High Rupturing Capacity (HRC) Fuse

What is meant by High Rupturing Capacity (HRC) Fuse?

The HRC fuse or High Rupturing Capacity fuse, works similarly to a standard fuse in that the fuse wire can only carry a set amount of short circuit current. It burns if the flow is higher than this. Glass or any other form of chemical component is used to make HRC fuses.

 Ceramic metal caps with flexible silver wire are used to secure the fuse’s ends. The wire, which would otherwise be the fuse’s element, is surrounded by a sizable quantity of interior space.

The HRC fuse or High Rupturing Capacity fuse is uniform and has the property of having a very quick trip time under high-pressure current. Similar to this, a low fault current results in a prolonged break time. Since it operates with high accuracy and dependability, it provides an advantage over a typical rewireable fuse. Normally, distribution networks and electric motors are protected by HRC fuses.

Key Terminologies of HRC Fuses

High Rupturing Capacity

This term refers to the fuse’s ability to safely disconnect the circuit when the current exceeds a certain threshold, preventing damage to the connected equipment.

Fuse Element

The fuse element is the component within the fuse that melts and breaks the circuit when the current surpasses the pre-set limit. This is the primary functioning part of the fuse.

Fusible Link

Similar to the fuse element, the fusible link is designed to melt and disrupt the circuit when the current becomes too high, acting as a critical safeguard.

Arcing Time

Arcing time is the duration it takes for the fuse to break the circuit connection once the current exceeds the fuse’s capacity. This is an important factor in the fuse’s performance.

Breaking Capacity

Breaking capacity denotes the maximum current the fuse can interrupt without causing damage to the circuit or itself. This is a key specification that determines the suitability of a fuse for a particular application.

Materials Used in HRC Fuses

The construction of HRC fuses involves materials that can withstand high temperatures. The exterior casing is typically made of ceramic, a robust insulating material that prevents electric shock or damage. Inside this casing, the fuse body is filled with a powder, often composed of silica sand, plaster of Paris, marble, chalk, or similar materials. This powder plays a crucial role in absorbing and dissipating the heat generated during the fuse’s operation.

Fuse Wire

The metallic strip inside the fuse, usually made of silver, is designed to melt when subjected to excessive current. The powder filling interacts with the vaporized silver, creating a high-resistance material that helps minimize sparking and prevents the fuse from reaching dangerous temperatures. This combination of materials and design ensures the fuse operates effectively under high fault conditions.

Construction of HRC Fuse

A ceramic-like material with a body capable of withstanding high heat makes up the HRC fuse. On this ceramic body, the end caps are made of metal. A substance that is currently containing a silver is connected to this. Inside the fuse body is a powder containing the materials that will be used, such as quartz, plaster of Paris, dust, marble, chalk, etc. Overheating of the essence cannot be caused by noise sources in the current. The heat generated evaporates the element that has been dissolved. The hrc fuse diagram is shown below.

The filling power and the silver vapour will undergo a chemical process that creates a high resistance material that will aid to lessen the arc inside the fuse. Because of their low resistance, copper or silver are frequently employed in fuses.

Typically, a fuse element has two or more pieces that are joined together by a tin. Tin’s melting point is 2400° C, which is lower than silver’s melting point of 980° C and keeps fuses from heating up to high temperatures in short-circuit and overload situations.

Working Principle of the HRC Fuse

Operation Under Normal Conditions

In normal operating conditions, the heat produced by the current passing through the fuse element dissipates without causing any harm. The element, typically made of silver, is designed to handle the rated current, such as 63 amperes, without overheating. The temperature remains below the melting point of the element, ensuring that the fuse does not interrupt the circuit. This allows the current to flow smoothly, fulfilling the intended function of the fuse.

Operation Under Short Circuit or Overload Conditions

When a short circuit or overload occurs, the current in the circuit exceeds the fuse’s rated capacity, such as 63 amperes. In this situation, the fuse element starts to generate excessive heat. However, the filling powder inside the fuse absorbs this heat, preventing the element from reaching its melting point immediately. This heat-absorbing property of the powder helps delay the melting of the fuse, allowing it to handle the increased current temporarily.

