Synchrophasor communication; Synchrophasor-Kommunikation;

ORIGINALARBEITEN Elektrotechnik & Informationstechnik (2014) 131/1: 8–13. DOI 10.1007/s00502-013-0193-6

Synchrophasor communicationT. Zseby, J. Fabini, D. Rani

Synchronized phasor measurements provide the basis for fine-grained wide area power quality monitoring in electric grids. Time-synchronized phasor measurement units (PMUs) are deployed at different locations in the grid and report 10–60 measurements/secondto energy management systems or other applications. For control applications it is crucial to receive measurement data as soon aspossible after a state change in order to trigger corrective actions in time to prevent incidents in the grid.

In this paper we analyze characteristics of synchrophasor M2M communication for different network technologies, including VDSL,HSPA and LTE networks. We briefly review synchrophasor communication approaches and real-time demands. We then emulate PMUtraffic and perform measurements on different networks. We show how the underlying technology influences one-way delay patternsfor synchrophasor communication, which has direct implication on the achievable real-time properties.

Keywords: phasor measurements; one-way delay; phasor measurement units; M2M communication

Synchrophasor-Kommunikation.

Synchronisierte Phasor Messungen stellen die Basis für Wide Area Monitoring Systeme in intelligenten Stromnetzen (Smart Grids) dar.Zeitsynchronisierte Phasor Measurement Units (PMUs) an verschiedenen Beobachtungspunkten senden 10–60 Messungen/Sekundean Energiemanagementsysteme und andere Anwendungen. PMU Messergebnisse müssen den Anwendungen möglichst schnell zurVerfügung stehen. Nur dann können Anwendungen korrigierend in Prozesse eingreifen und Störungen im Stromnetz verhindern.

In diesen Beitrag analysieren wir Synchrophasor Machine-to-Machine (M2M) Kommunikationsmuster für verschiedene Technologi-en, einschließlich VDSL, HSPA und LTE. Wir betrachten zunächst die Echtzeitanforderungen und die verschiedenen Ansätze für PMUKommunikation. Anschließend emulieren wir PMU Datenströme und führen damit Messungen in verschiedenen Kommunikationsnet-zen durch. In unseren Ergebnissen zeigen wir, wie die zugrunde liegenden Technologien die Verzögerungszeiten (One-way Delay), unddamit die Erfüllung von Echtzeitanforderungen, für die PMU Kommunikation beeinflussen.

Schlüsselwörter: Phasor Messungen; Verzögerungszeiten; Phasor Measurement Units; M2M Kommunikation

Received July 26, 2013, accepted October 16, 2013, published online December 12, 2013© Springer Verlag Wien 2013

1. Introduction

Phasor measurement units (PMUs) are time-synchronized devices

that measure power quality parameters, such as current, voltage,

frequencies and phase angles. The collection of data from multi-

ple distributed time-synchronized PMU devices allows the compari-

son of values from different locations and significantly improves the

situational awareness in the power grid. Synchrophasor measure-

ments can be used for post-incident analysis of events in the grid

(power outages, device failures, etc.), prediction of future values

and as input for control loops for the prevention of incidents. Es-

pecially if PMU measurements are used to prevent future incidents,

it is crucial that synchrophasor measurements reach energy man-

agement applications fast enough to trigger appropriate corrective

actions.

In this paper we investigate how different network technolo-

gies influence the latencies of PMU traffic. PMU traffic nowadays

is mostly transmitted via Ethernet (e.g. in substation LANs) or dedi-

cated fibers. Since PMUs become more widely deployed, we want to

check if typical access network technologies, which are widely de-

ployed, are suitable for the transmission of PMU traffic. For this we

emulate PMU traffic, perform measurements on Very-high-bit-rate

Digital Subscriber Line (VDSL), High Speed Packet Access (HSPA) and

Long Term Evolution (LTE) networks and compare results to timing

demands of different applications.

2. Related workXu and Fischione [1] recently investigated the transfer of data fordifferent smart grid applications over LTE networks. They measuredround-trip-times (RTTs) over an LTE network in Sweden with differentpacket sizes. For packets < 100 bytes they achieve mean RTTs below20 ms. They propose a new scheduler for LTE that prioritizes datafrom smart grid applications in order to reduce the latency over LTEnetworks.

