High-Voltage Capacitor Comprehensive Protection Solution

Rockwill

17yrs 700++ staff 108000m²+m² US$150,000,000+ China

Core Objective: To ensure the safe and stable operation of capacitors and the power grid, and to extend equipment lifespan.

When high-voltage capacitors are put into operation in the power grid, a robust protection system is crucial. This solution, based on industry standards and practical experience, provides configuration guidelines for key protection measures:

I. Core Electrical Parameter Protection

Overvoltage Protection:

Function: To guard against cumulative damage to capacitor dielectric or instantaneous breakdown caused by atmospheric overvoltages (lightning), switching overvoltages, and system steady-state overvoltages.
Configuration:

Surge Arrester (MOA - Metal Oxide Arrester): Installed at the line end and neutral end of the capacitor bank, especially on the line side and neutral point side, to effectively clamp the intrusion of lightning surges and the peak of switching overvoltages.
Overvoltage Relay: Continuously monitors the terminal voltage of the capacitors. When the voltage exceeds the set value (typically 1.1Un), it trips the capacitor bank after a time delay to prevent prolonged overvoltage operation. Setting determination requires comprehensive consideration of the system's permissible fluctuation range.

Overcurrent Protection:

Function: To respond to abnormal current rise due to internal or external overloads of the capacitor bank, or internal component breakdown.
Configuration:

Time-Delayed Overcurrent Protection: Serves as backup protection for the main capacitor bank protection and handles system overloads. The setting must coordinate with and ride through inrush currents during energization, typically set at 1.5 to 2 times the rated current.
Instantaneous Overcurrent Protection: Targets severe short-circuit faults and trips instantaneously to clear the fault.

Short-Circuit Protection:

Function: Provides extremely fast fault clearing in the event of internal or external phase-to-phase faults or single-phase-to-ground faults involving the capacitors.
Configuration:

Dedicated High-Voltage Fuse: The preferred protection for internal faults within an individual capacitor unit. Fuses instantly upon fault occurrence, isolating the faulty unit while allowing the rest of the bank to continue operating.
Circuit Breaker + Relay Protection: Provides backup short-circuit protection functionality. Coordination between fuse operation and breaker tripping times must be ensured.

II. Key State Monitoring and Protection

Temperature Protection (Thermal Protection):

Function: Prevents explosions or fires caused by abnormally high temperatures resulting from overcurrent, harmonics, poor ventilation, internal dielectric aging, or component breakdown (which may initially be indicated by fuse operation).
Configuration:

Embedded Temperature Sensors (PTC/Pt100): Embedded at key heat dissipation points (e.g., top of capacitor casing) to monitor internal hotspot temperature in real-time.
Temperature Relay / Intelligent Monitoring Unit: Receives signals from the sensors. Activates when the temperature exceeds a safe threshold (e.g., 75°C - 80°C), issuing alarms or trip commands.

Harmonic Protection and Mitigation:

Function: To suppress "harmonic amplification" effects on the capacitors caused by system harmonics, which lead to severe overcurrent, overheating, and rapid equipment aging.
Configuration:

Harmonic Monitoring Meter: Continuously monitors the Total Harmonic Distortion (THD) and individual harmonic content of current/voltage on the busbar or capacitor circuit. Issues alarms upon abnormality.
Harmonic Filters: In environments with severe harmonic pollution or for large capacitor banks, prioritize installing filter capacitor banks with matching reactance ratios (e.g., with 6%, 13% reactors) instead of pure compensation capacitor banks. In extreme cases, configure Active Power Filters (APF).

III. Safety Assurance and Operational Control

Grounding Protection:

Function: Ensures personnel and equipment safety by providing an effective path for fault current.
Configuration:

Reliable grounding of the metal enclosure; grounding resistance must comply with regulations.
One terminal of the secondary winding of the discharge coil/resistor must be grounded.
Install open-delta voltage protection in systems with non-effectively grounded neutrals.

Disconnecting Switch (Isolator):

Function: Creates a visible break during maintenance, ensuring no risk of back-feed and providing a safe isolation point.
Configuration: Install disconnecting switches with visible air breaks on the source side (line side) of the circuit breaker. Operation must strictly follow the "Five-Prevention" interlocking mechanism.

Automatic Trip Device (Interlock Protection):

Function: Comprehensively determines faults or abnormal operating conditions at the control system level to achieve intelligent tripping.
Configuration:

Multiple criteria (voltage, current, temperature, fuse operation signals, etc.) are integrated into the protection and control unit.
Automatically initiates trip logic during abnormal conditions, driving the circuit breaker to operate. Integrated within the Substation Automation System (SAS).

08/09/2025

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