Home » BASIC FUNDA » DIELECTRIC STRENGTH, B-D VOLTAGE, SUPERPOSITION AND HOMOGENEITY

DIELECTRIC STRENGTH: This is the maximum potential difference of a unit thickness insulating material can withstand under ideal conditions without breaking down.
In insulators there are no free electrons for conducting electric current. But if we raise the potential difference applied to the material, then it breaks down and allows a heavy electric current which is much larger than usual leakage current, to flows through it.
Its unit is v/m and usually expressed as kv/mm. The dielectric strength is 5 kv/mm means 1 mm thickness of that material can withstand 5 kv or 5000 volts without breaking down.

BREAKDOWN VOLTAGE: The disruptive or breakdown voltage of an insulator is the minimum voltage to breakdown its dielectric strength.
Mica (500 kv/cm) used for motor winding and stator bars. Glass and porcelain (1000 kv/cm) used for high voltage transmission line insulator. Paraffin and naptha based oil used for transformer and circuit breakers.

SAFETY FACTOR OF A DIELECTRIC: The ratio between dielectric strength of the insulator and the electric field intensity is known as safety factor of a dielectric.
Ebd = Dielectric strength.
E = Field intensity.
Then K= Ebd/E k = Safety factor.
If Ebd = 5 X 105 v/m, and E = 5 x 104 v/m,
Then K = 10.

SUPERPOSITION AND HOMOGENEITY: If the net effect of the sum of causes equals to the sum of their individual effects, then we can say the circuit obeys the principle of superposition.
As per superposition,
f(x1 + x2)= f(x1) + f(x2)
AS per homogeneity,
f(αx) = αf(x).
If any element of a circuit follows the superposition and homogeneity, then it is called linear circuit.