If you’re still using NTP, IRIG-B, or other protocols that fail to provide time accuracy down to the nanosecond level, you’re probably spending more time and money than you need on synchronizing your substation automation system (SAS). These outdated solutions generally require engineers to set up and maintain a separate and dedicated network to synchronize all the nodes in the power grid.
The advent of Ethernet-enabled IEDs, merging units (MUs), and protection devices has prompted substation engineers to look to Ethernet protocols for new ways to synchronize their networks. Thanks to the IEEE 1588 v2 precision time protocol that was ratified in 2008 and included in the IEC 61850 Edition 2 communication standard for electrical substation automation, you can use an Ethernet switch to provide high precision time synchronization (less than 1 μs) by using a transparent and boundary clock to offset any time delay inside your network.
IEEE 1588 v2 from Top to Bottom
In a network based on IEEE 1588 v2, the grandmaster clock determines the reference time for the entire substation automation system. The Ethernet switch acts as the boundary or transparent clock, and power devices (such as merging units, IEDs, and protection devices) are designated ordinary clocks. All of these devices are organized into a master-slave synchronization hierarchy with the grandmaster clock at the top. As illustrated in the figure below, exchanging PTP packets between master and slave devices, and automatically adjusting the ordinary clocks, effectively achieves synchronization in a 1588 network.
Every Nanosecond Counts
According to IEC 61850 specifications, digital current transformers (CTs) and voltage transformers (VTs) provide sampled measured values (SMV) of current and voltage through MUs to bay level IEDs with the process bus. In any given system there may be a great number of MUs operating at once. These different streams of sampled values must be accurately time-synchronized before they can be used. SNTP is able to provide synchronization accuracy within about 1 ms.
As precise as 1 ms may be, it still is not accurate enough for raw data sampled values. In mission critical applications, such as fault recording, remote monitoring and control in a SAS, every nanosecond counts. Fortunately, you can use Ethernet switches that support IEEE 1588 v2 to fulfill precise time synchronization requirements for protection and control applications. These Ethernet switches guarantee time-stamping accuracy within 1 μs for the IEC 61850 process layer, and can be configured for 1588 v2 Master, Boundary Clock, and Transparent Clock functionality.
How 1588 v2 Benefits You
By taking advantage of increased accuracy, high data sampling rates, phasor measurements, and synchronized GPS based time stamping, PTP 1588 v2 significantly improves the smart power grid’s security and reliability. The substantial reduction in distribution losses and real time congestion relief is also boosting power utility company profits by allowing for:
- Blackout prevention through the early detection of grid problems, early location of disturbances, and real time power islands.
- More efficient use of assets through congestion relief and equipment condition monitoring.
- Demand response through time-of-use billing, virtual power generators, and outage management.
The Moxa Advantage
Moxa’s PT-7728-PTP IEC 61850-3 Fast Ethernet switches support the latest version of IEEE 1588 v2 technology to fulfill precise time synchronization requirements for electric power protection and control applications. In addition, the PT-7728-PTP offers:
- Up to 14 100BaseFO (Multi-mode ST connector) or 100BaseTX, ports and 1 BNC connector, support for IEEE1588 v1 & v2 hardware time stamping on each port, and pulse outputs (pps) on one BNC port.
- 1 and 2-step for both transparent and boundary clock operation for under 1 μs high precision time in End to End mode.
- 2-step for both transparent & boundary clock operation for under 1 μs high precision time in Peer to Peer mode.
- Network clock synchronization accuracy in the nanosecond range.
- Synchronization of clocks to support large and distributed substation networks.
- Low-cost implementation in multicast messaging networks such as Ethernet.
- Fast re-synchronization when system changes occur.
- Simple installation and maintenance.
Moxa manufactures device networking products for industrial automation. Information about all Moxa products, which include industrial embedded computers, industrial Ethernet switches, serial device servers, multiport serial cards, embedded device servers, and remote I/O servers, is available on Moxa’s corporate website at www.moxa.com.
Edited by Tim(oseam.icn@gmail.com) of Industrial Communication Network, www.icnweb.co.kr.
