Conservation Voltage Reduction (CVR)

The CVRf is the primary metric for quantifying CVR effectiveness. It is a dimensionless ratio defined as the percentage change in active power (kW) divided by the percentage change in service voltage (V).

• Constant Impedance Loads (Z): Exhibit a CVRf near 2.0 (P ∝ V²).
• Constant Current Loads (I): Exhibit a CVRf near 1.0 (P ∝ V).
• Constant Power Loads (P): Exhibit a CVRf near 0.0 (electronic power supplies).

A typical residential feeder has a composite CVRf between 0.6 and 0.9, meaning a 1% voltage reduction yields a 0.6% to 0.9% demand reduction.

CVR operates within the legally mandated voltage limits defined by the ANSI C84.1 standard. The service voltage must remain within Range A (normal operating conditions) or Range B (infrequent excursions).

• Range A (Service): 114V to 126V on a 120V base (±5%).
• CVR Target: Utilities intentionally lower the feeder voltage to the lower bound of Range A (e.g., 114V-116V).
• End-of-Line Constraint: The voltage at the furthest customer must never drop below the minimum, which limits the depth of CVR on long feeders.

The energy savings achievable through CVR are entirely dependent on the load mix downstream of the voltage regulation point. Savings are not uniform across all feeders.

• High CVR Potential: Feeders dominated by resistive heating, incandescent lighting, and induction motors (constant impedance behavior).
• Low CVR Potential: Feeders with high penetration of switch-mode power supplies in consumer electronics and LED drivers, which act as constant power loads.
• Seasonal Variation: CVRf is often higher in summer due to air conditioning compressor loads (induction motors) and lower in winter with increased electronic load.

CVR reduces instantaneous power demand (kW) , but the impact on energy consumption (kWh) depends on load behavior.

• Thermostatically Controlled Loads (TCLs): A lower voltage reduces the heating/cooling output of resistive elements or heat pumps. The thermostat compensates by increasing duty cycle (run-time) , potentially eroding energy savings.
• Non-Thermostatic Loads: Lighting and non-cyclic motors exhibit a direct energy reduction proportional to the power reduction.
• Net Effect: CVR provides reliable demand reduction, but energy savings are typically lower than the instantaneous power reduction due to TCL payback effects.

The CVRf is the primary metric for quantifying CVR effectiveness. It is a dimensionless ratio defined as the percentage change in active power (kW) divided by the percentage change in service voltage (V).

• Constant Impedance Loads (Z): Exhibit a CVRf near 2.0 (P ∝ V²).
• Constant Current Loads (I): Exhibit a CVRf near 1.0 (P ∝ V).
• Constant Power Loads (P): Exhibit a CVRf near 0.0 (electronic power supplies).

A typical residential feeder has a composite CVRf between 0.6 and 0.9, meaning a 1% voltage reduction yields a 0.6% to 0.9% demand reduction.

Validating CVR savings requires rigorous Measurement and Verification protocols to isolate the voltage effect from other demand drivers.

• Reference Feeder Method: A statistically similar feeder without CVR is used as a control group to normalize for weather and calendar effects.
• Regression Modeling: Multivariate linear regression models correlate demand with voltage, temperature, and time-of-day to extract the CVRf.
• Time-Synchronized Data: Requires granular AMI voltage data and substation SCADA power measurements aligned to the same timestamps for accurate calculation.

The primary metric for validating CVR efficacy. CVRf is a dimensionless ratio quantifying the percentage change in active power consumption (ΔP%) relative to the percentage change in service voltage (ΔV%). A CVRf of 0.7 indicates that a 1% voltage reduction yields a 0.7% demand reduction.

• Constant impedance loads (resistive heaters) exhibit a CVRf near 2.0
• Constant power loads (regulated power supplies) exhibit a CVRf near 0.0
• Typical mixed feeders range from 0.5 to 0.8
• Calculation requires regression analysis of pre- and post-CVR measurement data to isolate the voltage-dependent component of load

The overarching control architecture that enables CVR as a specific operational mode. VVO coordinates the setpoints of voltage regulators, load tap changers, and capacitor banks to minimize system losses while maintaining voltage within ANSI C84.1 Range A limits (114–126V on a 120V base).

• CVR is implemented as a voltage reduction objective within the VVO cost function
• Centralized VVO solves a mixed-integer nonlinear programming problem
• Distributed VVO uses localized peer-to-peer control between intelligent electronic devices
• Without VVO infrastructure, CVR cannot be safely executed without risking undervoltage violations at feeder endpoints

The primary actuation mechanism for CVR on distribution feeders. An LTC is a mechanical or solid-state switching device integrated into a substation transformer that adjusts the turns ratio under load to regulate the secondary bus voltage.

• Each tap change typically adjusts voltage by 0.625% to 1.25%
• CVR operation deliberately lowers the LTC setpoint to depress the entire feeder voltage profile
• Tap change minimization algorithms penalize frequent operations to prevent mechanical wear
• Solid-state LTCs enable more aggressive CVR by eliminating arcing concerns during frequent adjustments

The algorithmic engine that provides the situational awareness required for safe CVR execution. A DSE processes redundant, noisy, and asynchronous sensor data to compute the most probable voltage magnitude at every unmonitored node in the feeder.

• Ensures that CVR voltage reduction does not violate ANSI C84.1 lower limits at remote endpoints
• Fuses data from SCADA, AMI, and line sensors using weighted least-squares estimation
• Provides the sensitivity matrix used by VVO to predict the impact of tap changes
• Without DSE, operators must maintain conservative voltage margins that limit CVR energy savings

The sensor network that provides end-of-line voltage verification for CVR programs. AMI smart meters report voltage and energy consumption at 15-minute or hourly intervals from customer service points.

• Enables calculation of CVRf using pre- and post-CVR regression analysis
• Provides the critical last-mile voltage data that SCADA cannot capture
• Voltage alerts from AMI can trigger automatic CVR relaxation if undervoltage conditions emerge
• Utilities typically use a statistical sample of meters rather than full population for CVR validation

A distributed reactive power resource that supports CVR voltage profiles at the grid edge. Per IEEE 1547-2018, smart inverters dynamically inject or absorb reactive power based on a piecewise linear curve referenced to terminal voltage.

• During CVR, inverters can inject reactive power to boost sagging voltages at feeder endpoints
• Volt-Watt mode reduces active power output if voltage rises too high during light load periods
• Dynamic VAR reserve from inverters provides fast voltage support without mechanical switching
• Enables deeper CVR penetration by mitigating the voltage drop that would otherwise constrain reduction