In addition, some work has been done on modeling PMU traf-fic in order to simulate different PMU communication approaches.Chenine and Nordstrom [2] model synchrophasor communication inOPNET by generating 30 IP packet/s of size 76 bytes that containthe C37.118 encoded phasor measurements. They compare 4 sce-narios using dedicated or shared links for transmitting PMU data.Hasan, Bobba and Khurana [3] simulate PMU data flows in the net-work simulator ns-2 with 30 samples/sec of 128 bytes. Kansal andBose [4] calculate the size of the C37.118 data frames based on thenumber of PMUs and the number of phasors in a substation in orderto emulate PMU traffic.

8 heft 1.2014 © Springer Verlag Wien e&i elektrotechnik und informationstechnik

Zseby, Tanja, Institute of Telecommunications, Vienna University of Technology,Gusshausstraße 25, 1040, Wien, Österreich (E-mail: [email protected]); Fabini,Joachim, Institute of Telecommunications, Vienna University of Technology,Gusshausstraße 25, 1040, Wien, Österreich (E-mail: [email protected]); Rani,Dipika, Institute of Telecommunications, Vienna University of Technology, Gusshausstraße25, 1040, Wien, Österreich (E-mail: [email protected])

mailto:[email protected]



T. Zseby et al. Synchrophasor communication ORIGINALARBEITEN

Table 1. Delay requirements according to [4]

Application Latency requirements

Transient Stability 100 msState estimation 1 sSmall signal Stability 1 sVoltage Stability 1–5 sPostmortem Analysis None

In our paper we emulate PMU traffic based on specifications in themost recent C37.118 standard. We compare different technologiesincluding VDSL, HSPA and LTE. With our measurement setup wecan measure round-trip times as well as one-way delay on uplinkand downlink. We consider the latency for reporting measurementresults as most critical. Therefore we here concentrate on the uplinkperformance and measure the one-way delay from the PMU to thecollecting application.

3. Synchrophasor communication requirementsDepending on the application field, synchrophasor communicationneeds to meet different requirements with regard to transmissiondelays, bandwidth, availability and security. Kansal and Bose [4] de-scribe latency and bandwidth requirements for five key applicationsof PMU data. They distinguish different demands for the maximumacceptable latency between the occurrence of a state change andthe invocation of corrective actions (Table 1).

A description of the applications can be found in [4]. We use theserequirements as basis for our assessment of network technologiesand their suitability for PMU data transfer. In our experiments weonly measure the network latency for reporting state changes. Inorder to comply with the demands in [4] one has to add the timethat is needed to invocate corrective actions. This time depends onthe particular system and can vary.

4. Synchrophasor communication protocolsDepending on the application synchrophasor measurement dataneeds to be transmitted within local networks, within different net-works of one utility or among utilities. There are currently severaloptions to transmit synchrophasor measurements.

4.1 IEEE C37.118The IEEE C37.118 standard consists of two parts. IEEE C37.118.1 [5]specifies the measurement of synchrophasors and IEEE C37.118.2[6] describes a protocol for the real-time transfer of phasor data. Theprotocol defines four different message types: Data messages con-tain the measured values (phasors, etc.). Configuration messagesdescribe data types and meta data for the measurement data thatis sent in data messages. Header messages contain descriptive in-formation about the PMU and command messages are sent to thePMU to configure PMU settings, request configuration informationor data. IEEE C37.118.2 allows sending everything via TCP (TCP-only), everything via UDP (UDP-only) or sending data by UDP andeverything else by TCP (TCP/UDP method). The standard also men-tions a spontaneous data sending method for just sending the data(and optionally PMU configuration reports) by UDP without the useof any control messages.

We consider the UDP-only or TCP/UDP method as most suitablefor PMU communication. Disadvantages of using TCP for real-timePMU communication is that it requires bi-directional communica-tion, generates more traffic, and requires state keeping in the de-vices. Furthermore, TCP timeouts, re-transmissions and head-of-line

blocking effects can cause critical delays. TCP also does not supportthe sending of PMU data via IP multicast. Drawbacks when usingUDP is that it does not support reliable transport and that transportlayer security solutions (TLS) are not applicable.

4.2 IEC 61850The IEC 61850 standard [7] defines an architecture and data mod-els for communication in electric power systems. Originally devel-oped for the communication of Intelligent Electronic Devices (IEDs)in substations, IEC 61850 now includes a variety of communicationfeatures. It supports the sending of real-time data and supervisorycontrol functions using the Manufacturing Message Specification(MMS) over TCP/IP and the transmission of Generic Object OrientedSubstation Events (GOOSE) directly over Ethernet within substationLANs.

