Arrangement having a power converter - which has at least one phase module (15, 24, 31), an AC voltage connection, a first DC voltage connection and a second DC voltage connection, wherein a first phase module branch is formed between the AC voltage connection and the first DC voltage connection, wherein a second phase module branch is formed between the AC voltage connection and the second DC voltage connection, wherein - the arrangement has a gas supply device, characterized in that - each phase module branch has at least two submodules (1_1, 1_2, 1_3, 2_1, 2_2, 2_3), wherein - the submodules (1_1, 1_2, 1_3) of the first phase module branch are surrounded by a first housing which is filled with a gaseous substance, and - the submodules (2_1, 2_2, 2_3) of the second phase module branch are surrounded by a second housing which is filled with the gaseous substance, - the gaseous substance has those gases which are included in air, wherein the concentrations of at least two of these gases of the gaseous substance differ from the concentrations of the respective gases in air, with the result that the dielectric strength of the gaseous substance is increased, wherein the gaseous substance has nitrogen and carbon dioxide, wherein the nitrogen concentration and the carbon dioxide concentration are increased in comparison with the respective nitrogen and carbon dioxide concentration in air, - the gas supply device has one or more gas stores, and the gas supply device is configured to deliver gas stored in this gas store to the interior of the housings (35, 37), and - the arrangement has a controller which is configured to keep the concentrations of constituent parts of the gaseous substance at a respective preselected value as long as the power converter is operating. - which has at least one phase module (15, 24, 31), an AC voltage connection, a first DC voltage connection and a second DC voltage connection, wherein a first phase module branch is formed between the AC voltage connection and the first DC voltage connection, wherein a second phase module branch is formed between the AC voltage connection and the second DC voltage connection, wherein - the arrangement has a gas supply device, characterized in that - each phase module branch has at least two submodules (1_1, 1_2, 1_3, 2_1, 2_2, 2_3), wherein - the submodules (1_1, 1_2, 1_3) of the first phase module branch are surrounded by a first housing which is filled with a gaseous substance, and - the submodules (2_1, 2_2, 2_3) of the second phase module branch are surrounded by a second housing which is filled with the gaseous substance, - the gaseous substance has those gases which are included in air, wherein the concentrations of at least two of these gases of the gaseous substance differ from the concentrations of the respective gases in air, with the result that the dielectric strength of the gaseous substance is increased, wherein the gaseous substance has nitrogen and carbon dioxide, wherein the nitrogen concentration and the carbon dioxide concentration are increased in comparison with the respective nitrogen and carbon dioxide concentration in air, - the gas supply device has one or more gas stores, and the gas supply device is configured to deliver gas stored in this gas store to the interior of the housings (35, 37), and - the arrangement has a controller which is configured to keep the concentrations of constituent parts of the gaseous substance at a respective preselected value as long as the power converter is operating.