Fusing Current

Fusing Current refers at which the fuse is designed to melt and disconnect the circuit.  Wiring rules specify the fusing current for different circuits.  It is also known as minimum fusing current.  

Fusing Factor
The Fusing Factor is the ratio of the rated current and the fusing current

Therefore,
Fusing Current = Fusing Factor x Rated Current

The fusing current will always be more than the rated current.  Thus, the fusing factor will always be greater than one.  

Polarization in Dielectrics

‘Polarization’, denoted by ‘P’ is defined as the difference between the induced electric field ‘D’ and imposed electric field ‘E’ within a dielectric medium due to immovable and free charge carriers respectively.

This phenomena occurs if an electric field distortion takes place between negatively charged electrons around positively charged atomic nuclei giving rise to slight difference of charges.

Mathematically, it is stated as-

P = (D-E)/4π

Polarization can also be expressed in terms of electric susceptibility Х_e, such as,

P = є₀ Х_e E

Where, є₀ = permittivity of free space, (= 8.85 x 10^-12 Farad/metre).

Quantitatively, it is denoted by-

P = p/V

Where, p =amount of dipole moment

  V = volume of polarized material

Susceptance

The term ‘Susceptance’ (symbolized as ‘B’) refers to the measurement of ease of dynamic effects of permitting the flow of charge or current to polarization. It is the imaginary part of admittance(vector quantity). Susceptance is a scalar quantity and is measured in siemens or S.

It was termed as permittance due to its property by Oliver Heaviside in June, 1887.

The susceptance may be negative or positive depending upon the inductive or capacitive circuitry respectively. However, the magnetic circuits are inductive an electric circuits are capacitive in this case.

The counter part of it is conductance (symbolized as ‘G’). Mathematical expression will be as understated:-

Y= G + jB siemens 

Erosion in Boilers

Erosion is caused when material in components is removed due to the collision of particles and gases at high velocity.  Erosion due to fly ash can damage the boiler tubes. 

In boilers, erosion can be caused by coal as well as by fly ash.  When fly ash and coal particles hit piping at high velocities, material is removed. 

Erosion can be minimized by choosing coal with lower fly ash content.  Reducing the velocity of the gases by effective flow modification techniques such as the use of baffles, perforated plates and metallic screens can also help reduce erosion. 

Coal Erosion
Coal erosion is caused when unburnt particles of coal hit the boiler tubes.  This can be controlled by reducing the velocity of the coal air mixture and designing the direction such that complete combustion occurs before the particle hits the tubes.

http://www.powermag.com/fly-ash-erosion-control-and-prevention/