From a Single 500 kV Alarm to a Deeper Design Question During commissioning on a 500 kV transmission project in 2024, a disturbance recorder captured something protection engineers never ignore: at the exact moment a test block handle was pulled quickly, the CT secondary circuit showed a transient open-circuit condition and raised an alarm. The team did what any good commissioning crew would do: Check wiring Check terminal torque Check device contact resistance The surprise c

One Loose Screw, One “Near Miss” – What Really Happened During commissioning of a protection scheme, an engineer completed relay calibration and started to restore the circuits. Everything looked normal—until one phase current value refused to match expectation. Further investigation revealed the cause: one CT secondary terminal screw had not been fully tightened , leaving that phase’s CT secondary circuit effectively open. The current circuit was abnormal, and the situatio