Medium) 2.5 22 190 30 100x100x15

Guy wire classification

Material: Steel wire, 7-wire; twisted to the right Classification of stay L (Light) M (medium)

Section (mm2) 20 64 Guy wire diameter (mm) 5 9

Ultimate load (daN) 1700 6000

α h

L

φD

H

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Chapter 7

7.6 Conductors and cables 7.6.1 Feature of Conductors and Cables The features of conductor and cable are shown in the following table

Merit Demerit

conductors - Cheap - Easy to connect each conductor

- Not safety

cables - Safety - Able to lay underground

- Expensive - Difficult to connect each cable

7.6.2 Sizes of Conductors Sizes of conductors should be selected taking into account amount of present load, forecasted load, short-circuit current, current capacity of conductors, voltage drop, power loss, mechanical strength, etc. Too many sizes should not be used for branch feeders. 7.6.3 Sag of Conductors Conductor sag is to be determined taking into account the allowable conductor tension, strength of the supporting structures, wind load on conductors, etc. Conductors sag is needed to be keep the height above ground as shown in the following table:

Conductor height above ground 20 kV Low Voltage Road crossing 6.5 m 4.0 m

Along road 6.0 m 4.0 m Other places 6.0 m 4.0 m

7.6.4 Load of Each Phase 3-phase distribution lines are needed to keep the load balanced. If the unbalance load becomes more than 20%, instruments receive a bad influence. 7.6.5 Case where 3-phase line is changed to single-phase line? To avoid the above problems, it is desirable that 3-phase distribution line is expanded to villages of demand. If it is not possible to do this because of the cost, we need to give attention to keep the balanced load.

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Chapter 7

7.7 Distribution Transformers In case 20kV distribution line is required in stead of 380/220V line due to long distance from power station to consumers for the reason of sending capacity, voltage drop etc., some step-up and step-down transformers shall be installed. The connection of both step-up and step-down is completely same. Step-up transformer is installed at power station side for step-up from 380/220V to 20/11.5kV and step-down transformer is installed in consumer areas for step-down and vice versa. 7.7.1 Type of Distribution Transformer Distribution transformers are classified into two kinds by insulation method as follows:

Oil-immersed transformer: Windings are immersed in insulation oil in tank and are cheaper.

Dry-type transformer: Windings are insulated with heat-resisting epoxy (H-class) without tank but expensive.

Distribution transformers are classified into two kinds by winding method as follows Three-phase transformer: λ - λ connection Suitable for grounding of neutral point Δ- λ connection Δ-Δconnection

Note: Δ; Delta connection λ; Star connection Single-phase transformer: Usually used for voltage step-down from 20/11.5kV to

220V near consumer’s area. Single-phase transformer can be also used both star and delta connection by outside connection with combination of 3 transformers

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Chapter 7

7.7.2 Necessity of transformers 1) At first, measure the distance from powerhouse to each center of community. distance a (km) distance b (km) distance c (km) distance x (km) 2) Calculate load current I of each distribution line (A) IXA , IXB , IPX = IXA+ IXB , IPC

Here in, Pa [kVA]: load from X to A (power of each household×number of household) VLV [V]: Low Voltage 3) Calculate voltage drop of each cable VXA [V] = IXA×0.443×a VXB [V] = IXB×0.443×b VPC [V] = IPC×0.443×c VPX [V] = IPX×0.443×x Resistance of 70 mm2 conductor = 0.443 [Ω/km] 4) Calculate total voltage drop Power house to A village: VXA + VPX = VA

If VA < (VLV× percentage of voltage drop), transformer is not necessary. Power house to B village: VXB + VPX = VB, If VB < (VLV× percentage of voltage drop), transformer is not necessary. Powerhouse to C village: VPC, If VPC < (VLV× percentage of voltage drop), transformer is not necessary.

PH

X

c (km)

A village

B village

C village

a

b

x

LVVP

×

×=

3103

a

LVVP

×

×=

3103

b

LVVP

×

×=

3103

c

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Chapter 7

7.7.3 Application of Distribution Transformers Step-up and step-down distribution transformers shall be of three-phase construction, and their standard capacities are as follows: 5 kVA, 10 kVA, 16 kVA, 25 kVA, and 50 kVA 7.7.4 Selection of Unit Capacity Capacity of transformer should be decided 125 % (= 100 % / 80 %) of the capacity of generator, if the power factor is 80 %. The maximum loading is 100%, and over loading shall not be allowed to protect life of transformers. The transformers tend to be used for a long time till their breakdown without regular maintenance. Following table shows the relation between capacity of transformer and generator.

