Significant increase of the dielectric performance of plastic sealed telecom relays

Initialized by Bellcore, the dielectric requirements on telecom relays have been significantly increased in recent years. In parallel the dimensions of the relays had to become smaller and smaller in order to save space on printed circuit boards in electronic equipment. By filling plastic sealed relays with the electro-negative gas sulfur-hexafluoride (SF₆), the dielectric withstand voltage of the relays was increased by a factor of 2 compared to that with a normal gasfilling with nitrogen. This method allows one to guarantee a lightning impulse withstand voltage of more than 3500 V between coil and contacts and more than 2500 V between open contacts without increasing distances in the design of the relay. The consequences of a SF₆ -filling on the life endurance of a relay were investigated extensively. The results show that the switching range of SF₆ filled relays could even be extended compared to relays with a N₂ -filling. The gas tightness of the relay housing is sufficient to guarantee an SF₆ loss of less than 10% during a lifetime of more than 25 years even under severe climatic conditions. The effects on the environment of using SF₆ in telecom relays turn out to be not significant at all