Smart Power Grid and Substation Automation

Introduction

Electric Utilities are looking to 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. IEEE 1588 PTP v2 has become a mature timing and synchronization standard in the telecommunication industry; the power industry has recognized that a network based precise and accurate time distribution protocol like IEEE 1588 PTP can be used to deliver sub one microsecond accuracy for power applications.


IEEE 1588 PTP v2 overcomes the drawbacks of previous solutions around accuracy, scalability and cost. For electric utilities, it meets the emerging timing accuracy need of the Station Bus and Process Bus eliminating the need to deploy a separate dedicated cable/bus for IRIG-B or 1PPS synchronization. With IEEE 1588, precise and sub microsecond time can now be distributed over the same Ethernet network that is used for data communications.

A power profile for IEEE 1588 v2 is currently being considered for inclusion in IEC 61850 Edition 2.

Why IEEE 1588 PTP v2?

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.

Subsation Automation with IEEE 1588

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.

IEC 61850 Station Bus

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.

IEC 61850 Process Bus

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.

Synchronous Phasor Measurement (Synchrophasors)

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 Solutions:

Qulsar’s Managed Timing Module (M64) and Managed Timing Boards (P62 or P64) can be used to construct green-field modern substations with IEEE 1588 PTP enabled devices. They can also be used to provide synchronization solutions to existing substations that are migrating towards the smart grid architecture.

Qulsar Managed Timing Module (M64) can be embedded as an IEEE 1588 PTP slave in IEDs to provide the PTP client functionality. It is a low cost, low power slave that accepts incoming PTP packets coming from Substation Grandmaster and provides 1PPS/TOD to the IED electronics.

Qulsar Managed Timing Board houses the Timing Module with additional electronics to function as a development/evaluation kit and can also be integrated as a IEEE 1588 master or slave inside Synchrophasor or IED. It has the flexibility to accept GNSS time reference as input in order to function as the Substation Grandmaster clock.

Qulsar Managed Timing Modules and Boards offer Grandmaster, Ordinary/Slave clock operation mode and are ideally suited for:



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