how electron flow in circuite, when wavelenght is very long such as 5 kilometer?
Electrons in a circuit move very slowly (much, much more slowly than the speed of light \$c\$). The change in voltage along the line you refer to is due to electromagnetic waves propagation, i.e. varying EM fields that travel along (and around) the line. EM fields travel at a speed that depends on line geometry and on the materials with which is built or that are around it. The traveling EM fields' speed is the one comparable to \$c\$. To compute it exactly you need transmission-lines theory or Maxwell's equations.

Kirchhoff's laws are only an approximation of Maxwell's equations useful for lumped element circuits. They are valid under some assumptions, the most important of which is that the dimension of the circuit \$d\$ must be much less than the minimum wavelength of the EM fields present in the circuit. This is often stated as a requirement on the maximum frequency component of the signals in the circuit:

\[
d &lt;&lt; \lambda_{min} \approx \lambda_{0(min)} = \dfrac{c}{f_{max}}
\]

Here for simplicity I used the formula that relates the vacuum wavelength \$\lambda_{0}\$ of a plane wave with its frequency. To be strictly correct you should compute the relationship between \$\lambda_{min}\$ and \$f_{max}\$ for the fields in the specific circuit (which is usually an intractable problem, except for very regular geometries such as transmission lines and waveguides). That's usually not a problem because \$\lambda_{0(min)}\$ is usually not very far from the exact theoretical value \$\lambda_{min}\$ and if \$d\$ is sufficiently small everything is OK anyway.