Capacitor Bank Control

The foundational control mode that executes capacitor switching based on a pre-programmed real-time clock (RTC) calendar.

• Seasonal Schedules: Different on/off times for summer and winter load profiles.
• Weekday/Weekend Profiles: Accounts for industrial vs. residential load patterns.
• Daylight Saving Compensation: Automatic adjustment prevents schedule drift.
• Holiday Exception Tables: Prevents unnecessary switching on low-load holidays.

This method is simple but blind to real-time grid conditions, making it suitable only as a fallback or for predictable industrial loads.

A closed-loop control mode that uses potential transformer (PT) inputs to switch capacitors when the measured voltage deviates from a configurable setpoint.

• Hysteresis (Deadband): A deliberate voltage band (e.g., 118-122 V on a 120 V base) where no action occurs, preventing hunting and excessive contactor wear.
• Time Delay (TD): A programmable delay (30-300 seconds) that filters transient voltage sags before initiating a close or trip command.
• Overvoltage Lockout: A hard threshold that forces capacitor trip to protect equipment if voltage exceeds safe limits (e.g., >126 V).

This is the most common autonomous control strategy for feeder-level voltage support.

An environmental compensation mechanism that modifies switching behavior based on ambient or internal bank temperature measured by thermocouples or RTDs.

• Cold-Load Pickup Anticipation: Proactively switches capacitors online during extreme cold to counteract the increased reactive demand from resistive heating loads.
• Thermal Derating: Reduces or blocks capacitor insertion when internal bank temperature exceeds safe operational limits (typically 55°C ambient).
• Seasonal Bias Adjustment: Automatically shifts the voltage setpoint higher in summer and lower in winter to align with utility conservation voltage reduction (CVR) goals.

This feature is critical for utilities in regions with wide seasonal temperature swings.

A transient-mitigation technique that synchronizes the vacuum or SF6 interrupter closing command with the zero-crossing point of the voltage waveform.

• Inrush Current Limitation: Closing at the voltage zero-crossing minimizes the capacitor inrush current, reducing stress on the dielectric and preventing nuisance fuse operations.
• Contact Erosion Reduction: Eliminates pre-strike arcing, significantly extending the mechanical life of the switching device.
• Harmonic Resonance Avoidance: Prevents the sharp voltage step change that can excite system resonances.

This feature is standard in modern intelligent electronic devices (IEDs) for capacitor switching and is essential for back-to-back capacitor bank configurations.

An advanced control mode that uses current transformer (CT) inputs alongside voltage to calculate reactive power (VAR) flow and power factor in real time.

• Target Power Factor: Switches capacitors to maintain a user-defined power factor (e.g., 0.98 lagging) at the point of common coupling.
• VAR Bias: Injects a precise amount of reactive power to offset measured inductive VARs, preventing both leading and lagging conditions.
• Reverse Power Detection: Blocks capacitor insertion during reverse power flow scenarios common with high distributed energy resource (DER) penetration.

This mode is preferred for industrial and commercial metering points where power factor penalties are a financial concern.

The communication backbone enabling centralized Distribution Management System (DMS) control via protocols like DNP3, IEC 61850, or Modbus.

• Remote Open/Close Commands: Allows system operators to manually override local logic during emergency or maintenance conditions.
• Analog Telemetry Reporting: Streams real-time voltage, current, VAR, and temperature data to the control center for situational awareness.
• Event Logging (SOE): Timestamps and stores operational events (switching operations, alarms, threshold violations) with 1 ms resolution for post-event forensic analysis.
• Distributed Control Coordination: Receives coordinated dispatch signals from centralized Volt-VAR Optimization (VVO) engines to harmonize operation with voltage regulators and LTCs.

This transforms a standalone controller into a node within a wider smart grid architecture.