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					                                                                                                                                                                                                                 Work In Progress
Eastern Interconnection Phasor Project
           Part 1: Targeted Applications: Raw Data Utilization
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                                      Standards and Performance Task Team

                                                                              Prepared by
                                                                      A. P. Meliopoulos, CERTS
                                                                     George Cokkinides, CERTS
                                                           Georgia Institute of Technology, Atlanta, Georgia
                                                            Bruce Fardanesh, NYPA, Chairman of S&PTT
                                                                         Henry Huang, CERTS
                                                                          Matthew Ford, SEL
                                                                         Fahrudin Mekic, ABB

                                                                                                                   Contributors/Task Team Members

                                                                                                                                                                             Ullattil Manmandhan, ABB
                                                                                                                                                                                  Ray Hayes, AEP
                                                                                                                                                                              Matt Donnelly, CERTS
              Standards and Performance Task Team

Scope: The scope of the Standards and Performance Task Team includes coordinating
and acting as liaison to standards efforts, determining consistent and satisfactory
performance of synchronized measurement devices, and insuring the security of the data
in accordance with best practices and the terms of the data sharing agreements.

The task force has identified potential applications of phasor data. Each application
places specific requirements on hardware and firmware of GPS-synchronized equipment.
The following four classes of applications have been identified ordered in increasing
hardware/software feature requirements:

1. Streaming data to displays (or utilization of raw data)
2. Data filtering via state estimation methods
3. Real time dynamic analysis of system performance
4. Relaying applications with GPS-synchronized data

The goal of the task force is to define hardware and firmware requirements for each
application class. Another goal is to determine testing procedures for evaluating existing
GPS-synchronized equipment as well as future products.

The goals of the task force will be achieved with two documents. The first document
(present) is focused on determining the requirements for the first application class. The
second document will cover the other application classes.




                                             2
                            Table of Contents


Definitions ____________________________________________________________ 4
1. Introduction _________________________________________________________ 8
2. Data Accuracy ______________________________________________________ 12
3. Reliability of Data Delivery ____________________________________________ 14
  Data Reliability of GPS-synchronized Equipment _______________________________ 14
  Data Access _______________________________________________________________ 14
  Communications Standards _________________________________________________ 15
  Communication Layers _____________________________________________________ 15
  Physical Communications Layer _____________________________________________ 15
4. Suggested Minimum Requirements _____________________________________ 17
  GPS-synchronized Equipment _______________________________________________ 17
  Phasor Data Concentrators (PDC) ___________________________________________ 18
  Databases ________________________________________________________________ 19
  Communication Network ___________________________________________________ 19
5. Characterization of GPS-Synchronized Measurement Devices________________ 20
6. Characterization of Instrumentation Channels ____________________________ 22
7. EMC Issues ________________________________________________________ 23
8. References _________________________________________________________ 24
Appendix A: GPS-Synchronized Measurement Devices _______________________ 27
Appendix B: Instrumentation Channel Characterization ______________________ 28
  B.1 CT Steady State Response _______________________________________________ 28
  B.2 PT Steady State Response________________________________________________ 28
  B.3 CCVT Steady State Response_____________________________________________ 29
Appendix C: SuperCalibrator ____________________________________________ 33
Appendix D: Testing of GPS-synchronized Equipment ________________________ 36




                                        3
                                                                     Definitions
This section provides some useful definitions pertinent to GPS-synchronized devices,
communication protocols and communications media.

DFR – Digital Fault Recorder

DDR – Dynamic Disturbance Recorder

SER – Sequence of Events Recorder

PMU – Phasor Measurement Unit. A device that samples analog voltage and current
data in synchronism with a GPS-clock. The samples are used to compute the
corresponding phasors. Phasors are computed based on an absolute time reference
(UTC), typically derived from a built in GPS receiver.

PDC – Phasor Data Concentrator. A logical unit that collects phasor data, and discrete
event data from PMU’s and possibly from other PDC’s, and transmits data to other
applications. PDC’s may buffer data for a short time period but do not store the data.

Relay – An electromechanical or electronic device applied to the purpose of power
apparatus protection. A relay typically monitors voltages and currents associated with a
certain power system device and may trip appropriate breakers when a potentially
damaging condition is detected.

IED – Intelligent Electronic Device. A general term indicating a multipurpose electronic
device typically associated with substation control and protection.

UTC – Coordinated Universal Time (initials order based on French). UTC represents the
time-of-day at the Earth's prime meridian (0° longitude).

IRIG-B – Time transmission formats developed by the Inter-Range Instrumentation
Group (IRIG). The most common version is IRIG-B, which transmits day of year, hour,
minute, and second once per second, over a 1 kHz carrier signal.

GOES – Geostationary Operational Environmental Satellites. Operated by the National
Oceanic and Atmospheric Agency (NOAA). Two GOES satellites broadcast a time code
referenced to UTC. Clocks based on this transmission are accurate to 100 microseconds.

GPS – Global Positioning System. A satellite based system for providing position and
time. The accuracy of GPS based clocks can be better than 1 microsecond.

pps – Pulse-Per-Second. A signal consisting of a train of square pulses occurring at a
frequency of 1 Hz, with the rising edge synchronized with UTC seconds. This signal is
typically generated by GPS receivers.


                                           4
kpps – One thousand pulses per second. A signal consisting of a train of square pulses
occurring at a frequency of 1 kHz, with the rising edge of synchronized with UTC
milliseconds. This signal is typically generated by GPS receivers.

Sampling Rate – The number of samples (measurements) per second taken by an analog
to digital converter system.

Navigation – The mode in which GPS receiver has locked onto signals from three or
more satellites thus providing accurate time, as well as position.

COMTRADE-file format – COMTRADE file format is a standardized ASCII text or
binary file (2 formats), originally designed for Digital Fault Recorders. It can be used to
transfer locally recorded values from a PMU over to the central data storage.
COMTRADE ASCII format is not efficient for long-term data storage but could be used
for event file retrieval.

PhasorFile – A binary storage format that is used by PDC for long-term storage of
SynchroPhasor data. Currently, this format is not standardized, and may be left in such a
state as long as stored data is made available in an industry standard format (i.e.
COMTRADE).

Communications Related Terms

Unicast – UDP transmission from one host to another (source/destination). When talking
about a link on a network, typically a unicast link is inferred.

Broadcast – Data transmission from one host to many. The destinations will be all
computers on a network, for example, all the computers in the office building. With
broadcast, every computer on the network must be trusted.

Multicast – Data transmission from one host to many. Data is transmitted to a group IP
address. Any member of the group can access the address to receive the data. Anybody
can then join in this multicast group, and when a server sends to the group, everyone in
the group will receive the data. The advantage is that it is very simple to set up groups.

WAN – Wide Area Network, stretching across large geographical distances. Latency’s
can be very large, up to many seconds.

LAN – Local Area Network, within a small building or office. Very low latency between
endpoints on the network, often less then a couple ms.

VLAN – A simulated LAN that is spread across a LAN, but uses special IP addresses so
that it appears a “physically” separate LAN.




