Brife Introduction of High Voltage Fuse

The fuse is a type of protective device in an electrical circuit. When the current in the circuit exceeds the specified value and persists for a certain period, the fuse melts to interrupt the current and disconnect the circuit. The main function of a fuse is to provide short circuit protection for circuits and devices, and some also have overload protection capabilities.

 

High-voltage fuses are primarily used in power plants and substations to protect factory transformers, power transformers, power capacitors, voltage transformers, etc. However, they have a small capacity and relatively poor protective characteristics, generally only suitable for voltage levels of 35kV and below.

High-voltage fuses consist of a metal fuse element, a supporting contact for the fuse element, and an outer casing (fuse tube). The core component of the fuse is the fuse element.

In high-voltage fuses, the fuse element is made of metals such as copper and silver, and small tin (lead) balls are soldered onto its surface. When the current is high, it will initially melt at these points. Some fuses also contain quartz sand; in the event of a short circuit, after the fuse element melts, it quickly infiltrates the narrow gaps in the quartz sand, causing rapid cooling and extinguishing of the electrical arc.

During usage, the fuse is connected in series with the protected circuit or device. Under normal conditions, the fuse element only carries a load current not exceeding its rated value, and its normal heating temperature does not cause it to melt. When the circuit experiences overload or a short circuit, the overload current or short-circuit current heats the fuse element. The fuse element melts before the temperature reaches a point that would damage the insulation of the protected equipment, thereby breaking the circuit and providing protection to the equipment.

High-voltage fuses are more like disposable devices (as people may gradually recognize, the fuse element in a high-voltage fuse is actually reversible within a certain time range), whereas high-voltage circuit breakers can be used repeatedly.

1. Technical Characteristics

The larger the current passing through the fuse element, the faster the fuse will blow. The fuse blowing time is inversely proportional to the square of the current passing through it (ampere-second characteristic).

a. When I < IN (rated current), the blowing time is 0.

b.When the same short-circuit current I flows through fuse elements with different rated currents, the fuse with a smaller rated current blows first. (t2 > t1) 2 - larger cross-section, 1 - smaller cross-section.

2. Technical Parameters

a. Rated current of the fuse (INt): Ensures that the current-carrying portion of the housing and the contact portion can pass through this current for an extended period without damaging the fuse.

b. Rated current of the fuse element (INs): The maximum current that the fuse element can carry for an extended period without blowing. (The rated current of the fuse and the rated current of the fuse element may not be the same, but INs < INt. In the same fuse, multiple fuse elements with different rated currents can typically be installed.)

c. Maximum breaking current (capacity): The maximum current that the fuse can interrupt.

Current-limiting High-voltage Fuses: After the fuse element melts, the short-circuit current decreases immediately to zero before reaching its maximum value. For example, fuses with quartz sand inside the fuse tube have a short arc extinguishing time, causing significant changes in current, which may generate overvoltage, possibly several times the normal power supply voltage. Devices protected by current-limiting fuses may not need to undergo dynamic and thermal stability checks during a short circuit.

Non-current-limiting High-voltage Fuses: Extinguishes the arc naturally. After the fuse element melts, the short-circuit current does not decrease but continues until it reaches the maximum value. The arc extinguishes after the first zero crossing or after several half cycles.