Precision Time Protocol Solutions

The Siemens Precision Time Synchronization solution is based on the IEEE 1588 v2 protocol that is capable of providing highly accurate timing signals over an Ethernet network and will become part of IEC 61850 Edition II. Precision timing solutions serve to increase efficiency and uptime by improving monitoring and troubleshooting capability while also reducing capital expenses by converging timing and data networks. With Precision Time Protocol enabled RUGGEDCOM products, it is possible to construct green-field PTP networks based on IEEE 1588 v2 or a migration path to get there using existing legacy IRIG-B IEDs.

IEEE 1588 v2 Applications and Solutions

Figure 1. The Modular Serial Device Server RS416 and Modular Managed Gigabit SwitchRSG2288 are synchronized with IEEE 1588 v2 for IEC 61850 Station Bus and Process Bus applications. 1588 v2 signals can also be synchronized with IRIG-B for distribution to legacy devices.

IEC 61850 Station Bus

Precision timing is required for IED fault recording on the IEC 61850 station bus allowing the sequence of events that led to a fault condition to be accurately time-stamped. With the events and timing recorded in the proper chronological order the cause of a problem can be quickly pinpointed and corrective actions taken. Siemens RUGGEDCOM devices are capable of receiving 1588 v2 through their Ethernet ports and distributing 1588 v2 or synchronized IRIG-B signal for legacy devices.

IEC 61850 Process Bus

Accurate time synchronization with the precision requirement of a few microseconds is essential for a properly functioning Process Bus. Sampled Measured Values of voltages and currents need to be synchronized between the Merging Units (MUs) and the receiving IEDs that perform the critical protection and control functions. Data shifted at the receiving IEDs by several microseconds will result in protection algorithm malfunction. The high speed fiber optic IEC 61850-9-2 Process Bus is used to transport the digitally formatted and time-stamped multicast Sampled Values.

Synchronous Phasor Measurement (Synchrophasors)

Synchrophasors are used in the utility industry to analyze the state of the power system and implement controls to maintain stability on the grid. Phasor Measurement Units, (PMUs), take measurements at given locations on the power system and calculate phasors that are synchronized to absolute time. The IEEE C37.118 Synchrophasor for Power System standard has provided a definition for synchrophasors and how they should be time-stamped and communicated. To achieve the total accuracy as defined in the standard it is required that the timing accuracy is in the order of microseconds and on a switched Ethernet network the only solution is to use IEEE 1588 v2.

Deploying IEEE 1588 v2 on an IEC 61850 Network

Synchronizing IEEE 1588 v2 with IRIG-B

In many situations it may be desirable to move to IEEE 1588 v2 in stages to examine the performance and benefits of the new protocol while still employing the existing protection and control IEDs that are using IRIG-B. Siemens RUGGEDCOM devices provide the solution by allowing a time conversion mechanism of the 1588 v2 protocol at the Ethernet ports to synchronize the IRIG-B signals on output. The IRIG-B signals are available over dedicated cabling with PWM or PPS outputs or integrated into serial port connections for legacy devices.

Precision Timing Source: Master / Grandmaster Clock Mode

The RUGGEDCOM RSG2288 has the flexibility to accept many time reference inputs including GPS in order to become the timing network Grandmaster clock. With these modes of operation, the RSG2288 can receive timing signals directly through GPS and through 1588 v2 over the network as a backup. The RSG2288 uses the Best Master Clock, (BMC), algorithm to determine and select the most accurate clock source as its timing input source. If there are existing GPS clocks in place with IRIG-B output, the RSG2288 can accept this signal as the timing source and convert it to IEEE 1588 v2 for distribution across the network.

Figure 2. The Managed Gigabit Switch RSG2288 accepts many clock inputs allowing back-up clock sources and connection to GPS clocks with IRIG-B output.

Transparent Clock Mode

The RSG2288 in transparent clock mode provides accurate propagation of timing signals without accumulation of timing jitter errors. The transparent clock measures peer to peer path delay and internal switch residence time.

Ordinary Clock Mode

RUGGEDCOM devices can be configured to fall back to their internal clock that has been synchronized to temporarily become the network timing master in case timing signals from GPS or other clock sources become lost.