PR521 are self-supplied relays and ensure complete protection of the installation without auxiliary power supply. They are used as protection units for HD4/R - HD4/S and VD4/R - VD4/S medium voltage circuit breakers with rated voltage up to 24 kV. For these relays appropriate current sensors are provided, available in four rated current values covering all the circuit-breaker application fields. PR521 are available in two solutions:
- PR521 (50-51 protections)
- PR521 (50-51-51N protections)