# Noise Source Diagnosis Method Based on Transfer Path Analysis and Neural Network
## 3 Transfer Path Analysis Test
### Testing Procedure  
During the actual operation of the converter, the fan must run continuously to dissipate heat from the transformer; therefore, only two representative operating conditions--full speed and half speed--are used to determine the vibration and noise characteristics of a single fan. This serves as the basis for testing the transformer's vibration and noise characteristics under complex working conditions with half load and full load. The working condition data are then measured. Close the cover plate of the converter cabinet and operate the converter cabinet according to the working conditions. Measure the noise and \begin{table}
\begin{tabular}{c c c} \hline \hline
**Test Type** & **Test Content** & **Remark** \\ \hline \multirow{4}{*}{Working signal} & The noise or vibration signals of I1b-I13a and A1–A6 points are collected under four working conditions & The signal is collected three times for each working condition, and the average value is obtained. \\ \hline \multirow{4}{*}{Transfer function} & force-sound & I1b–I13a was excited, respectively, and P1–P13 signals were collected & The signal was measured three times for each excitation point and averaged. \\ \cline{2-3}  & sound-sound & I1b–I13a was excited, respectively, and P1–P13 signals were collected & The signal was measured three times for each excitation point and averaged. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Test content. Figure 3: Schematic diagram of target point layout. vibration responses of target points and reference points. The reference point signal is used to calculate the path load, and each working condition is measured 3 times. The test conditions are shown in Table 2.  
(1) Working condition data measurement. Close the upper end of the cover plate of the converter cabinet, and operate the converter cabinet according to the requirements of the four working conditions in Table 2 under normal operation. The noise and vibration response of the target point and reference point are measured. The reference point signal is used to calculate the path load. Each working condition is measured 3 times. The test conditions are shown in Table 2.  
(2) Transfer function measurement. The reciprocity principle reveals the reciprocity between vibration and sound transmission in a linear time-invariant elastic system, that is, the ratio of an incentive applied at one point A in the system to the response generated by that incentive at another point B in the system is equal to the ratio of an incentive applied at B to the response generated at A. Due to the complexity of the structure of the measured object and the limited internal space structure, it is difficult to directly test the response of the reference point and the target point, respectively, with the excitation path points. The transfer function is an inherent attribute of the structure and does not change with the excitation force, so the reciprocity method is used for measurement. Remove the converter cabinet and fan, close the cover plate, open a hole in the cover plate to lead out the sensor cable, and seal it with mastic. Firstly, the reference point is stimulated by a hard hammer, the response of the internal path is measured, and the transfer function from the reference point to the path point is obtained. Then, the volume sound source excites the external target point, measures the response of the internal path, and obtains the transfer function from the target point to the internal path. At this point, the transfer function between the reference point, the path point, and the target point can be obtained and the contribution can be solved. The test procedure is shown in Figure 5. \begin{table}
\begin{tabular}{c c} \hline \hline
**Condition Number** & **Condition State** \\ \hline
1 & Fan at half speed and transformer at no-load \\
2 & Fan at full speed and transformer at no-load \\
3 & Fan at half speed and transformer at full load \\
4 & Fan at full speed and transformer at full load \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Test conditions.