Revisiting the Determination of Busway Impedance Using First Principles

An approach using a combination of well known circuit principles, is used to convert the impedance matrix - determined for three phase, single lamination/phase busway to industry specified ´average´ impedance values as specified by the National Electrical Manufacturers Association (NEMA). This paper details how this approach can be used to predict ´average´ busway impedance with reasonable accuracy, and therefore help to reduce the number of physical tests and related costs in the design process. Four cases are provided for validation purposes. The results show good correlation with published data. V phasor representation of voltage, volts, I phasor representation of current, f amperes frequency, Hertz omega angular frequency, radians/second R_i resistance of conductor i, ohms; i = 1,2,3 L_i self inductance of conductor i, Henry; i = 1,2,3 R_ij, M_ij mutual resistance and inductance of conductor i with respect to conductor j; ohms, Henry respectively; i = 1,2,3; j = 1,2,3 R_eq, L_eq equivalent resistance and inductance (including self/mutual inductance), for a single phase circuit; ohms, Henry respectively R_ieq, L_ieq per phase equivalent resistance and inductance, (including self/mutual inductance) for a three phase circuit, i = 1,2,3; ohms, Henry respectively L_m average inductance/phase, including self/mutual inductance, Henry R_m average resistance/phase, including inductive effects, ohms X_m average reactance/phase, including self/mutual inductance, ohms Rmeas per phase measured resistance, ohms Xmeas per phase measured reactance, ohms. All units are in SI unless otherwise specified.