Response to Fault or Overload Conditions

If the excessive current persists, reaching up to approximately 1.5 times the fuse’s rated value (around 94.5 amperes), and continues for more than 10-12 seconds, the fuse element will eventually reach a critical temperature. At this point, the element will melt and vaporize, resulting in the fuse opening and interrupting the current flow. This process prevents further damage to the circuit and connected equipment.

The precise design of the fuse element, including its material composition and structure, plays a crucial role in determining the fuse’s electrical characteristics. These characteristics influence how quickly the fuse responds to faults, its ability to withstand short circuits, and its overall performance in handling both amperage and voltage levels.

HRC Fuse Element

The element of an HRC fuse functions similarly to that of a standard fuse. It is typically made from a metal like silver, which is engineered to melt at a specific temperature. Under normal operating conditions, the current passing through the fuse is within the expected range, and the heat generated in the element dissipates without causing any harm. However, if the current exceeds this normal range, the element overheats and melts at predefined points, triggering the fuse to open and interrupt the current flow. Once this occurs, the fuse must be replaced.

Types of HRC Fuse

  The following are the three common types of HRC fuses:

• DIN Type Fuse,
• NH Type Fuse and
• Blade Type Fuse.

DIN Type Fuse

These are found in a wide range of electric currents. It is utilised in various temperatures and has various qualities. These can be found in a range of voltages and are used to safeguard the transformer.

Its cleansing ability is ideal for

• Short-circuit acts,
• Transformers,
• Gas-insulated switchgear, and
• Feeder partitioning

are all used in mining and the air.

NH Type Fuse

For low and medium voltage, NH type fuses are employed. In conditions like overload and short circuits, this provides protection. This fuse guards against overload and short circuits and safeguards other devices as well as the beginning of the motor. These fuses are offered in lightweight versions with particular specifications.

Blade Type Fuse

Plug I is another name for this type of fuse. A plastic body and two metal socket-fitting caps are offered for the fuse. In automobiles, it is utilised as backup protection for motors, wiring, and short circuits.

Generally, these have low cut-offs and are available in low weights. There are several sizes, forms, and current ratings of blade-type fuses available.

Characteristics of HRC Fuse

It possesses the three following important characteristics:

• Cut-off Characteristics,
• I²t Characteristics and
• Time – current characteristics.

Cut-off Characteristics

The HRC fuse’s cut-off characteristic is the graph that depicts how current and voltage change over time immediately following a malfunction. When a fault develops, the fault current has a significant positive peak, but the fuse melts before it reaches its peak. Prospective current is the name for this current. Cut-off current is the current at which a fuse blows and an arc begins.

When a fault happens, the voltage briefly drops, and when the fuse melts and an arc form, the arc voltage increases to a level that is several times greater than the supply voltage. This is entirely dependent on the cross-section and length of the fuse. The recovery voltage returns to normal when the arc entirely disappears. Here, the arc entirely disappears.

I²t Characteristics

I²t Characteristics reveal details on the timing of arc quenching and the heating effect brought on by pre-arcing current. When the fault current is interrupted, the I²t Characteristic indicates how much energy is liberated and transferred to the devices that need to be protected.

Time – Current characteristics

The time-current characteristics of the HRC fuse are the line drawn between the fault current and operating time in the case of the HRC fuse. The inverse time-current characteristic of the HRC-fuse is present. Accordingly, the fuse’s operational time reduces as the fault current’s value rises.

Selection of HRC Fuse

These elements should be taken into account while choosing an HRC fuse:

• Application type: cable protection/motor protection
• System voltage
• Current at full load.
• Inrush current and non-fault overload current for motors
• Maximum short-circuit current and potential fault circumstances.
• Periodic current curve.
• Size.
• Cut-off curve

Advantages of HRC Fuse

• Cheaper than circuit breakers with a same braking capacity.
• Easy installation and simplest construction.
• No maintenance is necessary.
• The fuse has a high breaking strength.
• Reliable in their performance.
• It doesn’t decrease performance over time.
• Faster and more reliable operation.
• Not impacted by external factors.
• Used to eliminate both big and small values of fault current.
• The fuse offers trustworthy discrimination.
• Due to its inverse time-current properties, it is suitable for overload protection.

