Vacuum Circuit Breaker Sealed Pole

Vacuum interruption technology is the leading arc interruption technology in the medium voltage field today. Based on the advantages of reliability, availability, compactness and environmental friendliness of vacuum as an interruption medium, vacuum interruption as an arc extinguishing technology leads to continuous growth in market demand.
During the contact breaking process, the disconnected current will produce a metal vapor arc discharge. The current flows through the metal vapor plasma until the next current passes through zero. Near the zero crossing point, the arc is extinguished. The metal vapor loses its conductivity after a few microseconds – the insulating capacity of the contact gap is quickly restored. In order to maintain the metal vapor arc discharge, a specific minimum current is required. If this minimum current is not reached, it will be cut off before the natural current zero. To prevent impermissible switching overvoltages when switching inductive circuits, the cut-off current must be limited to the lowest possible value. Using special contact materials, the cut-off value in vacuum circuit breakers is only 2 to 3A. Due to the rapid recovery of the voltage in the contact gap, the arc can be safely extinguished even if the contacts become smaller before the current passes through zero. Therefore, the arc discharge time of the last breaking electrode is up to 15ms. Depending on the breaking current and the size of the circuit breaker, different contact geometries are used. Due to the longitudinal magnetic field, the arc remains diffuse even at high currents. The disc-shaped contact surface is eroded evenly, avoiding local melting. This results in very low arc voltages in the range of 20 to 200 V. As a result, the energy converted in the contact gap is very low due to the short arc duration. Due to the relatively low erosion, the arc extinguishing system is maintenance-free. In the static state, the pressure in the interrupter is very low, less than 10-9 bar, so that a high dielectric strength is achieved with only 6 to 20 mm inter-contact distances. In addition to circuit breakers, vacuum interrupter technology can also be used in contactors and switches. Today, more than 70% of all circuit breakers installed in medium voltage systems are based on vacuum interrupter technology.
Embedded Pole vacuum circuit breakers use the latest proven technology of automatic pressure gel (APG) to cast the vacuum interrupter and the connection terminals in epoxy resin. The vacuum interrupter is cast in epoxy resin without screws that would cause concentrated electric field concentration and reduce insulation strength. Thanks to the solid-sealed pole technology, the assembly of the pole is simplified, and the assembly accuracy and quality of the solid-sealed pole are easy to control through the latest production processes. The solid-sealed pole technology will also improve the environmental resistance of the circuit breaker, because the primary circuit of the circuit breaker is completely inside the epoxy resin, and the risk of insulation failure caused by harsh operating environments (such as dust, moisture, pests, polluted environments) and high-altitude applications is completely eliminated.
The key knowledge of the solid-sealed pole technology is the buffer layer between the epoxy resin and the ceramic shell of the vacuum interrupter. The material and process of the buffer layer are crucial to ensure the integrity of the epoxy resin of the solid-sealed pole and sufficient adhesion at every point in any other case. The use of LSR (liquid silicone rubber) buffer layer and double APG (automatic pressure gelatin) process in the production of the solid-sealed pole completely eliminates the cracking of the epoxy resin under rapid changes in ambient temperature due to the large difference in thermal expansion coefficients between epoxy resin and ceramic. The APG process of the LSR buffer layer ensures that there are no air gaps or bubbles between the buffer layer and the ceramic shell, thus ensuring high electrical insulation strength of the circuit breaker sealed pole. The partial discharge value of the embedded electrode manufactured by the LSR (Liquid Silicone Rubber) buffer layer and the double APG (Automatic Pressure Gelatin) process is less than 5pc at an applied test voltage of 1.2Um.