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May 18 (Reuters) -
* President of Brazilian energy market clearing CCEE says some electricity distributors are in default for "important values"
* He said, if nothing was done, problem would likely worsen
* Brazil's electric energy sector is showing signs of extreme stress and fragility, after two years of drought that depleted hydroelectric reservoirs was followed by ample rains this year and a sharp economic slowdown and drop in demand Source text for Eikon: Further company coverage: [ ] (Reporting by Reese Ewing)