PMUPMUPMUPMUPMUPMU

PDCPDC

PDC

SIPS

PDCPDC

SPDC

PDC Phasor data concentrator PMU Phasor measurement unit SPDC Super data concentrator SIPS System integrity protection scheme

Synchrophasors Communication

by Herbert Falk, Solutions Architect, SISCO, USA

PAC.DECEMBER.2012

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The IEEE request to IEC for C37.118 dual logo in August 2009: The dual logo request was refused by IEC since IEC had protocol technology (IEC 61850-9-2) that could convey synchrophasor information. This resulted in a joint task force being formed between IEEE and IEC, which worked on methodologies/agreements that led to changes in IEEE C37.118 and the creation of IEC TR 61850-90-5

Besides these events, and the technical requirements for supporting synchrophasors, IEC TR 61850-90-5 was also designed to support the performance/use cases already supported by the Generic Object Oriented Substation Event (GOOSE) and Sampled Values (SV) parts of IEC 61850. The history of these requirements dates back to October 1995, and an integrated timeline/history of GOOSE, SV, IEEE Synchrophasors, and the resulting 90-5 can be found at the end of this article.

Requirements were developed, changed, and added. The initial focus of GOOSE and Sampled Values wa s on cont rol and automation applications. Some of these requirements were:

The development of the functional requirements for GOOSE performance. Initially, the original performance requirement was 4 msec in order to achieve protection

performance within a substation. It was revised to 3 msec with the publication if IEC 61850-5 in 2003

The development of Sampled Values, a streaming protocol, to allow high-speed sampled current and voltage measurements, from CTs and VTs, to be shared with mult iple IEDs . T he init ial measurement/deliver y rate, according to the UCAIug 9-2LE specifications were 80 or 256 samples/cycle for intra-substation

The development of security standards for IEC 61850, including GOOSE and Sampled Values. This development started in 2004 and was completed in 2007

In 2005, the work to use 61850 inter-substation and for substation-to-control center communications was started, but the technology of GOOSE remained non-routable although specified for use in these new communication architecture/deployments (IEC 61850-90-1 and IEC 61850-90-2)

In 2003 IEEE began the effort to transition from IEEE 1344 to IEEE C37.118 in order to improve the accuracy of the measurement of time-synchronized phasor measurements (synchrophasors). The need for this improvement was based on a post-mortem analysis of the 2003 North American blackout. In 2009, when the request for a dual logo standard was made, the IEEE

IEC TR 61850-90-5 is a protocol for transmitting digital state and time synchronized power measurement over wide area networks enabling implementation of wide area measurement and protection and control (WAMPAC) systems based on the IEC 61850 protocols commonly used in substation automation. The development of IEC TR 61850-90-5 was motivated by several major events:

The August 2003 blackout in the Northeastern United States: The analysis of this event indicated a need for a well-recogni zed synchrophasor standard that had explicit time synchronization/time-stamping algorithms. This was the major impetus for the creation of IEEE C37.118 to replace IEEE 1344 and the Eastern Interconnect Phasor Project (EIPP)

In May 2005, cyber security requirements were published regarding critical assets that indicated a need for securing wide area power system communications

In November 2006, the Eastern Interconnect Phasor Project (EIPP) was combined with Western and Texas initiatives to become the North American Synchrophasor Project Initiative (NASPI), which generates technical functional requirements for synchrophasor systems, architecture, and phasor measurement units

The article describes the requirements that lead to IEC 61850-90-5, overview of the technology, emerging implementation agreements, results of initial utility testing, and overall reliability of UDP/IP.

IEC 61850-90-5 Overview

Herbert Falk has been involved in

numerous projects involving the ap-

plication of information systems and

real-time communications technol-

ogy to automated manufacturing,

electrical distribution and automation

and power quality monitoring. He has

been a involved in the determination

of communication security needs and

standardization since 1996. In 1998, Mr.

Falk prepared the security specification

for UCA. Shortly thereafter, Mr. Falk as-

sisted in the design and implementa-

tion of SISCO’s first suite of “secure”

communication products. In 2000, Mr.

Falk completed an EPRI security assess-

ment of the United States Electric Util-

ity Infrastructure.

