Preparing technical studies For designing grids in private ......The Connected Loads Index/Guide...
Transcript of 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 developmentโs 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, โMathematical
Examples of Calculations.โ
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, schoolsโฆ 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,
โMathematical Examples of Calculations.โ
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:
ุจุงูู ุนุงุฏูุฉ ุงูุชุงููุฉ:ูุชู ุญุณุงุจ ู ุณุทุญ ุงูุจูุงุก ูููุญุฏุฉ ุงููุงุญุฏุฉ Per-unit area (m2) = lot area รท no. of units per lot
Per-unit area per floor (m2) = floor area รท no. of units per floor
Roof attachment area (m2) = built area of attachment floor รท no. of units
An example of this (Example 3) can be found in Appendix 6, โMathematical
Examples of Calculations.โ
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) ร load intensity
coefficient (VA/m2)] รท 1,000
2-3) An example of this (example 4) can be seen in appendix 6, โMathematical
Examples of Calculations.โ
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, โMathematical
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. Hereโs 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:
๐ถ๐ท๐ฟ = (โ ๐ถ๐ต๐ ๐ ร ๐ท๐น๐
๐
๐=1
) ร ๐ถ๐น(๐)
(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, โMathematical
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:
๐ถ๐ท๐ฟ = (โ ๐ถ๐ฟ๐ ร ๐ท๐น๐
๐
๐=1
) ร ๐ถ๐น(๐)
(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 fuseโs 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, โMathematical
Examples of Calculations.โ
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 gridโs 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
185 248 128 172 SS 1 1 2mm 300 Direct Feeder
249 368 173 255 SS 2 2 2mm 185 Direct Feeder
369 496 256 344 SS 2 2 2mm 300 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:
๐ถ๐ท๐ฟ ๐๐ ๐๐๐ก๐ค๐๐๐๐ธ๐๐๐๐๐๐ก
= (โ ๐ถ๐ต๐ ๐ ร ๐ท๐น๐
๐
๐=1
) ร ๐ถ๐น(๐)
(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 elementโs CDL and rating, as per this formula:
๐ฟ๐๐๐๐๐๐ % ๐๐ ๐๐๐ก๐ค๐๐๐
๐ธ๐๐๐๐๐๐ก=
๐ถ๐ท๐ฟ ๐๐ ๐๐๐ก๐ค๐๐๐
๐ธ๐๐๐๐๐๐ก
๐ ๐๐ก๐๐๐ ๐๐ ๐๐๐ก๐ค๐๐๐
๐ธ๐๐๐๐๐๐ก
ร 100
(See guidebook DPS-02 for more details on the variables in the formula.)
4-5) Example 9 in Appendix 6 clarifies this.
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 elementโs 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
cableโs CDL, K coefficient, and its length, as per this formula:
๐๐ท % ๐ฟ๐ ๐ถ๐๐๐๐ =๐ถ๐ท๐ฟ (๐พ๐๐ด) ๐๐ ๐ฟ๐ ๐ถ๐๐๐๐ ร ๐ฟ ๐ฟ๐ ๐ถ๐๐๐๐
๐พ ๐ฟ๐ ๐ถ๐๐๐๐
(See guidebook DPS-02 for more details on the variables in the formula.)
4-8) Example 10 in Appendix 6 clarifies this.
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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.
5-2-3) Example 12 in Appendix 6 clarifies this.
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 Affairsโ 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.
5-4-3) Example 13 in Appendix 6 clarifies this.
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:
๐ถ๐ท๐ฟ๐น๐๐ ๐๐๐๐ก ๐๐๐๐ = (โ ๐ถ๐ท๐ฟ๐
๐
๐=1
) ร ๐ถ๐น ๐๐๐ก๐ค๐๐๐ ๐ ๐ข๐๐ ๐ก๐๐ก๐๐๐๐ ร ๐ถ๐น ๐๐๐ก๐ค๐๐๐ ๐๐ ๐๐๐๐๐๐๐
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Where:
๐ถ๐ท๐ฟ๐น๐๐ ๐๐๐๐ก ๐๐๐๐( = Coincident Demand Load for entire development.
๐ถ๐ท๐ฟ๐ = calculated CDL for Single Loop substation (i ) within the development.
N = number of substations.
๐ถ๐น๐๐๐ก๐ค๐๐๐ ๐ ๐ข๐๐ ๐ก๐๐ก๐๐๐๐ = CDL concurrency factor among substations = 0.9
๐ถ๐น๐๐๐ก๐ค๐๐๐ ๐๐ ๐๐๐๐๐๐๐ = 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 developmentโs 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 โBuried 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 .Cยฐ 40
more oral Resistivity, at depths of one (1) meter mSoil Ther C.m/wยฐ 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 ร built ratio
60%ร600m2=360m2
Attachment area (m2) = roof area ร built ratio of attachment
40%ร360m2=144m2
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Total built area = (area per floor ร number of floors) + area of attachment
(360ร3)+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:
Mosqueโs built area (m2) = area of land ร built ratio ร number of stories
5%ร2,000ร2= 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.
Area per floor (m2) = area of land ร built ratio
60%ร500=300m2
Total floor area = area per floor ร number of floors
3ร300=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 ร number of floors
2ร3=6 units
Area per unit = total built area รท number of units
900รท6=150m2
Example 4
Find the connected load (CL) for a 2,000m2 mosque.
