IEEE C37.118 protocol

Description of the IEEE C37.118 protocol and its implementation in the Typhoon HIL toolchain.

Protocol introduction

Note: Only basic information will be presented in this section. For detailed information about the IEEE C37.118 protocol visit IEEE Standard for Synchrophasor Data Transfer for Power Systems

The C37.118 standard defines a method for exchange of synchronized phasor measurement data between power system equipment. It specifies messaging including types, use, contents, and data formats for real-time communication between Phasor Measurement Units (PMU), Phasor Data Concentrators (PDC), and other applications.

Note: Phasor Measurement Unit (PMU) is a device that produces synchronized phasor, frequency, and rate of change of frequency (ROCOF) estimates from voltage and/or current signals and a time synchronizing signal.

Synchrophasor definition

Phasor representation of sinusoidal signals is commonly used in ac power system analysis. The sinusoidal waveform defined as shown in equation below:

The synchrophasor representation of the signal x(t) in equation is the value where φ is the instantaneous phase angle relative to a cosine function at the nominal system frequency synchronized to UTC.

Under this definition, φ is the offset from a cosine function at the nominal system frequency synchronized to UTC. A cosine has a maximum at t = 0, so the synchrophasor angle is 0 degrees when the maximum of x(t) occurs at the UTC second rollover (1 PPS time signal), and –90 degrees when the positive zero crossing occurs at the UTC second rollover (sin waveform). Figure below illustrates the phase angle/UTC time relationship.

Figure 1. Convention for synchrophasor representation

Frequency and ROCOF definition

A PMU shall be capable of reporting frequency and ROCOF (Rate Of Change Of Frequency). ROCOF is defined by the equation:

Measurement time tag from synchrophasors

Synchrophasor measurements shall be tagged with the UTC time corresponding to the time of measurement. This shall consist of three numbers: a second-of-century (SOC) count, a fraction-of-second (FRACSEC) count, and a message time quality flag. The SOC count shall be a count of seconds from UTC midnight (00:00:00) of January 1, 1970, to the current second.

Synchrophasor transmission

Synchrophasor estimates shall be made so they can be reported (transmitted) as data frames at a rate Fs that is an integer number of times per second or integer number of seconds per frame as illustrated in the table below.

Table 1. Example of PMU reporting rates
System frequency 50 Hz 60 Hz

Reporting rates (Fs - frames per second)

10 25 50 10 12 15 20 30 60

The actual rate to be used shall be user selectable. Support for other reporting is permissible, and higher rates such as 100 frames/s or 120 frames/s and rates lower than 10 frames/s such as 1 frame/s are encouraged.

Message framework

Four message types are defined here: data, configuration, header, and command. The first three message types are transmitted from the PMU/PDC that serves as the data source, and the last (command) is received by the PMU/PDC.
  • Data messages are the measurements made by a PMU
  • Configuration is a machine-readable message describing the data types, calibration factors, and other meta-data for the data that the PMU/PDC sends
  • Header information is human readable descriptive information sent from the PMU/PDC but provided by the user
  • Commands are machine-readable codes sent to the PMU/PDC for control or configuration
  • A PMU or PDC may transmit multiple data streams, each with different content, rate, format, etc. Each data stream shall have its own IDCODE so that the data, configuration, header, and command messages can be appropriately identified. Each stream shall be independently operable including command execution and data, header, and configuration messages.

Message frames

Figure 2. Data Frame Organization
Figure 3. Configuration frame 1 and 2 organization
Figure 4. Header frame organization
Figure 5. Command frame organization

C37.118 communication scenario

The communication between PMU and Data Collector is illustrated on the picture below.

Figure 6. Communication scenario
  1. After the controller connects to the PMU server, it must retrieve the PMU configuration by sending the Configuration request frame.
  2. The PMU responds by sending the Configuration 2 frame. The controller uses the information from this frame to decode the data.
  3. After the Configuration 2 frame is received, the controller sends the request to start the data transmission.
  4. The PMU starts transmitting data at specified rate.
  5. The controller accepts and decodes the data form PMU.
  6. After some time, the controller sends the request to stop the transmission.
  7. The PMU stops transmitting data.

