Industrial and commercial power systems represent a microcosm of almost the full gamut of electrical supply systems with, in addition, a significant range of other more specialized applications of electrical, electronic, communications and electrical energy utilization systems. The term “building” will be used in this article to include any industrial and commercial installations with substantial internal electrical distribution infrastructure. It will thus include both commercial high-rise buildings and factory site with electrical supply at up to 11KV and with the possibility of both 11KV and extensive 415 volt distribution system.
· More energy efficient, with better energy management
· Safe in all aspects (including personal safety, fire and equipment safety)
· Of adequate power quality with regard to harmonics and over-voltages
· Able to accommodate modern information technology systems
· Be compliant with the new regulations electrical systems
· Provide monitoring systems to assess the condition of the electrical installation
Because of the potential dangers to personnel, safety precautions are stringently applied and there are a large number of codes and regulations that have to be complied with in the electrical system design and operation. Modern requirements impose a Duty of Care on the infrastructure operator and make safety of paramount importance. The aim of these codes is to give safe operation for both personnel and equipment. A detailed knowledge of these regulations is necessary for the design and operation of building electrical systems.
Power Requirements:
The type of electrical supply system used in a commercial building or a factory depends primarily on the total power requirements of the various utilization activities that are taking place within the building or factory site. These power demands must be estimated accurately before the details of the electrical supply configuration can be determined and designed. They will determine the ultimate form (and voltage level) of the supply system to and within the building/site.
The power requirements are obtained by an estimation of the maximum demand for electrical power. This will normally have three possible components:
· Manufacturing equipment requirements
· General fixed wiring infrastructure requirements
· General free-standing mobile equipment supply
An estimate will require detailed loading and duty cycle estimates of each of these. In the first of these, this is easily done as the manufacturing load is easily calculated. It may include large motors, arc furnaces, power electronic equipment, welders, assembly lines, ovens, presses. Some of these loads may require special supplies, such as constant voltage, low harmonic, low noise systems. In the second area, the total of all permanently installed infrastructure equipment such as heating, lighting, air-conditioning, lifts and any similar motor drives etc must be determined. The Wiring Rules has tables which will allow the determination of typical levels of such loads for buildings. In the third component, the estimate takes account of the number of general purpose power outlets (GPOs) in the building. In the last component, the method of determination of maximum demand for domestic and commercial type loads is specified in the Wiring Rules (Australian Standard AS, or the equivalent in other countries). The general details of the method of determination are shown in the following details.
| Type of Development | Range VA/m2 | Average VA/m2 | |
| Offices | Not air-conditioned Air-conditioned-Cooling only -Reverse cycle -Electrical reheat open areas -Electrical reheat zonal or package units -Variable volume | 40-60 70-100 60-90 80-120 90-130 60-80 | 50 85 75 100 110 70 |
| Car parking | -Open air -Ventilated | 0-10 10-20 | 5 15 |
| Warehousing | -Unventilated -Ventilated | 5-15 10-20 | 10 15 |
| Shops | -Not air-conditioned -Air-conditioned | 40-100 60-140 | 70 100 |
| Shopping centres (assumed air-conditioned shops) | -Not air-conditioned public areas -Air-conditioned public areas | 60-140 80-160 | 100 120 |
| Industrial | -Light -If ventilated add -If air-conditioned add | 10-20 10-20 30-50 | 15 15 40 |
| Theatres, halls, etc | -Ventilated - air-conditioned | 50-70 80-120 | 60 100 |
| Hotels, Restaurants (Residential section) | - | 60-100 | 80 |
In the estimation of the power demand requirements, it is necessary to make some allowance for future growth in power requirements, including possible additional switchboard circuits, in new building or in existing buildings. Typically:
· Residential premises, 10%
· Fully air-conditioned offices, 15%-20%
· Commercial premises, 20%-25%
· Shopping centers, light or medium industrial, 25%
This allowance for expansion of power supply capacity must also be included in the initial consideration of the selection of transformer capacity and cable sizes for feeder circuits and reticulation of power.
Means and Requirements of Electrical Supply:
The requirements of the electrical supply system may include any or all of the following features:
· Specified voltage levels
· Limited harmonic content (quality of supply)
· Method of supply
· Safety of supply
· Reliability of supply
· Maintenance
· Electrical protection
· Back-up supply (UPS)
· DC supply
Voltage Level:
The supply voltage levels which are available from the electricity supply utilities for use in commercial and industrial locations in urban areas are, typically:
High Voltage:
11KV, 3-phase supply [by cable or overhead line]
Low Voltage:
a) 240/415 volts, 3-phase, 4-wire system
b) 240 volts, Single-phase, 2-wire system
[By underground cable, aerial cable or by overhead line].
Once the power demand and supply requirements are determined by the system designer (usually an electrical consulting engineer), it is necessary to then contact the electricity distributor. They will have a range of additional requirements which must be complied with before they will connect supply from their network to the site.
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