                                            5
Lossless data compression – Data stored in a lossless format can be retrieved exactly as
it was created.

Lossy data compression – Data that is stored in a lossy format will have degraded
accuracy when retrieved. However, more data can be stored in the same amount of
space. Lossy data compression should be applied with caution and is not expected to play
major role in synchrophasor data collection.

Communication Protocols Terms

IEEE 1344 – A highly efficient protocol for real time SynchroPhasor data. Typically
data is streamed in this format over UDP/IP or across a serial link.

BPA/PDCStream – A variant of IEEE 1344, widely used by the BPA PDC and HMI
software on the West Coast.

IEEE C37.118 – Related to IEEE 1344, but adds much needed capability. This protocol
and its associated standard are intended to replace IEEE 1344 and the BPA/PDCStream
protocols. Typically data is streamed in this format over UDP/IP or across a serial link.

OPC DA – (Open Process Control Data Access) OPC was created for industrial
automation, for use within a factory, for example. It is designed to share simple data
between computers running only Microsoft Windows®. There are 3 revisions that are
commonly used. Different revisions are generally not compatible. This protocol is
useful for simple data sharing between computers in a small LAN, but has serious
security and performance issues when deployed across a WAN. OPC uses TCP/IP the
underlying link.

OPC HAD – (Open Process Control Historical Data Access) an offshoot of OPC DA
which allows a client to request stored data. This is a separate protocol, and different
servers/clients must be developed.

OPC AE – (Open Process Control Alarms and Events) an offshoot of OPC DA, which
allows clients to be notified on alarm conditions. As with OPC HAD, this is a separate
protocol, and different servers/clients must be developed.

OPC XML DA – (Open Process Control XML Data Access) – An OPC DA protocol
designed for use across a WAN. This protocol uses the standard Web Services structure,
using SOAP and XML. This protocol is simple to work with and will allow PMU
devices that don’t run Windows® as an operating system, to be an OPC server for
providing data to any client. The OPC Foundation is creating a ‘Unified Architecture’
using the XML-based structure as the foundation for future development.

TCP/IP – TCP/IP is a low-level protocol for use mainly on Ethernet or related networks.
Most of the higher-level protocols use TCP/IP to transport the data. TCP/IP provides a
highly reliable connection over unreliable networks, using checksums, congestion


                                           6
control, and automatic resending of bad or missing data. TCP/IP requires time to
handshake new connections and will block if missing data is being resent.

UDP/IP – UDP/IP is a low-level protocol that is typically unreliable. However it
provides low-latency communication across Ethernet or related networks. UDP/IP does
not provide any error-control or resending of missing or bad data. The Application will
need to check data for correctness. UDP/IP however, does not require time for
handshaking and will not block, making it ideal for real-time data communications.

HTTP – HTTP is a protocol made popular by the Internet and web pages. Web pages
are transmitted using HTTP. It has also become the mechanism for the Web Services
Paradigm using SOAP and XML. HTTP uses TCP/IP as the underlying protocol.

FTP – FTP is the file transfer protocol. It is a simple protocol where a client can connect
and request a file to be downloaded. A separate data connection is automatically created
where the data is then transferred across the network while the command connection
becomes unavailable. FTP is commonly used to get recorded data from devices.




                                            7
                                                                  1. Introduction

Digital data acquisition equipment with GPS synchronization adds another dimension to
the utilization and application of the data. The technology is young and as such the
performance of similar equipment from different manufacturers varies. Yet, for the
smooth development of applications using this data in a multi-vendor environment, it is
necessary to develop standards that will accommodate the rapid development and
deployment of such applications. The purpose of this document is to define the desirable
performance characteristics of GPS- synchronized devices. It is very common to refer to
these devices as Phasor Measurement Units (or PMU) because of the fact that the first
application of the GPS-synchronized measurements was to provide the phasor of the
positive sequence components. Today, it is not appropriate to use this term. Indeed these
devices are simply data acquisition units with the capability to time tag the data with GPS
time precision, i.e. better than one microsecond. The applications of utilizing this data go
beyond the initial objective of computing the phasor of the positive sequence component.

It is important to recognize that the GPS-synchronized measurement devices are normally
part of the overall data acquisition and utilization system. Figure 1.1 illustrates the basic
components of the overall system as it may appear in a present application. The
equipment comprising the system is organized in three layers: (a) the measurement layer,
consisting of instrument transformers, instrumentation cables, burdens, signal
conditioning circuits and GPS-synchronized equipment (PMUs), (b) a data collection
layer, consisting of equipment that receive the data, align the data and transmit them to
the various application layers, and (c) application layers, which utilize the phasor data to
generate displays, view events, archive data, perform state estimation, dynamic analysis
and other tasks. Our objective is to characterize the performance of the overall system.

There are two major issues associated with this system: (a) what is the accuracy of the
collected data? and (b) what is the reliability of the availability of the data for various
applications. The accuracy of the data is determined at the measurement layer.
Specifically observe that the measurement layer contains analog and digital systems.
Once in digital form, there is no further accuracy deterioration. Therefore, accuracy
issues are confined on the analog system, i.e. the instrumentation subsystem. The
reliability of data availability depends on the communication channels and software. Both
of these questions are addressed in this document. It is important to recognize that the
requirements for each one of the posed questions depend on the end application or
applications for this system. This is the reason why several application layers have been
defined. The first application layer is to utilization of the system for streaming data (and
all display, visualization and animation of the data) as well as event capturing and
visualization.




                                             8
It is also important to recognize that the system beyond the data acquisition unit (PMU)
is a digital system and as such it is flexible. This means that in many cases it is possible
to enhance the performance of the system with additional software development. Such
possibilities are identified in this document.

It has been mentioned that the question of data accuracy is confined within the
measurement layer. The objective of this document is to identify the performance criteria
of the measurement layer, identify the sources of errors and characterize the overall
performance of the various components of the measurement layer as well as the overall
measurement layer for specific applications.

The GPS-synchronized equipment may be part of an information network so that the
information can easily become available to (a) users and (b) application programs. It is
important to note that GPS-synchronized measurement technology and in particular
communications and protocols are in a flux as advances provide better products and
better approaches. Therefore it is important to recognize that maximum flexibility should
be maintained to adapt to new products and approaches as they become available.




                                             9
  Measurement Layer                                                                                  Data Collection Layer
   Phase Conductor                                                              PMU                   Data
                                                                                Vendor C              Concentrator
                                  Current
                                  Transformer
                                                             Optional
                                                             Analog
              Potential
                                                             Signal
              Transformer
                                                             Conditioning
                                                             Unit         PMU                         Data
                                                    Burden
                                                                          Vendor A                    Concentrator



               Instrumentation
               Cables


                                                                                PMU                    Data
                                                                                Vendor B   Proprietary Concentrator
                                                                                           Protocol
                                                  Burden



  WAMS Application/Energy Management Layer
                                        Comtrade '91
                                        PC37.118/OPC
                                                                                      VPN/Internet
              Database
              Data Archiving
                                                      1
                                               ade '9
                                         Comtr

                                                                           18
                                                                     7.1
                                                                                       C
                                                                 3
                                                                                     OP

                                                              PC

             Planning
             Model Validation
                                                                                                         Real-Time Data

                                                                                                         Firewall
                                 Global Trigger
                                 System Reader               SCADA
                                                             State Estimator



                            Figure 1.1: Typical Instrumentation Setup


Figure 1.1 illustrates the basic components of the overall system as it may appear in a
present application. Note that the PMUs may be communicating to Data Concentrators
via a standard protocol. A PMU may also directly communicate with the VPN/Internet
infrastructure. There is also the possibility that a MPU may communicated with a data
concentrator via a proprietary protocol. The last approach is not recommended. As a
matter of fact, the recommended architecture for the Phase 1 EIPP is illustrated in Figure
1.2.




