Industrial generator stability against prolonged grid voltage dips

The 1983 Energy Act allows private companies to run their machines in parallel with the grid, and to export excess power generated. Engineering Recommendation G59 includes a requirement that suitable undervoltage protection be installed to disconnect the private generator from an HV grid connection within 0.5 secs in case of 10% undervoltage, but it does not address specifically the requirements for the integrity of the private generation scheme in case of grid transient or dynamic disturbances over much shorter periods. Such requirements may be of prime significance for those installations where high security of supply is essential: imminent loss of synchronism of site generation with the grid supply should be detected and generators isolated before excess power flows cause shutdown of generation and uncontrolled disconnection from the grid. The authors briefly present the results of microcomputer stability studies which consider the effect of prolonged grid voltage depression leading to loss of generator synchronism, showing the times required for disconnection from the grid supply before pole-slipping occurs