WASHINGTON, Feb 10 (Reuters) - The United States on Friday set hefty preliminary anti-dumping duties on large power transformers made in its future free-trade partner South Korea and used in the electric utility industry.

U.S. Commerce Department officials estimated Hyosung Corporation and Hyundai Heavy Industries Co were selling the power transformers in the United States at prices 38.07 percent and 21.79 percent, respectively, below fair market value.

The department also set a preliminary anti-dumping duty of 29.93 percent on all other South Korean manufacturers of the devices.

Importers will be required to post a cash deposit or bond based on the preliminary rates.

The Commerce Department will announce its final duty calculations in July. The U.S. International Trade Commission has to give its approval for duties to take force and is expected to vote on the case by Aug. 16.

U.S. imports of the transformers from South Korea totaled $414.7 million in 2010, the Commerce Department said.

They are used to adjust voltage levels as electricity travels from the power plant where it is generated to the homes and businesses where it used.

ABB Inc, the U.S. division of Swiss engineering company ABB , joined Delta Star Inc and Pennsylvania Transformer Technologies Inc in filing the case.

The United States already has preliminary anti-dumping duties on refrigerator imports from South Korea, and on Friday approved an investigation that could lead to steep duties on washing machines from the long-time Asian ally.

Both of those cases were brought by Whirlpool against South Korean rivals Samsung Electronics and LG Electronics.

The U.S. Congress and the South Korean legislature approved a free-trade pact in 2011 to phase out most tariffs between the two countries, and officials from both countries are working to bring the deal into force.

The pact would still allow anti-dumping and countervailing duties to be imposed in cases where one side can prove to its domestic authorities that it has been hurt by unfair competition from the other.

Source: reuters.com