Darren's Diaries for Water Power

Diary 3 - Thursday 19 June 2008

Field Trip Name: Water Power Field Trip Place: Waitaki Diary number of total: 3 of 4 Weather: Chilly start to a sunny day Where's Darren: Waitaki Hydro Scheme

Hi everyone, Darren here.

The plan for today was to get up close to something few people get Fog over Benmore Dam. to see....no, not a great spotted kiwi in its burrow but a hydro Image: Heurisko Ltd generator operating at full speed! Did we make it? Read on to find out.

A cold start to the day when we arrived at a foggy Benmore Hydro Station this morning. We met up with Paul and Ben again and had a brief meeting to discuss our plans for the day. The aim was to try and get close to the generating equipment while it was operating. This is not easy to do because at hydro stations the generators and turbines are under the floor of the machine halls and are therefore difficult to get to safely. Paul explained that we couldn't access the generators at Benmore but then he came up with a cunning plan....

Fifteen minutes drive downstream from Benmore is Waitaki Hydro Inside the machine hall at the Waitaki Hydro Station. The tops of the generating units stick Station. This was the first hydro station to be built on the Waitaki up through the floor. Image: Heurisko Ltd River, starting operation in 1935. The layout of the machine hall gives far better access to the generators so we jumped into the car and set off in search of a wild generator.

Waitaki Hydro Station is an impressive sight. The machine hall has long thin windows similar to church windows and the dam curves beautifully across the . Take a look at the panorama images. Into the machine hall we went. The generating units stick up out of the floor but the part you see is just the tip of the iceberg. The blue top section contains a DC generator. This provides the current for the electromagnets in the rotor of the main AC generator just below the floor. This main AC generator produces the electrical energy to be transmitted by the national grid. A shaft connects the Up close to the generators at Waitaki Hydro main generator to the turbine spinning below. Benmore has Francis Station. Image: Heurisko Ltd turbines, Waitaki has a mixture of Francis and Kaplan turbines - the two types are different shapes designed to make use of different water flows. Ben explains the set-up in a video and we also took a panorama image of a model of the set-up at the end of the day.

Standing on the floor of the machine hall we could feel the vibrations caused by the spinning generators below. We went down a set of stairs so that we could see the rotor of a main generator in operation. Wearing full safety gear, including hearing protection we were able to stand below a rotor as it whizzed round at 125rpm. As well as being noisy it was very windy as the spinning rotor pulled air towards it. This was the moment we had been waiting for, right up Paul, Ben, Darren and Webster inside the close to an operating generator...quite an emotional experience for tunnels at Waitaki Hydro Station. those with a love of physics. Watch the video ! Image: Heurisko Ltd

It was still only 10.30am. Could the day get any more exciting.....oh yes. Ben pointed out a door at the far end of the machine hall and asked us if we wanted to see what was on the other side. Indeed we did. He grabbed a torch and through the door we went. Webster almost passed out with excitement. We found ourselves in a tunnel that ran the length of the dam wall. We were actually inside the dam wall! The tunnel

Page 1 of 3 was put in to allow internal inspections of the dam wall for things such as leaks.

All too soon we returned to the machine hall and spotted a few spare wicket gates leaning up against a wall. Remember, these wicket gates surround the turbines and can be adjusted to change the water flow through them. Hydro stations clearly look after their wickets better than the Black Caps. They seem to just give theirs away.

Our two audioconferences were fast approaching and we had decided to do them from a most special room - the old control room Wicket gates. Image: Heurisko Ltd at the Waitaki Hydro Station. Up we went in an old fashioned lift. We were joined by Dale who had helped out yesterday answering questions during audioconferences. The room was like something from a science fiction movie with dials and big switches everywhere. Nowadays all the hydro stations in the Waitaki Hydro Scheme are controlled remotely from but they were originally controlled on site. It was great fun throwing switches pretending to turn the power on and off. The only upsetting thing was the clash of our yellow overalls and the orange carpet. Great questions from Gleniti School and Rangiora High School today. Well done!

Between the Waitaki and Benmore Hydro Stations sits Aviemore Hydro Station. We headed there after lunch for two reasons. Firstly The old control room at Waitaki Hydro Station. to see the dam wall itself. Benmore has a solid earth dam, Waitaki a Image: Heurisko Ltd concrete one, and Aviemore has a dam wall that combines both types. The second reason for the visit was to learn about fish. Dams can affect the breeding of fish by preventing them swimming upstream to their breeding grounds. There are a number of ways of solving this problem - fish ladders and pipes, relocating fish and spawning races. Paul explained in a video how fish species are helped at Aviemore Hydro Station.

Like the fish we continued our journey upstream and back to Benmore Hydro Station. Once the electrical energy has been produced by the generators it needs to be fed into the national grid.

This is done through the switchyard. Benmore has two switchyards, The weir dam at Waitaki Hydro Station. one feeding alternating current into the 's grid, the Image: Heurisko Ltd other sends direct current to the North Island via the HVDC (High Voltage Direct Current) link. Why use DC and not AC? As Ben explained to us there are a number of reasons. Firstly over a long transmission line there are lower power losses with DC compared with AC as no eddy currents are created in the line. Also thinner diameter lines can be used because DC flows through the entire cross section of the line, AC flows only around the outer edges of the lines - it is called the "skin effect". In addition using DC to link the North and South Island grids means that they do not need to be synchronised. The DC can be converted back to AC when it arrives at Haywards substation near Wellington.

A number of students have wanted to know where the biggest hydro They think of everything. Image: Heurisko Ltd station in the world can be found. Well, it is in China and is called the Three Gorges Dam. It will be fully operational by 2011 and the statistics are mind blowing. You have already seen how big Benmore is but the Three Gorges Dam makes it look like a toy. Each generator at the Three Gorges Dam produces 700MW (the entire Benmore Hydro station produces 540MW). Guess what, there are 32 of these generators at this Chinese hydro station. The dam covers 1045km 2 compared with the 75km 2 of . The dam wall is 2.3km long, Benmore Dam's wall is 870m. That's one big hydro station. Thanks to the student who posted a question about this on the Web Board .

The spawning race at Aviemore Hydro Station. Page 2 of 3 It was a great day today. Tomorrrow we head to Twizel to see the Image: Heurisko Ltd control centre and have an appointment at Ohau with a big transformer.

Today's competition clues:

1. I am a type of water turbine.

2. I am named after the person who developed me.

3. There are six of me at Benmore Hydro Station.

The competition prize is a fantastic Power House DIY kit for your The DC switchyard at Benmore Hydro Station, class courtesy of Meridian. Remember you will also need the clues the southern end of the HVDC. from Wednesday and Friday. Image: Heurisko Ltd

See you in the morning.

Darren (and Webster )

Top The LEARNZ programme is provided by Heurisko Ltd Level 2, Spark House, 5 Durham St, Box 8577, Riccarton, 8440, New Zealand. Ph: +64 3 353-7360, Fax: +64 3 366-5488, NZ Teachers' FreePhone: 0800 CALL LEARNZ or 0800 22 55 53 [email protected] © Crown Copyright 2007

LEARNZ . . . virtually there

Page 3 of 3