                                                              10
  Measurement Layer                                                                             Data Collection Layer
   Phase Conductor                                                              PMU             Data
                                                                                Vendor C        Concentrator
                                  Current
                                  Transformer
                                                             Optional
                                                             Analog
              Potential
                                                             Signal
              Transformer
                                                             Conditioning
                                                             Unit         PMU                   Data
                                                    Burden
                                                                          Vendor A              Concentrator



               Instrumentation
               Cables


                                                                                PMU              Data
                                                                                Vendor B         Concentrator

                                                  Burden



  WAMS Application/Energy Management Layer
                                        Comtrade '91
                                        PC37.118/OPC
                                                                                      VPN/Internet
              Database
              Data Archiving
                                                      1
                                               ade '9
                                         Comtr

                                                                           18
                                                                     7.1
                                                                                       C
                                                                 3
                                                                                     OP

                                                              PC

             Planning
             Model Validation
                                                                                                     Real-Time Data

                                                                                                     Firewall
                                 Global Trigger
                                 System Reader               SCADA
                                                             State Estimator



                     Figure 1.2: Recommended Instrumentation Setup

Figure 1.2 illustrates the basic components of the recommended overall system for phase
1 of the EIPP system. Note that the PMUs should communicate with the Data
Concentrators via the recommended protocol to provide streaming data. A PMU may also
directly communicate with the VPN/Internet infrastructure via standard protocols.




                                                             11
                                                             2. Data Accuracy
GPS-synchronized equipment has the capability to provide a data acquisition system with
the following precision:

   1. Time tagging with precision better than 1 microsecond (or equivalently 0.02
      degrees of phase at 60 Hz).
   2. Magnitude precision of 0.1% or better.

This precision cannot be achieved for the overall system in any practical application, i.e.
in the substation environment. In addition, depending on the implementation approach
and equipment used, the accuracy of the collected data and the reliability of the data
availability may differ. Typical GPS synchronized equipment (PMU’s) are very accurate
devices. However, the inputs to this equipment are scaled down voltages and current via
instrument transformers, control cables, attenuators, etc. We collectively refer to it as the
instrumentation channel. The instrumentation channel components are typically less
accurate. Specifically, potential and current instrument transformers may introduce
magnitude and phase errors that can be magnitudes of order higher than the typical PMU
accuracy. Although, high accuracy laboratory grade instrument transformers are
available, their application in substation environment is practically and economically
infeasible.

For the first layer of applications (i.e. data streaming and event capturing) the typical
accuracy of the overall system may be acceptable. Specifically for this layer of
applications, it will be assumed that the requirements are: (a) recording of phasor
quantities (positive sequence or segregated phase), (b) time precision of several
microseconds and (b) magnitude precision of 1%. For the phase 1 of the EIPP system we
recommend adaptation of the IEEE Standard C37.118 that specifies that the total vector
error should not exceed 1%.

It is noted that for applications beyond the layer 1, a total vector error of 1% may not be
acceptable. For these applications the data accuracy can be improved with two distinct
approaches: (a) improving the hardware or (b) by software-based correction methods.
The first approach is a practical impossibility. The second approach is described in
Appendix C. Specifically, it is proposed to use a “super-calibration” approach based on
state estimation.

The proposed architecture for implementing the “super-calibrator” is illustrated in Figure
2.1. Specifically, Figure 2.1 illustrates an alternative organization of the overall system,
which facilitates the super-calibrator implementation. It includes a Phasor Data
Concentrator (PDC) at the measurement layer. The best placement of this PDC is at the
substation. It is also proposed that the PDC receives data from all GPS-synchronized
equipment (PMUs) and other IEDs existing in the substation. The super-calibrator PDC
will apply error correction on the collected phasor data and align the data before


                                             12
streaming the data to the system data collection layer. The data error correction and data
alignment will be based on a state estimation approach using mathematical models of all
the substation equipment.

                                                                                        IED Vendor D
  Measurement Layer                                                                                                                     Data Collection Layer
 Phase Conductor                           i(t)
                                                                                                                                              PDC
         v(t)                          Current                                          Relay
                                       Transformer                                      Vendor C

                Potential
                                                                                                                      Data
                Transformer                                    Attenuator                                             Processing
                                        i1(t)      i2(t)      Burden                    PMU
                                                                                        Vendor A
                                                                                                                Substation                    PDC
                                                                                                                PDC
                 Instrumentation
                 Cables                                          Attenuator
                                                                              Anti-Aliasing
                                                                              Filters




                                                                                                        Proprietary
                     v1(t)                      v2(t)




                                                                                                        Protocol
                                                                                        PMU
                                                                                        Vendor C
                                                                                                                                              PDC
                                                            Burden



  WAMS Application/Energy Management Layer
                                                           Comtrade
                                                           PC37.118/OPC
                                                                                                       VPN/Internet
                     Database
                     Data Archiving
                                                                  ade
                                                            Comtr

                                                                                             8
                                                                                        11
                                                                                      7.
                                                                                                         C




                                                                                  3
                                                                                                       OP




                                                                               PC

                    Planning
                    Model Validation
                                                                                                                                   Real-Time Data

                                                                                                                                   Firewall
                                          Global Trigger
                                          System Reader                       SCADA
                                                                              State Estimator



                 Figure 2.1: Alternative Approach to Instrumentation Setup

Figure 2.1 illustrates the basic components of the recommended overall system for phase
2 of the EIPP system. Note that it is recommended that a data concentrator be placed at
each substation (substation data concentrator) to handle the data from all PMUs, IEDs,
relays, etc. The substation data concentrator could communicate with other data
concentrators. The substation data concentrator may also directly communicate with the
VPN/Internet infrastructure via standard protocols. The advantages of the proposed phase
2 EIPP system are: (a) the substation data concentrator can provide proper filtering of the
data via the super-calibrator (see Appendix C), and (b) the substation data concentrator
can “fuse” data into a minimum set of unique data, i.e. bus voltages, circuit currents, etc.
but eliminating the redundant data. Best approach is via the functions of the super-
calibrator. This “fusing” of the data will drastically improve the throughput of the
system.


                                                                                13
                                        3. Reliability of Data Delivery

The reliability of data delivery depends on two requirements: (a) ability of the GPS-
synchronized equipment to output correct data continuously – for example, some
equipment may interrupt phasor computations for a short time, and (b) ability of the
communication layers to deliver data on-time.

Standards for item (a) above do not exist. Standards for item (b) exist in various forms
and in general are very complex. Discussion of these issues is provided below. For the
purpose of setting a goal regarding reliability of data delivery, the following requirements
will be placed for layer 1 applications:

   1. Correct data streaming from GPS-synchronized equipment will not be interrupted
      for more than 0.5 seconds and no more than once in 10 minutes.
   2. The reliability of the communication layer should be better than 0.999 with the
      ability to locally store data and avoid data loss.

