Preparing for the Smart Grid evolution

The key objectives of a Smart Grid are “improving power grid reliability and efficiency, maintaining power quality, minimizing outages, and reducing waste,” according to a paper delivered at the 2014 EMC Symposium. “However, with the interconnection of a large quantity of diverse distributed energy sources in the grid, multidirectional power flows, and fast responses to the demands and power interchange transactions, the SmartGrid will become more complex to maintain and operate and insecure without adequate control.”¹

One of the major ways in which that control will be provided is through the use of a large number of FACTS devices “… for better, finer, and more effective line flow control, loss minimization, and voltage control.”¹ FACTS (flexible alternating current transmission system) devices use power electronic components ranging from slow thyristors through fast MOSFETs as switches. The faster the edge rate for the switched current pulses, the wider the noise bandwidth.

Because most existing FACTS controllers use thyristors or gate-turn-off thyristors that operate at a few-kilohertz rate with edge speeds of hundreds of microseconds, the noise spectrum can extend up to a couple of megahertz. This paper reported on the increased level in radiated electric-field and magnetic-field emissions measured near power lines from two substations when FACTS devices were operating.

Switching noise from the first station’s 138-kV overhead power lines was detected near the line but more than four miles from the source. In this example, a unified power flow controller installed in 1998 managed the 320-MVA capacity.

At a second station, a 100-MVA static synchronous compensator had been regulating the 161-kV bus level and stabilizing the power system since 1995. Although switching noise was measured 12 miles from the source, in general, the noise levels at the second station were 10 dB to 20 dB lower than at the first. As the author commented, “It is believed that the installation of [an] interfacing inductor bank and a harmonic blocking transformer … helped to reduce the noise level.”

A new generation of FACTS devices will switch faster and have wireless capabilities, which will create higher frequency EMC concerns. The paper concluded by suggesting that these new devices need to be better hardened with respect to EMI to reduce the amount of high-frequency energy being propagated.

Related standards activities

NIST

A number of Smart Grid-related presentations were featured at the 2015 EMC & SI Symposium. One dealt with the work of the electromagnetic interoperability issues working group (EMII WG) and the National Institute of Standards and Technology (NIST) Smart Grid team. According to the presentation, “The primary goal for this working group is to identify and focus on the critical parts of the Smart Grid and develop a strategy to implement effective EMC, including standards, testing, and conformity assessment, with particular focus on issues directly affecting interoperability of Smart Grid devices and systems.”²

Much of the groups’ work references a 2012 white paper about EMC analysis of the Smart Grid published by the Smart Grid Interoperability Panel (SGIP). Several EM environments were identified in the paper, such as residential, commercial, and industrial, and particular application-specific aspects of the Smart Grid itself—power delivery, bulk generation, transmission, distribution, substations, distributed energy resources, and control centers among others.

The objective is to identify EMC standards for each environment and propose a new one if none exists. This is done within a framework that includes the establishment of strategy to maintain EMC as the Smart Grid evolves. Congress has directed, as part of the U.S. Energy Independence and Security Act, that ”… NIST has primary responsibility to coordinate development of a framework that includes protocols and model standards for information management to achieve interoperability of Smart Grid devices and systems.”²

CISPR/ACEC

Also at the 2015 symposium, a workshop presentation by Don Heirman, chairman of the International Special Committee on Radio Interference (CISPR) and the IEC Advisory Committee on EMC (ACEC), dealt with how international standards cover Smart Grid issues. Heirman had a good opening line: “Electric energy is the ultimate just-in-time product.”3 Think about it.…

Systems Evaluation Group 2 (SEG-2) within the IEC has a role similar to that of NIST. “SEG-2 has the primary responsibility for the development of a framework that includes protocols and model standards to achieve interoperability of Smart Grid devices and systems.”³

Within the IEC, the terminology is a little different, but like NIST, it too has a number of specialized groups—here called technical committees (TC). For example, TC57 is dealing with power systems management and associated information exchange. The objective is to form a demand response standard that applies to energy management systems for interconnecting lines and industrial consumers and producers and supervisory control and data acquisition (SCADA).

