Abstract: A computer-implemented method of monitoring power lines of a polyphase power system. Data indicative of coefficients of a linear transformation is updated based on a deviation of a calibration vector from an estimate thereof. The linear transformation relates electric field or magnetic measurements around the power lines to the calibration vector corresponding to voltages or currents, respectively, in the power lines. The estimate is determined based on the data and the plurality of electric field or magnetic field measurements. The data indicative of the coefficients of the linear transformation is then used to estimate voltages or currents based on electric or magnetic field measurements to monitor the voltages or currents. A recalibration condition indicative of time, sensed environmental conditions, or user inputs may be used to achieve adaptive real-time monitoring. A system including a processor and computer-readable memory configured to cause the processor to carry-out the method.