Introduction:
In medium transmission lines, the charging current flowing to earth refers to the current that flows between the conductors and the earth due to the capacitance between the conductors and the ground. This charging current is influenced by the capacitance of the transmission line and the voltage applied.

Explanation:
1. Charging Current:
- When a transmission line is energized, a voltage is applied across its conductors. This voltage creates an electric field between the conductors and the ground, leading to the formation of capacitance.
- The capacitance between the conductors and the ground allows a small amount of current to flow, known as the charging current. This current flows to or from the earth depending on the phase relationship between the voltage and the ground.

2. Magnitude of Charging Current:
- The magnitude of the charging current depends on the capacitance of the transmission line and the voltage applied.
- In medium transmission lines, the capacitance per unit length is relatively low compared to long transmission lines, resulting in a lower charging current.
- The charging current is also influenced by the line voltage. Higher voltages result in higher charging currents, while lower voltages result in lower charging currents.

3. Very High Charging Current:
- Very high charging currents typically occur in long transmission lines, where the capacitance per unit length is relatively high.
- In such cases, the charging current can be significant and may require compensation or grounding measures to control it.

4. Negligible Charging Current:
- Negligible charging currents occur in short transmission lines or when the conductor-to-ground capacitance is very low.
- In these scenarios, the charging current is so small that it can be considered insignificant and can be neglected.

Conclusion:
In medium transmission lines, the value of the charging current flowing to earth is considered medium. This is because the capacitance per unit length is relatively lower compared to long transmission lines, resulting in a lower charging current. Additionally, the voltage applied also influences the magnitude of the charging current.