What types of high-voltage capacitor protection fuses are there?

High-voltage capacitor protection fuses are important devices used to protect high-voltage capacitor banks. They come in a variety of types, each with its own structure, operating principle, and application scenarios. The following are common types of high-voltage capacitor protection fuses and their characteristics:

I. Classification by Installation Method

Indoor High-Voltage Capacitor Protection Fuses

Features: Suitable for indoor high-voltage capacitor installations. Typically installed in switchgear or dedicated protection cabinets, these fuses have relatively limited environmental adaptability and must be protected from rain, dust, and other environmental influences.

Applications: Indoor capacitor compensation systems in substations and high-voltage capacitor systems within industrial enterprises.

Outdoor High-Voltage Capacitor Protection Fuses

Features: Waterproof, dustproof, and UV-resistant, they offer stable operation in outdoor environments. Their housings are often made of weather-resistant materials (such as porcelain and epoxy resin).

Applications: Capacitor compensation systems for outdoor high-voltage transmission lines and capacitor protection in outdoor substations.

II. Classification by Structure

Ejector Fuse (Dropout Fuse)

Structure and Principle: Consists of a fuse tube, fuse element, insulator, and contacts. When the fuse element blows, the fuse tube automatically drops under gravity, creating a clear disconnection gap, providing both protection and isolation.

Features:

Strong arc extinguishing capability, extinguishing the arc when the short-circuit current passes through zero.

Easy maintenance: After blowing, the fuse element can be directly observed and replaced.

Applications: Outdoor high-voltage capacitor systems of 10kV and below, commonly used for capacitor protection in rural power grids and small substations.

Current-Limiting Fuse

Structure and Principle: The fuse is filled with an arc-extinguishing medium such as quartz sand. The arc generated when the fuse melts cools rapidly in the sand, limiting the rise of the short-circuit current and reducing overvoltage.

Features:

Extremely fast arc extinguishing, disconnecting the circuit before the short-circuit current reaches its peak, protecting capacitors from high current surges.

No significant disconnect gap, requiring use with a disconnector.

Application Scenario: High-voltage capacitor systems of 35kV and above, especially those requiring high short-circuit current limiting (such as large substations and high-voltage transmission lines).

Ceramic Plug-In Fuse

Structure and Principle: Consists of a porcelain base and a porcelain insert, with the fuse housed within the insert and installed by plugging and unplugging.

Features: Simple structure and low cost, but with weak arc extinguishing capability and low interrupting current.

Applications: Early small capacitor protection systems for low or medium voltage (e.g., 10kV). Currently, their use is declining.

III. Classification by Protection Characteristics

Overcurrent Protection Fuse

Features: Mainly protects against short-circuit current or overcurrent faults. When the current exceeds the rated value, the fuse heats up and melts, interrupting the circuit.

Application: Short-circuit protection for conventional high-voltage capacitor systems.

Overvoltage Protection Fuse (for use with a lightning arrester)

Features: Typically connected in parallel with a lightning arrester. When an overvoltage occurs in the system, the lightning arrester activates first to discharge the current. If the lightning arrester fails, the fuse can blow to protect the capacitor.

Application Scenario: High-voltage capacitor systems with frequent lightning activity or large voltage fluctuations.

IV. Classification by Voltage Level

Medium-voltage fuses (10kV, 35kV): Commonly used in capacitor compensation devices in distribution networks.

High-voltage fuses (110kV and above): Used for capacitor protection on ultra-high voltage transmission lines. They have a more complex structure and higher insulation requirements.

5. Special Type Fuses

Full-Range Fuses

Features: These fuses can protect against both small overload currents and large short-circuit currents. The fuse element design provides for both long-term overload and instantaneous short-circuit breaking characteristics.

Applications: High-voltage capacitor systems requiring high protection accuracy, minimizing false tripping and missed protection.

Resettable Fuse

Principle: Utilizing the physical properties of materials like metallic sodium, sodium vaporizes when heated during a short circuit, limiting current. Once the fault is cleared, the sodium cools and resumes conductivity, eliminating the need for fuse replacement.

Features: Fast action and reusability, but relatively high cost and currently relatively limited in use.

Application Scenarios: High-voltage capacitor systems (such as critical substations) requiring extremely high power supply reliability.

Selection Key Points

Select the fuse's rated voltage, rated current, and breaking capacity based on the voltage level, capacitance, and system short-circuit current parameters.

For outdoor applications, ejector or weather-resistant fuses are preferred. For indoor applications, current-limiting or indoor fuses can be used.

Consider coordination with other protective devices (such as relay protection and lightning arresters) to avoid nuisance tripping or blind spots.