Field Trip - Aratiatia Hydro Power Station - contributed by Noel Gomes and Sriram Ragunathan

On 3rd May 2008, the IEEE GOLD New Zealand North section along with ‘engenerate’ – the young engineers division of the Institute of Professional Engineers of New Zealand (IPENZ) jointly organised a field trip to the Aratiatia Power station. The event was well attended by GOLD members, IPENZ members and a number of young professionals.

The purpose of this event was to provide young professionals with an insight into the day to day operation of a hydro power station. The event started with a long 3.5hr drive from Auckland. The journey traversed through New Zealand’s largest thermal power station at Huntly, Carter Holt Harvey’s Kinleith pulp and paper mill and a number of dairy factories owned by Fonterra. The onward drive concluded with a welcome stopover at the Aratiatia Rapids to witness the release of water from Lake Aratiatia into the rapids.

On reaching the hydro power station, we were greeted with information on the history of the power station, how it got its name and where it sits on the Waikato River chain with respect to the eight other hydro power stations. The displays also had information on the owner of the power station (Mighty River Power’s) involvement with the local community and its plans on future investment in wind and geothermal energy. The entrance of the hydro power station had big LCD screens with real-time live displays of the lake levels, power generated, frequency and voltage levels at each of the stations. This site visit coincided with an Open day organised by Mighty River Power for the local residents of the region and since we were a set of young engineers, we had asked for a more detailed tour. It took us approximately 2.5 hrs to get around the hydro power station.

The tour began with a brief introduction of the plant, its capacity and illustration of the purpose of the surge tank. It was then followed by visits to the turbine pit, the generator floor, the transformer platform, the local control room and Transpower’s 220 kV outdoor switchyard. Along the way, there were several stops made to explain the functionality of various equipments in the plant and to answer any specific questions relating to the equipment. The tour ended with a refreshing sausage sizzle funded by Mighty River Power.

Some of the highlights of the power station are:

It is the smallest and the first hydro power station on the Waikato River and consists of three Francis turbines each of size 30 Mega-Watts (MW) which together generate an annual energy of 331 Giga-Watthours (GWh) at 11 kilo-Volts (kV).
It has a 900m tunnel that takes water from Lake Aratiatai in to an 18 million-litre surge tank. The surge tank has main gates that control the water leading to each of the generators via three separate underground penstocks.
In the turbine pit, the water from the penstock enters through a squirrel cage chamber which rotates the turbine propellers (runners). The turbine has series of wicket gates surrounding the runner which control the flow of water from the penstock. The movement of the wicket gates is controlled by a servo motor (PID controller) which receives hydraulic oil regulated by an actuator.
The rotation of the rotor induces an electro-magnetic field on the windings of the stator, which then generates electricity. The output voltage at each generator is controlled by an Automatic Voltage Regulator (AVR) also called Exciter.
The power generated at 11 kV and is stepped up to 220 kV via transformers. The outdoor switch yard facilitates this by providing an injection point for transmission over the national grid. The power station can be controlled manually or remotely from its local control room.

The initial feedback received during and after the event showed that it was a great success. The attendees were very well satisfied with the information provided and the extent of details covered by the tour guide. The collaboration of IEEE GOLD and engenerate IPENZ was first of its kind for an event like this and provided a great networking opportunity for all the attendees. This field trip has strengthened our ongoing relationship with IPENZ for future joint ventures. The committee would like to thank all the attendees for their participation and time.