CPC 100 + CP CU1: Protecting people and their surroundings Gustav Lundqvist writes about how he and his team at Kraftdiagnos test touch voltage levels on power lines in response to the growing demand for electric power in Sweden During the past year, the power industry in Sweden has increased the speed of building 130 kv and 400 kV power lines by up to four times the previous rate. This is necessary since Sweden’s estimated power production and power use are predicted to increase 120% by 2045. Before a new power line with a system voltage over 100 kV can be energized, it needs to be tested with regards to touch voltages in the nearby low voltage grid to detect potential earth (also known as ground) faults. The power line is not allowed to be energized if the touch voltage is above 600 V with a 3 kOhm resistance. The test is performed when the power line is finished and installed, such as when a wind park is waiting to be put into operation. This means that every hour that the power line is not in service, the grid company and the owner of the wind park may lose thousands of euros per hour. The test can also be performed on existing power lines, which can only be taken out of service for a few hours per year to avoid system disturbances. This means that the measurement must be performed quickly. At the same time, the measurement is highly dangerous. For this reason, there are very few engineers that perform these step and touch measurements. I invested in my first CPC 100 multifunctional testing device in 2019, and in the Spring of 2020, I took my starting business to a new level with additional OMICRON devices and added ten employees. In 2021, we tested about 21 high-voltage power lines with the CPC 100 and the CP CU1 multi-functional coupling unit. During this time, my job changed from performing the measurements myself, to teaching and leading younger engineers in the field. Performing the measurement The test is performed by switching off breakers at both ends of the power line. We use a special earthing tool, called the JK51, which is attached to the power line. The measurement is unique, so we have to figure out and build many of the components ourselves, and they need to be in accordance with safety regulations. When testing a power line, pylons within 1km of each other are tested. This means that on average, up to ten pylons are subject to testing every ten kilometers (roughly 6 miles). When performing the test, we simulate an earth fault in the 150 kV grid and measure the touch voltage in the surrounding low voltage grid. Over the past few years, the short circuit power in the grid has increased to about 10 to 39 kA, depending on the location in the grid. This means buildings that were once safe may 14
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