There are project committees (PC) as well; PC118 is working on “… standardization in the field of information exchange for demand response and in connecting demand side equipment and/or systems into Smart Grid.”³

Metatech

A tutorial “Immunity for Power Station and Substation Environments” expanded on the latest edition of IEC 61000-6-5, Electromagnetic compatibility (EMC) – Part 6-5: Generic standards—Immunity for power station and substation environments. The original document was an IEC technical specification published in 2001. Because of the link between application-specific environments and EMC, up-to-date environmental information from 61000-2-5 was included, and the document was revised as an international standard. Unless a product is specifically covered by a separate standard, it will fall under the generic 61000-6-5.

This presentation includes definitions of the various physical areas making up a power station, an air-insulated substation, or a gas-insulated substation. For each of these examples, there is an inside protected area, inside interface and/or control room area, inside or from process area, and connections from outside (HV area and external telecommunications). Several tables group relevant standards and tests that apply to each area in each example.

A few standards are listed under the heading “Future Plans.” One of these, IEC 61000-4-19, deals with differential-mode conducted disturbances below 150 kHz. An accompanying note states, “Should be considered for equipment sensitive to AC power supply disturbances in the frequency range 2 kHz to 150 kHz, generated, for example, by PLC systems or power electronic equipment.”⁴

ARC technical resources

This presentation discussed the process of extending IEEE 1613 to cover more types of equipment and included highlights of several relevant test requirements. For example, IEC 61000-4-10 deals with oscillatory magnetic-field immunity. Switching high-voltage bus bars can cause this disturbance, which could affect electronic equipment installed in high-voltage substations. These tests are run in all three axes at 100 A/m. In contrast, the effect of slower 50-Hz magnetic fields in electric plants is tested at 100 A/m for 60 s and 1,000 A/m for 3 s.

IEEE 1613 acceptance criteria include the following:

No hardware damage occurs.
No loss or corruption of stored memory or data, including active or stored settings, occurs.
Device resets do not occur, and manual resetting is not required.
No changes in the states of the electrical, mechanical, or communication status outputs occur. This includes alarms, status outputs, or targets.
No erroneous, permanent change of state of the visual, audio, or message outputs results. Momentary changes of these outputs during the tests are permitted.
During the tests, SCADA analog values shall not change by more than 2% of full-scale values. After the test, accuracy must revert to the manufacturer-claimed accuracy.

The revised IEEE P1613.1 was adopted and now is 1613.1-2013 – IEEE Standard Environmental and Testing Requirements for Communications Networking Devices Installed in Transmission and Distribution Facilities. As stated in the presentation, “This standard establishes the electromagnetic (EMC) testing requirements for all devices and/or systems utilizing analog and/or digital technology installed in transmission and distribution facilities. These devices and/or systems may or may not include communication ports and may or may not be port powered.”⁵

Summary

A lot of the work occurring within the various IEEE, IEC, NIST, and commercial groups has been bookkeeping: Which of the existing standards applies to the new situations we likely will face with Smart Grid technology? However, there also are new requirements which have to be addressed either by extending an existing standard or by drafting a new one.

There also are commercial reasons to be sure that the standards applied to a new product are the right ones. As reference 5 concluded, one of the reasons that the update to IEEE 1613 was important is harmonization with IEC requirements, which enables faster access to larger markets. And, the presentation also stated, “Reliability will be enhanced by using harmonized EMC immunity standards for type testing.”⁵

References

Yu, Q., “Applications of flexible AC Transmission System (FACTS) Technology in SmartGrid and its EMC Impact,” IEEE EMC Symposium Proceedings, August 2014, pp. 392-397.
Koepke, G., and Young, B., “SGIP EMII Working Group and the NIST Smart Grid Framework 3.0,” IEEE EMC & SI Symposium Proceedings, MO-PM-4-2, March 2015.
Heirman, D., “International Standards View of Smart Grid EMC,” IEEE EMC & SI Symposium Proceedings, SC1 workshop MO-PM-4-5, March 2015.
Radasky, W. A, Ph.D., “Immunity for Power Station and Substation Environments,” IEEE EMC & SI Symposium Proceedings, SC1 Tutorial: MO-PM-4-4, March 2015.
Ramie, J., “EMC Testing of Intelligent Electronic Devices for Substations and Distribution,” IEEE EMC & SI Symposium Proceedings, MO-PM-4-3, March 2015.