How to select auxiliary relays for isolation applications
Nuria Calvo Cuadra, Ricardo Calister, Santiago Rementeria · CIRED - Open Access Proceedings Journal · 2017
For a guarantee of durability and reliability in the manoeuvre, the breaking capacity that the contacts must support, and number of operations or manoeuvres required are fundamental parameters to select equipment. The breaking capacity is a critical parameter within the design and application of the auxiliary relay, (Tripping signal, Multiplication of signals, Current amplification, Signal for Opening/Closing/Blocking manoeuvre). The galvanic isolators' life is considerably reduced depending on the load, the number of operations and the environmental conditions such as temperature, vibrations and altitude. In addition, external effects to the relay, which are typical of the system, must be taken into account, as short-term peak current, capacitances that can appear in the circuits by the long distances of own cables, included the variations accused of voltage caused by external power supplies. The use of an auxiliary contactor of C range with magnetic blow-out system (through the polarisation of the Normally Open contact) is focused on applications where there are high requirement in manoeuvre operations number and highly inductive currents, reducing the number of relays to be installed (it would not be necessary to use relays in series of the “R” range) and thus increasing the reliability of the system.