Energy-efficiency policy in the electric power sector has often focused on consumers through end-use energy-conservation programs and incentives. However, significant opportunities also exist to reduce energy use through investments in the electric power supply infrastructure.

Besides reducing the losses in the infrastructure, there are also opportunities to reduce energy use on the customer side and peak demand through voltage management on the distribution system. A demonstration project has been designed to address the full range of these opportunities for energy savings. In many cases, the investments can be attractive alternatives to customer-side incentives and initiatives.

Potentials for Energy Savings

As part of an ongoing industry collaboration known as Green Circuits, 42 distribution circuits have been evaluated, with detailed simulations validated based on monitoring data, and six pilot demonstration projects have been operational for two to 12 months. Distribution losses range from less than 2% of energy delivered to almost 7%. The following various options for improving distribution efficiency and reducing losses were modeled and simulated as modifications to the base-case model:

• Phase balancing — Rearranging loads on each phase of the circuit to reduce residual flows

• Reactive power optimization — Additional capacitor banks or altered switching schemes

• Selected reconductoring — Replacing selected conductor sections with larger, lower-resistance conductors

• High-efficiency distribution transformers — Replacement of lower-efficiency line transformers with higher-efficiency units

• Voltage optimization or conservation voltage reduction (CVR) — Intentional lowering of distribution circuit voltage within the lower band of the allowed American National Standards Institute range.

Of these, voltage optimization was the most consistently beneficial option. Improvements to reactive power profiles — normally through capacitor optimization — and phase balancing provided cost-effective improvements in about 10% to 20% of cases. Voltage optimization provided cost-effective improvements in at least 80% of cases.

Circuit Modeling

Each circuit was modeled in detail from the substation to each customer meter. The analysis used a common platform, an open-source distribution system electrical simulation package known as OpenDSS, created by the Electric Power Research Institute (EPRI). Nearly all of the circuit models were augmented with historical circuit-measurement data that allowed for hourly simulation resolution of actual circuit-load patterns. This high-fidelity representation of the circuits' electrical characteristics, with the temporal and spatial diversity of the circuit loads, allows for capturing all loss sources. Several circuit models were also included:

• Primary distribution lines and cables (three-phase mains and single-phase laterals)

• Substation power transformers

• All distribution service transformers

• Secondaries and services (detailed models used when available)

• Voltage-regulation controls (load tap-changing transformers, regulators and capacitors)

• Detailed load representations, including the temporal variations in the load over the entire year.

Voltage Optimization

Voltage optimization strategies were developed on a circuit-by-circuit basis. In general, the strategy was developed without significant investments in new voltage regulators and capacitor banks. Voltage reduction was achieved by changing strategies with existing technologies on the circuits. The standard voltage-reduction approach involved the following assumptions:

• Use end-of-line feedback on all load tap-changing transformers and voltage regulators

• Voltage set point = 118.5 V

• Bandwidth = 2 V (+/- 1 V)

• CVR factor for watts = 0.8

• CVR factor for VARs = 3.0.

The median reduction in energy was 2%, with upper and lower quartiles of 2.8% and 1.3%. Because a constant CVR factor was used, these simulations mainly show how much room there is to drop voltage across the circuit throughout the course of an annual cycle. In about 10% of the circuits, the benefit was small or even negative. This is a result of limited availability to reduce the voltage on these circuits compared to the base case or cases where the existing voltage control was inadequate.

Voltage optimization can reduce energy consumption by several percent. Losses and end-use consumption are reduced when feeder voltage alone is managed to be within the lower end of the standard supply service voltage band. Additional reduction of both peak demand and energy consumption is possible with more aggressive investments in distribution voltage control to provide a flatter voltage profile. While end-point voltage monitoring technology is available, results of the initiative indicate it is also possible to obtain similar results using simple line drop compensator settings on these regulators.

EPRI's Green Circuits distribution project is validating the results of the Northwest Energy Efficiency Alliance (NEEA) Distribution Efficiency Initiative Study. Both indicate a 1% to 3% energy savings and a 1% to 4% demand reduction. A 5% to 10% reactive-power reduction can be achieved through voltage optimization. Assuming voltage optimization use achieves a nationwide penetration of 25% to 50%, an approximate annual savings range of 4 million MWh to 28 million MWh could be realized.