Utility Power Supply
for High-rise Buildings
Roland deSouza, FIEEEP
Fahim, Nanji & deSouza
Having moved into the 21st century, utility companies in Pakistan need to review their electricity supply policy
for high-rise buildings in urban areas, based on practices in other countries.
Situation in Pakistan
Pakistan is presently experiencing an explosion in high-rise commercial construction in
downtown precincts of major cities like Karachi, Islamabad, Lahore and Faisalabad.
Unfortunately, the corresponding increase in infrastructure (electricity, water, sewerage,
telecommunications, roads, etc) is not being designed and provided by the utilities. This will
lead to environmentally degraded concrete jungles and urban chaos.
An appreciation of the possible electrical demand loads of high-rise buildings constructed
on large plots with high plot-ratios/FARs (floor-area-ratios) in urban areas is given in
Annexure-1.
A partial list of upcoming high-rise buildings is attached as Annexure-2.
As a typical example of the load density that will evolve in downtown commercial zones,
consider the sample Urban Design Layout Plan of a 200-acre high-rise belt in a major city.
A preliminary estimate of the projected electrical demand load of all the commercial
buildings and utility/amenity structures located in this high-rise belt has been made at
around 100MW (see Annexure-3).
Existing Utility Practice in Pakistan
The electricity utility companies (ex-WAPDA DISCOs and KESC) in Pakistan presently
require bulk consumers with loads in excess of 5MW to take supply at high voltage, 132kV
under Tariff C-3, and install their own 132/11kV consumer grid-stations.
This becomes a virtual impossibility as grade-level space for a consumer grid-station in the
dense and crowded downtown plots is not available, and location of the grid-station in the
basement of high-rise buildings is fraught with hazards from fire (oil-filled transformers)
and electromagnetic radiation to building residents.
This also results in extra (unnecessary) transformers on the electrical network, additional
losses, and a waste of national resources.
Fahim, Nanji & deSouza
Consulting Engineers
Practice in Developed Countries
In major cities in developed countries, the utility/supply authority provides electricity to
large buildings or building complexes in densely populated urban areas at medium voltage
(11kV, 13.8kV or 10/20kV) or even at low (utilization) voltage (480/277V).
In Germany, the supply authorities set up their own HV/MV utility grid-stations in
proximity to load centres, and supply all large consumers at medium voltage, 10kV or 20kV.
Dry-type transformers are then used in consumer substations within buildings to provide
utilization voltage, e.g, 400/230V. See Annexure-5 which is an extract from Siemens
‘Electrical Installation Handbook’.
In the UAE, 11kV supply is given to high-rise buildings from utility grid-stations situated in
the centre of urban conglomerations. Shown in Annexure-6 is a 3 x 50MVA 132/11kV utility
(Dubai Electricity & Water Authority) indoor grid-station.
Some of the equipment installed at the upper levels in this layout could also be fitted in
basements, thereby reducing the bulk of the structure.
In the USA, in key metropolitan areas like New York City, the utility company provides
multiple 480Y/277V in-feeds to high-rise buildings at the basement level and from utility
vaults on the upper floors. See Annexure-7 which is an extract from Westinghouse
‘Consulting Application Guide’.
Recommended Practice for Pakistan
There is an urgent need for the local utility companies to review
their existing policy of supplying at 132kV all consumers with
loads in excess of 5MW.
It is necessary for the upper limit of 5MW to be removed for bulk
supply (under medium-voltage Tariffs C-2 or A-2(b)) to high-rise
commercial building consumers in downtown urban areas. All
high-rise buildings must be supplied at 11kV with multiple feeders
at their doorstep, whatever the load.
Distribution companies in Pakistan must take medium-voltage
11kV feeders from their grid-stations (sited on convenientlylocated plots provided by the municipalities), in radial or ring
configuration, to commercial consumers in the proximate area with
loads in excess of 5MW.
Commercial buildings can be supplied with Bulk Supply Tariffs
(C-2 or A-2b) or individual consumer meters (A-1R and A-2C).
Consumers who choose to obtain Bulk Supply for distribution/resale within their multistoried buildings will have to obtain a Distribution License from NEPRA.
Roland deSouza is the Principal E.E. of Fahim, Nanji & deSouza, a multi-disciplinary consultancy firm in electrical and
mechanical engineering. This paper was presented at the 2011 Multi-topic International Symposium of the IEEEP,
Karachi Centre
Fahim, Nanji & deSouza
Consulting Engineers
Annexure-1
Estimation of Electrical Demand Loads
In dense downtown areas of major cities
Plot-ratio/
FAR
Plot Area
(acres)
Covered Area 1
(sft)
Electrical Load 2
(MW)
1: 6 3
2
522,720
4.2
4
1,045,440
8.2
6
1,568,160
12.5
2
1,045,440
8.4
4
2,090,880
16.7
6
3,136,320
25.1
2
1,306,800
10.5
4
2,613,600
20.9
6
3,920,400
31.4
1: 12 4
1: 15 5
Note: 1. Demand load density for commercial buildings has been assumed as 8 watts/sft,
