The $900 million Mica Unit 5 & 6 project is nearing an end after five years of construction work
It used to be a big hole in the ground.
When Mica Dam was built in the 1970s, they installed four turbines and left space for two more. That space essentially amounted to a 35-metre deep pit in the floor of the powerhouse. They built the frame and left the rest for later.
Over the past five years, the pit was filled in by a $900 million project that saw two new generators installed at the dam. Unit 5, as it is known, was activated last year. Unit 6 was put in place earlier this year and is expected to be up and running by the end of 2015.
I received a tour of the dam last week as a follow-up to a story written by my predecessor almost exactly five years ago, when the project was starting up. Graham Fenwick, the senior construction manager for BC Hydro, led the tour. I was joined by Carly Moran, BC Hydro’s community relations advisor.
Into the mountain
I drove to the dam Thursday morning as the sun slowly burned the morning fog out of the valley, opening up the dramatic mountain landscape. I traveled 130 kilometres up Highway 23 North, past Mica Village, across the Blue Bridge and up the dam access road.
It’s hard not to be impressed by the dam. It towers 240 metres above the river and was the tallest earth-filled dam in the world at the time of construction.
However, the most impressive aspect is the underground powerhouse structure, which is built into the side of a mountain. Unlike the concrete powerhouse at the Revelstoke Dam, where the penstocks are visible from the outside, in the Mica Dam, the penstocks were blasted into the mountain.
The entrance to the dam is a massive tunnel carved into the rock. It swallows you up and makes you feel very small. It gives the impression of entering the layer of a comic super-villain, or a top secret government bunker.
We went through security and walked down a series of tunnels and took an elevator up to the offices that overlook the dam where we met Fenwick. In the past the public could take tours of Mica, and many of the historic photos and displays still adorn the office walls. The projector they used to show films to visitors still sits in what is now the conference room. Fenwick recalled taking a tour of the dam when he was in highschool.
I was worried my request for a tour might be an imposition on a very busy person, but Fenwick, a soft-spoken engineer with 25 years experience working on major projects for BC Hydro, was eager to show us around.
He’s taken part in many major projects across the province and before moving up to Mica, he worked on installing Unit 5 at the Revelstoke Dam. For him, this project was fairly routine — well, as routine as you can get for a $900 million project that involves placing machines that weigh in excess of 1,000 tonnes inside mountains.
There were several elements to the Mica project. The first was installing new switchgear that converts the electricity generated by the turbines from 16 kilovolts to 500 kilovolts before it is transmitted to the power grid.
The switchgear is located some 180 metres above the powerhouse. The electricity is sent up in big, gas-insulated aluminum ducts. As part of the work, the switchgear for the first four units was replaced and the new switchgear for Units 5 and 6 was installed. We walked into the switchgear room. It was filled with control panels and a maze of big pipes. It was strangely silent considering the amount of equipment around us. We peered down into the diagonal tunnels that descended into the darkness below. Somewhere down there was the powerhouse — the next stop on the tour.
We entered the powerhouse at ground level. The ceilings towered above us and the far end of the room was more than 200 metres away. We walked past the first four turbines, which were covered in tarps to protect them during construction. Finally, we reached the space where Unit 5 sat.
“This was a big hole,” said Fenwick. “They built a frame, then left it open.”
Now, that frame was filled in with two new generating units.
There were five main steps to put the units in place, with Unit 5 going first. First, the draft tube was installed and embedded in concrete. Then the spiral case that houses the turbine was installed and embedded in concrete. Next, the turbine was lowered into place and installed. Finally, the generator was installed. The switchgear work happened alongside all this.
The fifth turbine was lowered into place in April 2014 and went into service later in the year after the rotor and generator were installed. The massive pit that existed was slowly filled with concrete and control equipment as the project proceeded. At its peak, 400 workers were on site.
Just getting the 136.7 tonne turbine to Mica was a yeoman effort. It was manufactured by Andritz in Germany and then transported 13,000 kilometres by ship and truck to Valemount, where it was transported on Downie Timber’s barge down Kinbasket Lake to Mica in March 2013. Unit 6 followed a year later.
Unit 5 was operational last winter, but it was pulled out of service in order to make some adjustments and improve its efficiency. The turbines and their accompanying rotors and generators were custom made for the project, and last winter acted as a test run of sorts to see if there were any issues that needed to be addressed, explained Fenwick. It will go back online in November.
Our next stop was Unit 6, which was in the process of being tested before it enters service. They start by testing each component by itself. Then they’ll test them all together. Then they add water to the mix. If all goes well, Unit 6 will be running this winter.
We descended a series of staircases past the components. Each unit contains several parts. At the bottom is the turbine. This is where the water comes in from the penstocks. At the top is the generator, which produces the electricity. Connecting them is the shaft. Each piece of equipment is massive and required extreme precision to install. We descended five levels to a space where you could look up at the turbine; the entrance to the space was cordoned off with security tape to prevent people from entering while testing was ongoing. The area was a hive of activity as workers strived to get the equipment online.
We passed by Unit 4, which was active, on our way out. It emitted a loud rumble as it spun rapidly, sending power out to thousands of homes and businesses across the province.
After, we went back to the top of the dam and I got to ask Fenwick a few questions about the project in general. For the most part, it went smoothly but there was one thing I wanted to know about: What was going through his mind when they had to stop the crane while the 1,000-tonne rotor for Unit 5 was being lowered into place?
“That was a bit nerve-wracking, that’s for sure,” Fenwick said when I asked him about it.
What happened is while they were lowering the rotor, they heard a loud bang. They stopped the crane immediately to find out what happened. “The big thing is you don’t know what the issue is,” he said.
A bracket was installed on the crane to reinforce it while the massive equipment was suspended in mid-air and inspected. What they think happened is the shaft rubbed against its housing. “”It welded two metals together,” said Fenwick. “When we went to lower the rotor, it broke the weld and went bang.”
With the rotor hanging and the crane stopped, crews worked to make the gear box slightly bigger and added some grease. They then lowered into place without issue.
“In the end didn’t turn out to be much,” Fenwick said. “We could have lowered it and it would have been fine, but it was the bang and not knowing. If you don’t know you have to stop and investigate, but in hindsight we could have lowered it.”
The project team received a plaque from BC Hydro for their work successfully addressing the issue.
The Mica project is slowly winding down. There’s 160 workers on site, down from about 400 at the peak. Other than the incident with the rotor, the project has gone smoothly. Each unit will add 500 megawatts of capacity to the BC Hydro electric grid, bringing the total capacity of Mica Dam to 2,805 MW.
BC Hydro’s biggest project now is Site C on the Peace River. They are also in the planning stages to install the sixth and final unit inside the Revelstoke Dam.