Electric Utilities looking to implement precise timing solutions for improving resiliency, monitoring and troubleshooting capability of the transmission and distribution substations as well as gaining cost efficiencies by converging their timing and data communication networks will find that IEEE 1588 PTP v2 is now a mature timing and synchronization technology used extensively in the power and the telecommunication industries.
IEEE 1588 PTP (power profile) can be used to deliver sub one microsecond accuracy for power applications (IEC 61850 Edition 2).
In traditional substations, time synchronization of electronic devices has been realized via dedicated buses used for distribution of GPS, IRIG-B or 1PPS signals. With the transition to smart grid and automation of the substation, newer Intelligent Electronic Devices (IEDs) are capable of Ethernet connectivity and are enabled with packet based time synchronization protocols like NTP/SNTP and IEEE 1588 PTP.
Smart Substation with IEEE 1588 PTP Clocks
Though Network Time Protocol (NTP) or Simple Network Time Protocol (SNTP) have the advantage of being able to synchronize computers over a local area network, they do not have the accuracy required for the most demanding substation applications such as IEC 61850-9-2 Process Bus or IEEE C37.118-2005 Synchrophasors.
SNTP implementations provide accuracy of 1-3 milliseconds; they fail to achieve sub-one microsecond accuracy required for utility synchronization applications. Moreover, even where SNTP can deliver 1 millisecond, its behavior is indeterministic in heavily loaded networks.
The IRIG-B protocol provides an accuracy of 100 microseconds which is adequate for time stamping sequence of events recording and fault wave form capture, but falls short of microsecond accuracy for IEC 61850 Process Bus or Synchrophasor applications. Moreover IRIG-B requires dedicated cable to transport the timing signals which is costly and IRIG-B also offers no redundancy mechanisms.
GPS is a highly accurate timing solution but does not render itself to scaling well due to costs associated with cable installation and GPS is also vulnerable to interference, jamming and spoofing attack.
IEEE 1588 v2 on the other hand uses an Ethernet network to distribute timing signals, uses mechanisms that increase accuracy by accounting for switching time and peer to peer propagation delays that occur as timing signals traverse the network and ‘transparent clocks’ in Ethernet switches that eliminate the need for end-to-end delay measurement, reducing traffic congestion and eliminating switch jitter.
The IEC 61850 Station Bus is required to distribute accurate timing for IED fault recording, allowing the sequence of events that led to the fault condition be accurately time-stamped. This enables proper chronological sequencing of these events, thereby pinpointing the cause and corrective action.
The IEC 61850 Process Bus also needs to carry accurate time synchronization with precision of a few microseconds. Samples of 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.
Synchronized Phase Measurement Units (PMU) or Synchrophasors are used in the power utility industry to provide measurement of electrical quantities from across the power system at specific locations. The IEEE C37.118 standard for Synchrophasor defines how they should be time-stamped and communicated. To achieve the total accuracy of less than 1% as defined in the standard, it is required that timing accuracy is in the order of microseconds. IEEE 1588 PTP v2 is the only standard that can deliver this on a switched Ethernet network.
GNSS based satellite-synchronized clocks are a critical part of Synchroplasor timing subsystems.
Qulsar Qg 2 Grandmaster / Gateway clock solution includes ordinary / slave clock operational modes as well as boundary clock and master functionality. In addition, for indoor solutions, the system can be supplented with Quki to implement a full end to end in-building network.