At Luckett & Farley, our electrical engineers are sometimes called upon to provide medium-voltage (MV) design for systems. If you have zero experience, MV design can be intimidating. After all, electrical engineers designing for anything beyond 600 volts is a fairly new concept.

From a recent Consulting-Specifying Engineer web article:

Until recently, engineers didn’t work too frequently in the design of medium-voltage (MV) systems, mainly because anything over 600 V was primarily handled by the utilities. Exception included heavy electrical users such as government institutions, the mining industry, or industrial sites. However, in the past 15 years, there has been an explosion of MV electrical distribution systems used in large commercial complexes. Many of these complexes also have high-rise components with MV risers servicing unit substations at strategic locations on multiple levels. Another feature of large commercial complexes is the associated central plant function with MV chillers and unit substations.

The most common medium voltage design for Luckett & Farley electrical engineers are 4160V, 12.47 kV, and 13.8 kV. These are nominally classified as 5kV and 15kV. We have also worked with 24 kV systems. The most commonly used systems for power distribution are 15 kV and 24 kV. Distribution is the last link between the power company’s substation and the transformer at the building or utilization site. Voltages higher than this are considered high voltage, and are used for transmission. Transmission lines are the lines from the power generating facilities to and between the utility substations.

Almost every project we do involves some medium voltage. Whenever we include a service transformer in a design, there is a MV primary. Usually we show the path for the MV conduits or cables from the utility company pole or manhole to the service transformer. At times, however, the MV systems we design can be much more involved.

Since the utility companies normally own and maintain the distribution networks, they are usually responsible for designing additions and modifications to the MV systems necessary to support our designs. However, when we do projects on military bases, university campuses or large industrial plants where our client’s facility is large enough to warrant primary distribution on the premises, we provide MV design services.

A few of the medium voltage designs we've accomplished simply add a few poles to an existing overhead distribution network. This can be necessary when an overhead line is not close enough to the new service transformer. We have designed distribution systems for military housing neighborhoods. We have designed overhead, underground, and combined systems. At Ft. Knox, we assisted with the layout of an underground distribution system for 256 new homes. At Ft. Wainwright and Ft. Greely in Alaska, we have modified and extended the overhead distribution systems to accommodate hundreds of new homes in 10 different neighborhoods. At Wright-Patterson Air Force Base, we designed the replacement and upgrading of the overhead distribution system for a large part of the base known as Area B.

For industrial clients, our MV work can include unit substations and medium voltage switchgear. For the Ford Kentucky Truck Plant stamping plant original construction and subsequent addition, we incorporated double ended unit substations in our electrical design. For another project at KTP we accommodated the relocation of a unit substation from another plant. A plant expansion at an automotive manufacturing facility in Ohio included three new unit substations and additional medium voltage switchgear.

For the School of Dentistry renovation project at the University of Louisville's downtown campus, we modified the existing 15kV switchgear to relocate and update the building electrical system. At the Kentucky Women’s Correction Institution, we designed 15 kV main switchgear with a primary loop and sectionalizing switches around the campus. At a data center at WPAFB we provided the conceptual design of a high speed medium voltage transfer switch installation. This switch detects an outage on one medium voltage feeder, and transfers the data center to a backup feeder faster that the computers can be affected by the outage.

Perhaps the most complex MV design we have been involved with is an energy security project at a local military base. This project, which we are designing together with the mechanical equipment supplier, will add 21 medium voltage generators to six sites around the base. When the project is complete, the base will be completely backed up by generator. In addition to emergency power, the generators will be used for peak shaving and combined heat, chilled water, and power generation, enabling the project to be cost effective. This project is a huge undertaking, requiring coordination between two generator manufacturers, the switchgear manufacturer, emissions controls vendor, the utility company, and the mechanical equipment supplier. When complete, it will eliminate the likelihood of an outage event such as the one that resulted from an ice storm in 2009 had left the base without power for ten days.

To learn more about Luckett & Farley's medium-voltage design capabilities and additional electrical engineering experience, contact Electrical Engineering Department Manager, Mitch Thompson, PE, LEED AP at mthompson@luckett-farley.com or (502) 585-4181.

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