In 2009 IEEE and IEC started to work together on methods for syn-chrophasor communication based on IEC 61850 protocols. The jointwork led to a revision of C37.118-2005 in 2011 that splits C37.118into a part that describes the synchrophasor measurements itself(C37.118.1 [5]) and a part that describes the transfer of synchropha-sor measurement data (C37.118.2 [6]). With this C37.118 becamemore applicable to IEC standards, which generally separates mea-surement and communication specifications [8]. A second outcomeof the joint effort was the development of the technical report TRIEC61850-90-5 that describes synchrophasor communication usingC37.118 messages over IEC 61850. It also defines routable profilesfor IEC 61850-8-1 GOOSE and IEC 61850-9-2 Sampled Values (SV)packets in order to send such messages beyond the substation LAN.Historic developments of IEEE C37.118 and IEC 61850 are describedin [8].

4.3 PDC stackingPhasor Data Concentrators (PDCs) are devices that collect data frommultiple distributed PMUs. They can correlate and aggregate datafrom PMUs located within a local network (e.g. at a substation),in different networks of a utility provider or from different utilities.PDCs use the data received from PMUs to generate a new datastream that is then sent to an Energy Management Systems (EMS),data archiving or other applications that take the measurement asinput. PDCs can perform quality checks on the measured data, checkflags and provide interface to SCADA systems [6]. Multiple PDCs canbe deployed in a hierarchical structure or in a chain. The use of PDCshelps to aggregate and preprocess data on the way to the applica-tion that processes the data, but also introduces additional delays.

4.4 IP multicastUsing IP multicast for PMU data transmission has been proposedby Cisco Systems in [9] and is a suitable option according to IEEEC37.118.2 [6]. PMUs simply send their data to an IP multicast group.PDCs or applications that process the measurement data subscribeto the multicast groups of interest. For PMUs that are not capableof sending IP multicast packets, the first hop router can translate IPunicast packets to IP multicast packets [9].

IP multicast provides an efficient standardized solution to send thesame set of packets to multiple receivers, without sending multipleduplicates of the packet over the same link. Configuration of multi-cast routing and group control can be quite complex, but there aresimplified multicast models, such as the Protocol Independent Multi-cast Source Specific Multicast (PIM-SSM) that are applicable to PMUcommunication and have been proposed in [9].

Jänner/Februar 2014 131. Jahrgang © Springer Verlag Wien heft 1.2014 9

ORIGINALARBEITEN T. Zseby et al. Synchrophasor communication

Fig. 1. Measurement setup PMU traffic emulation

5. PMU traffic characteristicsC37.118 standardizes mandatory reporting rates for PMUs depend-ing on the power line frequency. For 50 Hz systems, mandatory PMUreporting rates are 10, 25, and 50 frames per second (fps), whereasPMUs for 60 Hz systems should support reporting rates of 10, 12,15, 20, 30, and 60 fps. Lower and higher reporting rates are en-couraged by the standard, mentioning values of 1 fps or 100 fpsas possible options. When transmitting over IP networks, the PMUencodes the measurement results into a C37.118 data frame, addsa UDP or TCP header and an IP header and immediately sends it tothe network. Therefore the reporting traffic generated by a PMU canbe expected to be constant bit rate (CBR) with constant packet size.The effective packet size depends on (a) the measurement unit usedwithin the C37.118 frame (16 bit integer or 32 bit float), (b) thenumber of phasors included into the frame, and (c) the number ofPMU reports within one frame. An example C37.118 frame is in-cluded in Annex D of C37.118.2.

6. MeasurementsFor the measurements presented in this paper we use a minimumC37.118 data frame, including three 16 bit integer phasors, totaling48 bytes of data per C37.118 frame. As reporting rate we select theminimum mandatory frame rate of 10 frames per second (fps), beingthe only rate that must be supported both by PMUs on 50 Hz and on60 Hz power systems. As extensions we test performance for twoPMU frames per C37.118 frame (96 bytes) and, alternatively, thedouble reporting rate (20 fps) for 60 Hz Systems. The overall packetsize at IP layer (including IP and Internet Control Message Protocol(ICMP) headers) is 76 bytes for 48 byte C37.118 payload and 124bytes for 96 byte C37.118 payload.

