MEASURED TIME-DELAY AND RE-SYNCHRONIZATION TIME IN DIGITAL MICROWAVE RADIO SYSTEMS

The transition from analog to digital transmission systems has been sl ower for Electric Power Utilities than other industrial sectors becaus e of concern that digital transmission system delay times could advers ely impact the response time of transfer trip protective relaying equi pment. Alcatel Network Systems has completed a comprehensive testing p rogram to measure the absolute time delay and various re-synchronizati on times through analog and digital transmission systems. The general conclusion is that the worst case absolute time delay of 577 microseco nds, VF to VF, through the digital microwave system is approximately o ne half the delay for a typical analog system. Absolute time delays of 500-600 microseconds should cause no problems to transfer trip protec tive relaying systems. The re-synchronization times encountered after any event that causes a break in the digital signal, such as the switc hing of hot standby transmitters on microwave systems, are of tremendo us concern to Electric Utilities. If a digital microwave system is des igned using hot standby transmitters and the assumption is made that o ne catastrophic event will cause simultaneous disruption of a power tr ansmission line and the microwave transmission system, then the signal disruption caused by switching hot standby transmitters must be taken into account in the design of the protective relaying system. These r e-synchronization times range from 11-19 milliseconds for a DS-1 inter face to 32-45 milliseconds for a VF interface through the digital chan nel banks.