The Value of Construction Work Plans

For an electric distribution cooperative to borrow money for system improvements, a Construction Work Plan (CWP) is required. The CWP is a four-year planning document establishing the improvement needs for the electric utility. The CWP is used to obtain a loan from Rural Utilities Services (RUS) or other sources to construct the required facilities. RUS, as the typical lender, establishes the required content for the CWP.

Establishing Costs

There are typical construction activities such as service extensions, service up-rates, pole replacements, conductor replacements, special equipment, and others. The cost for these activities is based on a four-year history and compared to the recommendations of the last four-year work plan, plus cost inflation. These costs are rounded and divisible by four making the estimate for each year the same. This historic cost method supports a significant portion of the work plan costs.  

Fixing System Problems

In addition to the historic cost items, some system improvements will be required. Each substation has a demand history when combined with Load Forecast Study or Power Requirements Study. These studies set a design level for each substation four years in the future. A line section-based model is developed for each substation. The model identifies regulators, capacitors, and auto-transformers when different line voltages are involved. However, the more important parts are the line sections of various conductor sizes. The line sections will receive a load allocation based on historic consumer use adjusted for the future projected substation demand. The consumer data comes in different formats. The data is carefully matched to the model and inserted in the matching line sections.

After the load allocation process is complete, the model can be tested with a voltage drop calculation. RUS limits primary line voltage by secondary voltage values developed along the line section. The “Range A” secondary voltage is to be between 126 and 118 Volts leaving 4 Volts for service voltage drop. An existing system voltage drop calculation with the future loading is made. Voltage failures of either High or Low are identified and the fixing process begins. 

Balanced conditions perform best. Several adjustments can be made to achieve this balance;

• Three-phase consumers may get allocated to one phase because of the data received. 

• You may just switch a tap to a different phase. 

• Maybe a single-phase tap has a current over 50 amps and needs to be converted to a three-phase for load balance. 

• Adding, relocating, or removing regulators and capacitors can help solve specific voltage problems.

• A smaller conductor may need to be replaced with a larger conductor. 

• Changing to a higher voltage distribution level may solve the problem. 

Experience helps to select the system improvements needed to fix voltage problems.

Operational Adjustments

After the voltage problems are corrected, a cooperative may have some operational choices to consider. These may involve high-capacity feeders between substations to support a back feed during a power outage. These improvements get added to the list. The list of improvements will require an environmental evaluation. The entire work plan gets an environmental evaluation with agency contacts when required for support.

History also has an impact on system improvements. An analysis of completed improvements included in the prior work plan is reviewed for actual cost compared to the estimates. The analysis provides unit costs to be used for proposed work plan projects. Projects not completed are evaluated as in process, delay, carryover or to be deleted. Repeated failure to complete system improvement projects impacts the justification for proposed system improvements. A potential solution worked out in a work plan is not a solution until understood, accepted, and implemented by the cooperative.

The Construction Work Plan

After the system improvements are identified, the CWP will involve descriptive text, supporting tables and substation drawings carefully drafted and checked to identify line sections and voltage levels at key locations. In the past we could reuse substation diagrams and make changes; however, today span-based models are reduced each time and are always different. They must be drafted anew after the analysis is complete.

After improvements, fault current calculations provide a basis to evaluate sectionalizing. When the device settings and ratings are in the model proper coordination can be checked. You can answer questions like:

• Can the device at a given location interrupt the fault current?

• Can it carry the load current and can it see the fault current downstream?

• Can coordination with upstream devices be improved? 

This information in the work plan model can support an arc flash study.

Once complete the Construction Work Plan (CWP) not only provides annual budget and loan support, the CWP provides guidance to develop system changes needed to reach projected load levels, keeps employees safe with properly working devices, and keeps the lights on for consumer-owners.