Disadvantages of HRC Fuse

• This fuse does not support interlocking.
• The arc-connected switch is impacted by the heat it produces.
• Cannot be used again once the fuse wire melts during usage.
• After each operation, replacement is required.
• Adjacent contacts becoming too heat.

Application of HRC Fuse

• High voltage switch gear is shielded from short circuits by HRC fuses.
• For MCB backup protection.
• Motor stators also require this kind of fuse.
• Required to protect electrical devices like motors, transformers, and cars.
• High selectivity radial and ring networks.

HRC Fuse with Tripping Device

In an HRC fuse with a tripping device, the fuse is designed to work in conjunction with a circuit breaker. When a fault occurs and the fuse blows, it activates the tripping device, causing the circuit breaker to operate and disconnect the circuit. The fuse body is made of ceramic material with metallic caps at each end, connected by a series of silver fuse elements. A plunger is positioned at one end of the fuse, which engages the tripping mechanism of the circuit breaker during fault conditions, ensuring the circuit is interrupted. This plunger is linked to the other end of the cap through a fusible link and a tungsten wire.

Operation of HRC Fuse with Tripping Device

When a fault occurs, the silver fuse element is the first to blow, transferring the current to the tungsten wire. The plunger is designed to travel in a controlled manner, ensuring it does not eject from the fuse body during the fault condition. This setup allows the fuse to effectively trigger the circuit breaker without compromising safety.

Advantages of HRC Fuse with Tripping Device

• Single-Phase Fault Protection: In a three-phase system, the plunger trips the circuit breaker during a single-phase fault, ensuring all three phases are disconnected, preventing a single-phase supply.
• Cost-Effective Circuit Breaker Usage: The fuse’s ability to trip the breaker during a short circuit allows the use of a less expensive circuit breaker, as the effects of the short circuit are managed by the fuse.
• Reduced Fuse Replacement: The fuse-tripped breaker can handle small currents without needing to replace the fuse, except in cases of very high current.

Low-voltage HRC fuses with tripping devices are available in capacities ranging from 16,000A to 30,000A at 400V, with options up to 80kA to 120kA. These fuses are commonly used in low-voltage distribution systems for protection against overload and short-circuit conditions.

FAQs on HRC Fuse

What is an HRC Fuse?

Definition: An HRC fuse, or High Rupturing Capacity fuse, is a vital component in electrical circuits designed to interrupt the circuit when the current exceeds a specific limit. It features a conductor that melts easily under excessive current, providing protection by safely handling short-circuit currents for a defined period.

Why is Filling Powder Used in HRC Fuses?

The fuse element or fuse wire in an HRC fuse is surrounded by a filling powder, typically made from pure quartz, plaster of Paris, or marble dust. This powder acts as an effective arc extinguishing agent, helping to quench the arc when the fuse operates.

Can HRC Fuses be Used for Both AC and DC Applications?

Yes, HRC fuses are versatile and can be used in both AC (alternating current) and DC (direct current) circuits. However, it is essential to select fuses that are specifically designed and rated for the type of current they will be used with to ensure safety and optimal performance.

Can HRC Fuses be Used for High-Voltage Applications?

HRC fuses are suitable for high-voltage applications, as they are available in various voltage ratings designed to accommodate different voltage levels. Their adaptability makes them appropriate for a wide range of applications, including those operating at high voltages.

What is the full form of HRC fuse?

The full form of HRC fuse is High Rupturing Capacity fuse.

What is difference between HRC fuse and MCB?

An HRC fuse melts and breaks the circuit during overcurrent conditions, requiring replacement once blown. In contrast, an MCB trips to disconnect the circuit and can be reset, providing reusable protection.