Line Clearance Production Incentives At Detroit Edison

Procedures

For many years, Detroit Edison’s line clearance maintenance program consisted of assigning contract crews to specific areas where they would obtain their own permission to do work, to trim and to remove trees. Our line clearance budget increased until it accounted for nearly ⅓ of the total Overhead Maintenance and Operating Account. It became apparent that there was a need for improvement in this costly area.

In 1955, we started two programs: one to establish units of tree work with standards of time, and the other a system of evaluation and inspection that would designate the work to be done in each area ahead of the crews. We divided our entire service area into approximately 900 numbered maintenance areas for scheduling and recordkeeping. These areas have geographical boundaries such as townships, villages, cities or parts of these.

Each of the Divisions then developed a schedule showing which areas would be worked each year and the type of work to be done. The basis for determining these schedules was tree growth as it related to tree species, soil conditions, amount of clearance obtainable, etc. A three-year cycle of trimming was selected for 95% of the areas. Some locations with fast growing trees were placed on two-year schedules, others on longer cycles where tree interference was minimal. The field work, trimming, removing, spraying, and brushing, was broken into a series of units each descriptive of a particular operation. The contractors bid on these units by Division. The contract crews reported units completed, hours work per unit, indirect time by category and the location of work. With this time reporting system, we were able to establish standards useful in estimating tree costs on new business. With records indicating the amount and cost of tree work done in an area, we were able to accurately forecast budgets for the next cycle in that area. We had a record of contractor crew production by which we could establish norms useful in determining optimum crew size and equipment.

Results

1. Our outages caused by trees on 4.8 kV and 24/40 kV lines have been reduced significantly. In the late 1950s, tree caused outages on 4.8 kV lines were as much as 26.2% of all outages reported for that voltage, 8.2% of all outages on 24/40 kV lines, and 10.3% of all outages on 120 kV lines. Along with this decline in tree-caused trouble, there was a significant decline in equipment failure on our 4.8 kV lines.

   Recently, outages caused by trees have increased on circuits installed at 13.2 kV lines. This indicates a need for greater tree clearance on a grounded wye system.

2. Formerly, contract crews had been left to themselves and obtained their own permission to trim or remove trees and were in many cases making their own decisions. Now the work is designated for them, the price is already established, and the utility has made the decision of what is to be done. Costly and doubtful practices have been recognized and eliminated.

3. Units have provided a means for non-tree people such as engineers, line designers and others to accurately estimate costs of tree work.