Because excitation winding short-circuit faults that occur in steam-turbine generator will lead to heavy financial losses, accurately detecting excitation winding short-circuits (EWS) can help power generation operations. It can allow them to take timely actions and shorten downtime as well as cut the costs of troubleshooting. This paper introduces a method for detecting EWS faults online using a new detection coil. Here, a large-dimension detection coil is installed inside the generator to span over an iron-core segment in the stator. The even or fractional harmonics induced by the detection coil are used to determine whether an EWS fault has happened, and the short circuit position can also be determined. This method can reveal short-circuit faults that occur in one turn of the excitation winding, and with obviously higher sensitivity.