BS IEC/IEEE 61869-21:2025 PDF

1 Scope This part of IEC 61869 provides the requirements, the methods and the guidelines to be applied on the evaluation of uncertainty in testing the accuracy of instrument transformers (IT) with an analogue or a digital secondary signal for measuring, protection and control purposes, with rated frequencies from 15 Hz to 400 Hz. This document covers the uncertainty evaluation in testing the accuracy of IT (including on-site testing of accuracy) independently of the technology used (either inductive or non-inductive). This document reports on how to take into account the sources of uncertainty in the setups for accuracy and how to combine their effects in order to evaluate the uncertainty in the test results. Metrological traceability to the International System of Units (SI) will always be assumed for both reference devices and devices under test.