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In the power grid, various conditions may occur that saturate the core of a current transformer. Saturation of the protection core of the current transformers can cause a malfunction in the protection relays. To prevent malfunction of the protection relays caused by the current transformer saturation, software and hardware methods can be used. In the software method changes in the protection relay algorithm are used. In the hardware method special devices are used. A new hardware method is presented here, which uses compensation to prevent the occurrence of current transformer saturation. In the proposed method, compensation is done by controlling an applied voltage to the current transformer secondary terminals using negative resistance. The proposed method, despite its simplicity and cost‐effectiveness, has good performance in preventing saturation in various conditions. The high reliability in terms of the risk of secondary open circuit and its application in various saturation conditions, even in the case of severe saturation are the main advantages of the proposed method. Also, the proposed method does not produce distortion in the transformation of high‐order harmonics by the current transformer. To verify the effectiveness of the proposed method, prototype design and construction have been performed. The simulation and experimental results of laboratory tests have been presented and analysed. [ABSTRACT FROM AUTHOR]

The loss of excitation (LOE) is one of the main faults of the synchronous generator, which may cause serious damages to generator and makes the power system unstable. The main problem to distinguish between LOE and stable power swing (SPS) is a time delay, which is a main part of the detection time in all recent protection methods. This study presents a new method for LOE detection in the synchronous generator, which reduces time delay by half. The proposed method exploits a new index which is based on the variation of the generator output reactive power. It is a combination of the first- and secondorder derivative of the generator output reactive power. In this method, after the generator losses its excitation, the proposed index will become and remain negative for a while. To prevent mal-operating under slowest power swing condition, the time delay of 0.85 s is used. The performance of the proposed method is evaluated under different conditions. The simulation results and experimental tests confirm the accuracy and fast operation of the proposed method. [ABSTRACT FROM AUTHOR]

Here, based on wide‐area measurement systems (WAMS), an adaptive tripping index (TI) is proposed for online prediction of tripping signals with respect to wide‐area out‐of‐step (WAOOS) protection of synchronous generators. The proposed TI included two different equations consisting of a straight line for unstable inter‐area oscillations and a sinusoidal line for WAOOS transient instability. For online identification of coherent generators with respect to inter‐area oscillations, based on evaluating the correlation coefficients between generator behaviours, an index is proposed from which the global tripping signals (GTS) are calculated. The GTS consist of the rate of change of inter‐area rotor angle oscillation between two oscillating areas in the centre of inertia frame. Actually, the proposed scheme is an adaptive and online index from which the critical inter‐area angle is adjusted individually by evaluating GTS at each sampling time gathered from the WAMS data. The proposed strategy is implemented on an IEEE 39‐bus test system and its performance is investigated by simulating typical scenarios during time‐domain simulations. The results show the effectiveness of the proposed scheme for fast prediction of WAOOS protection in real‐time environment. [ABSTRACT FROM AUTHOR]