Programmable testing equipment for power-system protective equipment

Present testing equipment does not enable the performance of protective equipment to be assessed over the wide range of conditions encountered on modern power systems. System behaviour may be determined by digital-computer studies or measurements made either on transient analysers or the actual networks. Thereafter it is desirable that the appropriate voltages and currents be regenerated in laboratories for use during the development of new protective equipment, or when assessing the suitability of established schemes for particular applications. The authors have developed equipment into which details of any desired aperiodic testing waveform can be fed, either in digital form on punched paper tapes, or in analogue form on magnetic tapes. Although the signals so derived may be amplified and fed to any voltage circuits associated with protective schemes, the apparent power demands made by current circuits under fault conditions may be so great, if current transformers are included, that the necessary amplifiers would be too large to be practical. An arrangement has been developed in which the correct currents are produced for feeding to the relay current circuits by including small model transformers that simulate the effects of the actual current transformers and enable the necessary allowances to be made. In this way the required power handling capability of each amplifier is much reduced. Details are given of the complete prototype equipment which has been produced, and test results are provided to illustrate its effectiveness.