The power spent establishing and maintaining the AC electrical field on distribution and transmission lines, even when there is no load, is typically referred to as charging power or capacitive charging losses. In technical terms, this is related to the reactive power required to charge the capacitance of the transmission and distribution lines.

Key Concepts:

1. Line Capacitance:

   • Transmission and distribution lines inherently have capacitance between the conductors and the ground (or between conductors in multi-phase systems). This capacitance needs to be "charged" with every cycle of the AC voltage.
   • In an AC system, this leads to a current flow even without any active power being consumed by loads. The current is out of phase with the voltage, representing reactive power rather than real power.

2. Charging Power:

   • The process of continuously charging and discharging the line capacitance each AC cycle requires reactive power. This is called the charging current, and it is proportional to the length of the transmission line and the voltage level.
   • Reactive power doesn't do useful work (like lighting a bulb), but it is essential to maintaining the AC electrical field. In large grids, significant reactive power can be needed to maintain the voltage levels across long transmission distances, even when no active loads are connected.

3. Reactive Power and VARs (Volt-Ampere Reactive):

   • The power used to charge the line capacitance is measured in VARs (Volt-Ampere Reactive), which is a unit of reactive power. It doesn't contribute to the net energy flow but is necessary to maintain the voltage and electric field in the system.
   • Generators or other sources (like synchronous condensers or capacitor banks) must supply this reactive power to maintain voltage stability and keep the electrical field established on the lines.

4. Effects on the Grid:

   • In long transmission lines (such as in large grids), the reactive power required for line charging can be quite significant, especially at high voltage levels. This leads to voltage rise along the length of the line (called the Ferranti effect) if no compensation is used.
   • In smaller grids (like microgrids), the effect is smaller but still present, especially for higher voltage distribution lines. Compensation devices (like capacitor banks or reactive power compensation units) are sometimes needed to manage the charging current and voltage stability.

Why It's Important:

• Although it doesn't represent real energy loss in the sense of heating wires (like resistive losses), capacitive charging losses are important because they influence grid stability, voltage regulation, and reactive power management.
• If left unmanaged, excessive reactive power demand for line charging can reduce the available capacity for real power, cause voltage instability, and force the system to work harder to maintain proper voltage levels.

In summary, the power spent in establishing and maintaining the AC electrical field on the distribution and transmission lines is called charging power or capacitive charging losses, and it is a form of reactive power.