2. Covered area does not include exempt parking, MEP plant, and other amenity areas
3. Standard FAR along I. I. Chundrigar Road, the ‘Wall Street’ of Karachi
4. Enhanced FAR being allowed to NLC-Ensha project in City Station Marshalling Yard in Karachi
5. Maximum FAR allowed in Manhattan, New York City.
Fahim, Nanji & deSouza
Consulting Engineers
Annexure-2
Estimated Loads of Major Upcoming Commercial Buildings
Project
Location
Floors
Approx
Electrical Load
Dolmen City
Clifton, Karachi
60
15MW
Soffitel Tower
Clifton, Karachi
27
8MW
43
9MW
Karachi Financial Tower
NLC-Ensha Tower
Railway Yard, Karachi
40
20MW
I. T. Tower
Gulshan-e-Iqbal, Karachi
42
30MW
Centaurus
Blue Area Islamabad
38
13MW
PACE Circle
Cantonment, Lahore
17
9MW
Zayed Centre
Ichra , Lahore
45
30MW
DHA Commercial Complex
DHA Beach, Karachi
50
25MW
LDA Tower
Lahore
40
Expo Centre
Lahore
60
Sign Tower
Karachi
46
Grand Hyatt
Islambad
45
PARCO Tower
Lahore
35
Alamgir Tower
Lahore
31
Kohinoor Heights
Faisalabad
28
Fahim, Nanji & deSouza
Consulting Engineers
Annexure-3
Electrical Load Estimate
Sample high-rise belt in urban area
Plot
DESCRIPTION
Plot
Area
(sq yd)
1
1A
P1
2
2A
3
P2
4
5
URBAN PUBLIC SPACE
SHOPPING MALL
MULTISTOREYED CAR PARK (4)
COMMERCIAL BUILDING
URBAN PUBLIC SPACE
COMMERCIAL BUILDING
MULTISTOREYED CAR PARK (2)
COMMERCIAL BUILDING
COMMERCIAL BUILDING
FRUIT MARKET
MOSQUE
COMMERCIAL BUILDING
MULTI STOREYED CAR PARK(1)
COMMERCIAL BUILDING
EXISTING TELEPHONE EXCHANGE
COMMERCIAL BUILDING
MULTISTOREDYED CAR PARK(4)
COMMERCIAL BUILDING
COMMERCIAL BUILDING
COMMERCIAL BUILDING
CAR PARK (5)
MOSQUE
PETROL PUMP/CNG STATION
COMMERCIAL BUILDING
MULTISTOREYED CAR PARK (6)
COMMERCIAL BUILDING
MOSQUE
FRUIT MARKETS/FOOD COURTS
COMMERCIAL BUILDING
MOSQUE
PETROL PUMP/CNG STATION
URBAN PUBLIC SPACE
TOTAL
2,566
34,896
5,400
14,505
1932
10,530
5,400
6,080
12,017
1,966
2,267
12,077
5,400
14,605
13457
20,277
5,400
16,891
16,921
8,533
5,400
2,021
2,791
24,263
5,400
12,961
2,332
2,332
18,290
1,496
1,244
5,838
_
6
P3
7
8
9
P4
10
11
12
P5
13
P6
14
15
21
23
25
Note:
Covered Area
(sft)
_
1,570,320
_
652,725
_
473,850
_
273,600
540,765
_
_
543,465
_
_
_
912,465
_
760,095
761,445
383,985
_
_
_
1,091,835
_
583,245
_
_
823,050
_
_
_
_
Demand Load
(MW)
0.08
12.56
0.08
5.20
0.08
3.76
0.08
2.16
4.32
0.40
0.24
4.32
0.08
0.08
0.40
7.28
0.40
6.08
6.08
3.04
0.08
0.24
0.16
8.72
0.40
4.64
0.24
0.40
6.56
0.24
0.16
0.08
78.64 MW
1.Covered area for commercial buildings has been calculated on a FAR = 1: 5
2. Demand load for commercial buildings has been estimated at 8 watts/sft
3. Other demand loads have been approximated (street lighting, public spaces, parking lets, etc)
Fahim, Nanji & deSouza
Consulting Engineers
Fahim, Nanji & deSouza
Consulting Engineers
Annexure-4
Power Supply to Large Building Complex in Germany
Fahim, Nanji & deSouza
Consulting Engineers
Annexure-5
Utility 132/11kV Grid-Station in Dubai
Fahim, Nanji & deSouza
Consulting Engineers
Fahim, Nanji & deSouza
Consulting Engineers
Fahim, Nanji & deSouza
Consulting Engineers
Annexure-6
Power Supply to High-Rise Buildings in USA
High-Rise Office Buildings
Over the past 30 years, most major cities have grown rapidly, and their central areas have been the sites for
construction of many high-rise office buildings. The distribution system in this is type of building is
worthy of discussion, because it represents very large loads and often high available short-circuit fault
currents. In most cases, the electric utility company serves these buildings at a secondary voltage of
480Y/277-volts from one or more spot networks. There are exceptions, such as one major office building in
Pittsburgh supplied at 13,800 volts primary service by the utility and feeding 67 building-owned unit
substations, but they are not common. At the other extreme would be a typical block square 60-story office
building in New York City. The utility would have one spot network in a utility vault under the sidewalk,
supplying services in the basement, and another in a specially constructed fireproof utility vault on the 40th
floor of the building, supplying additional services, to reduce the length of secondary feeder runs. Each
vault might have six 2500-kVA network transformer, supplying four 4000-amp 480Y/227-volt service
takeoffs. The fault current available at each service would be nearly 200,000Amps. Many high-rise offices
buildings fall between these extremes, served by a utility network system at 480Y/227 volts, and using a
secondary radial distribution system within the building. A typical single-line riser diagram for such a
building is shown, along with the arrangement of a typical electrical closet on each floor.
Fahim, Nanji & deSouza
Consulting Engineers