passive method

Islanding is one of the important challenges in power networks in the presence of distributed generation which is considered an undesirable incident due to the possibility of damage to operators, network equipment and consumers. Therefore, it is necessary to quickly detect islanding and make a decision regarding the connection status of local distributed generation units in the network. In this paper, a passive islanding detection method is proposed using adaptive threshold-based instantaneous frequency droop characteristic. The proposed threshold limit is dynamically changed depending on under studied conditions in order to discriminate the island from load changes, capacitor bank switching, motor start-up and short circuit types. Two medium voltage networks of Cigre and 34-bus IEEE are used to evaluate the proposed method. The simulations are performed in Digsilent software and implementation of the proposed method carried out in MATLAB software. The simulation results indicate that the island is correctly detected with appropriate accuracy in a short period of time from other disturbances in the presence of wind, solar and diesel types of distributed generations.

Since a high percentage of faults in underground power cables occur at the joint location of these cables, identifying the cable joints location is one of the most important challenges for power distribution companies. In this paper, a passive method to detect the underground electrical cable joints based on the variations of magnetic fields at the ground surface is proposed. For this purpose, the magnetic fields above a long cable containing a joint at the middle were first simulated using CST software. Simulation results showed that when scanning along the cable, the magnetic field changes at the joint position which can be used for finding its location. Simulations were repeated for different joints located at different depths and in different soils. The advantage of the proposed method is that it does not need any external source and causes no interruption of electric power in underground power cables.