We use the emulated PMU traffic to perform measurements us-ing the test setup depicted in Fig. 1. Measurement client (termi-nal) and server are both Linux hosts, global-time-synchronized us-ing the LinuxPPS kernel drivers, Network Time Protocol (NTP) andGlobal Positioning System (GPS) Pulse per Second (PPS) receivers.Only one of the depicted access technologies—HSPA, LTE or VDSLis connected during a specific measurement session. As access de-vices we use a Huawei E392 LTE USB stick for LTE measurement,the same device forced to HSPA-only for HSPA measurements and aThomson TG788a1vn VDSL Modem, configured for 768 kbit/s up-link (non-interleaved) and 8 Mbit/s downlink (interleaved) link capac-ity for VDSL tests. In addition we use an older Huawei E870 HSPAdevice, supporting a maximum downlink capacity of 7.2 Mbit/s toinfer on hardware-dependencies. As networks we use the publicmobile HSPA and LTE and fixed VDSL network of A1 Telekom Aus-tria AG.

The terminal host originates ICMP packets with pre-defined pay-load size at pre-defined points in time and records sending andreceiving timestamps. The measurement server, connected to theTU Vienna core network, timestamps incoming and outgoing ICMPpackets, too. Due to global time synchronization of client and server,we can compute accurate one-way delays of the transmitted pack-ets.

7. Measurement resultsIn the following we present the measurement results for the one-way delay measurements with different C37.118 frame sizes. Weperformed measurements with 10 fps and 20 fps for all three ac-cess technologies. Results for 20 fps turned out to be very similar tothe 10 fps tests regarding shape of the distribution and values. Wetherefore show only the diagrams for the 10 fps results. In the dia-grams we show the relative frequencies (primary y-axis, left) and thepercentiles (secondary y-axis, right). In all diagrams the last bin sumsup all measurements values equal to or larger than the displayedx-axis maximum value.

Figure 2 shows the results for uplink one-way delay measurementsfor VDSL and LTE. For both tested packet sizes VDSL achieves verylow latencies of 10 ms for more than 99 % of all transmitted pack-ets. With LTE the delay stays only below 20 ms for more than 99 %of the packets. Furthermore, the delay values for LTE are broader dis-tributed than those for VDSL, leading to a less deterministic behaviorfor the transmission.

The spikes in the LTE measurements probably originate from thehighly deterministic network behavior. The packets are sent global-time-synchronized with ms precision. The network is also clockedwith ms precision. Therefore we observe synchronization effects be-tween sending schedule and network timing and some delay val-ues occur more often than others. As verification for this presump-tion we have reversed the measurement setup of Fig. 1 such thatICMP requests measure LTE downlink and server-reflected echo mes-sages measure uplink. When adding artificial random microseconds-precision delay in the reflecting ICMP server as detailed in [10], theuplink.

Figure 3 shows downlink measurements for VDSL and LTE. Laten-cies for VDSL stay below 15 ms and for LTE below 10 ms for morethan 99 % of the transmitted packets. Furthermore, the delay valuesform quite narrow distributions, which leads to a more determinis-tic transmission behavior. It is worth noting that VDSL downlink issubject to significantly higher delay than VDSL uplink, despite thedownlink having the 10-fold nominal capacity of uplink. Main rea-son is interleaving, which is activated in downlink and deactivatedin uplink direction. For time-critical applications transferring data in



Fig. 2. One-way uplink delay for VDSL and LTE. Byte size represents actual C37.118 frame size

Fig. 3. One-way downlink delay for VDSL and LTE. Byte size represents actual C37.118 frame size

downlink direction it might be helpful to de-activate interleaving for

the downlink, too.

Figure 4 shows the results for the one-way delay measurements

on the uplink for HSPA and HSPA with the older E870 device. With

HSPA the delay for more than 99 % of all transmitted packets stays

below 50 ms. For HSPA using legacy modems (Huawei E870 mobile

broadband card, same HSPA network) we see much higher laten-

cies. For packet sizes of 96 bytes, more than 5 % of the transmitted

packets experience delays equal to or above 100 ms (Fig. 4d). With

latencies above 100 ms HSPA with the E870 device does not fulfill

requirements for transient stability as demanded in [4]. Furthermore,the latencies for HSPA with older equipment are much broader dis-tributed. So the transmission performance over the older technologyprovides a less predictable behavior.

