Power System Architectures for the Commercial Buildings

In the previous Topic; Specific Electrical Design Requirements for Commercial Buildings, I listed the famous power system architectures for the commercial buildings as follows:

1. Low building, type 1: One supply section. 
2. Low building, type 2: Two supply sections. 
3. High-rise building, type 1: Central power supply, cables. 
4. High-rise building, type 2: Central power supply, busbars. 
5. High-rise building, type 3: Transformers at remote location. 
6. High-rise building, type 4: Distributed supply, cables. 
7. High-rise building, type 5: Distributed power supply, busbars. 

And today, I will explain these types in detailed.


Low building, type 1: One supply section

Conditions for using this power system architecture:
1- If the following rule is verified:

The number of building floors must not exceed the max. Number of floors for one supply section (i) calculated by equation#1.

If:
Max. Side length of the building = a (in meter)

One Floor area A = a2 (in square meter)

Height per floor = h (in meter)


Then:

Max. Number of floors for one supply section (i) ≤ (100 – 2a) / h (equation#1)

If the number of floors exceed the max. Number of floors for one supply section (i) calculated by equation#1, then we must use other types of power system architecture.

Note: all buildings have number of floors ≤ 4 are low rise buildings.


2- If the (Ground area / total area) of the building ≤ 2,500 m2 / 10,000 m2

Note: if floor area ≤ 2,500 m2, so there will be only one central equipment room per floor feed from the LVMD (Low Voltage Main Distribution switchgear)


3- If the power density of the building loads have the following limits:

• Power required 1,000 to 2,000 kW 
• Segmentation of power required 85 % utilized area (i.e. functional area like Offices, Briefing rooms, Data center, Canteen kitchen with casino, Heating/ventilation/air conditioning, Fire protection and Transport) And 15 % side area (i.e. shafts, fountains, green area, sky lighting area and etc.) 

4- If the power supply needed for the building have the following requirements:

• Supply types 100 % total power from the public grid; (Supply of all installations and consumer Devices available in the building).
• 10–30 % of the total power for safety power supply (SPS) from generators; (Supply of life-protecting facilities in case of danger, e.g.: Safety lighting, Elevators for firefighters, Fire-extinguishing equipment).
• 5–20 % of the total power for uninterruptible power supply (UPS); (Supply of sensitive consumer devices which must be operated without interruption in the event of a NPS failure / fault, e.g.: Tunnel lighting, airfield lighting, and Servers / computers and Communications equipment).

Example for  one supply section  power system architecture:

We have a building with 1200 VA total load power, 4 floors and floor area 2,500 m2 with total area 10,000 m2.

Solution selected for this building is using the one supply section power system architecture as follows:

Design solution	Advantages of this solution	Benefits from this solution
Using Central transformer supply close to load center	Supply at the load center, short LV cables, low losses	Low costs, time savings during installation
Radial network	Transparent structure	Easy operation and fault localization
Transformer module with 2 × 630 kVA,	Voltage stability, lighter design	Optimized voltage quality, economical
Redundant supply unit: – Generator 400 kVA (30 %) (the smaller the generator, the greater the short-circuit current must be in relation to the nominal current) – UPS 200 kVA (15 %)	Supply of important consumers on all floors in the event of a fault, e.g. during power failure of the public grid	Increased reliability of supply
	Safety power supply	Safety power supply in acc. with DIN VDE 0100-718
	Supply of sensitive and important consumers	Uninterruptible supply of consumers, e.g. during power failure of the public grid
Use Medium-voltage switchgear from type SF6 gas-insulated	Compact switchgear; independent of climate	Minimized space requirements for electric utilities room; no maintenance required
Use Transformer from type cast-resin with reduced losses	Low fire load, indoor installation	Economical
Use Low-voltage main distribution with  central grounding point ( which splitting of PEN in PE and N to the TN-S system)	EMC-friendly power system	Protection from electromagnetic interference (e.g. to prevent lower transmission rates at communication lines)
Use Wiring / main route as cables	Central measurement of current,voltage, power, e.g. for billing, cost center allocation	Cost transparency
Use Connection inside substation ( Transformer – LVMD- NPS – SPS) as busbars	Easy installation

 And the power system architecture will be as follows:

one supply section  power system architecture

Where:

NPS	Normal power supply
PCO	Power company or system operator
FF	Firefighters
HVAC	Heating – Ventilation – Air conditioning
MS	Medium-voltage switchboard
LVMD	Low-voltage main distribution
SPS	Safety power supply
UPS	Uninterruptible power supply
z	Power monitoring system

In the next Topic, I will explain the “Low building, type 2: Two supply sections” power system architecture. So, please keep following.