A current transformer (CT) is a fundamental device used in power systems and industrial automation for measurement, protection, and control. CT polarity defines the directional relationship between the primary and secondary currents. If the polarity is incorrect, it can lead to reversed measurements, inaccurate fault current calculations, and even malfunction of protection systems such as relay misoperation or failure to trip. Because of this, verifying CT polarity is a critical step during installation and commissioning. In the following sections, we will introduce two reliable methods to test CT polarity: a simple DC method for quick field verification and a professional tester approach for more accurate and efficient testing.