This section presents discussion and evaluation of various options that affect reliability of
data delivery.


Data Reliability of GPS-synchronized Equipment

Present GPS-synchronized measurement equipment has different methods of data
generation priorities. For example dedicated GPS-synchronized equipment may have
independent channel for each measurement and computation of phasors frequency and
rate of change of frequency that is uninterrupted from other calculations. Other
equipment may use multiplexing and the priority of the phasor, frequency and rate of
frequency change computational algorithms may be affected by other functions. If the
priority of such computations is suspended, the accuracy of the data will be also
suspended.


Data Access

Present GPS-synchronized measurement equipment has different methods of data access
and different levels of data availability. For example one manufacturer outputs only the
phasors without access to the data of all three phases or point-on-waveform data. Some
devices have RS232 ports, other Ethernet, etc. Some devices are interfaced to data
concentrators at the substation and the data concentrator is charged with communications.
With the EIPP scheme, each GPS synchronized measurement device should
communicate with the PDC and each PDC should communicate with other PDCs. In
other words there are several levels of communications.


                                             14
Communications Standards

Within WECC, much work has been performed that resulted in standards for
communicating and transferring data. The C37.118 IEEE Standard defines the data
formats for PMU to PDC communications. WECC has also defined a standard protocol
for PDC to PDC communications. These standards are usable today and should be
retained.

There is also activity in defining communications protocols for more general
applications. The IEC Technical Committee 57 Working Group 03 (TC57 WG03) has the
responsibility of developing a standard for telecontrol, teleprotection and associated
telecommunications for electric power systems. The group has created the IEC 60870-5,
a group of five utility-specific protocol standards. The IEC standard is being accepted by
all major manufacturers of intelligent equipment for utility applications.

It is important to note that there is a way to merge the C37.118 standard within the IEC
60870.

The issue of network and protocols is a very complex issue and a moving target. There is
a great deal of activity that has resulted in several interoperability projects and
demonstrations. On the other hand BPA/PNNL has invested a great deal of effort in
developing communications/network/protocols that are close to some standards but not
interoperable with the new IEC standard. The issue of standardization should be
extensively discussed and decisions taking early in the game. One way to approach it is
to develop filters/converters at the PDC level that will make the EIPP interoperable with
other IEDs. It is important to recognize that the deployment of relays with GPS-
synchronization is presently occurring and it will proliferate in the future. If we tap on
this resource, it will dramatically boost the EIPP project. As the industry is moving in
this direction, the two major issues will be: (a) interoperability (the relay manufacturers
are addressing this issue) and (b) throughput.


Communication Layers

Data communications are usually organized as multilayer entities. The lowest layer upon
which all others rest is the physical layer. A multitude of layers exits above the physical
layers, where various protocols are implemented. Detailed analysis and evaluation of
each communication layer is beyond the scope of this document. However, it is useful to
touch on the requirements of the bottom layer – the physical layer.


Physical Communications Layer

There are several options for implementing the physical communications layer of the data
transfer:


                                            15
   •   Serial asynchronous communication channels (RS-232, 9.6 to 64 kbps)
   •   10/100 Mbps Ethernet network interface
   •   SONET

The RS-232 standard is relatively simple and has been effectively used for many years in
transferring data from PMU’s to data concentrators. The main drawback of the RS-232
based communications is limited bandwidth. Table 3.1 illustrates the bandwidth
requirements of PMU data transfers as a function of number of channels, and data format.
The communications channel bandwidth is expressed in kilo-bits per second (kbps). The
table assumes a rate of 60 phasors per second for each channel. The data from each
sampling instant are organized into packets which include the phasor values as well as
additional information such as PMU identification and status codes as defined in the
IEEE C37.118 Standard.
        Table 3.1: Required Communications Bandwidth for PMU Data
  Number of            Required Bandwidth                  Required Bandwidth
   Phasors            (16 Bit Integer Format)         (32 Bit Floating Point Format)
      2                      15.3 kbps                            21.1 kbps
      4                      19.2 kbps                            28.8 kbps
      6                      23.0 kbps                            36.5 kbps
     12                      34.6 kbps                            59.5 kbps
     24                      57.6 kbps                           105.6 kbps
     100                     203.5 kbps                          397.4 kbps

Comparing the required bandwidth to that of a standard 56kbps RS232 port it is
concluded that RS232 is usable for up to 24 channels for 16 bit integer phasor
representation, or 12 channels for 32 bit floating point phasor representation. Thus, for a
higher number of channels a different communications hardware layer must be selected.
For example, it is estimated that a 10Mbps Ethernet will support up to 1500 phasors
originating from 150 different PMU’s at a rate of 30 samples/sec, while a 100Mbps
Ethernet will support 15,000 phasors originating from 1500 PMU’s.

It is expected that due to bandwidth requirements, data links beyond the PMU to local
PDC will require faster communication hardware layer such as 10/100Mbs Ethernet. It is
important to note that the Ethernet network to be used for real-time phasor data
communications must be free of data transfer latencies. It is possible to deploy such
networks with proper equipment and protocol selection. The details of this process are
beyond the scope of this document and are best handled by IT staff.




                                            16
                        4. Suggested Minimum Requirements

This section provides the minimum requirements for the various components of the
phasor measurement network. It is based on the discussions and analysis of the issues
presented in the previous sections. The suggested minimum requirements are deemed
adequate for the layer 1 applications of this system, namely streaming of phasor data and
event capturing.


GPS-synchronized Equipment

Table 4.1 summarizes the minimum requirements for phasor measurement units.

      Table 4.1: Phasor Measurement Equipment Suggested Minimum
                             Requirements

Specification                Suggested Minimum Requirement
Synchronization Mechanism    Data synchronized with UTC time from a GPS receiver with
                             accuracy of 1 microsecond or better.
Measured Quantities          Voltage phasor, Current phasors, Frequency (f), rate of
                             frequency change (df/dt)
Frequency Response           At least ± 5 Hz . -40 dB at frequencies above the sampling
                             Nyquist frequency, -60 dB at power system harmonic
                             frequencies
Raw Data Sampling Rate       Minimum of 1440 samples per second
A/D Conversion Resolution    12 Bits
Phasor Data Rate             Support IEEE 1344, upgrade to IEEE C37.118, Default: 30
                             samples per second
Streaming Data Format        IEEE1344, upgrade to PC37.118 in 2005 if available
Event Triggering             Over-Current, Under/Over-Voltage, Under/Over-Frequency,
                             Under/Over df/dt, status change
Naming of Event Files        New Standard under development (WG Report: File naming
                             convention for time sequence data)
Event Data Formats           COMTRADE
Event Data Types             Phasors, Optionally waveforms, Individual phase phasors
Event Data Record Lengths    10 cycles of pre-trigger data, 1 second total duration
(Waveform Data)
Event Data Record Lengths    30 seconds of pre-trigger data, 120 seconds total duration
(Phasor Data)
Event Data Retention         1000 events
Continuous Data Retention    14 days
(Phasor Data)
Data Link                    Ethernet (Optional leased line, dial-up, microwave)
Protocol                     UDP, (Optional TCP/IP)




                                           17
Phasor Data Concentrators (PDC)

A Phasor Data Concentrator is a logical unit that collects phasor data, and discrete event
data from PMU’s and other PDC’s, and transmits data to other applications. PDC’s
should have storage capability to buffer data for a reasonable time to allow data
alignment and other vital tasks. Thus, a PDC is capable of receiving, aligning, storing and
transmitting GPS-synchronized data. Table 4.2 below summarizes the minimum
requirements for a phasor data concentrator. The minimum requirements enable
applications of streaming phasor data and event capturing.

