## 3 Evidential Reasoning Algorithm
### Decomposition Model and Transformer Condition Assessment
#### 3.5.2 Condition Assessment  
To assess the condition of the energy transformer, real maintenance data from the Croatian Transmission Grid Operator company are used; specifically, data regarding the energy transformer Koncar, type 1 ARZ 300000-420/A. The data cover the continuous period of six years. In general, the offline (Type 1) data were collected at least once a year to a maximum of four times a year and basically at irregular intervals, although for a certain subset of data, there were regular intervals between the collected data. For the first four years, data were obtained by measurement or assessment (offline data) and since the beginning of the fifth year, data from the remote monitoring system (online data) are also available. Therefore, it can be said that the data collected within the observed six years vary both in the amount of collected data (the number of baseline attributes for which data are available at a given time) and in the source of the data (data collected offline and/or online). After defining the available data by time points, it is possible to transform the existing quantitative data into a qualitative domain, i.e., to add corresponding ratings to the collected data that represent the evaluation of a certain baseline attribute. Table 2 also shows the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \#1 &
\begin{tabular}{c} **Baseline** \\ **Attribute Type** \\ \end{tabular} & **Description** & **Unit** & **Collection Means** & **Weight** \\ \hline
44. & Boiler air dryer & & Type 1 & \(\omega_{41}=0.33\) \\ \hline
45. & Boiler oil level & & Type 1 & \(\omega_{42}=0.33\) \\ \hline
46. & Seal loosening & & Type 1 & \(\omega_{43}=0.33\) \\ \hline
47. & tan 81 (N) & Conductor dielectric loss factor (N) & \% & Type 1 & \(\omega_{511}=0.143\) \\ \hline
52. & tan 86 (2V) & Conductor dielectric loss factor (2V) & \% & Type 1 & \(\omega_{516}=0.143\) \\ \hline
53. & tan 87 (W) & Conductor dielectric loss factor (2W) & \% & Type 1 & \(\omega_{517}=0.143\) \\ \hline
54. & C1 (N) &
\begin{tabular}{c} Conductor insulation capacity \\ (Ground point) \\ \end{tabular} & pF & Type 1 & \(\omega_{521}=0.143\) \\ \hline
55. & C2 (1U) & Conductor insulation capacity (Phase) & pF & Type 1 & \(\omega_{522}=0.143\) \\ \hline
61. &
\begin{tabular}{c} Conductor \\ thermal imaging \\ \end{tabular} & & Type 2 & \(\omega_{53}=0.10\) \\ \hline
62. & Phase shift index 1U &
\begin{tabular}{c} Primary side conductor capacity \\ change index (1U) \\ \end{tabular} & & Type 2 & \(\omega_{541}=0.33\) \\ \hline
68. &
\begin{tabular}{c} Number of tap \\ changer operations \\ \end{tabular} & & Type 2 & \(\omega_{51}=0.25\) \\ \hline
69. & Total switched current & kA & Type 2 & \(\omega_{52}=0.25\) \\ \hline
70. & Tap changer motor power & \% & Type 2 & \(\omega_{53}=0.40\) \\ \hline
71. &
\begin{tabular}{c} Tap changer boiler \\ air dryer \\ \end{tabular} & & Type 1 & \(\omega_{54}=0.10\) \\ \hline
72. & Pump 1 condition & & Type 2 & \(\omega_{711}=0.20\) \\ \hline
77. &
\begin{tabular}{c} Unitator 1 condition \\ \end{tabular} & & Type 2 & \(\omega_{721}=0.10\) \\ \hline
87. &
\begin{tabular}{c} Cooler 1 efficiency \\ \end{tabular} & \% & Type 2 & \(\omega_{731}=0.20\) \\ \hline
91. & Cooler 5 efficiency & \% & Type 2 & \(\omega_{735}=0.20\) \\ \hline \hline \end{tabular}  
* Some attributes from the same data spectrum are omitted in order to preserve space.  
\end{table} 
Table 2: _Cont._boundary conditions for data conversion and an indication of the qualitative ratings is given for each basic attribute for which input data are available. Condition assessment of a certain general attribute begins by going over the confidence rating in grade \(H_{n}\), its baseline attributes \(e_{i}\), respecting their weights \(\omega_{i}\) and performing the aggregation procedure as shown in Equations from (18-25). Condition assessment of the observed general attribute is then represented by a probability distribution, i.e., by the confidence rating in the assessments from set \(H_{n}\) as shown in (25).