(Adds comments from Ramos in paragraph 5, union president in paragraph 14)
NEW YORK, Nov 17 (Reuters) - The head of Puerto Rico's indebted utility has resigned following criticism of the slow restoration of power to the island after Hurricane Maria, the U.S. territory's governor said.
Ricardo Ramos, who was named head of the Puerto Rico Electric Power Authority (PREPA) in 2016, was also criticized over controversial contracts. His resignation was effective Friday, Governor Ricardo Rossello said in a statement, but no replacement was named.
PREPA's board will meet later on Friday to discuss who will succeed Ramos, who was appointed by Rossello.
Maria knocked out power to all 3.4 million residents of Puerto Rico in late September, and only about half the island has been restored. The island has also experienced intermittent power interruptions to populated areas that had seen electricity restored over the past few weeks.
In a webcast update on restoration efforts, Ramos said that 50.5 percent of generation had been restored as of Friday, and additional lines have been repaired that have not yet been charged to provide electricity.
"The highest peak of generation that we have had is 50 percent. In this week, we had about three general blackouts in the island that kept San Juan in the dark for most of the week. That is totally unacceptable," said Tomas Torres, executive director of the nonprofit Institute for Competitiveness and Sustainable Economy for Puerto Rico.
It took a week before PREPA was able to assess the damages from the storm, which knocked out about 80 percent of its transmission capabilities.
Ramos was criticized for signing a $300 million contract with a little-known Montana company, Whitefish Energy Holdings, to restore power, and because he did not request aid from U.S. utilities that is a normal procedure following storms.
A week after the storm, the Federal Emergency Management Agency put the U.S. Army Corps of Engineers in charge of restoring power, which is usually the responsibility of the local utility. The Corps has been working with several utilities, including PREPA.
On Oct. 31, the governor said early efforts had fallen short and finally turned to U.S. utilities for assistance, asking for hundreds of crews and vast fleets of trucks to repair the grid.
Transmission lines weaving through the mountainous center of the island were cut off by the hurricane, which hammered the island with winds up to 155 mph (250 kph) when it made landfall on Sept. 20.
PREPA has been hampered by years of underinvestment and frequent turnover in management, and inefficient collections that forced it to go deeply into debt. The utility had incurred about $9 billion in debt before declaring bankruptcy in July.
Regulators, including U.S. Congressional committees and the island's energy commission, are investigating PREPA's response and the contracts it awarded to Whitefish, along with a $200 million deal with Cobra Acquisitions, a subsidiary of Mammoth Energy Services.
"There are qualified people at PREPA to serve as director, if they take the political component out of it," said Ángel Figueroa Jaramillo, president of UTIER, the union representing PREPA's workers. Complexities of Puerto Rico's grid make it difficult for an outsider to take on the role, but anything is possible, he said.
Representatives from the island's energy commission were not immediately available for comment.
(Reporting By Nick Brown and Jessica Resnick Ault in New York; editing by Grant McCool and Marguerita Choy)