Magazine | Issue 2 2022 40 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 30 20 10 0 kHz ms Powered by Maschinenfabrik Reinhausen 30 20 10 0 –30 –20 –10 –40 Powered by Maschinenfabrik Reinhausen 3800 3900 4000 4100 4200 ms Decibel 0 4 8 12 16 A 200 300 400 500 600 700 s A (A-N) B (B-N) C (C-N) curve is the actual fingerprint of the tap switch. The results’ assessment is based on comparing these envelope curves with reference values. A comparison functionality in PTM 4.90 helps the test engineer check the results for any deviations which could indicate mechanical changes in the OLTC. Figure 2 shows the comparison of two tap switch recordings. On the top, two envelope curves illustrate the high reproducibility of the curves. The diagram on the bottom shows the comparison of the corresponding DRM curves. The most complete data set can be obtained when performing an offline measurement, consisting of the VAM and DRM traces and the motor current recording. Both measurements yield complementary results, which help minimize individual diagnostic blind spots from either method. The synchronous recording of the VAM and the DRM curves allows you to assess the entire switching operation from motor start to finish. 2nd feature – three-phase OLTC scan The other new feature for the TESTRANO 600 in PTM 4.90 is the threephase OLTC scan that complements the existing single-phase OLTC scan solution. By measuring all three phases simultaneously, as shown in figure 3, only one up/ down test cycle is required, effectively reducing the overall testing time by 66%. Additionally, a continuous recording has been introduced, illustrating the current behavior throughout the entire tap range. To assess the results, the test engineer validates that there are no current interruptions and evaluates the timing of each switching operation. The synchronicity between the phases can be measured using multiple cursors to identify possible linkage problems in the phases. Figure 3: Three-phase OLTC scan measurement curve Figure 1: The frequency-time diagram helps to evaluate the overall signal quality. Figure 2: Comparison of envelope and DRM curves «The vibration patterns are considered unique for each unit and can be used as a reference comparison for future measurements.» 4 3.5 3 4.5 5 A Powered by Maschinenfabrik Reinhausen 3800 3900 4000 4100 4200 ms 29
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