Monitoring changes in system variables due to islanding condition and those due to disturbances at the utilities' network

The continuous growth in embedded generation (EG) has emphasised the importance of being able to reliably detect loss of mains (LOM) especially when the EG is 'islanded' with part of the utility network. Current methods of detection have not proved completely dependable, particularly when the 'islanded' load's capacity matches that of the EG. This paper is the result of an investigation, using the Alternative Transients Program (ATP), into new methods of detecting LOM. To determine which system variables can be reliably used to detect LOM, it is necessary to accurately monitor all the relevant signals at the LOM relay location. This requires that the simulation realistically detects all the changes in system variables caused by disturbances on the network. In some cases, the results can vary markedly, depending on such factors as measurement technique and sampling rate. These problems can cause numerical instability leading to errors. The paper discusses these issues and the results obtained from ATP.