Simplifying and Enhancing Automated Source Transfer Using Protection with PLC Capabilities

Source transfer for important electricity consuming customers has often been accomplished using discrete relays, such as overcurrent, overvoltage, undervoltage, differential and sync check, plus logic created out of auxiliary relays and timers, or programmable logic controllers (PLCs). The advent of advanced digital protection systems with programmable logic capabilities and the proper I/O structure can now allow the entire transfer protection and control to be accomplished by a single intelligent electronic device (IED), thereby simplifying and enhancing the process. Simplification is the result of the protection and logic being linkable in software so all interlocking, timing and sequencing functions are made in a single or minimal amount of IEDs by programming. Enhancements include the elimination of discrete device interwiring, the ability to have concise event logging for all protection and logic functions to aid in documenting successful sequences, diagnosis of incomplete sequences and asset management of the switchgear involved in the transfer process. The transfer types discussed and illustrated include hot parallel (non-sequential), residual voltage and time delayed (sequential)