preparing technical studies for designing grids in private ......the connected loads index/guide...

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Preparing technical studies

For designing grids in private developments

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Introduction

Based on the sizes of land lots detailed in the survey of the property

development that had been approved by the Ministry of Municipal and

Rural Affairs, the study must be built upon these main points:

Area/load calculations

Calculations for built-up areas, connected loads, and coincident user-end loads

must be made for all tracts within a development and in accordance with the

standards approved by the Saudi Electricity Company.

Designing low- and medium-voltage grids

The development’s low- and medium-voltage grids will be designed according to

the above-mentioned calculations.

1. Calculating built-up areas 1-1) Determining built-up area per lot To find Built-up area per (residential or mixed-use) lot:

1. First determine the area of a given lot based on its basic dimensions (length x

width) as shown on the municipally approved survey.

2. Determine the municipally approved number of stories as per the local

building code.

3. Determine the ratio between the total area of all stories to the area of the land

as per the code.

4. Determine the percentage of the attachment (as to the total area of the roof) as

per the code (the municipality must provide a maximum approved percentage.)

5. Calculate the area of each floor using the following equation: Floor area (m2) = lot area x floor ratio

6. Calculate the area of the roof attachment using this equation: Built-up area per lot (m2) = (per-floor area x number of stories) + roof attachment area

7. An example of this (Example 1) can be found in Appendix 6, “Mathematical

Examples of Calculations.”

1-1-1) It is customary to calculate per-lot built-up areas for residential and

non-residential areas in accordance with the data in the municipally approved

building code, and the owner of the development will be asked to provide this

information as it is provided to them by the municipality on the survey. Only

in special cases where the municipality has failed to provide this information

for non-residential facilities (shopping centers, mosques, schools… etc.) will

the following parameters be accepted as absolutely minimum requirements,

and additions to which can be made by the architect/consultancy:

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Table 1

Type of building No. of stories Built-up ratio

Mosques 2 50 %

Schools 3 40 %

Shopping centers 2 60 %

For this case ONLY (non-residential facilities,) use this equation to find the built-

up ratio: Built-up area per lot (m2)= lot area x built-up ratio x no. of stories

1-1-2) An example of this (Example 2) can be found in Appendix 6,

“Mathematical Examples of Calculations.”

1-2) Finding per-parcel area

This is how to find the area of each unit:

It is customary to calculate per-unit areas in accordance with the data in the

municipally approved building code, and the owner of the development will be

asked to provide this information as it is provided to them by the municipality

on the survey. Only in special cases where the municipality has failed to

provide this information will the following parameters be accepted as

absolutely minimum requirements for the expected number units per lot, and

additions to which can be made by the architect/consultancy:

Table 2

Type of building Min. no. of units

Houses 1 unit

Buildings 2/floor + 1 roof unit

Commercial units in buildings 1 additional unit, ground floor

Other buildings (shopping centers,

mosques, schools, others) 1 unit

To find per-unit area:

بالمعادلة التالية:يتم حساب مسطح البناء للوحدة الواحدة Per-unit area (m2) = lot area ÷ no. of units per lot

Per-unit area per floor (m2) = floor area ÷ no. of units per floor

Roof attachment area (m2) = built area of attachment floor ÷ no. of units

An example of this (Example 3) can be found in Appendix 6, “Mathematical


2. Calculating connected loads (CL) The Connected Loads Index/Guide (DPS-01) is the reference for calculating

connected loads (CLs) for every unit of the development (in kVA.)

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To find CL:

2-1) For type C1 and C2 buildings: for each unit area (m2) there is an equivalent

CL/unit (in kVA) next to it in guide tables 4 and 6 in DPS-01.

2-2) For building types C3 through C17: CL/unit (in kVA) is based on the values of

the load intensity coefficient (in VA/m2) listed in table 8 of the DPS-01 guide

and the area of each built unit. To find the connected load for a given unit:

Connected Load (CL) per unit CL )KVA) = [area of given unit (m2) × load intensity

coefficient (VA/m2)] ÷ 1,000

2-3) An example of this (example 4) can be seen in appendix 6, “Mathematical


2-4) For street lighting, connected loads, in KVA, are calculated based on the sum

of the capacities of the fuses to be installed, the number of which should be

determined by the municipality.