Table 7.7.1 Relation between capacity of transformer and generator Capacity of transformer

5 kVA 10 kVA 16 kVA 25kVA 50kVA

Capacity of generator

-4 kW 4 kW – 8 kW

8 kW – 12.8 kW

12.8kW – 20 kW

20kW - 40 kW

Before deciding the unit capacity of new transformers, the supply area of new transformers is to be determined taking into account the following: (a) Supply area of new transformers shall not overlap with that of other transformers

supplied from other feeders. (b) Supply area of each transformer must be independent. (c) Voltage drop restriction should be satisfied at any part of the supply area. The capacity of new transformers should be determined taking into account the expected demand growth of the area, however the smallest capacity that satisfies present demand in the area is generally applied. 7.7.5 Location Step-up transformers shall be located near the powerhouse. Step-down transformers shall be located in or close to the load center of the area. In deciding the final location to install transformer, the following conditions should also be examined: (a) Easy to access and replacement works. (b) To be separated from other buildings or trees with enough clearance. (c) For pole-mounted type, pole assembly shall not be complicated. (d) Ground-mounted type structures shall be constructed so as to avoid troubles with the

public.

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Chapter 7

7.8 House Connection (HC) 7.8.1 Application of House Connection For HC, copper core or aluminum core twisted cable will be used. The sizes of the copper core are: 4 mm2; 6 mm2; 10 mm2; 16 mm2; 25 mm2 The sizes of the aluminum core are: 10 mm2; 16 mm2; 25 mm2; 35 mm2 It is preferred not to use a roof pole with the customers entrance line placed as such that it can be seen from the outside. The use of a roof pole is only to serve the connection from house to house or a house that is not situated on the same side of the street with the LVL, so that a roof pole is needed. The minimum clearance is 3 m for compounds, 4 m for public road, if the height of the house is less than 3 m, a roof pole will be used as such that requirement for clearance is met. However, if by using a roof pole it appears that the minimum clearance is not met, a supporting pole should be used for such house connection. The wires of the smallest sectional area shall be used from the following considerations: (a) Capacity of the wire is sufficient to carry peak load current (b) Voltage drop criterion is satisfied. The Maximum voltage drop calculated for HC is as follows: - For HC tapped from LV, the maximum voltage drop for HC is 2 %. - For HC tapped directly from the transformer, the maximum voltage drop for HC is 12 %. The house connection span is as shown in the following table.

From roof pole to roof pole

From LVL pole to roof pole crossing the village road

From LVL pole directly to house crossing the village road Section

(mm2) a (m) T (daN) S (m) a (m) T (daN) S (m) a (m) T (daN) S (m) 10 16 25

40 35 35

38 42 63

0.78 0.84 0.84

58 47 47

38 42 63

1.66 1.49 1.49

49 40 40

38 42 63

1.18 1.11 1.11

in which : a = span length (m) S = sag (m) T = pull/tension (daN) Assumption: Wind intensity = 40 daN/m2 Strength of roof pole: 76 daN Factor of cable shape with regard to wind = 0.6 Width of village road = 6 m with pavement on the right and left = 1 m Clearance over the road = 4 m

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Chapter 7

Refer to Ref. 7-2 about construction of house connection crossing village road. 7.8.2 In-house Wiring The typical wiring in-house is shown in Figure 7.8.1. The expected power consumption in each householder is 150W with following facilities:

1) Single phase MCB (Molded Circuit Breaker) for protection of short circuit and earth fault.

2) 2 ceiling lamps with on-off switch 3) 1 entrance lamp with on-off switch 4) 1 outlet for general use of electrical facilities

Figure 7.8.1 Typical In-house Wiring Diagram

R,S,TN

MCB

Lamp

Double Switch Angle Switch Electric Socket

Lamp Lamp

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Chapter 7

[Ref. 7-1 Standard of Steel Poles]

Work Load (daN) 100

A 89.1 B 114.3

Diameter of pole sections (mm)

C 139.8 A 3.2 B 3.5

Pipe thickness (mm)

C 4.5 Diffraction at work load (mm)

96

Cartridge thickness (mm) 5 Cartridge length (mm) 600

4,000

1,500

1,500 A

B

C

1,160

300

100

E : Welded part F : Sock-pen G : Holding plate

G

F

E

Manual for Micro-hydro Power Development Chapter 7 (Reference)

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[Ref. 7-2 Construction of house connection crossing village road]


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Documents

CHAPTER 7 DESIGN FOR DISTRIBUTION FACILITIES- 7-6 - Study on Rural Energy Supply with Utilization of Renewable Energy Manual for Micro-hydro power Developmen t Chapter 7 7.4 Pole Standard