Optimized Line Design in a Deregulated World
Routing
Angle point placement along a line route is critical to structure spotting. Subtle changes in alignment can mean the difference of several structures per mile. Many angle locations are fixed, but there may still be room to adjust the route, particularly with small angles. Striving to maximize span lengths between angles is the optimal approach. Designers frequently measure the distance between angle points then divide by the desired number of spans to obtain the span length. This is actually working backwards. The best solution results if the designer manipulates the angle points as closely as possible to multiples of the maximum span length. If a structure family has a maximum span of 350 feet, try to locate the turning locations at multiples of 350 feet (i.e. 350, 700, 1050, etc.). When laying out line routes, designers who think long spans, design long spans. If they think short spans, they design short spans. This is important when spotting around long gradual curves or along winding roads with the line
crossing back and forth.
Consider New Materials and Construction Practices
More alternatives to standard wood pole lines are available every year. Designers and standards departments should constantly seek new techniques and products and evaluate potential savings associated with them. Steel, concrete, or laminated poles often provide a cheaper installation with less maintenance. Alternative pole types often eliminate the need for guying, particularly for small line angles. Use of new pole materials can yield savings in easement costs, maintenance, and public relations (guy wires are never popular with the public). The same is true for crossarms, insulators, guys and anchors.
Underground Optimization Process Factors
Concepts that designers should consider during underground line design include:
- Number of lots to be served per transformer
- Front or rear lot design
- Radial or loop feed design
- Estimated load per customer and the effects of varying this load
- Available source voltage
Transformer Sizing
Optimized underground line design enables the utility to solve problems using analytical methods coupled with sound engineering judgment. The designer can consider key constraints to determine maximum allowable transformer sizing for a specific design type, including:
- Transformer, conductor, and equipment size
- Transformer rating factors
- Diversification of loads
- Primary conductor (sizing)
- Ampacities – thermal and economic loading
- Allowable voltage drop
- Allowable flicker
Routing
The allowable routing of primary and secondary circuits is critical to the design process. Factors that dictate routing are the location of easements for front or rear lot design, the attempt to minimize lengths of circuits and number of road crossings, and the requirement to have the appropriate number of services per transformer.
