Why Does a Straight 15mm Conductor Show Higher Inductance Than a 50mm or 300mm Loop?

When determining the (partial) inductance for a loop/loops of wire and comparing the results with the self inductance of the same length of straight wire, the straight wire has more inductance! This is counter intuitive. I am trying to determine how much effect curves have in a lightning conductor. Because of the high di/dt values in lightning, the inductance of the lightning protection system is a much more important factor than the resistance.Example: For 15mm diameter conductor.5omm loop, 40.3nH, straight equivalent, 95.3nH.300mm loop, 580nH, straight equivalent, 902nH.Two turns on a 300mm loop works out 2320nH and 2060nH equivalent straight, starting to give a coil more inductance than a straight conductor.

Just my pennies worth.It is not strictly true that it is only the inductance that must be considered. Equi potential bonding must be taken care of, high resistance in any part of such a system can result in lethal potentials being developed. Any loops in a conductor increase the possibilty of induced voltage, and hence flashover to adjacent circuits. The charge involved also causes heating effects, which can result in rupture of conductors. So there is more than just current rise time to consider.There is also skin effect, which must be factored into the design process.Re inductance, most calculators are approximations only, they are derived from a complex set of integral equations, and are only first order approximations. They are often corrected empericilly, which involves adjusting the equation based on real measured values, to try and get a best fit  over the widest range. This is further complicated by mutual inductance and skin effect. Additioanlly, test gear and measurement techniques usually fall over at the sort of values you are talking about. There is an interesting article hereCheers,Richard

The observation that a loop of wire has less inductance compared to an equivalent length of straight wire may seem counterintuitive, but it can be explained by the distribution of magnetic field lines around the conductor.
In a straight wire, the magnetic field lines produced by the current flow are concentrated within the immediate vicinity of the wire, resulting in a higher self-inductance. The magnetic field lines are more confined and contribute to a stronger magnetic coupling.
In contrast, in a loop of wire, the magnetic field lines generated by the current flow are more spread out, resulting in a weaker magnetic coupling between adjacent turns. This leads to a reduced self-inductance compared to the equivalent length of straight wire.
When calculating the inductance of a loop, it is important to consider the shape and size of the loop, the proximity of adjacent turns, and the distribution of the magnetic field lines. The inductance increases as the loop becomes larger, as more magnetic field lines pass through the loop.
In the case of lightning conductors, the inductance of the protection system becomes significant due to the high rate of change of current (di/dt) during a lightning strike. The inductance affects the behavior of the current flow and can help dissipate the high-energy transient. The resistance alone is not sufficient to handle the rapid change in current.
To accurately calculate the inductance of complex conductor shapes like lightning conductors, numerical methods such as finite element analysis (FEA) or circuit simulation software can be utilized. These methods take into account the geometry, thavatcalculator, material properties, and electromagnetic behavior to accurately determine the inductance and evaluate the system's performance in lightning protection.
In summary, the inductance of a loop of wire can be lower than the inductance of an equivalent length of straight wire due to the different distribution of magnetic field lines. Understanding and calculating the inductance of lightning protection systems accurately is crucial for their effectiveness in managing high di/dt events.