Investigation and performance evaluation of differential protection of phase-shifted transformers in an MV drive

A digital solution to current differential protection of non-standard phase-shifted transformers in an MV drive application is introduced. The protection decision is made by applying the angle compensation algorithm developed, percentage restraint differential protection algorithm in conjunction with wave shape identification algorithm so that the internal faults of the transformers can be not only timely reported but also robustly discriminated from inrush conditions. The solution takes into account the potential influence on the protection decision from the distortion of sampled primary and secondary currents of the transformers due to the saturation of current transformers or/and the limitation of ADC conversion range. The “combo” solution is validated by the presented simulation carried out on a full MV model.