CL per unit = (area per unit [m2] ร average load per square meter [VA/m2]) รท 1,000
As per guidebook DPS-01:
Average load (VA/m2) for mosque (C9) = 185
Therefore:
(185ร2,000)รท1,000=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) = ๐ถ๐ฟ๐๐ ๐พ๐๐ด =โ3ร๐ถ๐ฟ๐๐ ๐ด๐๐ ร รท1000
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1.73ร400ร400รท1,000= 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 thatโs 40
percent of the roof area. Find the coincident demand load (CDL).
Area per floor (m2) = area of land ร built ratio
60%ร600=360m2
Area of attachment (m2) = area of roof ร built ratio of attachment
40%ร360=144m2
Total built area (m2) = (area per floor ร number of floors) + area of attachment
(3ร360)+144=1,224m2
Area per unit in each floor (m2) = (total built area โ roof attachment area) รท number
of units per floor
(3ร360)รท6=180m2
Roof attachment area (m2) = built area of roof รท number of units
144รท1=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 breakerโs capacity for the 144m2 roof
attachment is 30 amperes. Therefor, the total breaker capacity for all units is:
(6ร40)+30=270 amperes
๐ถ๐ท๐ฟ = (โ ๐ถ๐ต๐ ๐ ร ๐ท๐น๐
๐
๐=1
) ร ๐ถ๐น(๐)
CDL=(0.6ร270)ร0.636= 103 amperes.
Example 7
A piece of land has been allocated for a two-story school building. The
undeveloped landโs area is 4,000m2, and the built ratio is 60%. Find the
coincident demand load (CDL.)
Area per floor (m2) = area of land ร built ratio
60%ร2,000=2,400m2
Total built area (m2) = area per floor (m2) ร number of floors
2ร2,400=4,800m2
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Connected load (CL) per unit (kva) = [per-unit built area (m2) ร average voltage per
square meter (VA/m2)] รท 1,000
The DPS-01 guide sets VA/m2 for schools (C8) at 180. Therefore:
CL=(4,800ร180)รท1,000=846kva
Since 846kva corresponds to 1,226 amperes:
1,226amp > 800amp, ergo:
๐ถ๐ท๐ฟ = (โ ๐ถ๐ฟ๐ ร ๐ท๐น๐
๐
๐=1
) ร ๐ถ๐น(๐)
846ร0.8ร1=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:
๐ถ๐ท๐ฟ ๐๐ ๐๐๐ก๐ค๐๐๐๐ธ๐๐๐๐๐๐ก
= (โ ๐ถ๐ต๐ ๐ ร ๐ท๐น๐
๐
๐=1
) ร ๐ถ๐น(๐)
40ร16ร0.6ร0.602=231.2 amperes=160kva
As such, the optimum means to power the building is via a 4ร300mm2 aluminum
power line directly from the distribution substation.
Example 9
Find the load ratio for a low-voltage, 4ร300mm2 aluminum power line powering
a CDL of 160kva.
CDL formula:
๐ฟ๐๐๐๐๐๐ % ๐๐ ๐๐๐ก๐ค๐๐๐
๐ธ๐๐๐๐๐๐ก=
๐ถ๐ท๐ฟ ๐๐ ๐๐๐ก๐ค๐๐๐
๐ธ๐๐๐๐๐๐ก
๐ ๐๐ก๐๐๐ ๐๐ ๐๐๐ก๐ค๐๐๐
๐ธ๐๐๐๐๐๐ก
ร 100
Guide DPS-02 sets the capacity of a 4ร300mm2 aluminum cable at 215kva. Therefore:
Load ratio = (160รท215)ร100=74%
Example 10
Problem:
- 4ร300mm2 aluminum power line
- CDL: 160kva
- Voltage: 230/400v
23
- Length: 120m from
Find the voltage drop.
Voltage drop formula:
๐๐ท % ๐ฟ๐ ๐ถ๐๐๐๐ =๐ถ๐ท๐ฟ (๐พ๐๐ด) ๐๐ ๐ฟ๐ ๐ถ๐๐๐๐ ร ๐ฟ ๐ฟ๐ ๐ถ๐๐๐๐
๐พ ๐ฟ๐ ๐ถ๐๐๐๐
The DPS-02 guide sets the K-factor for a 4ร300mm2 aluminum cable at 10,132.
Therefore:
Voltage drop (%) = (120ร160)/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:
6ร100=600 amperes.
Total breaker capacity for all three parcels:
3ร600=1,800 amperes.
CDL formula:
๐ถ๐ท๐ฟ ๐๐ ๐๐๐ก๐ค๐๐๐๐ธ๐๐๐๐๐๐ก
= (โ ๐ถ๐ต๐ ๐ ร ๐ท๐น๐
๐
๐=1
) ร ๐ถ๐น(๐)
CDL=1,800ร0.6ร0.598=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) ร average load (VA/m2)] รท 1,000
Since the unitโs 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:
(215ร3,200)รท1,000=688kva or 993 amperes > 800 amperes
CDL formula:
24
๐ถ๐ท๐ฟ = (โ ๐ถ๐ฟ๐ ร ๐ท๐น๐
๐
๐=1
) ร ๐ถ๐น(๐)
688ร0.7ร1=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:
๐ถ๐ท๐ฟ = (โ ๐ถ๐ฟ๐ ร ๐ท๐น๐
๐
๐=1
) ร ๐ถ๐น(๐)
12,000ร0.7ร1=8,400 kva
CDL=351 amperes
Capacity of panel needed: 400 amperes at a load ratio of 88%.