History A large testing hall construction was done in two phases. After concreting of a fi rst part a builder‘s staging was moved on railway lines to a second building part. A large testing hall construction was done in two phases. After concreting of a fi rst part a builder‘s staging was moved on railway lines to a second building part. Large testing hall – Originally a three-phase 400 kV line was connected two three wall bushings allowing the testing of three-phases systems. Small testing hall – An unique 250 kV test transformer with an air insulation system manufactured by company Fischer - Koln is situated in the small testing hall. The 250 kV test trasnformer was manufactured in 1932 and for the fi rst time used even before the Second World War at the fi rst high voltage testing laboratory in Prague and it is still in operation. Cascade transformers are used for the high voltage power frequency testing. A former cascade trasnformer set comprised three 750 kV transformer units, i.e. producing an output voltage of 3× 750 kV. Control and measuring devices met the highest at that day technical standards. A railway line build up within a large testing hall allowed testing of railway vehicles as well as large power transformers for nuclear power stations. A railway line build up within a large testing hall allowed testing of railway vehicles as well as large power transformers for nuclear power stations. Outdoor testing site - That testing area allowed to test large test objects at full test voltages without restrictions of laboratory indoor clearances. A power frequency voltage was supplied by means of a high voltage wall bushing Micafil. An impulse generator 7 MV manufactured by TuR Dresden. A building crane helped to simulate real test confi guration by lifting and hanging them up. Fast atmospheric impulses wave shapes were recorded by means of Polaroid cameras taking photos of oscilloscope screens. A military vehicle resistance test to nuclear electromagnetic pulses (EMP) generated through a nuclear explosion. A large spark produced by a 7 MV outdoor impulse generator manufactured by TuR Dresden. The dielectric testing of a 400 kV GIS disconnector. The atmospheric impulse testing simulating a lightning strike to an aircraft wing. A special Partial Discharge (PD) detector VYZER invented by Mr. Kocis. On-site testing using an impulse generator 750 kV during a building stage of a pumped storage hydro power plant Dlouhe Strane in Jeseniky. An Impulse current generator 200 kA. A cascade transformer set was moved to an outdoor test site in the 80s to provide the testing of insulation of planned 750 kV transmission grid. Fortunately that project was never realized. A large sphere gap was used in the past for impulse voltages measurements. Sphere gap diameter - 1500 mm.