# Turn-to-Turn Fault Diagnosis on Three-Phase Power Transformer Using Hybrid Detection Algorithm
## 2 Hybrid Algorithm in TTF Diagnosis System  
The hybrid algorithm's aim is to create a fault detection system in a PT, especially for TTF recognition. The algorithm uses a terminal current as an input and generatesa condition state of a PT regarding the TTF. The algorithm's output can be used as a supporting tool to monitor a TTF inside a PT while not connected to the protection breaker of the PT. In this research, we simulated the proposed algorithm into a PT model using MATLAB Simulink. This algorithm combined and obtained results from the subalgorithms (Figure 1b) to obtain the PT's final condition fault status.  
The sub algorithms are the conventional differential protection, negative-sequence directional algorithm, EPVA, negative differential sequence, and fuzzy EPVA algorithm. Each has a different role in PT fault diagnosis and generates different decisions (internal fault, external fault, and normal condition).  
The conventional differential protection can detect fault if the difference value of the phase current between primary and secondary winding is higher than the threshold value. This protection only detects a fault or normal state and is incapable of distinguishing the type of fault, either internal or external. The negative sequence directional algorithm and fuzzy logic detect three states of a PT's condition. Both can detect internal faults, which, in this case, was caused by a TTF.  
Figure 1: (**a**) User interface from the hybrid detection algorithm; (**b**) the flowchart of the hybrid algorithm.  
The differential negative sequence and EPVA only detect internal and noninternal fault states. The hybrid algorithm protection decides the internal, external, or normal conditions based on each sub algorithm's result. The hybrid algorithm chooses the most detected condition, which is generated by the sub algorithms.  
This method is used to distinguish the weaknesses for each sub algorithm. The conventional differential protection is unable to distinguish if a fault in the transformer, either an internal or external fault, occurs. This algorithm is not sensitive enough to detect low-level TTFs inside the transformer [3]. The negative-sequence directional algorithm can detect a TTF when external and internal faults occur simultaneously [10]. The differential negative sequence and EPVA only detect the internal fault and non-internal fault conditions. When there is an external fault, the algorithm detects a non-internal fault, which is the same as in the normal condition. The internal fault will decide if there are more than or equal to two internal fault states (n\({}_{\text{if}}\)), declared by the sub algorithm. This rule also applies to the external fault state (n\({}_{\text{ef}}\)). The external fault will declare if there are more than two external fault statuses. A noninternal fault in the differential negative sequence protection and EPVA could indicate an external fault or a normal condition. A normal condition is decided if all sub algorithms declare a normal condition and a non-internal fault condition for the differential negative sequence protection and EPVA. The rule for the hybrid detection algorithm is expressed in Equation (1). Principally, the hybrid detection algorithm declares a transformer condition based on sub algorithm results. The interface from the hybrid algorithm detection is shown in Figure 1a.  
\[\text{PT Fault Condition }=\left\{\begin{array}{l}\text{Internal fault, }n_{\text{if}}\geq 2\\ \text{External fault, }n_{\text{ef}}\geq 2\\ \text{Normal, }n_{\text{fault}}=0\end{array}\right. \tag{1}\]