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The basic theory and principle of operation of a new method of phase comparison for use in distance protection schemes is outlined. It is shown that the angular limits of comparison between signal pairs are determined by the setting of time-delay circuits, and that the new device is extremely variable. Comparator circuitry based on transistor logic is described in detail, and the effect of setting errors is analysed. The output from the device progresses from a short-duration pulse at the threshold to one of fixed duration, and the implications of such a response with regard to the overall performance are established. An introduction to generalised multi-input comparators is given, which, unlike conventional multisignal techniques, can be adjusted to give dissimilar limits of comparison between each signal pair.