Sync up: precision timing for smart grids
Time synchronization is the technology of making sure clocks agree — and we depend on it in all kinds of ways in our everyday lives. If your watch and the clock at the airport gate don’t match, you could miss your flight. If the stock ticker on the trading floor is out of sync with trades being posted, transaction errors could pile up. In some situations, synchronization to the minute is good enough, but in others, such as digital substations, precision down to the microsecond is critical.
Today, most power utilities use GNSS/GPS receivers at primary substations to receive satellite signals embedded with Coordinated Universal Time codes. The timing information gets relayed using IRIG (inter-range instrumentation group) signals through “hardwire” (direct cabling) to equipment such as digital fault recorders and differential relays to keep them all synchronized.
The trouble is that not all substations have such receivers installed. This setup is also limited in the number of devices connected and the length of the cables, which becomes increasingly challenging as more and more devices are deployed in substation switchyards. Furthermore, GPS signal reception can be disrupted by atmospheric disturbances, electromagnetic interference and even solar activities, causing timing loss. Past studies of digital fault recorders found fully half of them suffered from GPS timing loss at least occasionally.
These kinds of timing losses are a big issue in smart grid situations because many smart grid applications — such as synchrophasors to support the integration of distributed energy resources — require reliable and precise time synchronization to work properly.
Why time synchronization matters in distributed grids
In a traditional electricity grid, the flow of power is unidirectional from the source of generation to the endpoints where the electricity is consumed. An electric grid today, on the other hand, could have renewable sources such as wind and solar coming in at various points, making the flows multidirectional. Therefore, highly accurate, simultaneous and continuous monitoring are needed to avoid imbalances and detect DER islanding and other critical issues, and that monitoring capability demands extremely accurate micro- and millisecond-level time information.
Even before the arrival of smart grids, power utilities knew they needed better, more reliable time synchronization for troubleshooting purposes. Investigators reviewing logs in the aftermath of North America’s 2003 east coast blackout found conflicting time stamps on thousands of records across multiple grids — inconsistencies that made it extraordinarily difficult to reconstruct the incident and identify the root cause.
That led the North American Electric Reliability Corporation (NERC) to recommend internal clocks for disturbance measuring equipment be synchronized to within two milliseconds. While the sector overall has been slow to move on that guidance, the demands (and opportunities) of smart grids are spurring renewed interest and bringing the issue back to the forefront. New communications networking solutions are coming onto the scene to ensure reliable and accurate time distributions across the grid.
A new way to keep grids in sync
The new IEEE1588v2 standard combined with advanced network architectures make it possible to meet the NERC targets. IEEE1588v2 defines a Precision Time Protocol to synchronize clocks in a packet-switched network. It accurately distributes timing information to all substations connected to the network, using an algorithm to automatically compensate for accuracy loss incurred during packet transmission. In this way, it can act either as the primary timing source or as a backup to GPS timing in case of signal loss.
With the new standard, down-to-the-microsecond time synchronization is possible for synchrophasors, IEC61850 sampled values, differential protection and digital fault recording and other key applications. At Nokia, we support IEEE1588v2 with several products, including the 7705 Service Aggregation Router, the 7210 Service Aggregation Switch and the Network Services Platform. This enables utilities to distribute and manage time and frequency synchronization to all substations and devices inside substations.
Do not take a good “time” for granted. To learn more about synchronization for power utilities and what goes into the network architecture, I invite you to join my colleague Rob Wright and me for a webinar on October 19 at 11AM EDT. We’ll look at how to implement the standard and achieve the kind of highly precise time synchronization your network needs.