Understanding the Accuracy Class of Current Transformers (Protection Class)
Current transformers and voltage transformers are extensively used in power system to scale down the operating current and voltage. The scaling down of the current and voltage is required chiefly for measuring, metering and protection purposes. The relays and other measuring instrument operates and tolerates much lower values of current and voltage for their safe operation. In terms of usage, CTs are broadly classified as Protection CT or Metering CT. This article shall focus on Protection Class Current Transformers. It is imperative here to mention the instrument transformers (CTs & VTs) may have multiple cores, in which case separate cores may be used for metering and protection purposes, all in one instrument transformer. Multi Core CTs and VTs may have different designated class for each core. Before dwelling into explaining accuracy class of Current Transformers let us first outline the following terms: Accuracy Limit Factor At the time of fault, heavy current...