Fuses are often viewed as simple components, but they have a complex interplay of characteristic parameters and are subject to fascinating laws that govern their behavior. These discrete devices play a critical role in protecting electrical systems against overcurrents, and delving deeper into their fascinating world reveals their true complexity. Backup can permanently conduct at maximum current without breaking the circuit.

## Fuse properties and parameters

Fuses are important components in electrical systems. They provide important protection against overcurrents and ensure the safety and reliability of our devices and infrastructure. To choose the right fuse for a specific application, it is important to know the characteristic parameters of fuses.

### speed

The speed at which the fuse trips depends on the amount of current flowing through the circuit and the type of material the fuse is made of. The operating time of the fuse is not a fixed range, but decreases as the current increases. The operating time of fuses has different characteristics in relation to current fuses, being called fast or delayed depending on the response time to an overcurrent condition. Typically, a fuse takes twice its rated current to trip in 0.1 second, and a slotted fuse takes twice its rated current to trip in 10 seconds.

**Backup selection**may depend on load characteristics. Fast or ultrafast fuses are used in semiconductor devices because they heat up quickly when there is an overcurrent. Most fast-response electrical devices require faster-blow fuses because electrical machines can be seriously damaged by an overload current. These types of backups are used for general purposes. The slow blow fuse (delay fuse) is designed to allow current to pass through the fuse above the rated value for a short period of time without blowing the fuse. These fuses are used in motors that can draw higher rated currents for several seconds while reaching their rated speed.

### I2T Value

**I2T parameters**are provided in the manufacturer's technical data sheet table for each fuse. Backup coordination operations with upstream or downstream devices, I2T fusion and I2T extinction are indicated. I2T fusion corresponds to the energy required to fuse the fuse element. Clear I2T is proportional to the total power allowed by the backup when a fault is cleared. Power depends mainly on the current and time of the fuses and the available fault level and system voltage. Because the fuse's I2T rating is proportional to the energy it allows, it measures the thermal damage and magnetic forces that a fault produces.

### interrupt capacity

**breaking capacity**is the maximum current that can be safely interrupted by the fuse. In general, this should be higher than the expected short-circuit current.

**Miniature fuses**can have an interrupting rating of only ten times the rated current. Some fuses are marked HRC (High Rupture Capacity) and are regularly filled with sand or similar material. Fuses for small, low-voltage home wiring systems are typically rated for an interrupt of 10,000 A. Similarly, fuses for larger power systems have higher interrupt ratings, with some low-voltage current-limiting fuses rated at 30,000 amps. Circuit fault level total apparent power rates fuses for high voltage equipment up to 115,000 volts.

### rated voltage

### voltage drop

### Stress reduction

^{°}C can conduct up to 10 to 20% more electricity at 40 to 60 °C.

^{Ó}C and can open at 80% of its rated power at 100

^{Ó}C. Operating values vary depending on the fuse family and are specified in the manufacturer's technical sheets.

### Safety materials

## Security laws

^{2}R

^{2}ρ (l/a)

^{2}Ρl/πd

^{2}

^{2}/4

^{2}K

_{1}(l/d

^{2}) ——–>

**1**

_{1}is a constant. Heat loss ∝ Fuse wire surface ∝ πdl.

_{2}dl ———–>

**2**

^{2}K

_{1}(eu/d

^{2}) =k

_{2}dl

^{2}=Kd

^{3}

_{2}/K

_{1}

^{3/2}

^{1.5}

**.**

*the Security Act*## Magnetic circuit laws

It states that the laws governing the constant flow of electricity in a circuit can be easily changed. To be immediately applicable to the ** Magnetic Circuit** . Therefore

Magnetomotive driving force = flux x reluctance

F = ΦxS

Exactly corresponds to electromotive force = current x resistance

Reluctance = (Length/Area) x (1/Permeability)

= l/Aµ

For a magnet with a uniform cross-sectional area that exactly matches

Resistance = (Length/Area) x (1/Conductivity)

It is often convenient to calculate in unit dimensions. We then have

mmf per unit length = flux x reluctance per unit length

= (flow/area) x (l/permeability)

= flux density x (l/permeability)

Magnetic field intensity H = B/µ

This matches exactly,

For a material with uniformly distributed flow and length l, the total mmf is equal to the mmf per unit length xl

i.e. F=Hl or AT=Hl

By dealing with a **Magnetic Circuit** where the flux must pass through several parts in a matter of seconds, the methods used to deal with electrical circuits in series can be applied immediately, the total reluctance being the sum of the values of the various parts. Normally, the importance of reluctance is only significant to the extent that it allows determining the mmf necessary to produce a given flow in the circuit. It is often the easiest method to determine this total mmf value by adding together the mmf values needed to produce the change in the various parts of the circuit. This is equivalent to calculating the total voltage drop in an electrical circuit by adding the voltage drop values across multiple components.

Thus, the total value of the mmf around a complete magnetic field is given by

AT (or) F = ∫Hdl

Or if the circuit consists of several homogeneous parts, each of which has a uniform cross section and length _{1} L _{2,} etc.

total mmf F (or) AT = Σ Hl = H _{1} 1 _{1} +H _{2} I _{2} +….

= Φ (p _{1} +S _{2} +….)

If the values of the area and **permeability** of the different parts of the circuits are A _{1} μ _{1} etc. becomes all MMF

AT (or) F = (B _{1} /μ _{1} )i _{1} + (B _{2} /μ _{2} )i _{2} +…..

Where B _{1} =Φ/A _{1} etc.

Occasionally it is convenient to express the basic law of the magnetic circuit in form.

Flux = magnetomotive force x permeance

**Permeability** is nothing more than the reciprocal of **Reluctance to interact** for parallel paths, and total permeance is the sum of the values of the individual courses.

The main difference between electrical and magnetic calculations arises from the fact that the resistance of an electrical circuit does not directly depend on the value of the reluctance of a magnetic substance, but to a large extent on the value of the flux passing through it.