1. A method of avoiding inadvertent protective tripping as a result of measurement errors within a protection system for an HVDC transmission installation, the method which comprises: detecting state variables of components of the HVDC transmission installation with first instruments, to acquire a first measured value set, and with further instruments, which are redundant with respect to the first instruments, to acquire further measured value sets; supplying the first measured value set and the further measured value sets to a protection unit, and checking the first measured value set with an internal logic of the protection unit for a presence of any risk of protective tripping; if a risk of protective tripping is found to be present, checking one of the further measured value sets for a presence of switching conditions and, if switching conditions are present, switching over to the further measured value set and checking the further measured value set for the presence of a risk of protective tripping.