Grid Conductor Size Calculation
Overview
The grid conductor calculation tool based on IEEE Std 80 is used for determining the minimum conductor size based on the short time temperature rise.
Conductor material
Commonly used earth grid conductor materials are included in this dropdown and the material constants from IEEE Std 80-2013 (see the table below) are utilised for the calculations.
Symmetrical RMS current magnitude
This is the magnitude of the maximum fault current expected to flow in the conductor (this is often assumed to the total available fault current), with no dc offset included. The effect of the dc offset is introduced by specifying the Decrement factor.
Maximum fault duration
Enter the maximum fault duration, in seconds.
Ambient temperature
This is the ambient temperature of the soil. It must be specified in degrees Celsius.
Maximum allowable temperature
This is the allowable temperature limit: it can be the fusing temperature of the conductor or a limit based on the type of connections made between conductors or a limit imposed by the presence of nearby flammable materials. If Fusing temperature is selected then the fusing temperature will be obtained for the Conductor material specified. If Other is selected then the temperature limit must be specified, even if it is higher than the fusing temperature.
Decrement factor
Specifies the multiplicative constant by which the symmetrical RMS fault current magnitude must be increased in order to obtain an equivalent RMS current magnitude which accounts for the dc component of the fault current waveform. This DC component is zero when the fault is initiated at the point in the sinusoidal current cycle where the current amplitude is zero; the DC component is a maximum when the fault is initiated at the peak current value.
The overall DC component is negligible when the fault duration is long (e.g., 0.5 to 1.0 s or more) or when the X/R ratio at the fault location is less than 5.
Specify a value of 1 for no DC offset. Otherwise, enter a User-specified or compute from the X/R ratio and the system operating frequency. The X/R ratio is the ratio of the reactive component of the system sub-transient fault impedance to its resistive component.
Results
The minimum conductor sizes in mm2, in2 or kcmil and corresponding diameter in mm or in are displayed. When you press Update then the conductor material and calculated minimum size will be transferred to Design Settings for the main calculations.