Communication methods

The common methods for communication are as follows:

  • Client-server. The device providing data is the server and the device receiving data is the client. The device providing data can be a PMU, a PDC, or any other device that will output synchrophasor data. The device receiving data can be a PDC or any or other device that receives synchrophasor data. In cases where data transmission is initiated by command, the client initiates contact and controls data flow with commands
  • Basic modes of operation: spontaneous and commanded. With spontaneous, the server sends data by UDP to a designated destination without stopping, whether a receiving device is present or not. The stream is initiated by a function in the device accessed separately from data operations. With commanded operation, the server only sends data when a client requests it using the standard Start and Stop commands. Both modes may support commands to retrieve configuration and header data.

C37.118 protocol in Typhoon HIL tool-chain

In Typhoon HIL toolchain, C37.118 protocol is implemented using PMU Send and PMU receive components. The PMU Send implements a server that sends synchrophasor data on request, whereas PMU Recive implements a client that connects to the server and can request the data.

Synchrophasor data can be send either using TCP or UDP protocol.

Currently, the synchronization using GPS or other methods is not supported on the Typhoon HIL devices, and the HIL devices cannot be synchronized to other external devices.

PMU Send

PMU Send component implements a server that sends synchrophasor data on request. The data can be sent either using TCP or UDP protocol.

When using TCP protocol, the server can accept up to 15 independent clients connections. Once a client connects, it can request Configuration 2 frame, Header frame, start and stop the data sending.

When using UDP protocol, the server can accept only one client at the time. Also the user can select if the communication is Unicast or Broadcast type.
  • The Unicast method accepts the request from the client and then sends the data only to that client.
  • The Broadcast method accepts the request from the client and then sends the data to everyone on the network by using broadcast IP address of 255.255.255.255. Using Broadcast, the problem of serving one client at the time can be overcomed.
UDP protocol also introduces the posibility of Spontaneous and Commanded mode of operation.
  • In Spontaneous mode, the server sends the synchrophasor data automatically when the simulation is started. The client can request the Configuration 2 and Header frames at any time but cannot stop the data sending. The sending is stoped only when the simulation is stopped.
  • In Commanded mode, the server behaves as ilustrated on Figure 6, as described before. The server waits for the client request and sends data only when asked to do so.

The PMU Send component icon and dialog window are shown in the table below.

Table 2. PMU Send component
Icon Dialog window

PMU Send

The PMU Send component properties are described in the table below.

Table 3. PMU Send component properties
Tab name Property name Description
General Stream source Each data stream can have multiple PMU data. This property helps the user chose if the component creates a new data stream or is appending data to an existing stream.
PMU index Choose the index inside the stream on which the PMU data will be stored.
Stream source ID Unique ID of the data stream.
Data rate Chose how often the data will be sent.
Data rate type The user can choose if the data is sent multiple times per second or if it is sent onece every N seconds.
Header data Human readable string that will be reported on Header frame request.
Choose existing stream If the user defines that the data from the component will be appended to an existing stream, this property defines which is that stream.
Network Protocol type Chose between TCP and UDP protocol
IP address IP address of the server (in TCP mode)
Netmask Netmask value
Port Port value (in TCP mode)
Gateway Define gateway if needed
Use Gateway If check box is True, gateway will be enabled
Operation mode Choose between Spontaneous and Commanded mode
Communication type Choose between Unicast or Broadcast communication
Local port Define local port value (in UDP mode)
Remote port Define remote port value (in UDP mode)
Destination IP address Define destination IP value (in UDP mode)
PMU Station PMU Station name Defines the PMU Station name
PMU Station ID Defines the unique PMU Station ID
Nominal frequency Choose between 50 or 60 Hz for nominal frequency.
Configuration Defines the configuration number
Data Generate values Pressing the button will present an additional dialog window that allows the user to specify the data values in more intuitive manner.
STAT type Choose if STAT value will be specified using a signal from the model or if the value will be fixed. Choosing Variable will generate additional terminal on the component that lets the user connect the signal from the model.
STAT value Specify the fixed STAT value
FREQ/DFREQ type Choose between integer or floating point type for FREQ and DFREQ data
Phasor data type Choose between integer or floating point type for Phasor data
Phasor representation Choose the representation of Phasor signals. The Phasors can be specified using real and imaginary representation or magnitude and angle.
Phasor signal names Define the Phasor names
Phasor signal types Define the Phasor signal type. Phasor can be either voltage or current.
Phasor scale values Define the Phasor signal scaling.
Analog data type Choose between integer or floating point type for Analog data
Analog signal names Define the Analog signal names
Analog signal types Define the Analog signal type. Signal type can be single point, rms, peak or user defined. In case of user definition, signal type is defined by a number between 65 and 255.
Analog scale values Define the Analog signal scaling
Digital signal names Define the Digital signal names
Digital signal normal state Define the Digital signal normal state of operation
Digital signal valid bits Define the Digital signal validity

