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time-synchronization in-a-digital-substation-automation (ประโยชน์ของ IEEE…

- - - - Global Positioning Satellite
      - highly redundant
      - 10 nSec of UTC
      - use for Direct time syn. /a time source
    - - Inter-range instrumentation group time codes B
      - is the industry standard for GPS time synchronization
      - be applied in a substation for power quality and system stability monitoring, sequence of events recording and accurate time stamping for revenue billing (1 ms)
      - needs an external time source
      - IRIG-B time code can only be transmitted via dedicated twisted pair or coax cable
      - it is not a low-cost solution for time synchronization
      - needs an external time source
      - The accuracy of time sampled values depends on availability and quality of time synchronization can be in the microsecond range (typ. 100 ps)
    - - one pulse per second
      - high-precision time pulse from precision clocks like a GPS receiver that very precisely indicates the start of a second
      - 1PPS is sent to every user over separate lines and entails an enormous additional wiring effort
      - The accuracy of time synchronization of 1 PPS can be in the micro-second range (typ. 1 ps)
  - - - Simple Network Time Protocol
      - It is basically NTP but lacks some internal algorithms that are not needed for all types of servers
      - It is widely distributed in LANs or on the Internet
      - allows accuracy of time synchronization into the millisecond range (typical 1-10 ms)
      - suitable for a station bus but does not achieve the accuracy required by a process bus with GOOSE and SV messages
    - - Precision Time Protocol
      - standards IEEE 1588 and IEC61588 for time synchronization
      - It is a cost-efficient solution and can be applied on the basis of the existing Ethernet network in a substation
      - applies master/slave time synchronization mechanisms and sup-ports hardware time stamps.
      - has two versions and they are not directly compatible
      - IEEE 1588 v2 is required mostly for IEC61850-9-2 Process Buses or IEEE C37.118-2005 Synchrophasors in sub-station automation and can be converted to IRIG- B
      - Distributed clocks in end devices can be synchronized with IEEE 1588 v2 in the sub-microsecond range (type 30-50 ns)
- - - - has shorter frame sizes in order to reduce the bandwidth consumed by the network traffic messaging and requires minimum processor performance
- - - - End-to-End TCs (E2E)
        
        only measure the time taken for a PTP event message (those that get time stamped) to transit the bridge and provide this information to the receiving clocks in the correction field.
      - Peer-to-Peer TCs (P2P)
        
        use the peer delay mechanism and measure the port-to-port propagation delay time between two directly connected ports sharing the same communication technology. The peer delay mechanism is independent of the state of a port (master or slave). It operates separately in both directions of the link.