2-5) For public parks, connected loads, in KVA, are calculated based on the sum of

the capacities of the fuses to be installed, the number of which should be

determined by the municipality. If and only if the municipality was unable to

provide this information, CL shall be calculated as per the DPS-01 guide.

2-6) An example of this (example 5) can be seen in appendix 6, “Mathematical

Examples of Calculations.

3. Calculating Coincident Demand Load (CDL) The DPS-01 guide is the reference for calculating Coincident Demand Load (CDL)

for every parcel of land in a given development. Here’s how to find CDL (in KVA):

3-1) For units with connected loads (CLs) of no more than 800 amperes (the distribution

supply lines for which are designed with low-voltage outgoing fuses):

3-1-1) To find fuse capacity for each unit based on its CL:

For type C1 and C2 units, fuse capacity for each unit is determined as per CL per

unit values in tables 4 and 6 of the DPS-01 guide.

For units of types C3 through C29, the suitable fuse capacity for each unit (A) shall

be based on the nearest fuse with the highest capacity (in KVA.)

For street lighting, fuse capacities shall be determined by the municipality.

For public parks, fuse capacities shall be determined by the municipality. Is and

only if the municipality was unable to provide this information, CL shall be

calculated as per the DPS-01 guide.

3-1-2) To calculate Coincident Demand Load (CDL) for a whole parcel based on

fuse capacities of all of the built units within that parcel:

𝐶𝐷𝐿 = (∑ 𝐶𝐵𝑅𝑖 × 𝐷𝐹𝑖

𝑁

𝑖=1

) × 𝐶𝐹(𝑁)

(See the DPS-01 guide for more detailed definitions of the elements in the

equation above.)

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3-1-3) An example of this (example 6) can be seen in appendix 6, “Mathematical

Examples of Calculations.

3-2) For units with Connected Loads (CLs) greater than 800 amperes (with their own

distribution substations or medium-voltage control panels):

3-2-1) To calculate Coincident Demand Load (CDL) for a whole parcel based on

the loads supplied to it:

𝐶𝐷𝐿 = (∑ 𝐶𝐿𝑖 × 𝐷𝐹𝑖

𝑁

𝑖=1

) × 𝐶𝐹(𝑁)

(See the DPS-01 guide for more detailed definitions of the elements in the

equation above.)

For private distribution substations, the appropriate capacity of a given substation

(in KVA) is determined according to the nearest highest standard capacity of the

total Coincident Demand Load (CDL) per parcel (in KVA).

For medium-voltage control panels, the medium-voltage fuse’s capacity (in

amperes) is set to match the total CDL for the entire parcel.

An example of this (example 7) can be seen in appendix 6, “Mathematical


4. Designing low-voltage grids The Underground Low-Voltage Grid Design Guide (DPS02) is the reference for

designing low-voltage grids within a given development.

4-1) Requirements for designing entire low-voltage grids and public distribution

substations for a development:

The grid(s) must be able to handle the needs and loads of all low-voltage outgoing

fuses (20, 30, 40, 50, 70, 100, 125, 150, 200, 250, 300, 400, 500, 600 and 800

amperes) within the development, except parcels the Connected Loads (CLs) of

which exceed 4MVA.

Parcels with anticipated CLs ranging from 4MVA to 16 MVA shall be included

in the technical study as loads only, without substation locations being allocated

to them, but future owners may apply for new connections to these parcel,

including substations, as per the rules and according to anticipated loads and

voltages.

Grid voltage: 230/400v.

Grid type: underground, unless the grid’s prevalent voltage is 33kv,in which case

the it would be an overhead grid with overhead transformers.

Design: radial.

