Shankar V. Achanta

Understanding and applying precision time protocol

Precise time synchronization has become a critical component of modern power systems. There are several available methods for synchronizing the intelligent electronic devices (IEDs) in a power system. In recent years, there has been great interest in providing time to the IEDs using the same infrastructure through which the data are communicated. Precision Time Protocol (PTP) is a promising technology for achieving submicrosecond synchronization accuracy between IEDs over Ethernet. This paper presents the protocol fundamentals and discusses considerations for designing power system networks to achieve submicrosecond accuracies. Specific provisions made in the profile for power system applications to support IEC 61850 substation automation systems are also discussed.

Millisecond, microsecond, nanosecond: What can we do with more precise time?

Our industry moves energy at the speed of light, at the flick of a switch. A transmission line transporting 1500 megawatts delivers the equivalent of 250 pounds of coal per second, already converted into a convenient form of energy. For decades, we considered time in seconds or cycles: such as fuse curves and breaker clearing times. About three decades ago, our thinking moved into milliseconds because we needed to get better at quickly understanding wide-area events, protection was getting faster allowing for more power transfer, and the technology made it possible. Over the past decade, we have come to appreciate how synchrophasors can help us understand, control, and protect our power systems. One electrical degree at 60 hertz is about 46 microseconds, so measurements accurate to ten microseconds give us accurate synchrophasors. Traveling-wave technologies can put nanosecond resolution to good use. Achieving nanosecond absolute time is practical, affordable, and useful. In this paper, we explore how more-accurate time can improve the performance of electric power systems.

Speed and security considerations for protection channels

Communications play a vital role in the fast and reliable operation of protection systems. Advances in communications technologies have enabled utilities to improve the speed, security, and dependability of these systems. Communications-based protection schemes have employed power line carrier (PLC), microwave, fiber-optic communications, time-division multiplexing, Ethernet, and spread-spectrum radio systems. Each communications transport system must provide low latency and be deterministic, secure, and dependable. Pilot protection schemes are not one size fits all. The clearing time requirements for a protected line or a breaker failure transfer tripping scheme can vary based on loading and system stability requirements. This paper describes the communications requirements for various protection and control applications, including channel time, channel asymmetry requirements, and jitter. We discuss the advantages and disadvantages of communications technologies, including PLC, microwave, fiber optics, synchronous optical networks, and spread-spectrum radios. We describe how network topologies can improve security and dependability. We also discuss cybersecurity practices that are suitable for securing protection communications links.

Mitigating the impacts of photovoltaics on the power system

Integrating photovoltaic generation plants into electric power systems can impact grid stability, power quality, and the direction of power flow. To minimize such impacts, this paper proposes a simple and practical solution that uses high speed control and radio communications to quickly reduce the output of the entire plant to match local loads and limit the amount of power flowing toward the closest substation. The paper discusses how the proposed curtailment algorithm can minimize the impacts on the power system, installed equipment, and protective relays while taking into account system parameters such as availability, latency, security, and dependability.

Apply a wireless line sensor system to enhance distribution protection schemes

Traditionally, utility crews have used faulted circuit indicators (FCIs) to locate faulted line sections. FCIs monitor current and provide a local visual indication of recent fault activity. When a fault occurs, the FCIs operate, triggering a visual indication that is either a mechanical target (flag) or LED. There are also enhanced FCIs with communications capability, providing fault status to the outage management system (OMS) or supervisory control and data acquisition (SCADA) system. Such quickly communicated information results in faster service restoration and reduced outage times. For distribution system protection, protection devices (such as recloser controls) must coordinate with downstream devices (such as fuses or other recloser controls) to clear faults. Furthermore, if there are laterals on a feeder that are protected by a recloser control, it is desirable to communicate to the recloser control which lateral had the fault in order to enhance tripping schemes. Because line sensors are typically placed along distribution feeders, they are capable of sensing fault status and characteristics closer to the fault. If such information can be communicated quickly to upstream protection devices, at protection speeds, the protection devices can use this information to securely speed up distribution protection scheme operation. With recent advances in low-power electronics, wireless communications, and small-footprint sensor transducers, wireless line sensors can now provide fault information to the protection devices with low latencies that support protection speeds. This paper describes the components of a wireless protection sensor (WPS) system, its integration with protection devices, and how the fault information can be transmitted to such devices. Additionally, this paper discusses how the protection devices use this received fault information to securely speed up the operation speed of and improve the selectivity of distribution protection schemes, in addition to locating faulted line sections.

Is your clock ticking all the time? Characterizing substation-hardened clocks for automation

Modern power systems rely on precise and accurate time signals for efficient operation. Time-based measurement of power system signals is now possible with high-speed signal sampling combined with precise time sources. This paper describes advances in time sources, protocols, and distribution methods supported by modern substation clocks. It also describes how each of these time sources and protocols is characterized for performance. Affordable time technology for power utilities has advanced from milliseconds of accuracy 40 years ago to a few tens of nanoseconds in the past few years. Time distribution capabilities have improved as well with new ways of distributing time over local-area and wide-area networks. Technologies like traveling wave fault location (TWFL) have been in existence for decades but did not advance for years. With advances in precise and accurate time sources as well as distribution, there has been a fresh look at TWFL. Applications based on TWFL, synchrophasors, and Sampled Values can now take advantage of nanosecond timing accuracies. These solutions depend on reliable substation clocks designed, built, and tested with the same rigor as other protection and automation equipment in the substation. This paper also describes some of the common failure modes for substation clocks and their recovery mechanisms, including how these conditions are tested prior to deployment. Substation clocks need to withstand the same electrical and environmental stress conditions that protective relays are designed to withstand. This paper describes test setups with pass/fail criteria to characterize substation-hardened clocks during these conditions.