Short answers, pulled from the story.
Alternating current is an electric current that periodically reverses direction and changes its magnitude continuously with time. Direct current flows only in one direction. AC is the form in which electric power is delivered to homes and businesses worldwide.
The first alternator to produce alternating current was built by French instrument maker Hippolyte Pixii in 1832, based on principles established by Michael Faraday. The earliest recorded practical application was by Guillaume Duchenne, who in 1855 announced that AC was superior to direct current for electrotherapeutic triggering of muscle contractions.
AC voltage can be raised or lowered using a transformer, which allows power to be transmitted efficiently at very high voltages over long distances. Higher transmission voltage reduces energy lost as heat in the wires by reducing the current required. Direct current lacked an economically viable way to change voltage in the early days of power distribution.
The war of the currents was a public campaign launched in late 1887 by Thomas Edison, a proponent of direct current, who attempted to discredit alternating current as too dangerous. The campaign followed the rapid spread of Westinghouse and other AC systems across the United States after William Stanley's demonstration in Great Barrington in March 1886.
ZBD transformers were designed by Károly Zipernowsky, Ottó Bláthy, and Miksa Déri of the Ganz Works in Budapest, described in their 1885 patent applications. Their closed-core design with parallel-connected loads was 3.4 times more efficient than the open-core devices of Gaulard and Gibbs. This made it technically and economically feasible to provide electric lighting in homes, businesses, and public spaces.
The skin effect is the tendency of alternating current to flow toward the outer surface of a conductor rather than uniformly through its cross-section. At 60 Hz, the skin depth of copper is approximately 8.57 millimeters. This reduces the effective cross-sectional area carrying current, raising AC resistance above DC resistance and increasing energy losses to Ohmic heating.