High Rupturing Capacity (HRC) । A fuse is a protection device that is used to protect a device or a circuit from fatal damage caused by an additional degree or short circuit fault. High Rupturing Capacity (HRC) fuses are certainly familiar with fully enclosed fuses, the high breaking capacity that has been developed after intensive research by manufacturers and supply engineers.
Construction
An HRC High Rupturing Capacity fuse is a type of cartridge fuse where the fuse component is enclosed in a transparent capsule, usually steatite – a ceramic component that has good mechanical strength. Manufacturers are now using epoxy resins instead of ceramic materials.
What is a relay?
The capsule is supplied with two end caps. The fuse component is attached to the end caps in the body. The whole setup is designed in such a way that it can withstand advanced high pressure in short circuit situations. Powdered quartz, which acts as an arc extinguishing agent, fills the space between the fuse material and the envelope.
Fuse element
Silver or copper is usually used as a fuse material due to its low specific resistance. The fuse components are usually held together in two or more sections by means of tin connections.
Tin has a low melting point of 2400 C which is 9 times lower than that of the sun (980o C). Therefore melting the tin joints prevents the fuse from achieving high temperatures in case of overload and short circuit.
Fusing process
In the event of an error, the current flowing through thefuse component exceeds its predetermined maximum value and the temperature ofthe fusing component increases and the results are as follows:
- Silver material melting (pre-arcing)
- Evaporation of elements (arcing)
- Combination of silver vapor and filling powder
- Arch extinction
Fuse action
Usually the fuse components are connected in the middle by a tin bridge. This tin bridge has a specific melting point of 230 oC. Once the temperature of the material rises above this temperature, the tin bridge begins to melt.
This creates a pressure between the molten ends of the fuse component. The temperature produced by the pressure is suddenly sufficient to melt the remaining fuse components. The silver vapor reacts with the filling of the quartz powder thus produced.
The chemical reaction between the silver vapor and the filling powder establishes a high resistance between the edges of the blown fuse components. Gradually, this high resistance changes into insulator and the current is cut off.
A transient voltage is created in the fuse at the instantaneous moment of the fuse current barrier. Temperature and internal pressure of the fuse increase to a higher value. HRC fuses are sometimes used as backup protection for circuit breakers.
The fuse and circuit breaker feature is integrated in such a way that all defects within the range of the circuit breaker are cleared by it, whereas those exceeding its range are cleared by the fuse.
Preferred ratings for HRC fuses are 2, 4, 6, 10, 16, 25, 30, 50, 63, 80, 100, 125, 160, 200, 250, 320, 400, 500, 630, 800, 1000, and 1250 amperes
High rupture ability HRC fuse
This type of fuse was made by General Electric. In the case of these fuses, the braking capacity is increased by using two or more separate silver components in parallel.
The sizes of the components are different so that the components are blended one after the other in sequence. The body is made of cylindrical ceramic material and is closed by metal edge caps where the fuse elements are fixed.
The fuse components are surrounded by silica, which acts as a means of purifying the arc. An indicator, usually a fine resistance wire, is connected in parallel to the fuse component.
In this type of fuse, the whole fault current is not driven instantly due to the use of multiple fuse components. This construction avoids voltage transfers in the circuit.
Advantages of HRC fuses
- HRC fuses of the same capacity are cheaper to compare with other circuit breakers.
- Simple and easy to install.
- No maintenance required.
- High braking capacity.
- They are consistent in performance.
- Their reverse time feature makes them suitable for overload protection.
- These are capable of clearing high and low currents.
- Quick operation.
- They are capable of high currents as well as low currents.
- During severe faults, the HRC fuse breaks the circuit before it reaches the peak current of the fault.
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