In the paper described construction, work system and selected circuits: supply system, control and diagnostic system of the mine converter type NTP 54A 250/6/0,25DC. Control and diagnostic system cooperate with microprocessor controller. Converter NTP 54A 250/6/0,25DC have a modern compact construction. Converter construction contain a system of chambers separated apart with thermal isolation about the degree protection IP 54, the closed cooling system with the air inside chambers of the rectifier without external filters. In chambers "6kV" of the rectifier one used barriers of gas-the blast making possible relaxation of gases from the arched short-circuit inside chambers of the rectifier. The application of the rectifier NTP 54A 250/6/0,25DC in the supply system of the line-traction should cause the considerable improvement of the work safety, diminish the number of damages of line-motors by the improvement of the efficiency of getting down to work of protections of the rectifier. In the article one introduced example-algorithms of the control of the rectifier, and findings of laboratory and exploitive of the rectifier. Proposing solution of the system of the power supply of the line-traction makes possible the running inspection of exploitive parameters, and visualization and the diagnostics of states of the computer run supplied of the line-electric traction. The rectifier was tested in several mines of the pit-coal, and worked failure-freely through the period of 2 months in different operating conditions.