Electric Field Intensity Between Concentric Cylinders

The electric field intensity, or its opposite the voltage gradient, is of great importance in the operation of high-voltage single-conductor cable. If the electric field intensity or voltage gradient is excessive the life of the cable is shortened. In fact, a high enough electric field intensity may cause the dielectric to puncture almost instantaneously. The expression for the electric field intensity at a distance x from the center is obtained from Eqs. 2-34, 2-35, and 2-36 and is as follows

[2-38]

If x is in meters, then the electric field intensity is in volts per meter; if x is in some other unit, E is the volts per that unit of distance. r₁ is the lowest value of x that has practical significance. This means that the maximum electric field intensity occurs at the surface of the inner conductor. The minimum electric field intensity occurs at the inner surface of the outer conductor, and we have

[2-39]