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Auxiliary Relay :-
It is generally combiplex relay/ Contact multiplier of TRIPPING iNPUT. Say for a TG we are having different Relays, like Diffferential, O/C, E/F,NPS,OVER/UNDER Voltage/Frequency etc.... . In case of any fault in a system, Say O/C realy got acted, it will innitiate A closed loop Tripping Commands/ Feedback to Master Trip Relay, or to a Combiplex realy Or to a Contact Multiplies OR AUXILIARY RELAY.From their different Interlock different TRIP command/ Feedback will go to Different Interconnected Panels to Protect the TG & their auxiliaries.
Safety Relay :-
A safety Relay are like TG Control OIL Trip Solenoid Valve, or Mechanical-OVER-Speed Tripping Relay, Boiler-Safety-Vent-Valve, or EMERGENCY_STOP-VALVE.. etc ETC.... . All this are Electro-Mechanical Relay.All this having Trip-Solenoid ( Say Operating Voltage V/ V ac.dc) along with Mechanical Spring Operated Trippng Mechanism. Suppose TG control Oil pressure Reached LOW-LOW set point. Trip solenoid will pick-up at the same time due to low control Oil Pressure Mechanical-Spring_Operates. Results both Electrical & Mechanical Tripping. If your Electrical Tripping Fails Mechanical Trip is Healthy. So your Equipment is Safe. This is called Safety Relay.
But Auxiliary & Safety Relay are used for safeguard of our equipment, accoding to different purposes, different process......
Both are same, but due to application, we distinguish them.
Auxiliary are used to supplementary control/supply of signal.
Safety for securing our components.
Generally the main difference is that safety relays are "force guided", this ensures that in the event of the relay contacts welding together the operating mechanism will force them apart. A standard relay does not have this action and the contacts will remain welded together when de-energized. The certification associated with a safety relay is to ensure that this function meets safety standards. some manufacturers make safety contactor as well where the auxiliary contacts are force guided to be used for the feedback (diagnostic coverage). Safety Relays such as those used for e-stop and interlock evaluation have more complex features, a good book to understand all of this is the Pilz safety manual.
auxiliary relays are common relay types that isolate initiating signal from power sourcewhere safty relays have some more options and inputs/outputs and can have wide configuration - could be a good replacement for small PLC units as some are programmable .
Auxiliary relay is used to operate second equipment using its contacts where we have separate power source or voltage level etc.
wherever safety relay is used for safety purposes(shutdown or bypass) i.e it will disconnect or connect its I/O contacts when its safety relay will de-energized by some safety equipment (Level, pressure or temperature switch etc)