8. ConclusionWe reviewed different options to transmit synchrophasor data andinvestigated the transmission of emulated synchrophasor traffic overdifferent technologies. For VDSL, LTE and HSPA networks accessedwith modern equipment the vast majority of packets experiences


ORIGINALARBEITEN T. Zseby et al. Synchrophasor communication

Fig. 4. One-way uplink delay for HSPA and HSPA-old. Byte size represents actual C37.118 frame size

latencies below 100 ms. For VDSL most values stayed even below10 ms. They are good candidates to fulfill requirements for transmit-ting synchrophasor data in time for many analysis and control appli-cations. With HSPA using older mobile broadband modem equip-ment more than 5 % of the packets experience delays equal to orlarger than 100 ms. Such latencies are too high for reporting PMUdata for transient stability applications.

AcknowledgementsThe authors would like to thank Waltraud Müllner and Werner Wie-dermann from A1 Telekom Austria AG, Philipp Svoboda and MarkusLaner from the Institute of Telecommunications for providing LTEmodems and SIM cards, which have facilitated measurements in mo-bile cellular networks.

References

1. Xu, Y., Fischione, C. (2012): Real-time scheduling in LTE for smart grids. In 2012 5thinternational symposium on communications control and signal processing, ISCCSP(pp. 1–6).

2. Chenine, M., Nordstrom, L. (2011): Modeling and simulation of wide-area communi-cation for centralized PMU-based applications. IEEE Trans. Power Deliv., 26(3), 1372–1380.

3. Hasan, R., Bobba, R., Khurana, H. (2009): Analyzing NASPInet data flows. In Powersystems conference and exposition. PSCE 09 (pp. 1–6). New York: IEEE Press PES.

4. Kansal, P., Bose, A. (2012): Bandwidth and latency requirements for smart transmis-sion grid applications. IEEE Trans. Smart Grid, 3(3), 1344–1352.

5. IEEE (2011): Standard for synchrophasor measurements for power systems. IEEE StdC371181-2011 revis. IEEE Std C37118-2005, pp. 1–61.

6. IEEE (2011): Standard for synchrophasor data transfer for power systems. IEEE StdC371182-2011 Revis. IEEE Std C37118-2005, pp. 1–53.

7. IEC 61850 communication networks and system in substation automation. 2005–2002.

8. Martin, K. E. (2011): Synchrophasor standards development—IEEE C37.118 amp; IEC61850. In 44th Hawaii international conference on system sciences, HICSS (pp. 1–8).

9. Cisco (2012): Whitepaper: PMU networking with IP multicast.10. Fabini, J., Abmayer, M. (2013): Delay measurement methodology revisited: time-

slotted randomness cancellation. IEEE Trans. Instrum. Meas., 62(10), 2839–2848.

Tanja Zsebyreceived her Dipl.-Ing. degree inelectrical engineering and herDr.-Ing. degree from TechnicalUniversity Berlin, Germany. Sheworked as a scientist at theFraunhofer Institute for OpenCommunication Systems (FOKUS)in Berlin, where she later becamehead of the Competence Centerfor Network Research (CC NET).From September 2011 to Febru-ary 2013 she was a visiting scien-

tist at the San Diego Supercomputer Center at the University of Cali-fornia, San Diego (UCSD). Since March 2013 she has been professorof communication networks at the faculty of electrical engineeringand information technology at Vienna University of Technology.



Joachim Fabiniholds a diploma degree (Dipl.-Ing.) in Technical Computer Sci-ences and a Ph.D. (Dr. techn.)in Electrical Engineering, bothfrom Vienna University of Tech-nology. After five years of R&D intelecoms industry he joined theInstitute of Telecommunications(formerly Institute of BroadbandCommunications) at Vienna Uni-versity of Technology in 2003,where he is teaching and leading

applied research projects. His main research interests include han-dover in heterogeneous access networks, measurement method-ologies and metrics in packet-switched networks, Location BasedServices and NGN architectures with particular focus on the IP Mul-timedia Subsystem and Evolved Packet System.

Dipika Ranireceived her bachelor in Elec-tronics and Communication En-gineering from S.B.M.N Collegeof Engineering, Rohtak, India.She is currently working as aproject assistant at the commu-nication networks group at theFaculty of Electrical Engineeringand Information Technology atVienna University of Technology.


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Synchrophasor communication; Synchrophasor-Kommunikation;