Other approaches to improved reliability include development
of dielectric polymers or copolymers for which the crystallite
melting temperature is well above the operating temperature. This
would ease the development of accessories, resulting in improved
accessory reliability, as well as reduce the interaction of thermal
expansion with conducting particulate contamination. Finally,
more care can be given to the conductivity as a function of temperature.
The activation energy can range from about 0.5 eV to
well above 1 eV. However, the field-dependent conductivity is
anti-correlated with the temperature-dependent conductivity.
Thus, reducing the activation energy to reduce the temperature
dependence of the conductivity would increase the field dependence
of the conductivity, and transmission class XLPE cables
operate at maximum fields beyond the range where conductivity
is independent of field. Thus, any optimization of the dielectric
in this context must balance the temperature dependence and field
dependence to increase the space charge limited field at the normal
operating field and maximum operating temperature.