Technical Analysis of Thermal Shrinkage Material before Its Application in Insulation Protection of Substation

- Mar 22, 2019-

With the continuous development of industry and the increasingly serious environmental pollution, the requirement of insulation protection for substations is constantly increasing, especially for old substations. In fact, pollution flashover, condensation flashover, ice tripping, short circuit of small animals and bare bus discharge accidents occur from time to time in substations. Therefore, it is of great significance to select and use high-quality insulation materials for the safe operation of power systems.

Before making insulation protection for substations, we should first analyze the technical parameters of variable thermal shrinkage insulation materials.

1. Types of heat-shrinkable materials

Thermal shrinkage materials used in substations include MPG, FJRD, insulating shield, cable terminal and climbing distance increaser.

MPG is used for insulation protection of bus bar in substation with excellent insulation performance and good process characteristics.

FJRD is a composite thermal shrinkable insulating cladding tape. Its structure consists of thermal shrinkable layer and adhesive layer of low melting point polymer. When heated, the outer layer shrinks and the inner layer melts, so that the insulated charged body can be sealed and insulated. It is used in old substations where the phase spacing is insufficient, pollution flashover and icing are serious, and insulation treatment is not easy to implement. Insulation protection boxes are used for insulation protection at joints, as well as special contact protection such as disconnectors and oil circuit breakers on cabinets.

Cable terminal has superior performance, easy installation and no need for special equipment and technology. It is widely used in power system and becomes the latest development direction of power cable accessories.

The climbing distance expander is used to solve the pollution flashover problem caused by the improvement of the pollution grade. Generally speaking, these problems can be solved by shrinking the umbrella skirt of corresponding size on the original post insulator or ceramic bottle.

2. Technical performance

(1) The thermal shrinkable material used in bus bar of substation will not affect the temperature rise of bus bar.

The temperature rise experiment of 1000A thermal shrinkable material used in switch cabinet in a research institute has proved that the temperature rise is not affected by the same temperature measurement point when the bus bar is coated with thermal shrinkable material (MPG and FJRD). In this regard, ABB, GE, Siemens and Westinghouse Electric have all provided us with the most convincing examples of practical application technology in the application of thermal shrinkable materials. Therefore, the insulation protection of thermal shrinkable material on substation bus will not affect its temperature rise, and will not reduce the bus's carrying capacity.

(2) Technical parameters of thermal shrinkable materials

The breakdown strength, power frequency voltage withstanding, lightning impulse and dynamic thermal stability parameters of thermal shrinkable materials used in substations are shown in Table 1.

Table 1 Technical parameters of thermal shrinkable materials for Substation

MaterialBreakdown Strength
kv/mm
Power Frequency Voltage Resistance
(kv)
Standard Lightning Impulse
(kv)
Dynamic and Thermal Stabilized Current
(kA)
FJRD3842/1min75dynamic steady current 31.5
MPG27-3842/1min75thermally stable current 80.0

(3) Flame Retardant Properties of Thermal Shrinkable Materials

In the power system, flame retardant materials are required for indoor insulation. The thermal shrinkable material used for substation insulation protection is mainly rubber-plastic blended polymer. The flame retardant with excellent performance is added. The oxygen index of the thermal shrinkable material is 32, which has good self-extinguishing property. It can meet the flame retardant requirements of power system.

(4) Aging Resistance of Thermal Shrinkable Materials

Power supply equipment in power system needs long-term operation reliability. Therefore, radiation cross-linked thermal shrinkable materials have been widely used in foreign power systems because of their superior performance over other materials. As we know, from the point of view of heat shrinkage principle, heat shrinkage property and microscopic essence, the cross-linking structure originated from the internal network. It is for this reason that the aging resistance of heat shrinkable materials is superior to that of other insulating materials. Accelerated aging experiments show that the thermal aging life of the materials can reach 20 years, and the polyolefin thermal shrinkage materials used in artificial satellites have been in normal operation for 21 years.

(5) Temperature Resistance of Thermal Shrinkage Materials for Substations

Because of its special micro-nature, the performance of thermal shrinkable materials has not changed greatly after 158 (+2 C) and 168 h thermal aging experiments (for special series of thermal shrinkable materials for substation). Generally speaking, the maximum operating temperature of substation bus is 70 C. Therefore, the special thermal shrinkage material for substation can meet the requirements of substation operation on its temperature resistance.