The design and choice of supply source (be it a distribution cabin or directly from

a substation) to low-voltage fuses and the specification of low-voltage cabling

depends upon the coincident demand load (CDL) of a given parcel, as described

in table 3:

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Table 3 Coincident

Demand

Load

(Amps)

Coincident

Demand Load

(KVA) for

230/400 (V) Supply

Source

No. of

Outgoing

Fuses /

MCCBs

No. of

LV

Cables

to

Customer

Size of

LV

Cables

to

Customer

Main LV Feeder

From To From To

No. of

Cables

to DP

Cable

Size

1 108 1 75 DP 1 1 2mm 70 1 2mm 300

109 184 76 127 DP 1 1 2mm 185 1 2mm 300

185 216 128 150 DP 2 2 2mm 70 1 2mm 300

217 248 150 172 DP 2 2 2mm 185 1 2mm 300

1 184 1 127 SS 1 1 2mm 185 Direct Feeder




(See guidebook DPS-02 for more details.)

4-2) CDL is calculated for each individual element of a low-voltage grid (such as service

cables, distribution panels, low-voltage distributors, and distribution substations)

based on the low-voltage fuses intended to be used with that element, as per this

formula:

𝐶𝐷𝐿 𝑜𝑛 𝑁𝑒𝑡𝑤𝑜𝑟𝑘𝐸𝑙𝑒𝑚𝑒𝑛𝑡

= (∑ 𝐶𝐵𝑅𝑖 × 𝐷𝐹𝑖

𝑁

𝑖=1

) × 𝐶𝐹(𝑁)

(See guidebook DPS-02 for more details on the variables in the formula.)

4-3) Example 8 in Appendix 6 clarifies this.

4-4) The load ratio is calculated for each individual element of a low-voltage grid (such

as service cables, distribution panels, low-voltage distributors, and distribution

substations) based on that element’s CDL and rating, as per this formula:

𝐿𝑜𝑎𝑑𝑖𝑛𝑔 % 𝑜𝑛 𝑁𝑒𝑡𝑤𝑜𝑟𝑘

𝐸𝑙𝑒𝑚𝑒𝑛𝑡=

𝐶𝐷𝐿 𝑜𝑛 𝑁𝑒𝑡𝑤𝑜𝑟𝑘

𝐸𝑙𝑒𝑚𝑒𝑛𝑡

𝑅𝑎𝑡𝑖𝑛𝑔 𝑜𝑓 𝑁𝑒𝑡𝑤𝑜𝑟𝑘


× 100



4-6) The load ratio each individual element of a low-voltage grid (such as service cables,

distribution panels, low-voltage distributors, and distribution substations) must not

exceed 80% of that element’s rating.

4-7) Voltage drop ratios across low-voltage cables (distribution cabin to parcel; from

substation to panel; from substation to parcel) are calculated based on a given

cable’s CDL, K coefficient, and its length, as per this formula:

𝑉𝐷 % 𝐿𝑉 𝐶𝑎𝑏𝑙𝑒 =𝐶𝐷𝐿 (𝐾𝑉𝐴) 𝑜𝑛 𝐿𝑉 𝐶𝑎𝑏𝑙𝑒 × 𝐿 𝐿𝑉 𝐶𝑎𝑏𝑙𝑒

𝐾 𝐿𝑉 𝐶𝑎𝑏𝑙𝑒



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4-9) The aggregate drop ratios of direct cables between a substation and a land parcel

must not exceed 5%.

4-10) Distribution cabin locations

The locations of distribution cabin should be chosen such that they are as central as

possible to the loads of the parcels to be powered, and cabins should be installed on

streets adjacent to the perimeters of any parcel. The parameters for selecting a

suitable location for a distribution cabins are as follows:

If the cabin is to power only one parcel (regardless of type): the cabin will be

installed at the frontage side of that parcel.

If the cabin is to power one utility or non-residential structure along with one or

more residential or residential/commercial parcel: the cabin will be installed at

the frontage side of the non-residential utility or structure.

If the cabin is to power multiple residential or residential/commercial parcels

ONLY: the cabin will be installed between the frontages of the two parcels

located at the load center of these parcels.

