Method for AC Powerline Impedance Measurement

Methods exist today to estimate the AC powerline impedance by taking into account the various components in the distribution system. These calculations are fraught with error due to inaccurate electrical documentation and a lack of information about the physical construction of the system. However, the accuracy of these results is critical because they feed into the calculation of available energy for establishing the degree of arc flash hazard present at a location. This paper presents a novel method for determining the AC powerline resistance and inductance through a process of measuring the real-time reaction of the line to the controlled application of two known impedances. This method has been realized and tested to accurately measure powerline impedances as high as 84 kA in 480-V motor control centers. The available energy can be calculated from this impedance to assist in the determination of the appropriate equipment necessary for arc flash protection.