What is the types of Fuses?

What is the types of Fuses?

A fuse is a current - interrupting device. It breaks or opens the circuit by melting its fuse element, thereby isolating the faulty device from the main supply circuit. Fuses are mainly classified into two types based on the input supply voltage: AC fuses and DC fuses. The various types of fuses are depicted in the image below.

DC Fuse

A DC fuse functions to open or break the circuit when an excessive current passes through it. However, the major challenge with DC fuses lies in extinguishing the arc generated by direct current. Since there are no natural zero - current crossings in a DC circuit, unlike in an AC circuit, arc extinction is extremely difficult. To mitigate this, the electrodes in a DC fuse are placed at a greater distance from each other. As a result, the size of a DC fuse is larger compared to an AC fuse of similar rating.

AC Fuses

AC fuses are classified into two main types: low - voltage fuses and high - voltage fuses. The alternating current in AC fuses has a frequency that causes its amplitude to vary from 0º to 60º within one second. This characteristic of AC allows for easier arc extinction in an AC circuit compared to a DC circuit.

Low - voltage fuses can be further categorized into four classes, as depicted in the image below. Semi - enclosed or rewirable fuses, along with totally enclosed or cartridge - type fuses, are the most frequently used types of fuses.

Rewirable Fuses

Rewirable fuses are predominantly utilized in small - current circuits, such as those for domestic wiring. The rewirable fuse consists of two main components: the fuse case and the fuse carrier. The base of the fuse, typically crafted from porcelain, is designed to hold the fuse wires. These wires can be made of materials like lead, tinned copper, aluminium, or a tin - lead alloy. One of the advantages of rewirable fuses is that the fuse carrier can be effortlessly inserted into or removed from the base without the need to open the main switch. This feature allows for convenient replacement of the fuse wire when it has blown due to excessive current, making it a practical choice for home electrical systems where simplicity and ease of maintenance are valued.

Totally Enclosed or Cartridge Type Fuses

In totally enclosed or cartridge type fuses, the fuse element is completely encased within an enclosed container, with metal contacts positioned on both ends. These fuses can be further categorized into two subtypes: D - type cartridge fuses and Link - type cartridge fuses. Each subtype has its own distinct design and characteristics, which are tailored to different applications and electrical requirements. The enclosed structure of these fuses offers enhanced protection against environmental factors and accidental contact, making them suitable for a wide range of electrical systems where safety and reliability are crucial.

D - Type Cartridge Fuses

The key components of a D - type cartridge fuse include the base, adapter ring, cartridge, and a fuse cap. The cartridge is housed within the fuse cap, and the fuse cap is securely attached to the fuse base. When the cartridge is fully screwed into the base, the cartridge tip makes contact with the conductor, thereby completing the circuit via the fuse links. This design allows for easy installation and replacement of the cartridge, ensuring efficient electrical connection and protection within the circuit.

Link Type Cartridge or High Rupturing Capacity (HRC) Fuses

In link type cartridge or HRC fuses, the fuse element is designed to carry fault current for an extended period. In the event that the fault persists, the fuse element will melt, effectively opening the circuit and interrupting the current flow. One of the significant advantages of HRC fuses is their ability to clear both low and high fault currents. This makes them highly reliable in protecting electrical systems from a wide range of abnormal current conditions.

HRC fuses are characterized by their high - speed operation. They also require minimal maintenance, which is a major plus in many applications. However, after each operation, the fuse element of HRC fuses needs to be replaced. Additionally, during faults, these fuses generate heat, which can potentially impact the operation of nearby switches.

The enclosure of an HRC fuse is filled with powdered pure quartz, which serves as an effective arc - extinction medium. The fuse wire in HRC fuses is typically made of silver and copper. This fuse wire consists of two or more sections that are joined using a tin - joint. The tin - joint helps to reduce the temperature under overloaded conditions, enhancing the overall performance and durability of the fuse.

