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Example PTP solutions (3.1. PTP timing in a new substation automation…

- - - - flexibility :check:more switches, more ports
      - reliability :warning: single of failure
      - robustness :warning: if a switch fails, how many items of HV plant will you lose control of?
    - - TC - :check: simple, work with Wireshark :red_cross:Consider the the case of a network failure between the root switch and the 132 kV switch. If the 132 kV switch was a transparent clock, each slave device (the protection relays) will “drift” away from the true time, and from each other, due to unavoidable manufacturing variations in their internal oscillators. The rate of drift depends upon a range of factors, including the quality of the oscillator and local temperature changes. If the outage is prolonged then the clock error between the individual 132 kV protection relays may become significant. This is similar to the situation where an IRIG-B cable was broken in a conventional timing system.
      - BC :check: provide a degree of isolation between the upstream grandmaster and downstream slave clocks. This is because they maintain a true clock internally, rather than just estimating residence times. :star: If the network connection to the grandmaster is lost the protection relays will remain synchronised to the boundary clock. The local time in the boundary clock will slowly drift away from the grandmaster, and hence the slave clocks will drift too—but at exactly the same rate. The quality of the internal clock references in the protection relays is now less important, as it is only the internal oscillator in the boundary clock that determines the drift rate.