signature=bdc2c981d0d42e9ef4eccdd6455d2700,Residual Current Protection of a Meshed DC Distribution G...

摘要：

Due to the emergence of renewable sources of energy and the progress in sustainable technologies, it could become very interesting in terms of energy savings and cost efficiency to switch the consumer level of the electrical network from AC to DC. This way, less power conversion would be required, and the meshing of the grid would be possible, hence increasing the reliability and flexibility of the power supply. Meshing the grid, however, is a challenge in itself. Indeed, it can be desirable to have several power sources connected to the same system, in order to provide for all the loads connected to the network when one of the sources fails. But having multiple sources in the network also means having several grounding points. Using the AC grounding methods, such as resistive grounding, proves problematic. As a matter of fact, as there are several grounding points in the network, they form a loop in the ground where the current can flow. If the voltage across the grounding points is not null, then a current will be able to flow through the ground. In AC, this was not such a problem, but DC ground currents will corrode the infrastructure around the network, which will prove harmful over time. It is thus necessary to devise a new way of grounding the system. The method proposed in this MSc thesis is capacitive grounding, which consists of using capacitors to ground the system, instead of resistors or inductors. This will ensure that no current flows through the ground in steady-state, and will consequently prevent corrosion. Grounding the grid through capacitors enables the use of the residual current measurement method to protect the meshed network against ground faults. Coupled to a smart communication system that divides the network in protection zones, this method will ensure the selectivity of the protection scheme, and will also discriminate net currents circulating through the grid from actual ground fault currents. The protective relays will be able to determine where the ground fault is on the poles with the polarity of the residual current measurement, and will only disconnect that pole, leaving the other half of the network in operation. This selective disconnection will also help improve the reliability of the system, and the consumers will be able to use the network safely.

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