The EU watchdog fined Swiss engineering group ABB 33.8 million euros and Japan's Toshiba Corp 13.2 million for taking part in a "gentlemen's agreement" not to compete against each other in Europe and Japan.
Germany's Siemens had its fine waived because it blew the whistle on the cartel. The Commission's investigation started with surprise inspections in February 2007.
"The Commission has now put an end to this rip-off by the self-appointed 'gentlemen'," European Union Competition Commissioner Neelie Kroes said in a statement. "The Commission will not hesitate to increase fines for repeat offenders until they have learned the lesson that cartels do not pay," Kroes said.
Power transformers are used to modify the voltage in electricity transmission networks. The fine for ABB was increased by 50% because it had previously taken part in a similar infringement, the Commission said.
The Commission imposed a joint total fine of 16.5 million euros on French firms Areva and Alstom. It fined Japan's Hitachi Ltd 2.4 million euros and Fuji Electric 1.7 million for their roles in the cartel.
Siemens said that since 2007, when allegations about the cartel were made, it had taken measures to prevent any such problems in the future.
"After the allegations were made in February 2007, Siemens immediately launched its own investigations and suspended the employees at Siemens' former Power Transmission and Distribution Group and an Austrian subsidiary who had been involved in the violations," it said in a statement.
The EU's move follows a 2007 crackdown an on energy-gear cartel which saw the Commission slap a record 750 million euro fine on a group of heavy power-gear suppliers, including Germany's Siemens AG (EurActiv 25/01/09).
(EurActiv with Reuters.)
