This document describes functions and working principles, specifies requirements, interfaces and test methods of uncontrolled rectifiers for DC electric traction systems. Uncontrolled rectifiers connect a 3AC power network with a DC electric traction system with an unidirectional power flow using diode assemblies. The coordination between the transformer and the rectifier diode assembly is included. This document applies to fixed installations of following electric traction systems: " Railway networks " metropolitan transport networks including metros, tramways, trolleybuses and fully automated transport systems, magnetic levitated transport systems, electric road systems.