Additionally, Mr. Falk is a technical

leader within IEC TC 57 WG15 whose

scope is “Data and communication se-

curity in the field of IEC/TC 57”. He is

also actively involved in security efforts

within IEEE.

Function C37.118 IEC 61850 GOOSE and SV

Streaming Protocol Yes Sampled Values

Rate of Measurement/Reporting 10 -30 samples/sec. 80-256 samples/cycle (4800–15360 samples/sec.)

Natively Routable using IP Yes No. Must use bridged-routing (brouting)

Application Focus Situational Awareness Control

Standard Addresses Security No Yes

Communication profile fully specified No Yes

Measurement Specification for synchrophasors Yes No

Event Driven Capability No GOOSE

Protocol is semantically driven (e.g. object oriented) No Yes

Standardized configuration language No Yes

Comparison of IEEE C37.118 and IEC 61850table 1

Synchrophasor Measurements for IEEE C37.118.1

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IEC 61850-7-4 MMXU

IEC 61850-7-2 Objects DataSets Control Blocks

IEC 61850-7-4 GOOSE

IEC 61850-7-2 Objects 61850-8-1 61850-9-2

Control Blocks

Sampled Values

IEC 61850-90-5KDC

Transport LayerTCP

Session Protocol

IEC 61850-7-4 IP IP QOS: DSCP

UDP

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requirements for compliance with the standard under both steady-state and dynamic conditions. Time tag and synchronization requirements a r e i n c l u d e d . P e r fo r m a n c e requirements are confirmed with a reference model, provided in detail. This document defines a phasor measurement unit (PMU), which can be a stand-alone physical unit or a functional unit within another physical unit. This standard does not specify hardware, software, or a method for computing phasors, frequency, or ROCOF

IEEE C37.118.2: A method f o r r e a l - t i m e e x c h a n g e o f synchronized phasor measurement dat a bet ween power system equipment is defined. It specifies messaging that can be used with any suitable protocol for real-time communication between phasor measurement units (PMU), phasor data concentrators (PDC), and other applications. It defines message

types, contents, and use. Data types and formats are specified. A typical measurement system, as well as communication options and requirements are described

IEEE C37.118.1 remains as the global standard for defining the measurement technology for synchrophasors while IEEE C37.118.2 is the IEEE protocol to address current system requirements enabling IEC TR 61850-90-5 to be the basis for a more scalable, and secure, protocol to meet NASPI requirements. IEC TR 61850-90-5 has normative references to IEEE C37.118.1 as the method for measuring synchrophasors. The scope of IEC TR 61850-90-5 is to:

Enhance the 61850 object model for proper representation of synchrophasors

Provide a routable and secure protocol that can transmit either GOOSE or Sampled Value using those IEC 61850 Application Protocol Data Units (ADPUs)

Provide migration capability from the C37.118, and its typical deployment architecture, to that of IEC TR 61850-90-5

IEC 61850 Object Model Enhancements

IEEE C37.118.1 specifies how to measure synchrophasor measurements that are in the form of voltage or current vectors (e.g. magnitude and angle), frequency, and Rate of Change of Frequency (ROCOF). A goal for IEC T R 61850-90-5 was to find the proper IEC 61850 Logical Nodes to represent this information.

IEC Technical Committee (TC) 57 WG10 chose to utilize the

C37.118 and IEC 61850 standards were evaluated and resulted in the comparison shown in table 1.

Prior to the request for dual logo the NASPI activity created many more requirements for synchrophasor measurement. These requirements included the need for secure large scale wide area distribution of synchrophasor information across the North American continent. The joint IEC/IEEE task force developed a strategy to split C37.118 into two parts while accommodating a migration to IEC 61850 based technology to meet the NASPI requirements:

IEEE C37.118.1: Synchronized p h a s o r ( s y n c h r o p h a s o r ) measurements for power systems are presented. This standard defines synchrophasors, frequency, and rate of change of frequency (ROCOF) measurement under all operating conditions. It specifies methods for evaluating these measurements and

Figure 1 depicts

the major

technological

parts of IEC

611850-90-5.

The development of IEC TR 61850-90-5 was motivated by several events.

