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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]

In some conditions, the flux in the core of current transformers (CT) increases. If this increase in flux leads to saturation of the protective core, it can create a lot of problems in power system protection. One of the hardware solutions to prevent the occurrence of core saturation in CT is the fixed switched resistor demagnetization method. Due to disadvantages such as dependence on CT parameters and inefficiencies in severe core saturation, the use of this method has not been expanded. This paper proposes a new method to improve the fixed switched resistor demagnetization method. In the proposed method, instead of using a fixed resistor in the circuit topology, an adjustable resistor with an auxiliary transformer is used. In the previous method, the control process is based on flux estimation from the secondary terminal voltage. The control process in the proposed method is based on the second derivative of CT secondary current. To verify the effectiveness of the suggested method, first simulation is done using COMSOL and MATLAB softwares and then all necessary electronic and control circuitry are designed and built. Experimental test is carried out on a 20 kV- 500/5 A CT. The simulation and experimental results show that this method prevents the CT from saturation in case of short circuit faults. The main advantages of this method are independent to CT parameters and efficient in severe core saturation. [ABSTRACT FROM AUTHOR]

The proposed method in the paper offers several key contributions. • Accurate detection of inrush current during the activation of crowbar and DC-link protection schemes in wind farms, specifically addressing the challenges of DFIG-based systems. • Effective differentiation between CT saturation and inrush currents, ensuring reliable detection in various operating conditions. • Utilization of harmonic phase signs (HPSs) for the 1st to 10th harmonics of the collector transformer (CTr) primary current, enabling real-time comparison with a predefined pattern for inrush current detection. • Distinguishing between inrush currents and internal faults of the CTr even during FRT of DFIGs, providing enhanced protection capabilities. As doubly-fed induction generator-based (DFIG-based) wind farms become increasingly widespread, the need for ongoing improvement in their protective studies becomes imperative. This paper focuses on the protection of the collector transformer (CTr), a key component of DFIG-based wind farms. One of the critical requirements for the differential protection of the CTr is the detection of inrush current. However, internal faults in the CTr can lead to harmonic interference and cause false detection of inrush current, resulting in the maloperation of the CTr differential protection. To address this issue, a new harmonic-based method for identifying inrush current in DFIG-based wind farms is introduced. The method is based on analyzing the phase signs of harmonics (HPSs) from the 1st to 10th harmonic. The proposed method ensures the accurate operation of the CTr differential protection and effectively distinguishes inrush currents from internal faults in the CTr. The effectiveness of the proposed method is validated through simulation and experimental results. The proposed method showcases several notable advantages, including precise detection of inrush current during the activation of crowbar and DC-link protection schemes, and effectively distinguishes between CT saturation and genuine inrush currents. [ABSTRACT FROM AUTHOR]