Keeping voltage balanced is important to the overall "health" of the electrical system. Voltage is the measurement of the force (pressure or electric potential) between two points that results in the movement of electrons from one atom to another. In the presence of an electric potential, free electrons move in a conductor by jumping from atom to atom. The transmission line (conductor) provides the path for the electrons to move from a point of high electric potential (generation) to lower electric potential (consumers). The movement is measured as the current.
There are two types of electric current, alternating and direct. In an alternating current, the point of high potential and low potential — the "poles" switch at an interval known as the frequency. Outlets in a standard home are alternating current. Under direct current, the poles do not change. Direct current transmission lines are used for carrying very high voltages over long distances. Batteries are direct current devices.
Distribution centers (substations) and transmission lines have an inherent resistance to electric flow that causes loss of voltage in the system. Generally, the longer the transmission line, the more losses. Electrical lines and equipment are also rated for maximum voltage carrying capacity, often limiting the amount of current the line can carry. If the load is too great and the voltage is too high, the breaker shuts off to protect the equipment. This is similar to "overloading" a circuit at home by using too many appliances. "Voltage support" refers to modifications on the system, either physical or through controls, to keep the system at a sufficient voltage to meet the load demands.
To meet consumers’ needs for power (keep current flowing on the line), the voltage of the line must be kept in balance. This can be done by building or upgrading transmission systems and facilities to carry more electricity to the load, increasing generation, managing the use of electricity (demand side management) or bringing generation to the load (distributed generation).