## 6 On-Site Experimental Measurement and Results Analysis of Converter Transformer
### Measurement Results and Error Analysis  
In the experimental measurement of the demagnetization effect on the converter transformer, taking the C-phase of the pole 2Y-Y converter transformer tested with 10 A DC resistance as an example, the experimental process and results are described in detail. The experimental data show that the remanence rate significantly decreases after demagnetization, and the demagnetization effect is significant. The demagnetization device is placed in a safe environment to ensure the correct connection between the device and the transformer, including the connection between the output voltage terminal and the ground wire. After starting the device, impedance measurement is first performed under low voltage to obtain the initial inductance value of the transformer in the demagnetized state. The voltage set for this measurement is 380 V, and the measured inductance value is 329.3 H, which will serve as the benchmark for subsequent demagnetization effect evaluation. The on-site experimental diagram of the device is shown in Figure 18.  
According to the characteristics and demagnetization requirements of the transformer, the demagnetization starting voltage is set to 1100 V, the expected demagnetization time is 2000 ms, the demagnetization termination voltage is 2 V, and the termination current is 1 mA. After completing the parameter settings, the energy storage capacitor is pre-charged until it reaches the set voltage value. During the pre-charging process, the changes in capacitor voltage are closely monitored to ensure that it steadily rises to the target voltage. After the pre-charging is completed, the demagnetization process is initiated, and the energy storage capacitor releases energy through the transformer winding, generating a demagnetization current that decays and oscillates. During this process, real-time monitoring of voltage, current waveforms, and related parameter changes is carried out. The experimental data show that the peak voltage reaches 1131 V, the peak current is 9775.12 mA, and the oscillation frequency is 7 times. The waveform diagrams of voltage and current clearly demonstrate the attenuation process of oscillation, indicating that the demagnetization current gradually decreases and energy is gradually released. Table 7 shows the main parameters during the demagnetization process. Figure 18: On-site experimental setup diagram. From Figure 19, it can be seen that after 40 s, the voltage and circuit changes approach zero, indicating that the demagnetization process has ended. Therefore, by integrating the voltage data within the time range of 0 s to 40 s, the magnetic flux variation curve over time in Figure 20 can be obtained. After obtaining the current and magnetic flux change curves during the demagnetization process separately, the dynamic demagnetization loop can be drawn according to the previous method. The dynamic hysteresis curve is shown in Figure 21.  
After the demagnetization process is completed, impedance measurement under low voltage is performed again, and the measured inductance value is 717.5 H. Compared with the inductance value before demagnetization, the change in inductance value reflects the decrease in remanence rate. The residual magnetization rate after demagnetization is \begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Value** \\ \hline Estimated demagnetization time (ms) & 2000 \\ Demagnetization start voltage (V) & 1100 \\ Demagnetization end voltage (V) & 2 \\ Demagnetization end current (mA) & 1 \\ Resistance measurement voltage (V) & 380 \\ Resistance measurement frequency (Hz) & 50 \\ \hline \end{tabular}
\end{table} 
Table 7: Main parameters of the demagnetization process. Figure 19: Voltage and current variation curve during demagnetization process (software interface. The yellow curve represents the voltage curve, and the red curve represents the current curve). Figure 20: Magnetic flux variation curve during the demagnetization process.