 Table 4.2: Phasor Data Concentrator Suggested Minimum Requirements

Specification                 Suggested Minimum Requirement
Input Data Format             IEEE1344, upgrade to PC37.118 in 2005 if available
                              Optional: COMTRADE, OPC
Output Data Format            COMTRADE. IEEE 1344. Upgrade to PC37.118 in 2005 if
                              available. (Optional: PDC Stream, PDCxchng)

Data Alignment                Adopt BPA standard*
Output Data Rate              It should support IEEE1344 and PC37.118 (future). Default
                              value: 30 samples per second
Streaming Channels            User Defined Configuration
Continuous Data Retention     32 Days

* We recommend adaptation of the BPA standard described in reference [19].

It is important to note that it is possible that a PDC may receive data from PMUs from
different manufacturers. Aligning data from different manufacturer PMUs may be a
complex task that requires knowledge of the characteristics of each unit. For application
level one, the alignment of data is done on the basis of the time tag that each PMU data
has. This may result in misalignments of several microseconds. For streaming data
applications and event capturing applications, this misalignment is not critical. For other
applications it may be critical.




                                            18
Databases

A database resides locally with the PDC to read record store and manage phasor data.
Table 4.3 below summarizes the minimum requirements for a phasor database. The PDC
software should be flexible to accommodate user selections.

       Table 4.3: Phasor Database Suggested Minimum Requirements

Specification                 Suggested Minimum Requirement
Data Recording Organization   Circular Buffer (new data overwrites oldest data) – Length of
                              buffer should be user selected
Data Retention                Archive important data
Data Compression              Lossless Compression
Input Data Format             OPC, PDCstream, COMTRADE. IEEE 1344. Upgrade to
                              PC37.118 in 2005 if available
                              Optional: (Optional PDCxchng, Phasorfile, XML)
Output Data Format            OPC. Optional: IEEE 1344, PC37.118, PDCstream,
                              COMTRADE, PDCxchng, Phasorfile, XML
Continuous Recording          Yes




Communication Network

The network comprises the physical communication paths for phasor data exchange.
Table 4.4 summarizes the minimum requirements for a network.

  Table 4.4: Communication Network Suggested Minimum Requirements

Specification                 Suggested Minimum Requirement
PMU to PDC                    Ethernet (Optional dial-up, microwave)
PDC-PDC                       Leased Line
DB-DB                         Internet (Optional NERCNet)
Bandwidth PMU to PDC          36800 baud (Optional 10/100 T-Base)
Security                      VPN/Internet
Latency                       20-100 milliseconds
Protocols                     See section 3




                                            19
                 5. Characterization of GPS-Synchronized
                                    Measurement Devices

Equipment for synchronized measurements from various vendors may have different
designs and therefore different ways of data acquisition and processing and different
precision characteristics. As an example, in a recent characterization of devices from two
different manufacturers we have found a difference of one degree at 60 Hz (this is
equivalent to 46 microseconds error). This error can not be ignored. When all PMUs
come from the same manufacturer, the systematic errors are irrelevant. However, in a
multi-vendor environment (which is the case presently, and as more manufacturers will
start offering GPS synchronization) this issue must be addressed. It is important to note
that PC37.118 provides instructions for compliance verification. As a minimum PMU
should be PC37.118 compliant.

The objective of this section is to identify the issues related to data acquisition, data
processing and data output of GPS-synchronized devices. The discussion in this section
will be used as a blueprint for testing GPS-synchronized equipment.

The following performance issues will be addressed:

Data Types
      Phasor (positive sequence)
      Phasor (segregated phases)
      Time samples

I/O Characteristics
       Reporting rates
       Computational algorithms
       Streaming data capability (throughput capability)
       Supported formats
       Time tagging
       Time tagging precision (true synchronization/multiplexing)

Precision characteristics
        Frequency error
        Magnitude error
        Phase error
        Total Vector Error
        Transfer function
        Output time latency

Disturbance recording capability


                                           20
       Trigger options
       Data length capability
       Throughput capability

Phasor computation priorities
       Determine whether phasor computations may be disrupted for any reason

This section describes the known approaches and the characteristics of each approach
relative to the above items. Appendix A provides a list of US products and their major
specification. The list in Appendix A will increase in the near future as more
manufacturers planning the release of new products with GPS-synchronization. In
addition, many foreigner manufacturers are already offering GPS-synchronized
equipment.

In view of the multiplicity of manufacturers, it is necessary and recommended that GPS-
synchronized equipment be tested to quantify their performance. Testing results are
available in the literature and from the manufacturer. It is also recommended that a
standard testing procedure be developed for characterizing this equipment. Appendix E
provides a proposal for this standard testing.




                                          21
    6. Characterization of Instrumentation Channels

High voltage instrumentation channels introduce errors to phasor measurements. The
level of error is dependent upon the type of instrument transformers, control cable type
and length and protection circuitry at the input of the A/D converters. Depending on the
instrumentation channel, the characterization of these errors may be possible. Reference
[35] provides some additional information. In most cases these errors can be accounted
for and corrected via software. Two approaches are very promising: (a) model the
instrumentation channel and provide model based correction algorithms, and (b) use state
estimation methods to correct the error. A combination of the two will be ideal. This
issue is very important to the EIPP.

Appendix B provides examples of instrumentation channel characterization and the
effects on the overall precision of the GPS synchronized measurements. We recommend
that further work be contacted to develop methodologies for characterizing the
instrumentation channel errors and algorithms to correct for these errors. This work
should be coordinated with the work on remote calibration.

It should be recognized that GPS-synchronized equipment may be also connected to
existing instrumentation in substations that may be for other purposes, i.e. metering.
Many times the instrument transformers are connected in an arrangement that generates a
phase shift, for example delta connection. The resulting phase shift must be accounted
for.




                                          22
                                                               7. EMC Issues
Synchronized measurement equipment is highly sensitive electronic systems that must
perform satisfactory under adverse conditions in the harsh electromagnetic environment
of a substation. There are two issues: (a) what should the withstand capability of the
equipment be and (b) how they should be installed (shielding, grounding and bonding).

There is a plethora of work in this area already. We recommend the following.

Equipment should be designed to withstand 3 kV of transient input voltages.

Equipment should be properly grounded.

Equipment should have a common mode rejection of -60 db minimum.