5. Designing public and private distribution substations and medium-

voltage panels 5-1) Public distribution substations

5-1-1) To be used to power 20-, 30-, 40-, 50-, 70-, 100-, 125-, 200-, 250-, 300-,

400-, 500-, 600-, and 800-ampere fuses.

5-1-2) The load on a 1,000kva public distribution substation must not exceed 80

percent of its rated capacity.

5-1-3) Example 11 in Appendix 6 clarifies this.

5-1-4) Locations of public distribution substations

When selecting a location for a distribution substation, care must be taken to locate

it at the center, or as close as possible to the center, of the loads of land parcels to

be powered by it. The location must be choses such that it falls on the perimeter of

any parcel adjacent to a street, and with the following guidelines:

If the substation is to power only a single parcel of any type of usage, the substation

must be built on the perimeter of that parcel.

If the substation is to power one utility or non-residential structure along with one

or more residential or residential/commercial parcel: the substation will be built on

the perimeter of the non-residential utility or structure.

If the substation is to power multiple residential or residential/commercial parcels

ONLY: the substation will be built between the two parcels located at the load

center of these parcels.

5-2) Private distribution substations

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5-2-1) To be used to power multiple parcels in a single block with a coincident

demand load (CDL) exceeding 800 amperes and a coincident demand load of no

more than 4mva per parcel.

5-2-2) The load on a 1,000kva public distribution substation must not exceed 100

percent of its rated capacity.


5-2-4) Locations of private distribution substations

A private distribution substation must be located within, and adjacent to, the

perimeter of the parcel to be powered by it, with access from an adjacent street.

5-3) Street lighting stations

5-3-1) To be used to power street lighting power meters.

5-3-2) Each street lighting power meter will have its own dedicated ring main unit

(RMU) of a capacity determined by the municipality; the owner is responsible for

supplying a lighting transformer that conforms with the Ministry of Municipal and

Rural Affairs’ specifications and connecting it to the RMU.

5-3-3) Locations of street lighting substations

Substations assigned to street lighting must be located on service land.

5-4) Medium-voltage control panels

5-4-1) To be used to power multiple parcels in a single block with a coincident

demand load (CDL) exceeding 4mva per parcel.

5-4-2) The number and capacities of medium-voltage control panels (400 or 630

amperes) needed to power a single parcel based on its anticipated CDL is to be

calculated such that the loading on the panels must not exceed 100 percent of their

rated capacity.


5-4-4) Locations of medium-voltage control panels

A medium-voltage control panel must be located within and on the perimeter of

the parcel to be powered by it, with access from the adjacent street.

6. Calculating coincident demand load (CDL) of entire development Coincident demand load (CDL) for the entire development is calculated as a factor

of the CDLs of individual distribution substations within the development that have

been calculated according to the formula in section ??????? above. The following

formula is to be used:

𝐶𝐷𝐿𝐹𝑜𝑟 𝑃𝑙𝑜𝑡 𝑃𝑙𝑎𝑛 = (∑ 𝐶𝐷𝐿𝑖

𝑁

𝑖=1

) × 𝐶𝐹 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑠𝑢𝑏𝑠𝑡𝑎𝑡𝑖𝑜𝑛𝑠 × 𝐶𝐹 𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑀𝑉 𝑓𝑒𝑒𝑑𝑒𝑟𝑠

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Where:

𝐶𝐷𝐿𝐹𝑜𝑟 𝑃𝑙𝑜𝑡 𝑃𝑙𝑎𝑛( = Coincident Demand Load for entire development.

𝐶𝐷𝐿𝑖 = calculated CDL for Single Loop substation (i ) within the development.

N = number of substations.

𝐶𝐹𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑠𝑢𝑏𝑠𝑡𝑎𝑡𝑖𝑜𝑛𝑠 = CDL concurrency factor among substations = 0.9

𝐶𝐹𝑏𝑒𝑡𝑤𝑒𝑒𝑛 𝑀𝑉 𝑓𝑒𝑒𝑑𝑒𝑟𝑠 = concurrency factor among medium-voltage transformers =

0.9

7. Designing medium-voltage grids within development 7-1) Standards for designing medium-voltage grids

The following standards must be applied when designing medium-voltage grids for

private developments:

The grid(s) must cover the needs and loads of all parcels, utilities and services

located within the boundaries of the development, except parcels whose

connected loads exceed 16mva.

