The latest issue of alstom Power’s magazine High Voltage has just been published, providing news on the high voltage generator Powerformer. Alstom also gives an update on the most recent Powerformer order for the Höljebro hydro power plant in Sweden, as well as projects at Eskilstuna and Porsi which are nearing completion.
The Porsi hydro plant is located on the Lule river in northern Sweden. It was constructed in 1958 and has a total output of about 300MW. One of the three existing units will be replaced with a Powerformer high voltage generator, the commissioning of which is scheduled to take place in March 2001.
The generator is being constructed on site in the power plant’s machine hall and will produce 75MVA at 155kV when it starts operating. The stator for the generator was constructed on site at Porsi while the other units were still in operation. Besides the cable winding procedure, the completion of the stator involved the development of methods for stacking the core laminations. The stator was sewn together with 16,000m of high voltage cable.
Long-running test programmes on a Powerformer unit at the Porjus Hydropower Centre in northern Sweden are still continuing. The Powerformer has been in operation at Porjus for about 9500 hours and has a mean voltage value of 44.5kV, with a power output of 11MVA.
Since the plant started operating, the generator has undergone a number of tests and measurements, including loss, stator vibration, thermal time constants, short circuit tests, voltage harmonics, acoustic noise measurements, external magnetic fields, load shedding tests and tests on the auxiliary winding. Alstom claims that the generator has performed as expected and no mechanical degradation on the stator or other parts of the generator has been found.
More tests are planned for Powerformer, including short circuit tests with the generator connected to the grid. Regular inspections will also be performed during the continued operation of the Porjus plant.