A large number of existing industrial applications utilize a converter to transfer power from a three-phase source to a DC installation, or vice versa. This thesis presents a systematic approach for protecting a line commutated inverter and load in the event of a line disturbance induced converter fault. The overall problem of protection is classified in terms of a three part process. Firstly, a simplified means of characterizing the line voltages during a line voltage disturbance is determined. An experimental fault network power circuit is then developed for purposes of simulating a wide variety of possible fault situations. Secondly, methods of detecting a converter fault quickly and reliably are proposed. An optimal approach, based upon load considerations, is presented. A description and design thereof are presented. Thirdly, methods of removing post fault stored energy in the load and line are discussed. Four commutator configurations satisfying these requirements are described. Logic requirements and a functional description of the logic, for each commutator is subsequently presented. This is followed by a transient analysis for each commutator, utilizing simplifying assumptions regarding the load power switches and the characterization of the line as viewed from the DC side. The transient analysis for each commutator is experimentally verified. The results obtained from the transient analysis and experimental results are used to develop design equations and to establish a series of design requirements. Practical methods of sizing a non-ideal voltage clamp are determined. Design procedures for each commutator are developed based on the requirements and on the results obtained for sizing the non-ideal voltage clamp.

The procedures are illustrated by way of a 350 kW load shaving example. Finally a comparison of each commutator is made with reference to post fault peak load and line currents, post fault load and line time durations, commutator component ratings, and application suitability.