5.1 Introduction

The impedance of a Busbar System comprises three components:

In a DC circuit, the steady-state current will be proportional to the applied voltage and depends only upon the resistance. Inductance and capacitance also play a part in transient conditions when switching on and off a circuit. In an AC circuit, the steady-state current will be proportional to the applied voltage and depends upon resistance, inductive reactance, and capacitive reactance. Inductive reactance is proportional to the frequency while the capacitive reactance is inversely proportional to the frequency. Resistance is frequency-dependent These three parameters are most crucial in the design of the Busbar Systems as they quantify and help in keeping the constraints imposed by the specification on temperature rise, power loss, and voltage drop or a selected combination of the three. The discussions in this chapter will be limited to Busbar Systems with Copper and Aluminium conductors, installed in DC and AC Systems, at 50 Hz and 60 Hz.

5.2 Resistance

Resistance is a measure of the opposition of the flow of current in a conductor when a DC voltage is applied across its ends. (If an AC voltage is applied across the ends of a conductor, opposition to the flow of current is offered not only by the resistance but also by inductive & capacitive reactance).

5.2.1 Formulae

Resistivity is a specific property of the conductor material and it increases with the increases in temperature. It is governed by the equation:

ρ_T2= ρ_T1 {1+ β_T1T2 (T₂ – T₁)}

ρ_T1 Resistivity at temperature T1 ρ_T2 Resistivity at temperature T2

β_T1T2 Temperature co-efficient of resistivity for the temperature range of T1 to T2

The value of β_T itself varies with the temperature (T ℃), as given by the relationship