Simple, Low Cost, Method for Measuring Single Phase Line Impedance

Line impedance (sometimes referred to as line stiffness) and its associated voltage sag is a common key noise parameter that consumer electronics and industry engineers must consider in product design. This parameter can have significant interactions with the power input stages of equipment or appliances, such as the performance of EMI filters and the sensitivity of protection devices. These effects can vary widely by location and construction of industrial, commercial, and residential power systems and in some cases exhibit high variation within a single location. Unfortunately, line impedance has been historically difficult to measure and characterize as it is distributed along the length of each feed from the source. This paper describes an innovative technique to determine line impedance by loading the system to generate a large impulse current which produces a significant voltage sag without the need for intricate switching logic and circuitry. This method will be validated empirically on a 120V residential electrical system and compared to LTspice simulation results to confirm accuracy.