Grid voltage: the design of the grid must correspond to the prevalent medium

voltage around the area where the development is located (13.8kv or 33kv.)

Grid type: underground; unless the prevalent type in the area is the overhead type,

in which case the development’s grid must be an overhead one.

Design: a loop system with single medium-voltage loops comprising two

opposite medium-voltage transformers with a normal open point in between, as

seen in diagram 1 in Appendices.

Firm capacity (N-1) for each individual single-loop medium-voltage grid, which

represents its maximum allowable load, is 100 percent of the de-rated capacity of

a medium-voltage cable; 50 percent for each transformer.

The maximum allowable voltage drop between the entry point of the loop and the

farthest distribution substation is five percent (5%).

Cable gage: aluminum medium-voltage cabling with a 500mm2 cross-section

must be used for 13.8kv voltages, and copper cabling with a 240mm2 cross-

section must be used for 33kv voltages.

7-2) Specifications of medium-voltage cables

Direct-buried cable ratings for medium-voltage cables are as stated in table 4

below:

Table 4

MV Cable Size Voltage

Direct –Buried Cable

Rating

(Amp) (MVA)

3X 500mm2 Al 13.8 KV 380 9

10

3X 240mm2 Cu 33 KV 350 20

De-rated cable capacities for medium-voltage cables with underground cable

proximity factored in are as stated in table 5 below:

Table 5

MV Cable Size Voltage De-rated Capacity

(Amp) (MVA)

lA 23X 500mm 13.8 KV 320 7.6

uC 23X 240mm 33 KV 290 16.6

Conditions under which de-rated capacities of medium-voltage cables have been

calculated are as stated in table 6 below:

Table 6

perature Direct Buried/Underground Ducted, at mbient TemAmore ordepths of one (1) meter .C° 40

more oral Resistivity, at depths of one (1) meter mSoil Ther C.m/w° 2.0

Burial Depth (to the center of the cable) m 0.65

Multiple Cables Circuit Spacing (center to center) m 0.30

Voltage drop constants (K-factors) for medium-voltage cables are as stated in

table 7 below:

Table 7

Cable Voltage K

lA 23X 500mm 13.8 KV 15170

uC 23X 240mm 33 KV 71222

7-3) Routing medium-voltage cables

Underground medium-voltage cables must be laid underneath the tarmac of the

street, and never under sidewalks.

Underground medium-voltage cables must never be laid under pedestrian paths

unless they are paved with tarmac with a minimum width of six (6) meters.

Digs perpendicular to the direction of traffic must be kept as narrow as possible.

7-4) Designing medium-voltage grids within private developments The following requirements must be met when designing medium-voltage grids for

private developments:

The number of transformers within a loop must not exceed 30.

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Four-cell RMUs must be installed for substations 11-21.

If the quantities needed exceed the requirements above, the excess will be treated

as a new single loop.

Each 30-transformer loop connects to the next as outlined in figure 2 in

Appendices.

The number of single loops needed to meet the demands of all parcels, utilities

and services within the development is determined based on the above-mentioned

parameters and standards.

8. List of relevant SEC guidebooks

Guidebook

reference Title of guidebook

1 DPS-01 Load calculation guide

2 DPS-02 Low-voltage underground grid design guide

9. Appendices

Appendix Title

1 Figure 1: single-line drawing of a standard medium-voltage single loop in a

private development.

2 Figure 2: single-line drawing of medium-voltage single loops in a

development.

3 Form 1: calculations for areas and loads of land parcels in private

developments.

4 Form 2: calculations for designing low-voltage grids.

5 Form 3: calculations for the design of distribution substations.

6 Mathematical numerical examples

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Appendices

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Figure 1: single-line drawing of a standard medium-voltage single loop in a private development.

