What Is The Function Of A Fuse?

drop out fuse, in daily life, we call it a fuse, which is used to protect against circuit overload and short circuits. When the current passing through the fuse exceeds the specified value, the heat generated by the fuse itself melts the fuse element, automatically disconnecting the circuit. Fuses are divided into general-purpose fuses and semiconductor device protection fuses according to their purpose.

(I) Selection of general-purpose drop out fuse fuses is divided into:
1. Wire (circuit) protection
Overload and short-circuit currents in the circuit can cause excessive temperature in wires and cables, leading to damage or even breakage of the insulation. Wire and cable overload protection can be achieved by reasonably selecting fuses based on the current carrying capacity, installation method, type, and insulation material grade of the wires and cables. Fuses for wire and cable overload protection can be installed at the input or output end of the wires and cables, while fuses for short-circuit protection must be installed at the input end of the wires.
2. Motor protection
A simple motor circuit usually consists of drop out fuse—contactor—thermal relay—motor. Based on experience, in this circuit, the rated current of the selected fuse should be approximately 1.2 to 1.5 times the rated current of the motor.
3. Short-circuit and overload protection for mining circuits
Fuses complying with mining electrical regulations can be used for short-circuit and overload protection of mining circuits.
4. Capacitor switching equipment protection
In capacitor switching equipment, fuses are recommended for short-circuit protection. The rated current of the selected fuse should not be less than 1.6 times the rated current of the capacitor.

(II) Selection of fuses for semiconductor device protection
During the operation of rectifier devices, fault currents can occur due to internal or external faults in the semiconductor device. Therefore, fuses must be used to quickly interrupt the fault current. Correct selection of fuses can reliably protect semiconductor devices and converter devices. The general principles for fuse selection are as follows:
1. Rated voltage
The rated voltage of the fuse is determined by the operating voltage at the installation point, and it must be greater than or equal to the operating voltage. If the line's operating voltage exceeds the fuse's rated voltage, two fuses can be used in series. In this case, it must be ensured that the short-circuit current at the installation point is at least 10 times the rated current.
2. Rated Current
The rated current of the fuse is determined by the effective value of the current at the installation point. The effective value of the current at the installation point depends on the different lines of the power conversion device. If the fuse current rating does not meet the line requirements, two fuses of the same specifications can be used in parallel. When used in parallel, the current distribution difference between the fuses is approximately ±5%.
3. Switching Overvoltage
During the arc extinguishing process, the fuse generates overvoltage in the line. Excessive overvoltage can cause reverse breakdown of semiconductor devices. Therefore, the switching overvoltage of the fuse can be found from the charts in the sample data. The switching overvoltage must be less than or equal to the allowable reverse peak voltage of the semiconductor device.
4. Rated Breaking Capacity
The rated breaking capacity of the fuse should be greater than the maximum short-circuit current that may occur in the line.
5. Protection Characteristics
The time-current characteristics of the fuse can be found from the time-current characteristic curve chart in the sample data. Overload protection of the rectifier device can be provided by other switching devices, such as DC fast switches.
However, in practical work, we often encounter many isolating fuse sets (referred to as knife-switch fuses), which require the selection and configuration of fuses. These fuses are generally classified by shape, including blade type, cylindrical type, spiral type, etc. Among them, the blade type is further divided into 00C (000), 00, 0, 1, 2, 3, and 4 specifications in terms of size. Most of the fuses configured with isolating fuse sets are blade-type fuses. During configuration, it is important to ensure that the size specifications match the requirements of the isolating fuse set. For example, the ABB OS-160 isolating fuse set uses a 00-size blade-type fuse.