SiC bonded disc の電圧-電流特性(計算)

抄録

Following the author's previous report on the electrical behaviour of silicon carbide single crystal contacts, the case of granular silicon carbide bonded discs is discussed.
These resistors are used as voltage limiters in many kinds of electrical equipment because of their non linear relation between current and voltage. Calculations of the typical characteristics are made for 100φ×25 mm and 150φ×20 mm lightning arresters and 15φ×0.56 mm and 15φ×0.89 mm varistors. In the treatment SiC grains is regarded as a sphere of radius r (0.035mm for arrester and 0.05 mm for varistor) with which the contact area is determined from the Hertz's formula as 1, 2 and 10^-2cm² for 100φ, 150φ and 15φ resistors respectively. In lightning arrester, the restriction voltages at 5000 A and 1500 A are important. According to the author's theory, these are given as follows: for 100φ×25 mm element
V_5000A=4400+470δ Volt
V_1500A=3700+429δ _??_,
and for 150φ×20mm element
V_5000A=3150+327δ _??_
V_1500A=2500+295δ _??_,
where δ(10^-7cm unit) is the thickness of the oxide film on SiC surface. For commercial resistors δ=2_??_4 must be used. For varistors, if we consider the effect due to carbon content amounting several percent, their Current-Voltage characteristics are satisfactorily interpreted.