Excellent Characteristics Of Insulating Sleeving Manufactured by ZTELEC GROUP
A single insulating casing is insulated with pure porcelain or resin and is often made into a wall casing for 35,000 volts and below voltage levels. Its insulating parts are tubular, central card or rubber flange to be fixed on the perforated wall. Generally, the flange is gray cast iron, when the working current is greater than 1500, the insulating casing is often non-magnetic to reduce heat. The insulating structure of single insulated casing is divided into two types: air cavity and air cavity short circuit. The air chamber casing is used for 10,000 volts and the following voltage grades, and the air chamber between the conductor and the porcelain sleeve is an auxiliary insulation, which can reduce the casing capacitance and increase the corona voltage and the sliding lightning pressure of the casing.
When the voltage level is higher ($number kv), the cavity inside the air chamber will be corona and the above effect is ineffective, then the air cavity short circuit structure is adopted. The inner wall of the porcelain sleeve is coated with a semiconductor glaze, and a spring sheet and a conductor are connected to make the air cavity short-circuit to eliminate the corona. Corona and slippage may still occur near the flange. Usually a large umbrella skirt is arranged on the surface of the porcelain sleeve near the flange, and a half conductive layer is applied near the flange to distribute the electric field evenly and to improve the discharge characteristic of the casing.