This project investigates aspects of microprocessor based control and protection schemes for high voltage direct current convertors. To enable this investigation to be carried out, a multiple microprocessor HVDC development system has been assembled. This provides the necessary hardware resources, as well as providing the software development facilities necessary for the implementation of real time control and protection tasks. In order to assess and optimise the performance of the various control and protection systems, considerable interactive monitoring facilities are provided as part of the HVDC development system's software. The development system is used to implement real time control of a small scale convertor model. It is also used to implement a new form of convertor fault detection, which is in turn used as the basis for an implementation of convertor fault development control techniques for the first time on an operating convertor. The operation of the fault development control scheme is examined in some detail, and results are presented showing its operation over a wide variety of fault types and system conditions.