To increase the breaking capacity of the fuses, two or more silver wires are connected in parallel. These wires are arranged in such a way that only one wire will melt at a time. HRC fuses are of two types

Knife Blade Type Switches

In knife blade type switches, the replacement of the fuse wire within a live circuit is facilitated using a fuse puller. This tool allows for the safe removal and substitution of the fuse wire without directly handling it, reducing the risk of electric shock. Bolted type HRC fuses, on the other hand, feature two conducting plates that are securely bolted to the fuse base. However, when removing this type of fuse switch, an additional safety circuit is required to prevent the user from receiving an electric shock. This extra circuit ensures that the electrical current is properly isolated before the switch is removed.

Dropout Fuse

A dropout fuse functions in a unique way. When the fuse element melts due to excessive current, it drops out under the influence of gravity around its lower support. This characteristic makes dropout fuses particularly suitable for the protection of outdoor transformers. In an outdoor environment, where transformers are exposed to various weather conditions and potential electrical faults, the dropout fuse can quickly and effectively isolate the faulty component, safeguarding the transformer and the overall electrical system.

Striker Fuse

A striker fuse is a mechanical device equipped with sufficient force and displacement capabilities. This allows it to be used for closing tripping or indicator circuits. When a fault occurs in the electrical system, the striker fuse can be triggered, and its mechanical action can close the relevant tripping circuit, which in turn can disconnect the power supply to protect the system. Additionally, it can also activate an indicator circuit to signal the occurrence of a fault, providing an important visual or audible indication for maintenance personnel.

Switch Fuse

Switch fuses are designed for use in low - and medium - voltage circuits. The fuse units within these switches are available with ratings in the range of 30, 60, 100, 200, 400, 600, and 800 amperes. They come in 3 - pole and 4 - pole configurations, offering flexibility in different electrical setups. The making capacity of these fuses can reach up to 46 kA. Depending on their rating, they are capable of safely breaking currents that are approximately 3 times the load current. This makes switch fuses reliable components for protecting electrical circuits from overcurrents and short - circuits in low - to medium - voltage applications.

High Voltage HRC Fuses

One of the primary challenges faced by high - voltage fuses is the issue of corona. Corona occurs when the electrical field strength around a conductor is high enough to ionize the surrounding air, resulting in a discharge. To address this problem, high - voltage fuses are designed with special features. These fuses are mainly classified into three types, each type tailored to meet the specific requirements of high - voltage applications while minimizing the effects of corona and ensuring reliable performance.

Cartridge Type HV HRC Fuse

In a cartridge - type high - voltage (HV) high - rupturing capacity (HRC) fuse, the fuse element is wound in a helical shape. This design effectively mitigates the corona effect at high voltages. The fuse contains two parallel - arranged fused elements: one with low resistance and the other with high resistance. Under normal operating conditions, the low - resistance wire carries the normal current. However, during a fault, it is the first to blow, reducing the short - circuit current. This sequential operation helps in safeguarding the electrical system by quickly limiting the excessive current flow.

Liquid Type HV HRC Fuse

Liquid - type HV HRC fuses are filled with carbon tetrachloride and have sealed caps at both ends. When a fault occurs and the current exceeds the permissible limit, the fuse element melts and blows out. The carbon tetrachloride liquid within the fuse serves as an efficient arc - extinguishing medium for HRC fuses. These fuses find applications in transformer protection as well as providing backup protection for circuit breakers. Their ability to rapidly quench arcs makes them reliable components in high - voltage electrical setups.

Expulsion Type HV Fuse

Expulsion - type fuses are popularly used for feeder and transformer protection due to their cost - effectiveness. They are typically designed for 11 kV systems and have a rupturing capacity of up to 250 MVA. This type of fuse consists of a hollow, open - ended tube made of synthetic resin - bonded paper. The fuse elements are inserted into the tubes, and the tube ends are connected to appropriate fittings. When an arc is generated, it is forced against the inner coating of the tube. The gases produced during this process help in extinguishing the arc, effectively protecting the electrical system from over - current conditions.