Design Of Molds For Cold-shrink Cable Accessories

Outdoor and indoor terminals and intermediate connections involve a series of issues related to restoring the cable structure and electric field.  Comprehensive factors such as conductor shielding, main insulation, insulation shielding, stress control, and creepage distance of rain sheds should be considered.  Furthermore, the molding process of different materials and structures is important; single-stage molding can reduce interlayer gaps compared to two or three-stage molding, thus greatly improving product operating quality.
(1) The design of creepage distance and installation distance between Cold Shrink Cable Accessories phases shall refer to the national regulations on pollution level 1 for external insulation of high-voltage power equipment.

For different pollution levels, at the same voltage level, the higher the pollution level, the longer the creepage distance. The insulation length of cable terminals and intermediate connections should be determined by the surface leakage distance and have a certain insulation margin. Indoor and outdoor terminals and intermediate insulation should be designed separately. For harsher outdoor environmental conditions, the maximum allowable surface stress is 200V/mm [3]: The surface distance between the live terminal and the grounding part is calculated based on the ratio for both indoor and outdoor terminals and intermediate connections; in addition, when the cable terminal is installed at an altitude above 1000 meters, due to the decrease in air pressure, the gas dielectric strength decreases, and the length of the terminal must be increased. For every 300 meters increase in altitude, the length should be increased by 3%; the intermediate connection insulation length is generally designed according to the minimum nominal creepage distance classification, 20% to 50% lower than the lowest level value. Both indoor and outdoor terminals are designed with rain sheds, which can increase the surface discharge path, and may also retain some dry areas during outdoor rain; 10kV indoor terminals are designed with 3 rain sheds, and outdoor terminals are designed with 5 rain sheds. (2) Mold Materials
The mold should be made of hard metal materials, taking into account the flow rate of the rubber, injection pressure, and friction coefficient. The mold life should be at least 500,000 cycles. Key points in mold manufacturing: ① Runner: Semi-circular, diameter 1.5–3.2 mm, depth 1.28 mm; ② Injection gate: Circular or conical, diameter 0.75–2.05 mm, depth 1.28–2.55 mm; ③ Venting: Width 1.55–3.2 mm, depth 0.0051–0.0128 mm; ④ Electrical discharge machining (EDM) is helpful for product demolding.