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AC vs. DC and a slice of family lore

Paul Kando

Kálmán Kandó, inventor, railway electrification pioneer and grand uncle/ role model of mine, died 90 years ago this month. A contemporary of Nikola Tesla, another progressive denizen of the Austro-Hungarian monarchy, Kálmán earned a mechanical engineering degree from Budapest’s Technical University in 1892. After military service in Vienna, he worked in France, designing motors for railway locomotives as a junior engineer for the Fives-Lille Company. In his first year there, he developed a completely new design-calculation method for the production of alternating current (AC) traction motors and was appointed chief engineer.

Kando Kalman Stamp
photo credit: Magyar Posta

Why AC? Ohm’s law states that electric current is directly proportional to voltage and inversely proportional to resistance. At higher voltages, the same power can be transmitted at much lower current, meaning less power lost due to resistance in the wires. However, in the late 1800s, direct current (DC) voltage could not be easily raised or lowered. Indeed, Thomas Edison proposed a system of small, local power plants within 1 mile of the end user to power individual neighborhoods, making power distribution in rural areas near-impossible.

Then Pittsburgh industrialist George Westinghouse, working to perfect an AC distribution system, purchased Tesla's patents for AC motors and transmission. Transformers provided an inexpensive method to step up AC voltage to several thousand volts and back down to usable levels, so large power plants could be located many miles away and service a greater number of people and buildings. For long distance railways too, AC promised to be much more practical and economical.

In 1894 the managing director of Hungary’s Ganz and Co. — which in 1886 electrified Rome, Italy, with AC — invited Kálmán to return to Budapest. At Ganz Works, under Kálmán’s leadership, work began on a three-phase AC system for railways, based on which the Italian Ferrovia della Valtellina was electrified in 1902, making it Europe's first electrified main line railway. As part of that project, Kálmán invented the “kandó triangle,” a multi-wheel driving gear for electric locomotives.

The Valtellina line used 3,000 volt three-phase power via two overhead lines, the running rails supplying the third phase. At switches, the two overhead lines had to cross, preventing the use of much higher voltages — a severe limitation. Even so, in 1907, the Italian government decided to electrify another 2000-kilometers of rail line, insisting on manufacturing all the equipment in Italy.

So, Kálmán moved his family to Vado Ligure, where Società Italiana Westinghouse bought his patents and put him in charge of developing new Kandó-type engines, paying a license-fee to Ganz for each electric motor produced. Italy honored Kálmán’s work with the Commendatore dell'Ordine della Corona d'Italia in 1915. Alas, that year Italy also entered World War I, declaring war on Austro-Hungary, and forcing Kálmán to flee via Switzerland back to Budapest.

In 1916-1917, Kálmán, a reserve lieutenant, served at the Ministry of Defense in Vienna. There he worked out a system of locomotives powered by the standard, single-phase AC of the national electric grid, At war’s end he returned to Ganz, becoming its managing director. He invented a synchronous rotary phase converter, consisting of two independent windings sharing a common stator and rotor. The outer winding created a single-phase synchronous motor that took power from the overhead catenary. The inner winding formed a three-phase synchronous generator powering the three-phase traction motors. A major benefit of this arrangement was the high power factor of the catenary-connected equipment, fulfilling the electric grid’s strict load-distribution requirements, while isolating the poorer-performing pre-2nd World War electric motors from the overhead wire.

The phase converter enabled electric locomotives to use three-phase motors supplied via a single overhead wire carrying the standard single- phase AC of national power grids. Semiconductors had not yet been invented, so the Kandó locomotives had to rely on electromechanics and, for speed control, electrochemistry.

Kálmán died three years before the electrification of Hungary’s first main line was completed. He never saw his “kando engines” in commercial operation. Many modern electric trains work on his three-phase high voltage AC principle. However, his rotary converter and resistance-based speed controls have been replaced by semiconductor devices. In addition to secondary schools, a university, and countless streets and squares bearing his name, the minor planet “126245 Kandókálmán” is also named after him.

His strong suit was not just his knowledge but his “outside the box”, beyond-conventional thinking. He could have spent his time and energy on improving the external combustion engine of the ever-faster steam locomotives of his day. Instead he focused on better solutions to problems long considered solved. I can think of several such problems today. They all invite me to follow Kálmán Kandó’s inspiration.