Differential protection network for change in current systems with parallel generators

摘要

In systems, such as aircraft electric power generation systems, three phase AC generators are often operated in parallel when supplying power to load busses and differential protection networks are utilized in each phase of each generator for detecting current imbalance between the phase conductor at the load and the neutral conductor of each phase. In this invention there is provided voltage limiter means such as back-to- back Zener diodes across each of the current transformers related to the phase and neutral conductors which, in conjunction with the other portions of the differential protection networks: (1) prevents nuisance tripping on the occurrence of high current faults outside the differential protection zone (such as bus faults) due to normal variations of the current transformers, and (2) at the same time, provides differential protection for a generator channel over the required range, generally from very low differential fault currents to the very high differential fault currents. The high differential fault currents will appear as high through current faults for the unfaulted parallel channels.