Time-out on synchronization sourcesAll synchronization interfaces has a time-out and a configured interface must receivetime-messages regularly in order not to give an error signal (TSYNCERR). Normally, thetime-out is set so that one message can be lost without getting a TSYNCERR, but if morethan one message is lost, a TSYNCERR is given.15.2.8.3 Synchronization alternativesTwo main alternatives of external time synchronization are available. Thesynchronization message is applied either via any of the communication ports of the IEDas a telegram message including date and time or via IRIG-B.Synchronization via SNTPSNTP provides a ping-pong method of synchronization. A message is sent from an IEDto an SNTP server, and the SNTP server returns the message after filling in a receptiontime and a transmission time. SNTP operates via the normal Ethernet network thatconnects IEDs together in an IEC 61850 network. For SNTP to operate properly, theremust be an SNTP server present, preferably in the same station. The SNTPsynchronization provides an accuracy that gives +/- 1 ms accuracy for binary inputs. TheIED itself can be set as an SNTP-time server.SNTP provides complete time-information and can be used as both fine and coarse timesynch source. However shall SNTP normally be used as fine synch only. The only reasonto use SNTP as coarse synch is in combination with PPS as fine source. The combinationSNTP as both fine and coarse source shall not be used.SNTP server requirementsThe SNTP server to be used is connected to the local network, that is not more than 4-5switches or routers away from the IED. The SNTP server is dedicated for its task, or atleast equipped with a real-time operating system, that is not a PC with SNTP serversoftware. The SNTP server should be stable, that is, either synchronized from a stablesource like GPS, or local without synchronization. Using a local SNTP server withoutsynchronization as primary or secondary server in a redundant configuration is notrecommended.Synchronization via IRIG-BIRIG-B is a protocol used only for time synchronization. A clock can provide local timeof the year in this format. The “B” in IRIG-B states that 100 bits per second aretransmitted, and the message is sent every second. After IRIG-B there numbers stating ifand how the signal is modulated and the information transmitted.To receive IRIG-B there are one dedicated connector for the IRIG-B port. IRIG-B 00xmessages can be supplied via the galvanic interface, where x (in 00x) means a number inthe range of 1-7.1MRK 511 287-UUS A Section 15Basic IED functions597Technical manual