1 IEC TR 61850-90-5 Overview

includes

includes

includesTunnel

Detail Format

Choice of

Choice of

1...n

GOOSE

SV

Mngt

Session Identifier

SPDU Length

SPDU Number

Version

TurnofCurrentKey

TurntoNextKey

SecurityAlgorithms

Key ID

Length

Payload

Signature

Simulation

APPID

APDU Length

GoosePdu

General Format

includes

Session Identifier

Session Header

SecurityInformation

Session User Information

Simulation

APPID

APDU Length

GooseMngtPdu

MNGT APDU

Simulation

APPID

APDU Length

SavPdu

SV APDU

Simulation

SV APDU

APPID

DestMAC

VLAN

IEEE 802.1p

Frame Length

GOOSE or SV Ether type pack-ets + Ethernet

Pad Bytes

PDUs

PDUs

PAC.DECEMBER.2012

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measurement logical node (MMXU). However, there was a need to specify if the measurements were Protection Class (P-Class) or Measurement Class (M-Class) as defined in IEEE C37.118.1. To accomplish this, the result was to extend the IEC 61850 Calculation Method (ClcMth) enumeration to include P-Class and M-Class. The existing MMXU definition contained DataObjects that represented Voltage and Current measurements as well as frequency. However, IEC 61850 did not have a semantic for ROCOF. To provide an ROCOF measurement capability, IEC TR 61850-90-5 added the DataObject of HzRte (Hertz Rate) to the Measurement Unit Logical Node (MMXU). Another important aspect of synchrophasor information is to be able to understand the sampling rates. In IEC 61850, this is accomplished through the proper configuration of the pre-existing MMXU DataObjects of:

ClcMod (Calculation Mode): Since IEEE C37.118.1 allows the specification that the method of measurement should be periodic.The IEC 61850-7-4 value used for ClcMod is specified to be PERIOD

ClcIntvTyp (Calculation Interval Type): IEEE C37.118 typically is measured in per-second intervals. However, IEC T R 61850-90-5 needed to allow more flexibilit y to address other applications. Therefore, support for MS (millisecond), PER-CYCLE, and CYCLE interval types were added. To mimic the C37.118 capability, the MS value would be used

ClcIntvPer (Calculation Interval Period): Is set according to the value of ClcIntvTyp

IEEE C37.118 also allows discrete digital information to be conveyed. These semantics/DataObjects already existed in IEC 61850 as the individual members of DataSets.

IEC TR 61850-90-5 Routable Protocol

IEC 61850 has the Abstract Communications Service Interface (ACSI) that provides a definition of the various communications services supported by IEC 61850. Here we will concentrate only on those services of IEC 61850-7-2 that are utilized for synchrophasor exchange only according to IEC TR 61850-90-5 (Figure 1).

The MMXU Logical node is used to represent synchrophasor measured values which are generated as specified by IEEE C37.118.1

The information from the MMXU is placed into one or more DataSets whose transmission is controlled by the appropriate Control Blocks (e.g. GOOSE or Sampled Value Control Blocks). It should be noted that the DataSets can contain information other than just synchrophasor measurements

IEC TR 61850-90-5 defines new Control Blocks to handle the Routable 90-5 semantics. “RS” control blocks are used to control routable SV data and “RG” control blocks are used to control routable GOOSE state information

The DataSet and Control block combination determines which services will be utilized to exchange the DataSet information

Depending upon the control block (RS or RG type), an application message is created/encoded per the rules specified in IEC 61850-9-2 and IEC 61850-8-1 respectively

The application messages are enc apsulated in an IEC T R 61850-90-5 session layer, which provides security and management v i a t h e 9 0 - 5 s p e c i f i c K e y

IEC TR 61850-

90-5 enables

implementation

of wide area

measurement

and protection

and control

(WAMPAC)

systems based

on the IEC

61850 protocols

commonly used

in substation

automation.

2 Layout of IEC TR 61850-90-5 session protocol

IEC TR 61850-90-5 is a protocol for transmitting digital state

and time synchronized power measurement over wide area

networks .