                                          23
                                                          8. References


1. IEEE Std 1344-1995, IEEE Standard for Synchrophasors for Power Systems,
    1995.
2. C37.118, IEEE Standard for Synchrophasors for Power Systems, 2004 Draft.
3. IEEE Std C37.2 – 1991, IEEE Standard Electrical Power System Device Function
    Numbers and Contact Designations.
4. IEEE Std 1379-1997, IEEE Trial-Use Recommended Practice for Data
    Communications Between Intelligent Electronic Devices and Remote Terminal
    Units in a Substation.
5. IEEE C37.111-1999, IEEE Standard Common Format for Transient Data
    Exchange (COMTRADE) for Power Systems, June 1999.
6. IRIG Standard 200-98, IRIG Serial Time Code Formats, May 1998,
    Telecommunications Group, Range Commanders Council, US Army White Sands
    Missile Range, NM.
7. K. E. Martin, J. F. Hauer, W. A. Mittelstadt and A. Ellis, “WECC
    Disturbance/Performance Monitor Equipment: Proposed Standards for WECC
    Certification and Reimbursement”, March 17, 2004
8. IEEE-PES-PSRC, Working Group H-8, K. E. Martin, Chairman, “IEEE Standard
    for Synchrophasors for Power Systems”, IEEE Transactions on Power Delivery,
    Vol 13, N0. 1, pp 73-77, January 1998.
9. IEEE C37.111-1999, IEEE Standard Common Format for Transient Data
    Exchange (COMTRADE) for Power Systems, June 1999.
10. IRIG Standard 200-98, IRIG Serial Time Code Formats, May 1998
11. IEC 60870, Telecontrol Equipment and Systems, Transmission Protocols.
12. A. P. Meliopoulos, F. Zhang, S. Zelingher, G. Stillmam, G. J. Cokkinides, L.
    Coffeen, R. Burnett, J. McBride, 'Transmission Level Instrument Transformers
    and Transient Event Recorders Characterization for Harmonic Measurements,'
    IEEE Transactions on Power Delivery, Vol 8, No. 3, pp 1507-1517, July 1993.
13. A. P. Sakis Meliopoulos, F. Zhang, and S. Zelingher, 'Power System Harmonic
    State Estimation,' IEEE Transactions on Power Systems, Vol 9, No. 3, pp 1701-
    1709, July 1994.
14. A. Arifian, M. Ibrahim, S. Meliopoulos, and S. Zelingher, ‘Optic Technology
    Monitors HV Bus’, Transmission and Distribution, Vol. 49, No. 5, pp. 62-68,
    May 1997.
15. B. Fardanesh, S. Zelingher, A. P. Sakis Meliopoulos, G. Cokkinides and Jim
    Ingleson, ‘Multifunctional Synchronized Measurement Network’, IEEE
    Computer Applications in Power, Volume 11, Number 1, pp 26-30, January 1998.
16. T. K. Hamrita, B. S. Heck and A. P. Sakis Meliopoulos, ‘On-Line Correction of
    Errors Introduced By Instrument Transformers In Transmission-Level Power



                                     24
    Waveform Steady-State Measurements’, IEEE Transactions on Power Delivery,
    Vol. 15, No. 4, pp 1116-1120, October 2000.
17. A. P. Sakis Meliopoulos and George J. Cokkinides, “A Virtual Environment for
    Protective Relaying Evaluation and Testing”, IEEE Transactions of Power
    Systems, Vol. 19, No. 1, pp. 104-111, February, 2004.
18. Evaluating Dynamic Performance of Phasor Measurement Units: Experience in
    the Western Power System, J. F. Hauer, Ken Martin, and Harry Lee. Interim
    Report of the WECC Disturbance Monitoring Work Group, partial draft of April
    28, 2004.
19. Synchronized System Measurement Networks in North America: Operating
    Process and System Formats Based Upon BPA's Phasor Data Concentrator, K. E.
    Martin. WAMS Working Note, June 1, 2004.
20. Integrated Monitor Facilities for the Western Power System: The WECC WAMS
    in 2003, J. F. Hauer, W. A. Mittelstadt, K. E. Martin, and J. W. Burns. Interim
    report of the WECC Disturbance Monitoring Work Group, June 25, 2003.
    (Available at http://www.wecc.biz/committees/JGC/DMWG/documents/).
21. "Performance of 'WAMS East' in Providing Dynamic Information for the North
    East Blackout of August 14, 2003", J. F. Hauer, Navin Bhatt, Kirit Shah, and
    Sharma Kolluri. IEEE/PES Panel on Major Grid Blackouts of 2003 in North
    America and Europe, IEEE PES General Meeting, Denver, CO, June 6-12, 2004.
22. "Dynamic Signatures Recorded on the "WAMS East" Monitor Backbone: August
    14, 2003 vs. Other Days", J. F. Hauer, Navin Bhatt, Rajesh Pudhota, Sujit
    Mandal, and Michael Ingram. Presented by J. F. Hauer to the IEEE/PES IEEE
    Work Group on Power System Dynamics Measurements, IEEE PES General
    Meeting, Denver, CO, June 7, 2004.
23. Juancarlo Depablos, Virgilio Centeno, Arun G. Phadke, and Michael Ingram,
    “Comparative Testing of Synchronized Phasor Measurement Units”, Paper
    presented at the IEEE/PES General Meeting, Denver, CO, June 2004.
24. S. Zelingher, G.I. Stillmann, A. P. Sakis Meliopoulos, “Transmission System
    Harmonic Measurement System: A Feasibility Study," Proceedings of the Fourth
    International Conference on Harmonics in Power Systems (ICHPS IV), pp. 436-
    444, Budapest, Hungary. October 1990.
25. A. P. Sakis Meliopoulos, F. Zhang, and S. Zelingher, "Hardware and Software
    Requirements for a Transmission System Harmonic Measurement System,"
    Proceedings of the Fifth International Conference on Harmonics in Power
    Systems (ICHPS V), pp. 330-338, Atlanta, GA. September 1992.
26. A. P. Meliopoulos, F. Zhang, S. Zelingher, G. Stillmam, G. J. Cokkinides, L.
    Coffeen, R. Burnett, J. McBride, 'Transmission Level Instrument Transformers
    and Transient Event Recorders Characterization for Harmonic Measurements,'
    IEEE Transactions on Power Delivery, Vol 8, No. 3, pp 1507-1517, July 1993.
27. Real-time applications task team, EIPP goals and objectives
28. EIPP evaluating dynamic performance of phasor measurement units, March 2004
29. EIPP Standards and Performance Task Team preliminary report, August 2004
30. Marzio Pozzuoli, Ethernet in Substation Automation Applications – Issues and
    Requirements, www.ruggedcom.com



                                      25
31. Cisco Systems, QOS Quality Of Service, web published document,
    http://www.cisco.com/en/US/tech/tk543/tech_topology_and_network_serv_and_p
    rotocol_suite_home.html,
32. IEEE Power Systems Relaying Committee, Application Considerations of UCA 2
    for Substation Ethernet Local Area Network Communication for Protection and
    Control,    http://www.pes-psrc.org/h/DRAFT%235(7-16-04)H6%20PAPER.zip,
    WEB published paper.
33. IEC 61850 consists of the several parts.
34. A. P. Sakis Meliopoulos and G. J. Cokkinides, ”Visualization and Animation of
    Instrumentation Channel Effects on DFR Data Accuracy”, Proceedings of the 2002
    Georgia Tech Fault and Disturbance Analysis Conference, Atlanta, Georgia, April 29-30,
    2002.




