1. Basic Functions of Fuses

Fuses, also referred to as safety fuses, are essential electrical protective components dedicated to preventing circuit overload and short-circuit faults. Once the operating current exceeds the fuse’s calibrated rated value, the internal fusible element will melt instantly to cut off the circuit automatically, effectively avoiding equipment damage and circuit failure expansion. In general, fuses are divided into two major types: standard general-purpose fuses and specialized fuses for semiconductor equipment protection.

2. Key Selection Criteria for Fuses

2.1 Selection Rules for General-Purpose Fuses

(1) Circuit and Cable Protection

Overload and short-circuit faults will induce excessive current in wires and cables, leading to sharp temperature rises. This will damage the insulating layer of lines, and even cause cable burnout and line breakage in severe cases. The selection of protective fuses for lines should be based on the cable’s current-carrying capacity, laying mode, model specification and insulation grade. Overload protection fuses can be installed at both ends of lines, while short-circuit protection fuses are mandatory to be arranged at the line inlet and outlet terminals.

(2) Motor Circuit Protection

A basic motor control system is mainly composed of a fuse, contactor, thermal relay and motor. According to industry practical experience, the optimal rated current of the matching fuse is 1.2 to 1.5 times the rated working current of the motor.

(3) Protection for Mining Power Lines

Fuses that comply with national mining electrical safety standards can be applied to mining lines to provide reliable overload and short-circuit protection.

(4) Protection for Capacitor Switchgear

For capacitor switching equipment, fuses are the preferred component for short-circuit protection. The rated current of the selected fuse shall be no less than 1.6 times the rated current of the supporting capacitor.

2.2 Selection Specifications for Semiconductor Protection Fuses

During the operation of rectifier equipment, internal or external faults of semiconductor components will generate dangerous fault current. Specialized fuses are required to quickly break the faulty circuit to protect semiconductor devices and complete converter equipment. The core selection parameters are as follows:

(1) Rated Voltage

The fuse’s rated voltage is determined by the actual working voltage of the installation position and must be equal to or higher than the system operating voltage. When the line working voltage exceeds the single fuse’s rated voltage, two fuses can be used in series. In series connection scenarios, the short-circuit current at the installation point must reach more than 10 times the fuse’s rated current to ensure normal operation.

(2) Rated Current

The fuse rated current is configured according to the effective RMS current of the installation circuit, which is affected by the structural form of the converter device. If there is no matching single-specification fuse, two fuses of the same model can be connected in parallel. It should be noted that parallel connection will cause a current distribution deviation of about ±5% between the two fuses.

(3) Breaking Overvoltage

The arc extinguishing process of fuses will produce transient overvoltage in the circuit. Excessively high overvoltage will trigger reverse breakdown and damage semiconductor components. Therefore, the fuse’s breaking overvoltage must be checked against the official product curve, and the value must not exceed the maximum allowable reverse peak voltage of semiconductor equipment.

(4) Rated Breaking Capacity

The fuse’s rated short-circuit breaking capacity must be greater than the maximum possible short-circuit current that may occur in the operating circuit.

(5) Protective Characteristics

The fuse’s time-current protection characteristics can be queried from the product characteristic curve provided by the manufacturer. In addition, auxiliary switching equipment such as DC high-speed circuit breakers can be used to assist the rectifier device in overload protection.

3. Matching Guidelines for Fuses of Fused Isolating Switches

Fused isolating switches are widely used in industrial electrical systems and need to be matched with supporting fuses. According to structural appearance, fuses are classified into knife-type, cylindrical and spiral types. Knife-type fuses are the most commonly used supporting type for isolating switches, with complete dimensional specifications including 00C (000), 00, 0, 1, 2, 3 and 4. In actual configuration, the size and specification of the selected fuse must strictly match the installation size of the fused isolating switch to ensure safe and stable operation.