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Insulation sleeve
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Insulation sleeve

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Insulation tube is a kind of insulation material. It is a collective name. There are glass fiber insulation tube, PVC tube, heat-shrinkable tube and so on in electrical materials.

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Detailed introduction:

Insulation tube is a kind of insulation material. It is a collective name. There are glass fiber insulation tube, PVC tube, heat-shrinkable tube and so on in electrical materials.

Single insulating sleeve:

Insulated with pure porcelain or resin, often made of wall bushings for voltage levels of 35 kV and below. Its insulation is tubular, and the middle is clamped or glued to fix it on the perforated wall. The flange is generally gray cast iron. When the working current is greater than 1500 amps, non-magnetic materials are commonly used to reduce heat generation. The insulation structure of a single insulation sleeve is divided into two types: air cavity and air cavity short circuit. Air cavity bushings are used for voltage levels of 10 kV and below. An air cavity is provided between the conductor and the porcelain sleeve as auxiliary insulation. When the voltage level is high (20-30 kV), corona will occur inside the air cavity and the above-mentioned effect will be invalidated. At this time, the air cavity short circuit structure is adopted. The inner wall of the porcelain sleeve of this porcelain sleeve is coated with semiconductor glaze, and the spring cavity is connected with the conductor to short-circuit the air cavity to eliminate internal corona. However, corona and flicker may still occur near the flange. Usually, a large umbrella skirt is set on the surface of the ceramic sleeve on both sides near the flange, and a semi-conductive layer is coated near the flange to uniformly distribute the electric field and improve the discharge characteristics of the sleeve.

Composite insulating sleeve:

Oil or gas is used as the insulation medium, and it is generally made of transformer bushings or circuit breaker bushings, which are often used for voltage levels below 35 kV. The inner cavity between the conductor of the composite insulation sleeve and the porcelain sleeve is filled with transformer oil, which acts as a radial insulation. When the voltage exceeds 35 kV, the conductor is covered with an insulation tube or a cable to strengthen the insulation. There are two types of conductor structures for composite insulation sleeves: cable-through and guide-rod. The cable-through type uses the lead-out cable of the transformer to pass directly through the sleeve, which is convenient to install. When the working current is greater than 600 amps, it is difficult to install a cable-through structure, and a guide-rod structure is generally used. Capacitive bushing is composed of capacitor core, porcelain sleeve, metal accessory and conductor. Mainly used in extra high voltage transformers and circuit breakers. The upper part works in the atmosphere and the lower part works in a fuel tank. The capacitor core of the capacitive sleeve serves as internal insulation, and the porcelain sleeve serves as external insulation, which also protects the capacitor core. The electric field on the surface of the porcelain sleeve is uniformly distributed by the voltage equalization of the internal capacitor core, thereby improving the electrical insulation performance of the sleeve. Metal accessories include intermediate connection sleeves (flange), end caps, pressure equalizing balls, etc. The conductor is a cable or a rigid steel pipe.

Capacitive bushing insulation bushing:

When the capacitor core is made of adhesive tape, it has high mechanical strength, can be installed at any angle, has good moisture resistance, simple structure and maintenance, can be used without a casing, and can be turned into a short tail type to reduce its size. The disadvantage is that at high voltage levels, the requirements for the grade materials and processes are high, and it is not easy to eliminate the air gap in the heart, resulting in a low partial discharge voltage. Due to the problems of high dielectric loss and low partial discharge voltage, tape-type capacitor bushings have gradually been replaced by oil-paper-type capacitor bushings. The use of oil paper as the capacitor core generally requires a lower porcelain sleeve, the lower size is larger, more sensitive to moisture, and high sealing requirements; the advantage is that the insulating material and process are easy to solve, the dielectric loss is small, and the partial discharge performance is good. Since the 1970s, China has widely used 110-500 kV ultra-high pressure oil-paper capacitor bushings.

In the 1980s, China also developed a rubber-impregnated paper sleeve. The capacitor core was made of insulating paper rolls and then impregnated with synthetic resin under vacuum, and then heat-cured. Its performance has the advantages of both adhesive tape and oil-paper capacitive sleeve.