Photo story reveals design and construction details of a substation expansion that combines new 15kV equipment with existing 5kV systems.

Flexibility of power for new facilities and planned future growth are outstanding features of a revamped outdoor substation serving the large Ciba-Geigy campus, Summit, N.J. After careful analysis, engineers on the project decided to merge a higher voltage at 13.8kV with existing 4160V equipment. The result is greatly increased power capacity, higher reliability, and lower overall costs.

Project details

The local utility supplies 34.5kV to the facility's outdoor substation, where existing transformers step down the incoming voltage to 4160V for underground distribution to more than 35 buildings on the 60-acre campus. The recently expanded substation incorporates new 34.5kV-to-13.8kV transformers that provide for 13.8kV distribution for present and future loads.

The new scheme, which allows for growth and has very high dependability, was done at significantly lower costs than if the design had stayed with the 4160V level. At 4160V, feeders to unit substations required massive amounts of copper (many 5kV feeders consist of multiple 750kcmil conductors). The 13.8kV feeders use two-thirds less copper than the 4160V distribution. This results in huge reductions in conductor ratings, conduit sizes, trench work, and overall time and labor involved.

Presently, both 4160V and 13.8kV primary feeders supply power to complex loads. Future plans call for eventual elimination of the 4160V systems entirely, with only 13.8kV being used for primary distribution.

During early planning, facility engineers considered adding a third 10,000kVA transformer to two existing 10,000kVA transformers in the substation. This would provide capacity to power two new large structures, yet leave enough spare capacity so one transformer could be redundant and serve as a spare in the event of problems. High dependability of power is vital because of the many critical experiments and processes carried out at this pharmaceutical research and development center.

New 15,000kVA transformers

Design engineers on the project, Nordling Dean Electric Co., Chatham, N.J., are particularly aware of the merits of using 15kV versus 5kv, because they are design/build contractors and engineers. Jerry Murphy, P.E., president, provided basic concept and practical design of the substation, including advantages to be gained with a 13.8kV distribution system. He proposed the installation of two new 15,000kVA, 34.5/13.8kV transformers and appropriate 13.8kV primary distribution.

Because of his proposals, it became clear that using 13.8kV for the expansion would permit the use of much smaller conductors, smaller trenches, less labor, a minimum of interference with daily operations, higher reliability, and much lower total costs. Typically, 750kcmil and 500kcmil, 5kV, shielded, EPR conductors serve 4160V feeders. The 15kV conductors are shielded, EPR, sized typically at 4/0 AWG.

As a result, the plant decided to use the savings to pay for the "second" 15,000kVA transformer. In other words, the cost of installing a new 5kV, 10,000kVA transformer and related distribution approximately equalled the cost of two 13.8kV, 15,000kVA transformers and distribution. Simply put, one 15,000kVA transformer cost nothing.

Triad Engineering, consulting engineers located in Morris Plains, N.J., assisted with design details and did short-circuit studies and the protective-relay coordination plan.

To see the end result, look at the modified single-line diagram, on page 31, and related photos, which permit a walkthrough of the substation, illustrating many design and construction details.