The product testing department at Maschinenfabrik Reinhausen (MR) in Regensburg tests tap changers for high-voltage transformers under extreme conditions, and the precision monitoring of this process is carried out by high-speed cameras from PCO. It is claimed that 50 per cent of the total energy worldwide flows through MR tap changers and so the monitoring is of great importance.
In a high-voltage grid, electricity is generated continuously at different locations. To transport the electricity via overhead power lines, for example, the voltage first has to be boosted by a transformer to 380,000 volts and then – before it reaches the end user – reduced stepwise to 230 volts. In the event of a sudden fluctuation in the voltage in the grid due to increased consumption in the early morning, for example, the corresponding transformer would fail and there would be no power. This is where the tap changer comes into play: it can change the transformation ratio in the transformer so the voltage in the grid remains constant.
Up to two pco.dimax cameras from PCO film the test object, either from one side or synchronously from two sides, depending on the test setup. If a flashover occurs during the test, the high-speed camera records this in an image to give entirely new analysis capabilities.
MR invests a large amount in the testing of its products. The MR Test Center conducts electrical and mechanical load tests under normal and extreme operating conditions to detect any weak points in material and construction. In high-voltage testing, an AC voltage cascade is used that can generate 700,000 volts with a frequency of 50 hertz from an electrical outlet, and a lightning generator can simulate standard lightning impulses of up to 1.8 million volts in order to simulate the power grid getting struck by lightning. The MR tap changers have to be able to withstand such a lightning impulse without the occurrence of an electric flashover or sparkover.
The images are recorded in black and white as colour information is not needed for the test. However, this makes the camera about three times more photosensitive, which facilitates illumination by means of movable LED spotlights with an output of 400 watts each. The image of the lightning impulse is recorded with 10,000 frames per second – an exposure time of 90 to 91 microseconds per frame.
