how to check phase sequence of transformer?

To check the phase sequence of a transformer, you can use a phase sequence indicator or a multimeter. First, ensure the transformer is de-energized for safety. Connect the phase sequence indicator to the primary side terminals. The device will indicate the phase sequence as either clockwise (ABC) or counterclockwise (ACB). Alternatively, measure the voltage between phases using a multimeter; the phase sequence can be inferred from the voltage readings and their phase relationships. Always follow safety protocols when working with electrical equipment.