Systems and methods according to these exemplary embodiments provide for methods and systems related to optical current sensors used to monitor standby power transformers, specifically fiber optical current and voltage sensors and, more particularly, to applications involving filters for use in such sensors, such as frequency tracking comb filters. According to one embodiment, a method for monitoring a connection condition of a stand by power transformer includes the steps of measuring a current flowing through a high voltage side of the standby power transformer using at least one optical current sensor disposed proximate to a current flow path of the high voltage side, using a comb filter to filter the measured current, determining whether the filtered, measured current is less than a predetermined threshold value; and generating an alarm indication that the high voltage side of the standby power transformer is unconnected.