The application of transistors to phase-comparison carrier protection

The paper shows the potentialities of the junction transistor when applied to phase-comparison carrier protection, and the flexibility of transistor circuits for the effective performance of a number of different relaying functions. High-frequency high-power transistors, which are now available, make it possible to obtain the required level of carrier output power. The paper also deals with the general aspects of a phase-comparison carrier system of protection, some appraisal being necessary because of the speed of operation and general performance of the equipment described. The most important of these aspects are the choice of the relaying quantities, and the effect of load current on the phase representing quantity, with its consequent effect on the minimum possible settings for earth faults. A sequence network is also described which produces all the relaying quantities simultaneously, using only three main current transformers. This sequence network has two important advantages: first, it does not impose any limitations on the relaying impedance, and secondly, means are provided for very easy variation of the proportions of the combined positive- and negative-sequence component output. The effect on the relaying system of a d.c. transient component in the fault current is analysed; a filter network is used to eliminate the d.c. transient and harmonic components, thereby producing uniform performance under differing fault conditions. Two successive equipments have been built and tested under steadystate and transient conditions. The transient test results of the final equipment are given. Since the transistor is a temperature-sensitive device, exhaustive temperature tests have been carried out, and the results are summarized.