What primarily causes a low power factor in underground systems?

A low power factor in underground systems is primarily caused by capacitive loads of the conductor. In underground distribution systems, the capacitance of the cables can lead to a situation where the reactive power, which is power that does no useful work, is substantial. This reactive power causes the current to be out of phase with the voltage, resulting in a lower power factor.

Capacitive loads contribute to this because they store energy in the electric field and can cause the current to lead the voltage in phase angle, contributing to the power factor being less than one. This becomes particularly significant in long runs of underground cables, where the effects of capacitance can be exaggerated.

Other factors, such as excessive voltage, resistance of the soil, and short circuiting, do affect system performance but do not primarily cause a low power factor. Excessive voltage can lead to insulation failures and safety issues, soil resistance affects grounding and losses but does not directly relate to power factor, and short circuiting is a fault condition rather than a normal operational characteristic contributing to power factor. Therefore, capacitive loads of the conductor stand out as the main reason for a low power factor in underground systems.