How Do You Calculate Fault Resistance For Phase And Earth Faults In A 400Kv Double Circuit For REL670 & 7SA522?
Fault resistance has been described as a ‘theological’ issue – God only knows what it is. Seriously, fault resistance is a function of a lot of factors, many of which are variable and almost impossible to predict accurately. A traditional approach is to start with an assumption of the voltage in the arc. One commonly used assumption is that the arc voltage will be 550 volts per foot of arc length in instances where the fault current is 1000 amperes or greater. The arc length is the phase-to-phase conductor spacing for phase faults, or the phase-ground spacing for earth faults. However, it is also known that wind can lengthen the arc. Some people simply double the actual physical phase-to-phase or phase-to-ground spacings to account for this extension, while others calculate a length from this formula: Length = 3vt + L where v is the wind velocity in miles/hour, t is the time in seconds after inception of the arc, and L is the initial length (the physical spacing). In instances where th