Dest 1

Dest 2

Dest 1

Dest 2

WAN WAN

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Distribution Center (KDC) protocol The encapsulated application

messages are published via UDP/IP multicast services, which utilize the Differentiated Service Control Protocol (DSCP) to provide IP priority tagging so that the packets are less likely to be lost due to router congestion

In order to configure the new transport and control blocks, the Substation Configuration Language (SCL) of IEC 61850-6 was extended

The 90-5 session protocol provides the capability to convey groups of GOOSE or SV application messages (APDUs) in a single Session Protocol Data Unit (SPDU). It also has the ability to support secure tunneling of the Ethernet based GOOSE and SV packets to facilitate easier exchange between substations and control centers for the currently existing GOOSE and SV messages (Figure 3).

In order to provide security, the concept of “perfect-forward” security was implemented. The security paradigm was designed to allow encryption key rotation in such a manner that the subscriber is given advanced warning of when the next key rotation is to occur (TimeToNextKey) and to detect if it is out-of-sync with the current key.

IEC TR 61850-90-5 security mandates the use of a signature

over the entire SPDU contents. The signature is provided through the use of symmetric keys being applied to create a secure Hashed Message Authentication Code (HMAC). And finally, the 90-5 session protocol supports the ability to encrypt the SPDU payload contents.

The Session Protocol Data Unit (SPDU) is transmitted using multicast UDP/IP. In the past, the use of UDP/IP multicast has been problematic due to the packet delivery paths being difficult to determine/configure. Many IP multicast packets are delivered over every path that a router supports. In order to aid in the control and path determination, IEC T R 61850-90-5 specifies the use of the Internet Group Management Protocol, Version 3 (IGMP V3: RFC 3376). IGMP V3 differs from previous IGMP versions in that the subscription to a multicast address can be filtered based upon the source IP address of the publisher - known as “source filtering”.

Through the use of source filtering, routers can determine the appropriate path(s) through which to deliver the multicast, thereby preventing the delivery of the packet over all possible paths (Figure 4).

The key management and Key Distribution Center protocol is based upon Group Domain of

Interpretation (RFC 3547 – GDOI). GDOI provides the capability of the KDC to exchange keys securely via either clients requesting the keys or the KDC pushing keys to the appropriate subscribers. GDOI originally allowed keys to be associated with IP addresses only. This proved insufficient for the security model/requirements for 90-5. Therefore, the GDOI protocol was extended to provide key management based upon destination addressing, service, and DataSet definitions. This allows keys to be assigned and managed based upon its delivery service (e.g. GOOSE or SV) even if the destination address and DataSet contents are the same.

Migration of C37.118.2 to IEC 61850-90-5

There are several aspects of migration from IEEE C37.118.2 to IEC 61850 that are provided in IEC TR 61850-90-5. Key items that provide gradual migration toward IEC 61850 include:

Changes for IEC 61850-6 to support the configuration of C37.118.2 via SCL

Use of GOOSE or SV, in the context of 90-5, without explicit control blocks interaction being required. This allows the SCL configuration to be utilized and IEEE C37.118.2 to be replaced with IEC

The 90-5

session protocol

provides the

capability to

convey groups

of GOOSE or

SV application

messages

(APDUs) in a

single Session

Protocol Data

Unit (SPDU).

IGMPv2 - Filters on destination only IGMPv3 - Filters on destination & Filters on source address that makes sure routers can determine a consistent and optimum path

Free range IP multicast: IGMPv2 and IGMPv3 4

The Session Protocol Data Unit

is transmitted using multicast UDP/IP.

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IEC 61850 SCSM 61850-8-1 61850-9-2

