Magazine | Issue 1 2025 The MUs also calculate neutral current and voltage from phase measurements. A single-phase injection is ideal for checking these neutral quantities. It was found that the neutral current of one MU was in phase with the tested phase current, while the other had a 180° phase shift due to different configurations (“IN = –3I0” vs. “IN = +3I0”), which was then corrected. resin partition with integrated voltage and current measurements. Voltage measurement is based on a capacitive voltage sensor, while current measurement is redundant with two separate Rogowski coils. The merging units (MUs) are also redundant and equipped with dedicated LPITIO-cards. MU1 digitizes the voltage measurement and one current measurement for main 1 protection (line protection), while MU2 digitizes the other current measurement for main 2 protection (busbar protection). Comprehensive commissioning tests of the LPIT system To test the LPITs, the test setup consisted of a CPC 100 for primary injection and a DANEO 400 hybrid signal analyzer. This allowed analysis of the SV streams of both MUs, the primary test current, and the secondary voltages of the Rogowski coils together. A special characteristic of LPITs is that they usually have individual ratios, which are determined and made available by the manufacturer. To avoid typos, these parameters can be obtained in a file or by entering the LPIT serial number in the engineering software. Possible errors include a wrongly selected Rogowski coil and incorrect assignment of the LPIT pole to the power system phase. Pole 1 / phase L3 is a good example, as the ratios between the two Rogowski coils (0.76%) and also in comparison to the other poles (up to 1.8%) are significantly different. The secondary voltage measurement showed a difference of 0.73%, which was expected, while the SV streams of both MUs showed this difference was eliminated. This confirmed correct connections and parameter loading. «This GIS uses ‹clean air› (80% N₂ and 20% O₂) as the insulation medium. Additionally, the substation features other innovations, including lowpower instrument transformers (LPITs), process bus, and vacuum circuit breakers.» Setup for the LPIT test with CPC 100 and DANEO 400 Recording of IN and IL1, top with “IN = –3I0”, bottom with “IN = +3I0” LPIT Reference meas. Process bus SV1 SV1, SV2 SV2 Vs MU1 MU2 43
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