What types of high-voltage capacitor protection fuses are there?
High-voltage capacitor protection fuses are crucial devices used to protect high-voltage capacitor banks. They come in various types, each differing in structure, working principle, and application scenarios. Below are some common types of high-voltage capacitor protection fuses and their characteristics:
I. Classification by Installation Method
Indoor High-Voltage Capacitor Protection Fuse
Features: Suitable for indoor high-voltage capacitor installations, typically installed in switchgear or dedicated protection cabinets. Environmental adaptability is relatively weak; it must be protected from rain, dust, etc.
Application Scenarios: Indoor capacitor compensation devices in substations, high-voltage capacitor systems in industrial enterprises.
Outdoor High-Voltage Capacitor Protection Fuse
Features: Waterproof, dustproof, and UV-resistant design, allowing stable operation in outdoor environments. The casing is typically made of weather-resistant materials (such as ceramic or epoxy resin).
Applications: Capacitor compensation devices for outdoor high-voltage transmission lines; capacitor protection in outdoor substations.
II. Classification by Structural Form
Ejection-Type Fuse (Drop-Out Fuse)
Structure and Principle: Composed of a fusible tube, fusible element, insulator, and contacts. When the fusible element melts, the fusible tube automatically drops under gravity, forming a clear disconnection gap, thus providing both protection and isolation functions.
Features:
Strong arc-extinguishing capability; extinguishes the arc when the short-circuit current crosses zero.
Easy maintenance; the fuse element can be directly inspected and replaced after blowing.
Applications: 10kV and below outdoor high-voltage capacitor systems; 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-quenching medium such as quartz sand. When the fusible element melts, the electric arc generated is rapidly cooled in the quartz sand, limiting the rise rate of the short-circuit current and reducing overvoltage.
Features: Extremely fast arc extinguishing speed; it can disconnect the circuit before the short-circuit current reaches its peak, protecting the capacitor from high-current surges.
No obvious disconnection gap; requires the use of a disconnecting switch.
Application scenarios: 35kV and above high-voltage capacitor systems, especially in applications with high short-circuit current limiting requirements (such as large substations and high-voltage transmission lines).
Porcelain plug-in fuse
Structure and principle: Composed of a porcelain base and a porcelain plug-in, the fusible element is installed inside the porcelain plug-in and installed by plugging and unplugging.
Features: Simple structure and low cost, but weak arc extinguishing capability and small breaking current.
Application scenarios: Early low-voltage or medium-voltage (e.g., 10kV) small capacitor protection systems, but its application is gradually decreasing.
III. Classification by Protection Characteristics
Overcurrent Protection Fuse
Features: Primarily designed for short-circuit or overcurrent faults. When the current exceeds the rated value, the fuse element heats up and melts, cutting off the circuit.
Application Scenarios: Short-circuit protection in conventional high-voltage capacitor systems.
Overvoltage Protection Fuse (Used in conjunction with surge arresters)
Features: Typically connected in parallel with a surge arrester. When an overvoltage occurs in the system, the surge arrester trips first to discharge current. If the surge arrester fails, the fuse will blow to protect the capacitor.
Application Scenarios: 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 in ultra-high-voltage transmission lines; they have a more complex structure and higher insulation requirements.
V. Special Types of Fuses
Full-Range Fuses
Features: Simultaneously protects against small overload currents and large short-circuit currents; the fuse element design accommodates both long-term overload and instantaneous short-circuit fusing characteristics.
Application Scenarios: For high-voltage capacitor systems requiring high protection accuracy, reducing malfunctions and leakage protection.
Self-resetting fuse
Principle: Utilizing the physical properties of materials such as metallic sodium, sodium vaporizes upon heating during a short circuit, limiting current. After the fault is cleared, the sodium cools and regains conductivity, eliminating the need to replace the fusible element.
Features: Rapid action and reusable, but relatively expensive, and currently less commonly used.
Application scenarios: High-voltage capacitor systems with extremely high power supply reliability requirements (such as important substations).
Key Selection Points
Select the rated voltage, rated current, and breaking capacity of the fuse based on the voltage level, capacitor capacity, and system short-circuit current parameters.
For outdoor applications, prioritize ejector or weather-resistant fuses; for indoor applications, choose current-limiting or indoor-type fuses.
Consider the coordination with other protection devices (such as relay protection and surge arresters) to avoid malfunctions or protection blind spots.