Maraetai Power Station facts for kids
Quick facts for kids Maraetai Power Station |
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 Location of Maraetai Power Station in New Zealand
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| Country | New Zealand |
| Location | near Mangakino, Waikato |
| Coordinates | 38°21′9″S 175°44′38″E / 38.35250°S 175.74389°E |
| Status | Operational |
| Construction began | 1946 |
| Opening date | September 1953 |
| Owner(s) | Mercury Energy |
| Dam and spillways | |
| Type of dam | Arch dam |
| Impounds | Waikato River |
| Height | 87 m (285 ft) |
| Length | 133 m (436 ft) |
| Width (crest) | 11 m (36 ft) |
| Width (base) | 15.2 m (50 ft) |
| Spillways | 1 |
| Reservoir | |
| Creates | Lake Maraetai |
| Surface area | 4.1 km2 (1.6 sq mi) |
| Power station | |
| Commission date | September 1953 (Maraetai I) February 1971 (Maraetai II) |
| Type | Conventional |
| Hydraulic head | 61 m (200 ft) |
| Turbines | 10 × Francis |
| Installed capacity | 360 MW |
| Annual generation | 885 GWh |
The Maraetai Power Station is a huge hydroelectric power station in the North Island of New Zealand. It's built on the Waikato River. This station is the fifth of eight power stations along the Waikato River. It's also the biggest hydroelectric station on the Waikato, producing 360 megawatts of power.
The station actually has two separate powerhouses. Maraetai I is right in front of the Maraetai Dam. Maraetai II is about 550 metres downstream from Maraetai I. Even though they are separate, they work together as one big power station. Mercury Energy owns and runs Maraetai.
Contents
Building the Maraetai Power Station
Maraetai I: The First Powerhouse
Building the Maraetai Power Station started in 1946. Engineers had looked at the site between 1940 and 1945. The location was a very deep and narrow gorge west of Tokoroa. Because the gorge was so narrow, the powerhouse had to fit right at the base of the dam. This meant the spillway (where extra water flows out) had to be part of the river diversion tunnel. The ground was made of volcanic rock called ignimbrite. This rock had many cracks, so it needed a lot of special work to make it strong.
Early Challenges and Solutions
Construction began with building a road from Tokoroa. They also set up homes and services for the workers. This camp became the town of Mangakino. There were many problems from the start. World War II had just ended, causing shortages of workers and materials. There wasn't enough concrete or steel. Also, workers sometimes went on strike. These issues made it hard to finish the project by the planned date of 1951.
Work on the diversion tunnel began in late 1946. This tunnel was 25 feet wide and 1685 feet long. It was very wet inside because water kept leaking in. Workers often had to work in knee-high or even waist-high water. They had to seal the tunnel with cement and bitumen. By 1948, about 800 people were working on the site.
The tunnel was finished in March 1949. Then, they built cofferdams to block the river's natural path. This allowed them to start building the dam. The gates at Taupō were closed to lower the river's water level. Bulldozers then pushed dirt into the river to stop its flow. Heavy rain made this difficult, causing the river to rise quickly. It took 27 hours to finally block the river. After that, the spillway tunnel was built.
Building the Dam and Powerhouse
In late 1949, work started on the dam's foundations. They drilled thousands of holes and used 11,000 tonnes of cement to strengthen the rock. This process is called grouting.
Building the dam itself began in September 1950. The number of workers reached its peak at 1200. A large machine was brought in to mix the huge amount of concrete needed for the dam. About 5000 tonnes of steel were used to reinforce the concrete. For the first time in New Zealand, they used a system to cool the concrete. This involved pipes with refrigerated water running through them.
The powerhouse was built very quickly. Its foundations started in early 1950, and the building was done within a year. It had a steel frame and a roof made of pre-cast concrete sections. The transformer station was placed behind and on top of the powerhouse. This was because of the limited space in the gorge.
Getting the Equipment
The Public Works Department looked for equipment outside the United Kingdom. They needed faster delivery and firms with more experience. They chose companies from Canada for the generators and the United States for the turbines. These companies offered better prices and had more experience. For the spillway gates, a company from West Germany offered a much lower price and faster delivery. This offer was accepted, even though it was only five years after World War II.
By mid-1951, the penstocks (large pipes that carry water to the turbines) were installed. The first three machines were also put in place. On October 31, 1952, Maraetai made its first electricity. The station was officially opened on September 5, 1953. This was two years later than first planned. The fourth machine was installed in January 1954, and the fifth in April. After that, the lake was filled to its full height.
Maraetai II: The Second Powerhouse
Construction of the Maraetai II powerhouse began in 1959. A 500-metre long canal was dug to carry water to this new powerhouse. In 1961, work on Maraetai II stopped. The government decided to focus on building the HVDC Inter-Island (the "Cook Strait cable"). This cable would bring electricity from the South Island to the North Island.
Work on Maraetai II started again in 1965 after the inter-island link was finished. The first two turbines and generators were ready in July 1970. The last turbine and generator, and the very last one on the Waikato River, started working in February 1971. This was almost 25 years after the Maraetai project first began.
The Maraetai Dam
The Maraetai Dam is a concrete arch dam. It holds back the Waikato River, forming Lake Maraetai. The dam is 133 metres long and 87 metres high. It is 15.2 metres wide at its base and 11 metres wide at the top. At one time, this dam was the largest hydroelectric dam in the Southern Hemisphere.
The dam's spillway is located south of the dam. Because the dam is in a narrow gorge, there wasn't enough space for a normal spillway. So, the tunnel used to divert the river during construction was changed to become the spillway. This spillway tunnel is 521 metres long and 7.6 metres wide. It is blocked by three large gates.
How Maraetai Generates Electricity
Maraetai I: Making Power
Water for Maraetai I comes from Lake Maraetai at the dam. It flows through five large steel penstocks. Each penstock is 70 metres long and 4.8 metres wide. The force of this water spins five vertical Francis turbines. These turbines then turn generators.
Each of the five generators makes 36 megawatts of electricity. To make one megawatt of electricity, 2000 litres of water must flow through the turbines every second. The electricity then goes to a transformer. Here, its voltage is increased to 220,000 volts for sending it out on power lines. Maraetai I also has a sixth penstock. This one sends water to two smaller turbines. These make electricity for the power station's own needs.
Maraetai II: More Power Generation
Water for Maraetai II is sent down a canal south of the dam. This canal is 550 metres long, 12 metres wide, and 12 metres deep.
From the canal, water flows through five more steel penstocks to the powerhouse. These penstocks are 102 metres long and 4.6 metres wide. The water spins five vertical Francis turbines, which turn generators. The generators at Maraetai II also produce 36 megawatts each. Their electricity is also increased to 220,000 volts by transformers for transmission.
Sending the Electricity Out
Electricity from both Maraetai I and Maraetai II goes to the Maraetai switchyard. This switchyard is located between the two powerhouses. Electricity from the nearby Waipapa Power Station also connects here. From Maraetai, the electricity is sent to Whakamaru using two 220 kV power lines.
From Whakamaru, the electricity generated at Maraetai is sent across Transpower's 220 kV grid. It travels to cities like Hamilton, Taupō, Palmerston North, and Auckland.
