Protection systems have vital role in network reliability in short circuit mode and proper operating for relays. Current Transformer often in transient and Saturation under short circuit mode causes mal-operation of relays which will have undesirable effects. Therefore, proper and quick identification of Current Transformer Saturation is so important. In this paper, an Artificial Neural Network (ANN) which is trained by two different swarm based algorithms; Gravitational Search Algorithm (GSA) and Particle Swarm Optimization (PSO) have been used to discriminate between Current Transformer Saturation and fault Currents in power Transformers. In fact, GSA operates based on gravity law and in opposite of other swarm based algorithms, particles have identity and PSO is based on behaviors of bird flocking. Proposed approach has two general stages. In first step, obtained data from simulation have been processed and applied to an ANN, and then in second step, using training data considered ANN has been trained by GSA & PSO. Finally, a proposed technique has been compared with one of the common training approach which is called Genetic algorithm (GA).

This study presents a modified transient Current limiter (MTCL) for mitigation the inrush Current of Transformers. The MTCL is based on conventional transient Current limiter (TCL), which, its configuration is modified to overcome the TCL drawbacks of operation. The proposed MTCL offers lower power losses and voltage/Current THD during normal operation mode. It needs only one limiting reactor instead of two limiting reactors, which results in cost saving. The theoretical analysis of the MTCL for suppressing the inrush Current has been presented and the performance was tested by PSCAD/EMTDC simulation anda experimental prototype. Both simulation and experimental results showed that the MTCL is effective for suppressing the Transformer inrush Current. Also, the capability of the MTCL for suppressing the Transformer inrush Current was compared with the conventional TCL.

Numerous methods exist to distinguish between inrush Current and internal faults, but these approaches have not yet become practical due to their inherent limitations. As a result, conventional methods, despite their well-known drawbacks, continue to be widely used in practice. In this paper, a new method based on time-frequency analysis is presented for detecting inrush Current situations. To do this, a diverse array of scenarios involving a power Transformer switching ON and internal fault cases are simulated using the PSCAD/EMTDC software package. Then, a hyperbolic S-Transformer is employed to extract a determining index from the simulation results. Finally, a suitable threshold value for this index is computed so that inrush Current can be distinguished from fault Current by comparing the index with its threshold.  Evaluation of the efficiency of the proposed method using simulation and real data confirms its excellent accuracy. Therefore, it can be used in algorithms for power Transformer differential protection to improve their stability during inrush Current transients.

< p>The restricted earth fault (REF) protection is provided for electrical power Transformer in order to sense internal earth faults, mainly because it is more sensitive than the main differential protection. However, The REF relay may maloperate when Current Transformer (CT) Saturation happens following a severe external fault. In this paper, a new simple algorithm is proposed for REF protection scheme which is realized by considering four fundamental conditions. These conditions are defined based on the differential and neutral Currents as well as sum of phase Currents. When these conditions are simultaneously satisfied, the relay detects the internal ground fault. This algorithm is implemented and evaluated by MATLAB program based on obtained result data from simulation of a real power system using PSCAD/EMTDC software package. The well-known Jiles-Atherton (JA) model is used to simulate the transient behavior of CTs. The satisfactory results obtained from exhaustive investigation justify the high security of the proposed protection scheme.

A transient phenomenon that leads to the false trip of the power Transformer dierential protection during the energization of a loaded power Transformer is the ultra-Saturation phenomenon. In this paper, at rst, a new algorithm for three-phase power Transformer dierential protection, considering the eect of the ultra-Saturation phenomenon, is presented. To model the ultra-Saturation phenomenon, the nonlinear characteristic of the Transformer core and the eect of Saturation of the Current Transformers are taken into account. It is assumed that the load of the Transformer is resistive and inductive. In this algorithm, the ultra-Saturation phenomenon, external and internal faults of the power Transformer and magnetic inrush Current are simulated, and appropriate criteria using the signal harmonic components of the dierential Current will be presented for the Discrete Fourier Transform (DFT) algorithm to distinguish between. In this paper, simulation is done by PSCAD and MATLAB programs.