Temporary Power Distribution Within Industrial Construction Projects|
Article- December 2011 By Larson Electronics.com
Larson Electronics Portable Temporary Power Substation
Under normal conditions, providing power for electrical equipment is as simple as plugging into a wall outlet. For many industrial jobsites however, conditions are anything but normal. Particularly in new construction involving large scale projects, providing power becomes a large scale project all on its own. With no established power supplies, no existing distribution systems, and the need to provide power for a large variety of equipment requiring everything from high voltages to common 110-120 VAC current, providing power becomes a major issue. In many cases, contractors must develop a complete power supply and distribution system of their own that can not only meet the needs of equipment, but serve only in a temporary capacity and be removed once the project is completed as well.
Because of the large scale and extended duration of many industrial construction projects, the need for electrical power requires power systems that while temporary, have all the functionality and reliability of permanent connections to the local grid. Meeting these requirements are a challenge due to the voltages involved and the need to maintain safety as well as make electrical power readily available throughout the entire structures involved. In most cases, electrical contractors are consulted who develop an electrical plan based on the size and load requirements of a particular site. These contractors often consult with local utilities who then provide access to a very high voltage primary power source, which the contractor must then step down to useable levels and distribute throughout the project area.
Problems encountered with providing temporary power to industrial job sites include adhering to OSHA regulations, providing enough load handling capability, and reducing the chances of voltage drops, overloads, and overheating that could arise due to excessive cord lengths and insufficient connection points resulting in overloaded lines. Contractors meet these issues through the use of large temporary substations to manage high primary voltages, carefully installed temporary conduit or wiring systems for distribution of this reduced voltage, and multiple step down distribution transformers which provide useable end voltages. The result is nothing less than an entire power grid system of a temporary nature with all the functionality of normal permanent connections.
The electrical power utilized by contractors often starts out as a primary high voltage connection to the local grid. These voltages vary according to the utilities involved and can exceed 11,000 volts. The first step is to reduce this to manageable voltages through the use of temporary power substations which reduce this current to 480VAC. Once this is achieved, the 480VAC power can be fed into distribution panels for routing through the structure. To provide power to every location within the structure, conduit or wiring is run to every level and or most convenient point and terminated at each location with an access made up of receptacles, panels, or other similar connecting points. With 480VAC current now available at the required locations within the site, it is then necessary to further reduce this current to useable levels and provide easy access for connection to equipment.
Power for equipment is normally required to be 110, 120, 208 and 220-240 for power lighting, fans, drills, motors, welders and other construction equipment. Additionally, cords should not exceed 100 feet in length in order to avoid voltage drops and cord overheating, so access to these voltages needs to be convenient. To step down the supplied 480VAC power, smaller temporary transformer/distribution centers are installed at each 480VAC access point and connected. These portable step down transformers come in a wide variety of configurations, but generally contain a 480VAC primary input side, which is then stepped down via a small transformer to 110, 120, 208 and 220-240 VAC. These transformers feed this power through breaker and or fuse protected circuits which in turn fed integral secondary output receptacles which may or may not be GFI/GFCI protected depending upon the distribution center’s configuration and worksite requirements.
These distribution centers must manage a wide range of loads and be suited to the particular conditions they will be operated under. For instance, some welding equipment requires very high voltages to operate, and thus 120-220 will be insufficient. As a result, the transformer/distribution center will require additional feed through capability to provide direct 480VAC current. In other applications, wet conditions or hazardous flammable materials may be present. In these instances, distribution centers will require at least an IP67 waterproof rating in the case of exposure to wetness, or hazardous location certification in the case of flammable environments.
Additionally, it is necessary to assume the highest possible loading that may occur and install power step down and distribution systems that will allow a safe margin for error. A system with load handling capability which exceeds load requirements presents little problems, but one with insufficient capability can be easily inadequate if expected loads are accidently exceeded by a small margin. Although grounding and breaker/fuse protection may provide the necessary precaution against faults and overloading, frequent system shutdowns due to overloading can have a serious impact on productivity and still potentially lead to workplace accidents. Also, the transformer needs to be situated so that all equipment operated will be within 100 feet of the system to avoid excessive cord lengths and thus protected against voltage drops.
Another consideration for installation of portable step down transformers and distribution centers is their size and weight. The transformers and materials used can lead to systems that although portable, are anything but easily relocated. For large scale sites, transformer systems are often quite heavy, and as a result are best configured as self contained systems which can be easily managed with small forklifts or lifting equipment. With the transformer, circuits, breakers and receptacles all contained within a single package encased within a solid frame or similar housing, it is a simple matter for operators to relocate the system to a desirable position using powered transport.
Providing power for large scale industrial construction projects is no longer a simple matter of running a few generators and rigging up some lights and outlets. OSHA regulations, site size, and the load requirements of today’s equipment require comprehensive systems that provide safety as well as reliable operation on a temporary basis. These systems in essence represent a miniaturized version of the local power grid and as such, require the same forethought and planning to maintain safety as well as productivity.