Online locating of voltage sag sources requires fast and accurate methods. In this context, this paper describes and compares the positive-sequence phasor-based (PB) and instantaneous-based (IB) methods during both transient and steady-state periods of voltage sags caused by grid faults and transformer energizing (TE). The methods are evaluated by applying 1992 voltage sags in a Brazilian power network. For fault cases, PB methods work better than IB. Some methods perform well within the transient period, and some do not work good enough and need improvements for online applications. For TE cases, IB methods are ahead of PB and most IB methods work very well in a half-cycle window of the transient period, whereas the PB methods must be improved. Regardless of the sag sources, the real current component method using IB values during the half-cycle window of transient period is the best method currently available, which can be used in online applications.