                                         26
       Appendix A: GPS-Synchronized Measurement
                                        Devices
This Appendix lists the presently available GPS-synchronized measurement devices for
power system applications. The list will always be a moving target since many data
acquisition system manufacturers are adding GPS synchronization capability. Presently
the US based manufacturers of this equipment are:

MACRODYNE 1620,
ABB 521,
SEL 421,
Arbiter 1133A

A checklist for the major specifications of any GPS synchronized device is given in
Table A-1.

  Table A-1. Specifications of US Based GPS-Synchronized Measurement
                                  Systems

                                                                   Device ID
                A/D Converter Technology
               A/D Converter Word Length
      Sampling Rate (samples per second per channel)
                  Automatic Calibration
                   GPS Time Tagging
                 Simultaneous Sampling
                GPS synchronized sampling
                  Voltage Input Isolation
                  Current Input Isolation
                   Anti-Aliasing Filters
                     Communications
              Support of IEEE Standard 1344
                 Support of IEEE C37.118




                                            27
                                       Appendix B: Instrumentation Channel
                                                          Characterization
This Appendix provides characterization of errors resulting from instrumentation
channels. The instrumentation channel may be current (CT based) or voltage (PT based
or CCVT based).


B.1 CT Steady State Response
The conventional CT steady state response is very accurate. The steady state response
can be extracted from the frequency response of the device. Figure B.1 provides a typical
frequency response of a CT. Note that the response is flat in the frequency range of
interest. It is important to note that errors may be present due to inaccurate determination
of the transformation ratio. These errors are typically small.


                          1.25                                                      45.0
   Normalized Magnitude




                                                                                            Phase (Degrees)
                                                               Magnitude


                          1.00                                                       0.0

                                                       Phase

                          0.75                                                      -45.0
                                 0     1       2        3          4       5    6
                                                   Frequency kHz


                          Figure B.1: Typical 600 V Metering Class CT Frequency Response


B.2 PT Steady State Response
Wound type PTs are in general less accurate than CTs. Again the steady state response
can be obtained from the frequency response of the device. Figure B.2 provides a typical
frequency response of a wound type PT. Note that the response is flat in a small
frequency range around the nominal frequency. Our work has shown that the higher the
transformation ratio of the PT the higher the errors will be.




                                                        28
                          0.0012


                          0.0008
             Magnitude
                          0.0004


                          0.0000
                                   0   500   1000        1500   2000    2500   3000
                                                Frequency (Hz)

                          90.00

                          45.00
           Phase (Deg)




                           0.00

                          -45.00

                          -90.00

                         -135.00
                                   0   500   1000        1500    2000   2500   3000
                                                Frequency (Hz)


       Figure B.2: 200kV/115V Potential Transformer Frequency Response


B.3 CCVT Steady State Response
By appropriate selection of the circuit components a CCVT can be designed to generate
an output voltage with any desirable transformation ratio and most importantly with zero
phase shift between input and output voltage waveforms. In this section we examine the
possible deviations from this ideal behavior due to various causes by means of a
parametric analysis, namely:

   •     Power Frequency Drift
   •     Circuit component parameter Drift
   •     Burden Impedance

The parametric analysis was performed using the CCVT equivalent circuit model
illustrated in Figure B.3. The model parameters are given in Table B.1:




                                                    29
                                        CP

         C1
               LC        RC
Vin
        A                                           RF
         C2                                                             Cable          RB Vout
                                                                        Model

                                             LF          CF
        LD




                        Figure B.3: CCVT Equivalent Circuit

                 Table B.1: CCVT Equivalent Circuit Parameters
                Parameter Description                         Schematic           Value
                                                              Reference
CCVT Capacitance Class                                                             Normal
Input Voltage                                                                      288 kV
Output Voltage                                                                      120 V
Upper Capacitor Size                                               C1             1.407 nF
Lower Capacitor Size                                               C2              99.9 nF
Drain Inductor                                                     LD             2.65 mH
Compensating Reactor Inductance                                    LC             68.74 H
Compensating Reactor Resistance                                    RC           3000 Ohms
Burden Resistance                                                  RB            200 Ohms
Ferroresonance Suppression Damping Resistor                        RF            70 Ohms
Ferroresonance Suppression Circuit Inductor                        LF             0.398 H
Ferroresonance Suppression Circuit Capacitor                       CF             17.7 uF
Cable Type                                                                          RG-8
Cable Length                                                                      100 Feet
Transformer Power Rating                                                           300 VA
Transformer Voltage Rating                                                       4kV/120V
Leakage Reactance                                                                    3%
Parasitic Capacitance                                              CP              500 pF

Figure B.4 shows the results of a frequency scan. Note that over the frequency range of 0
to 500 Hz the response varies substantially both in magnitude and phase. Near 60 Hz (55
to 65 Hz) the response magnitude is practically constant but the phase varies at the rate of
0.25 degrees per Hz.




                                             30
Table B.2 shows the results of a parametric analysis with respect to Burden resistance
and instrumentation cable length. Note that the system is tuned for zero phase error for a
short instrumentation cable and with a 200 Ohm Burden.

Table B.3 shows the results of a parametric analysis with respect to CCVT component
parameter inaccuracies. Specifically the varied parameters were the compensating
reactor inductance and the capacitive divider capacitance.

 Table B.2: Phase Error (in Degrees) Versus Burden Resistance and Cable
                                  Length

                                             Cable Length (feet)
                  Burden              10’          1000’         2000’
                Resistance
                 50 Ohms            0.077           -0.155           -0.365
                100 Ohms            0.026           -0.096           -0.213
                200 Ohms            0.000           -0.063           -0.127
                400 Ohms            -0.013          -0.047           -0.080
                1000 Ohms           -0.022          -0.036           -0.052

  Table B.3: Phase Error (in Degrees) Versus Capacitance and Inductance

                                             Inductance Error (%)
                Capacitance           0%             1%           5%
                 Error (%)
                    0%               0.000          -0.066           -0.331
                   -1%              -0.066          -0.132           -0.397
                   -5%              -0.330          -0.396           -0.661




                                            31
Figure B.4: CCVT Computed Frequency Response over 10-600 Hz




                            32
                                        Appendix C: SuperCalibrator

Background: GPS-synchronized equipment receives inputs from instrument
transformers, control cables, attenuators, etc. Many utilities will use CCVTs for
instrument transformers. While GPS-synchronized equipment are more accurate devices
than typical utility SCADA and other monitoring equipment, the overall precision of
GPS-synchronized measurements is limited by the instrumentation channel. For example,
while GPS-synchronized equipment has the capability of measuring the phase angle to a
precision of 0.01 degrees, the instrumentation channel may introduce a phase error that
may be ten times larger. In particular, CCVTs introduce an error to the measurement that
is appreciable at the power frequency as compared to the precision of PMU equipment
and very large with respect to PMU equipment at other frequencies. Depending on the
application, this performance may be unacceptable.

