Classification of wire casing tube:
Wire casing tube, among the electrical materials, there are fiberglass wire casing, PVC sheath, heat shrinkable casing, etc., all belong to a kind of insulation casing. Generally speaking, the wire casing can be divided into a single wire casing , Composite wire sheath, capacitive wire sheath, stainless steel sheath.
1. Single wire sheath:
Use non-magnetic materials to reduce heat generation. The insulation structure of a single wire sheath is divided into two types: air cavity and air cavity short circuit. The air cavity bushing is used for voltage levels of 10 kV and below. There is an air cavity between the conductor and the porcelain sleeve as auxiliary insulation, which can reduce the bushing capacitance and increase the corona voltage and sliding voltage of the bushing. When the voltage level is higher (20-30 kV), corona will occur inside the air cavity and the above effects will be invalid. At this time, the air cavity short-circuit structure is adopted. The inner wall of the porcelain sleeve of the porcelain sleeve is coated with semiconductor glaze, and the spring sheet is connected with the conductor to make the air cavity short-circuit, so as to eliminate the internal corona.
2. Composite wire sheath:
Oil or gas is used as the insulating medium, generally made into 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 wire sheath 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 insulating tube or cable to strengthen the insulation. The conductor structure of the composite wire sheath has two types: cable type and guide rod type. The cable-through type uses the lead-out cable of the transformer to directly pass through the bushing, which is convenient for installation. When the working current is greater than 600A, the installation of the cable-through structure is difficult, and the guide-rod structure is generally adopted.
3. Capacitive wire sheath:
It is composed of capacitor core, porcelain sleeve, metal accessories and conductor. When the capacitor core of the capacitor wire sheath is made of adhesive tape, it has high mechanical strength, can be installed at any angle, has good moisture resistance, and is simple in structure and maintenance. It does not need to be piped, and the bottom of the core can be turned into a short tail type. , Reduce its size. The disadvantage is that at high voltage levels, the requirements for insulating materials and processes are high, and it is difficult to eliminate the air gap in the heart, resulting in low partial discharge voltage.
4. Stainless steel sheath:
The stainless steel jacket tube is made of 304 stainless steel or 301 stainless steel. It is used as a wire and cable protection tube for wires, cables, and automation instrument signals. The specifications are from 3mm to 150mm. The ultra-small diameter stainless steel sheath (inner diameter 3mm-25mm) is mainly used for the protection of the sensing circuit of the precision optical ruler and the protection of the industrial sensor circuit. It has good flexibility, corrosion resistance, high temperature resistance, abrasion resistance, and tensile resistance.