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This study presents a study on the time when the short-circuit fault current in an MV distribution network will cross the zero point in the presence of DC offset affected by the local synchronous and/or induction machines. The motivation of the study is to examine using thyristors to bypass a series compensator in the network while the subsequent turning-off of the thyristors depends on the zero-crossing of the current. One of the main uncertainties is the DC offset in the fault current due to the machines connected locally, which may defer the thyristor turning-off. This possibility has been examined in this study and the results demonstrate the parameters of the machines that have most influence on the time when the fault current will pass the zero point. It is shown that machines with higher unit ratings usually cause more delays in comparison with smaller units.

To control power flow and manage fault level in meshed MV networks, back-to-back voltage source converters (B2B-VSCs) are being used. However, their high cost and relatively low efficiency are of concerns. Partially rated series compensators, such as SSSCs or UPFCs, are desired but come with the challenge of protecting the device during grid faults. Their potential of use has been limited in comparison with the fully rated back-to-back converters. This paper proposes a new system topology including thyristor crowbars and a varistor to protect the SSSC in an MV network and improve the reliability and flexibility of the network operation. Using the proposed method, the time required for isolating the series compensator from the grid is reduced from at least 20 ms, corresponding to the interruption time of conventional circuit breakers, down to 3 μs in the worst case in addition to the grid fault detection delay. The performance is evaluated by simulation. A small-scale single-phase prototype operating at 230 V/16 A is tested in order to demonstrate the concept.

A new packaging structure for clamping the temperature of a thyristor die is analysed in this paper. The proposed structure aims to absorb the heat released from the thyristor during a short circuit protection operation, to maintain the temperature within a defined range even when the current through the thyristor is temporarily very high. The defined range is below the maximum tolerable temperature and is controlled by using phase-change material (PCM). This has the potential to reduce both space and cost when compared to traditional packaging structures which utilise heat sinks. In the course of this investigation, a thermal model of a thyristor is used for comparison. COMSOL Multiphysics was used to simulate the thyristor temperature during a fault and the effect that the PCM has on the thyristor temperature. Experiments have been performed to verify the models and validate the feasibility of the proposed concept.

The main requirements of the wide-area monitoring system is to acquire the real-time measurement of state variables that can be provided by phasor measurement units (PMUs). The optimal PMU placement is the leading object of this paper, which is presented as an integer linear programming problem. The zero injection buses (ZIBs) and conventional measurements (CMs) enhance the system observability. In this paper, a novel integrated model is presented to consider the effects of the ZIBs and CMs for PMU placement. The proposed model considers limitations caused by ZIBs and CMs that have not been studied earlier. The single branch and single PMU outage, as two common contingencies, are also separately and simultaneously taken into account. The proposed method is applied to five different IEEE test systems (14, 30, 39, 57, and 118 bus) in order to demonstrate its effectiveness. The obtained results are compared with that of the other studies.

Magnetic gears (MGs) offer significant potential advantages relative to conventional mechanical gears, such as: no contact, no friction, no lubrication, inherent overload protection and free from noise and vibration. Despite of these superior features they have received little attention due to complexity of operation and relatively low torque density transmission. This paper introduces a new magnetic gear topology with a highly competitive torque density transmission capability. This configuration is inspired of combination of the traditional radial and axial flux MGs. The assurance of accuracy based on a basic design of axial flux magnetic gear dimensions leading to Proof-of-Concept “Arcuate Double-Sided MG”. The Proof-of-Concept seeks to provide a better solution to the problems of flux maldistribution and concentration compared to what has been proposed previously. Thus, torque density performance of this MG is intensively augmented. The cogging torque is also computed in further simulations. However, the above requires advanced numerical techniques and hence 3-Dimensional simulations for calculating localized flux density and the corresponding torque density. Completion of this development will mark an important milestone in magnetic gear technology, and significant performance improvement will be realized.