Conceptually, the overall precision issue can be resolved with sophisticated calibration
methods. This approach is quite expensive and faces difficult technical problems. It is
extremely difficult to calibrate instrument transformers and the overall instrumentation
channel in the field. Laboratory calibration of instrument transformers is possible but a
very expensive proposition if all instrument transformers need to be calibrated. In the
early 90's I directed a research project in which we developed calibration procedures for
selected NYPA’s high voltage instrument transformers [1]. From the practical point of
view, this approach is an economic impossibility.

We propose a viable and practical approach to correct for these errors. The approach is
based on an estimation process at the substation level for correcting for these errors.
Specifically, we propose to develop a methodology and a software product that will
perform as a “supercalibrator”. This product may reside at the PDC level, and it will
operate on the streaming data. The process is expected to be fast and therefore it will
introduce only minor time latencies. The procedure will maintain the data format
including the time tags of the data.

A brief description of the methodology follows. A detailed model of the substation (from
which PMU data are originating) will be constructed. This model will be an integrated
model, i.e. it will include the three phase model of the substation, the model of the
instrumentation channels that feed inputs to the PMUs and the model of the PMUs. As
the data stream, each set of data at a specific time tag will be processed via a general state
estimation process. The procedure will provide the best estimate of the data as well as
performance metrics of the estimation process. The most important metric will be the
expected value of the error of the estimates. The software will continuously display these
metrics and it will also store the computed metrics. The best estimate of the data will be
used to regenerate the streaming data flow.




                                             33
It is important to note that the proposed super-calibrator is also a tool for remote
calibration. Since these equipment are digital and since the super-calibrator will
determine what the “reading” of each device should be, a calibration factor can be
inserted into each channel of the GPS-synchronized equipment. This very simple method
is also very effective.




                                         34
                                                                              IED Vendor D
Measurement Layer
Phase Conductor                       i(t)


        v(t)                      Current                                     Relay
                                  Transformer                                 Vendor C

               Potential
                                                                                               Data
               Transformer                               Attenuator                            Processing
                                   i1(t)      i2(t)     Burden                PMU
                                                                              Vendor A
                                                                                             Substation
                                                                                             PDC
                Instrumentation
                Cables                                    Attenuator
                                                                       Anti-Aliasing
                                                                       Filters
                    v1(t)                  v2(t)
                                                                              PMU
                                                                              Vendor C         Proprietary
                                                                                               Protocol
                                                      Burden
              Appendix D: Testing of GPS-synchronized
                                           Equipment

This appendix defines testing procedures for GPS-synchronized equipment. It defines the
functions/accuracy/data reliability/noise immunity etc. and test procedures to quantify the
performance of the GPS-synchronized equipment to all these metrics. It provides
information on the type of testing that is appropriate for PMUs. The objective of this
testing is to characterize the performance of PMUs in a system wide environment.
Additional testing that is not included in this discussion is: (a) environmental testing of
the devices and (b) seismic testing.

The test system is illustrated in Figure D.1. It is a PC based testing procedure. The PC
generates the tests signals injected into the GPS-synchronized equipment under tests and
also collect the data from the GPS-synchronized equipment as well as data from high
precision GPS-synchronized instrumentation. The details of the hardware selection are to
be determined. The PC software includes two major modules: (a) an integrated high
fidelity power system simulator, (WinIGS-T) which can generate test waveforms for a
variety of power system operating scenarios (steady state, faults, switching transients,
harmonics etc). The simulator includes full 3-phase models of major power system
components (generators, transmission lines transformers etc) including explicit
representation of grounds. The models are physically based and represent phase to phase
asymmetries, frequency dependent phenomena, grounding effects etc. and (b) a
waveform analysis and comparison software package (XFM). This software has the
capability to compute even the smallest time/phase variations between two waveforms or
the smallest magnitude differences. This capability is necessary for the purposes of this
project. The program XFM is fully developed. The program WinIGS-T is also a
developed program – however this program requires continuous development for the
purpose of increasing the modeling capabilities of the program.

It is important to note that the same approach can be achieved by using the PC to “play”
back COMTRADE files into the relays. This approach will severely limit the testing
capabilities of the system. Another alternate approach is to use commercially available
simulators, such as the EMTDC. This approach will be costly and again it will be limited
by the size of the hardware. The proposed approach is much more flexible, its
implementation requires only a PC and the high precision GPS-synchronized
instrumentation.
                                                  digital


                                                                Relay
            PC                                    analog
                                   D/A

                                                                PMU
                     digital




                                                            Devices Under Test

                       High Precision
                     GPS synchronized
                   Data Acquisition System

                   Test Instrumentation

           Figure D.1: Test Setup for GPS-synchronized Equipment

The waveforms generated by the simulator are converted to analog form via a D/A
converter, and amplified to the standard voltage and current levels normally interfaced
with standard digital relay and PMU inputs. There are commercially available D/A
converter hardware.

The digital streaming data generated by the PMU or relay under test are transferred to the
same PC for accuracy evaluation. The accuracy of the phasor data is performed by
comparison to waveforms simultaneously captured by a reference data acquisition
system. The reference data acquisition system will be a high precision system with
simultaneous sampling capability and GPS synchronization. The reference data
acquisition system hardware will be selected on the basis of cost and requirements for
this testing.

The PMU data and reference data acquisition system data comparison is performed with
the aid of a second PC Software component (Program Xfm). This program has been
developed for the purpose of waveform and phasor data analysis (the first version of this
program was developed for NYPA for exactly this purpose – to compare waveforms.
Later it was further improved with work for ENTERGY. Recently this program has been
upgraded to commercial program running under any Microsoft Windows system). It
accepts data in many custom/proprietary formats, including standard COMTRADE files.
The software has extensive data analysis, plotting and visualization capabilities.
Analysis examples include harmonic analysis, frequency estimation, fault distance


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estimation, transformer thermal modeling etc. A notable feature that is particularly
useful for the present application is the waveform calculator. This feature allows any
operations among any number of the input waveforms to be easily defined by the user in
the style of a RPN (Reverse Polish Notation) calculator.

The proposed test setup will provide accurate performance evaluation of PMUs and
Digital Relays. Specifically, it will measure both magnitude and phase accuracy, under
various power system operating conditions, such as faults, harmonic distortion, frequency
swings, etc.

The proposed system will allow testing various GPS-synchronized equipment under
various conditions. For example in case of relay equipment with GPS-synchronization,
the proposed testing system it will be able to generate a plethora of disturbance data
going into the relay and at the same time will characterize the phasor data coming out of
the relay. This type of testing will reveal whether the phasor computations are less
accurate during this period, how long it takes after the disturbance has been removed for
complete restoration of phasor computations, etc. We do not know of any system that has
this capability presently.

It is expected that once this system is developed, it will be available to other organization
that may wish to set-up their own test facility.

The proposed system will address the following issues regarding GPS-synchronized
equipment.

Data Types
      Phasor (positive sequence)
      Phasor (segregated phases)
      Time samples

I/O Characteristics
       Reporting rates
       Computational algorithms
       Streaming data capability (throughput capability)
       Supported formats
       Time tagging
       Time tagging precision (true synchronization/multiplexing)

Precision characteristics
        Frequency error
        Magnitude error
        Phase error
        Transfer function
        Output time latency

Disturbance recording capability


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       Trigger options
       Data length capability
       Throughput capability

Phasor computation priorities
       determine whether phasor computations may be disrupted for any reason




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