IEC 61850-90-5

Transport Layer

Session Protocol

UDP

Use of data example3

Oct-95 Dec-01

Oct-95RP 3599

IEEE 1344 PublishedDec 95

Ethernet TestingNov 96 - May 97

SRS LAN SimulationJun 97

SV Implementation Agreements Started Aug 99

LAN Congestion Scenario PaperNov 97

Sep 96 LAN Simulation

Apr 98 GOMSFE 0.4 Jan 99

IEEE 1550

May 98 Goose Requirements

Sep 01 Goose Grammar

"Chicago 7" May 98

Feb 98 Scenario and WG10 - WG12

Sep 98 - Sep 01Work within IEC TC57 WG10

Sep 97 Discussion of results

SV Implementation Agreements Feb 04

IEC 61850-5Jul 03

Nov 06 EIPP Transitions to NASPI

Aug 03EIPP Started

Jul 05 IEEE C37.118 Published Dec-01

Jan-02Dec-95

61850 Security Work PublishedJun 07

May 04Start of 61850 Security Work May 03

UCA IUG Interest Group Formed

Dec 02Optical CT/VT Interest Group Formed

61850-90-1 and 90-2 ProposedApr 05

IEC 61850-90-2 PublishedJun 04

NorthEast US BlackoutAug 03

LAN Congestion Scenario PaperNov 97

Dec 072007 Energy Independence & Security Act

Aug 09PAP-13 Started

Dec 11IEEE C37.118.1 & 2 Approved

Sep 11IEC 61850-9-2 ED.2

IEEE Request for Dual LogoMar 09

IEEE /IEC JTF ProposedAug 09

IEC 61850-8-1 ED.2Sep 11

IEC 61850-90-5 CompletedOct 11

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TR 61850-90-5 without requiring the full IEC 61850-8-1 profile over TCP/IP (e.g. MMS)

The use of IEEE C37.118 has resulted in an architectural deployment entity known as a Phasor Data Concentrator (PDC) to be used in existing systems. The primary purpose of PDCs are to provide more scalable distribution of synchrophasor measurements since substation typically have limited communication capability and are not generally capable of distributing the measurements to the required number of clients. The other typical purpose of PDCs is to provide a measurement time-alignment function between measurements from different PMUs so that clients of that data are not required to provide this function (e.g. the PDC is an extension of the client applications). In the realm of IEC TR 61850-90-5, PDCs need to be configured based upon the proxy/modeling capability of 61850 and SCL. IEC TR 61850-90-5 contains

explicit modeling that supports the PDC concept.

Another issue being addressed is that of implementation agreements that explicitly define how to translate C37.118.2 information into IEC 61850 and how to utilize IEC 61850 Sampled Values to reliably deliver synchrophasor measurements. These implementations will be codified by IEC TC57 WG10.

History: The start of the IEC 61850 GOOSE requirements has its basis in the introduction of the ASEA high speed (4 ms) auxiliary tripping relay. This introduction occurred in the mid-1970s and had a direct impact on the performance requirements included in the EPRI RP 3599 report - known as the Utility Communication Architecture (UCA) version 1.0. At the time, there were several parallel standardization efforts that would in time impact IEC TR 61850-90-5. The major efforts were:

The potential standardization of UCA into an IEEE standard

IEEE’s work on synchrophasor standards. This work started before the publication of IEEE 1344 (circa 1995) and continues today with the publication of IEEE C37.118.1 and IEEE C37.118.2

IEC’s work on IEC 61850It is important to note that the

UCA/IEEE and IEC standardization activities were attempting to address the same issues within the industry and therefore would have competed with each other globally. In late 1996, it was agreed to see if the concepts of UCA, including the use of multicast for high speed peer-to-peer communication (i.e. the original GOOSE), could be harmonized/accepted as part of IEC 61850. The results are evident today in the fact that IEC 61850 (circa 2004) is an international standard and the UCA documents were placed into IEEE Technical Report (TR) 1550 for posterity.

In parallel, without coordination with IEC, IEEE continued to address the requirements of synchrophasors. The efforts within IEEE accelerated due to deficiencies found during the analysis of the August 2003 blackout. This effort resulted in IEEE 1344 being superseded by IEEE C37.118. When IEEE published C37.118, it approached IEC with a request for dual logo (circa March 2009). IEC rejected the request for dual logo since IEC 61850-9-2 (SV) and GOOSE were both capable of carrying synchrophasor information.

This refusal led to the creation of a Joint Task Force between IEEE and IEC, and thus the beginning of the d e v e l o p m e n t o f I E C T R 61850-90-5. Figure 5 shows the important events that eventually produced IEC TR 61850-90-5.

Relevant events - 1995 and December 20115

Figures 5 shows

the important

timeline events

that eventually

produced IEC TR

61850-90-5.

The 90-5 session protocol has the ability to support secure tunneling of

the Ethernet based GOOSE and SV packets.