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Figure 2: single-line drawing of medium-voltage single loops in a development.

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Form 1: calculations for areas and loads of land parcels in private developments.

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Form 2: calculations for designing low-voltage grids.

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Form 3: calculations for the design of distribution substations.

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Mathematical

Numerical Examples

Example 1

For a piece of residential land with an unbuilt area of 600m2 and a built ratio of

60 percent with three stories and an attachment covering 40 percent of roof

area, find the total built area.

Area per floor (m2) = area of land × built ratio

60%×600m2=360m2

Attachment area (m2) = roof area × built ratio of attachment

40%×360m2=144m2

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Total built area = (area per floor × number of floors) + area of attachment

(360×3)+144= 1,224m2

Example 2

The area of an undeveloped piece of land allocated for a mosque is 2,000m2. No

information as to the number of stories and built ratio has been provided by the

municipality. Find the built area.

Since no information as to the built ratio and number of stories is available, the data

in table 1 is the default minimum set by the building codes the govern such facilities.

Therefore:

Mosque’s built area (m2) = area of land × built ratio × number of stories

5%×2,000×2= 2,000m2

Example 3

A piece of residential land is 500m2 with a built ratio of 60% in a three-story

building. There is no municipal information as to the number of units. Find the

area of each unit.


60%×500=300m2

Total floor area = area per floor × number of floors

3×300=900m2

In case no data is available as to the number of units, the default is two units per

floor, as per table 2. Therefore:

Number of units = units per floor × number of floors

2×3=6 units

Area per unit = total built area ÷ number of units

900÷6=150m2

Example 4

Find the connected load (CL) for a 2,000m2 mosque.

CL per unit = (area per unit [m2] × average load per square meter [VA/m2]) ÷ 1,000

As per guidebook DPS-01:

Average load (VA/m2) for mosque (C9) = 185

Therefore:

(185×2,000)÷1,000=370kva

Example 5

Find the connected load (CL) for a street to be lit with a 400-ampere switch at

a voltage of 230/400 volts.

CL (kva) = 𝐶𝐿𝑖𝑛 𝐾𝑉𝐴 =√3×𝐶𝐿𝑖𝑛 𝐴𝑀𝑃 × ÷1000

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1.73×400×400÷1,000= 277kva

Example 6

A residential piece of land is 600m2 with a built ratio of 60% in a three-story

building. Each story is made up of two units, plus one attachment that’s 40

percent of the roof area. Find the coincident demand load (CDL).


60%×600=360m2

Area of attachment (m2) = area of roof × built ratio of attachment

40%×360=144m2

Total built area (m2) = (area per floor × number of floors) + area of attachment

(3×360)+144=1,224m2

Area per unit in each floor (m2) = (total built area – roof attachment area) ÷ number

of units per floor

(3×360)÷6=180m2

Roof attachment area (m2) = built area of roof ÷ number of units

144÷1=144m2

Tables 4 and 6 of the DPS-01 guide set the capacity of the breaker corresponding to

a 180m2 residential unit at 40 amperes. The breaker’s capacity for the 144m2 roof

attachment is 30 amperes. Therefor, the total breaker capacity for all units is:

(6×40)+30=270 amperes

𝐶𝐷𝐿 = (∑ 𝐶𝐵𝑅𝑖 × 𝐷𝐹𝑖

𝑁

𝑖=1

) × 𝐶𝐹(𝑁)

CDL=(0.6×270)×0.636= 103 amperes.

Example 7

A piece of land has been allocated for a two-story school building. The

undeveloped land’s area is 4,000m2, and the built ratio is 60%. Find the

coincident demand load (CDL.)


60%×2,000=2,400m2

Total built area (m2) = area per floor (m2) × number of floors

2×2,400=4,800m2

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Connected load (CL) per unit (kva) = [per-unit built area (m2) × average voltage per

square meter (VA/m2)] ÷ 1,000

The DPS-01 guide sets VA/m2 for schools (C8) at 180. Therefore:

CL=(4,800×180)÷1,000=846kva

Since 846kva corresponds to 1,226 amperes:

1,226amp > 800amp, ergo:


𝑁

𝑖=1

) × 𝐶𝐹(𝑁)

846×0.8×1=677kva

Example 8

A piece of land will be developed into residential building of 16 units, each with

a 40-ampere breaker. Find the coincident demand load (CDL) and then

determine the best way to power those units.

