in Upper Silesia region. It is quite common to use those locomotives in couples, with one of them pulling and the other pushing the train. In the years 1973-1980 PKP borrowed several items of 3E/1 locomotives and changed their designation to ET21 with adding additional 9 figure to serial number. Such locomotives were running for PKP for over two years. In exchange PKP sold in the 1980s 14 units of ET21 locomotives to the industry. Those locomotives remained named ET21 but additional 1 figure was added to serial number. Technical data ET21 is a Co-Co electric locomotive, suited for pulling freight trains weighing up to 2500 t. with top speed of 65 km/h or passenger trains with top speed of 100 km/h. Engines The locomotive is equipped with six LKb-635 (though some sources give LKa-635) engines which are mounted on the bogies with a tram system. The engines propel the axles with an 85:24 transmission. There are three ways of connecting the engines: series connection (all six engines in one series), series-parallel connection (three engines in one series - two groups) and parallel-series connection (two engines in one series - three groups).[9] Four-step reduction of engine excitation (up to 50%) is made by bypassing parts of main pole's windings with shunts and resistors. Shunts and resistors are in parallel connection with main pole's winding. Each engine has four steel main poles, isolated with varnish and four commutation poles made of one steel block. Bogies A Co′Co′ type of the locomotive means it is equipped with two bogies, each of them having three axles with separate propulsion for each wheel set. Bogies are coupled with each other. Box is supported on bogies with three slides. Middle slide supports it chassis in horizontal position during start and braking. Body The body and chassis are completely welded construction with crew compartments on both ends. It contains two machine compartments and one high voltage compartment. Moving between crew cabins is enabled by 570 mm wide corridor running along the box wall. machine compartments are reached through the doors in the back walls of crew compartments. Both crew compartments are equipped in exactly the same way. It includes switch board, hand-brake and electric cooker on the left-hand side, drive controller, direction controller and brakes valves on the right-hand side. Air manometers and Hasler type train event recorder are mounted in front of the engineer's place.