CDL formula:



𝑁

𝑖=1

) × 𝐶𝐹(𝑁)

40×16×0.6×0.602=231.2 amperes=160kva

As such, the optimum means to power the building is via a 4×300mm2 aluminum

power line directly from the distribution substation.

Example 9

Find the load ratio for a low-voltage, 4×300mm2 aluminum power line powering

a CDL of 160kva.

CDL formula:

𝐿𝑜𝑎𝑑𝑖𝑛𝑔 % 𝑜𝑛 𝑁𝑒𝑡𝑤𝑜𝑟𝑘

𝐸𝑙𝑒𝑚𝑒𝑛𝑡=

𝐶𝐷𝐿 𝑜𝑛 𝑁𝑒𝑡𝑤𝑜𝑟𝑘


𝑅𝑎𝑡𝑖𝑛𝑔 𝑜𝑓 𝑁𝑒𝑡𝑤𝑜𝑟𝑘


× 100

Guide DPS-02 sets the capacity of a 4×300mm2 aluminum cable at 215kva. Therefore:

Load ratio = (160÷215)×100=74%

Example 10

Problem:

- 4×300mm2 aluminum power line

- CDL: 160kva

- Voltage: 230/400v

23

- Length: 120m from

Find the voltage drop.

Voltage drop formula:

𝑉𝐷 % 𝐿𝑉 𝐶𝑎𝑏𝑙𝑒 =𝐶𝐷𝐿 (𝐾𝑉𝐴) 𝑜𝑛 𝐿𝑉 𝐶𝑎𝑏𝑙𝑒 × 𝐿 𝐿𝑉 𝐶𝑎𝑏𝑙𝑒

𝐾 𝐿𝑉 𝐶𝑎𝑏𝑙𝑒

The DPS-02 guide sets the K-factor for a 4×300mm2 aluminum cable at 10,132.

Therefore:

Voltage drop (%) = (120×160)/10,132=1.89%

Example 11

Three residential land parcels are to be powered through six, 100-ampere

breakers each. Find the right capacity of the distribution substation needed.

Total breaker capacity per parcel:

6×100=600 amperes.

Total breaker capacity for all three parcels:

3×600=1,800 amperes.

CDL formula:



𝑁

𝑖=1

) × 𝐶𝐹(𝑁)

CDL=1,800×0.6×0.598=646 amperes or 447kva

The capacity of a suitable public distribution substation would be 1,000kva at a

load ratio of 45%.

Example 12

A single commercial unit has a total built area of 3,200m2 and is to be powered at

a voltage of 230/400 volts. Find the right capacity of the distribution substation

needed.

Connected load (CL) per unit = [area per unit (m2) × average load (VA/m2)] ÷ 1,000

Since the unit’s area (3,000m2) is beyond the scope of our area tables, the calculation

is made based on the average loads (AV/m2) of commercial units in guide DPS-01

(C2), which is set at 215. Therefore:

(215×3,200)÷1,000=688kva or 993 amperes > 800 amperes

CDL formula:

24


𝑁

𝑖=1

) × 𝐶𝐹(𝑁)

688×0.7×1=481kva

The unit will be powered from a private 1,000kva distribution substation at a load

ratio of 48 percent.

Example 13

What is the capacity of a medium-voltage control panel needed to power a

shopping mall with a connected load of 12mva at a voltage of 13.8kv?

CDL formula:


𝑁

𝑖=1

) × 𝐶𝐹(𝑁)

12,000×0.7×1=8,400 kva

CDL=351 amperes

Capacity of panel needed: 400 amperes at a load ratio of 88%.

preparing technical studies for designing grids in private ......the connected loads index/guide...

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