If floating point type is selected for Phasor and Analog types, the scaling values are ignored.

No mater if the rectangular or polar representation is selected for Phasor signals, data connected to the input of the PMU Send component should be in magnitude and angle representation, where angle is specified in degrees. The input data is then transformed according to the selected representation and stored in the message frame.

When connecting, Phasor signals to the PMU Send component, the values must be in order of magnitude, than angle. If three Phasors are defined, six values must be defined in order [Ph1 mag, Ph1 ang, Ph2 mag, Ph2 ang, Ph3 mag, Ph3 ang]. This can be observed on the picture Figure 7.

Phasor scaling is used to define the resolution of Phasor data. The value is represented as 16bit integer, so the magnitude value can go from -32767 to +37265. In some cases this is not enough, so the scaling is needed. The scaling is calculated based on the maximal allowed Phasor value. For example, if the maximal allowed magnitude is 300 kV, the scaling is calculated:

Scale = (Max Phasor value / 32768) x 10e5= 300000 / 32768 x 100000 = 915527

Scale for Analog signal is simply a multiplier. User just specifies the value by which the Analog value is multiplied.

PMU Send example

The example below is considered.

Figure 7. PMU Send example

A simple three phase source is used and a rectifier. The grid voltages and currents are measured and sent using C37.118 protocol. The two PMU Send components are used to form one data stream. The PMU Send 1 component is configured to create a new data stream with ID 1000, and the PMU Send 2 component is configured to append data to an existing stream. This configuration is shown on the picture below. The configuration of data is also presented.

Figure 8. PMU Send component configuration

The PMU Send 1 component sends Voltage Phasors, 4 analog signals and 1 Digital word. All signals are defined as integer. The PMU Send 2 component sends only Current Phasors in floating point representation. For both components, the nominal frequency is 50 Hz and STAT value is fixed.

Wireshark was used to capture the message on the network and it is presented below.

Figure 9. Message frame captured by Wireshark

PMU Receive

PMU Receive implements a client that connects to PMU Server and sends the request frames. The request can be sent either using TCP or UDP protocol.

PMU Receive component can work in auto start mode. When the simulation starts, the client will try to connect to the server immediately. If the connection is successful and auto start mode is enabled, the client will automatically send the request for Configuration 2 frame, and when the frame is received, and start data sending request. In other case, the user must manually send these requests.

PMU Receive component icon and dialog window is shown on the table below.

Table 4. PMU Receive component icon and dialog window
Icon Dialog window

The PMU Receive component properties are described in the table below.

Table 5. PMU Receive properties
Tab Property name Description
General Execution rate Execution rate of the PMU Receive component
Network Auto start If the property is selected, the client will automatically connect to server and send the requests for Configuration 2 frame and start data transmission.
Protocol type Chose between TCP and UDP protocol
IP address IP address of the server (in TCP mode)
Netmask Netmask value
Port Port value (in TCP mode)
Gateway Define gateway if needed
Use Gateway If check box is True, gateway will be enabled
Local port Define local port value (in UDP mode)
Remote port Define remote port value (in UDP mode)
Destination IP address Define destination IP value
Data Stream source ID ID of the stream source to receive
Number of PMU Number of PMU Stations in the received data frame
Number of Phasors Number of Phasors per PMU Station
Number of Analogs Number of Analogs per PMU Station
Number of Digital words Number of Digital words per PMU Station

Dimension of output signals from PMU Receive component is dictated by Number of PMU property value. The values will be scalars if Number of PMUs is 1 and vector otherwise. The Phasor output is always vector and the dimension is Number of PMU x 2.

When receiving Phasor data, the output signal will be packed as a pair of Phasor magnitude and Phasor angel values. For example, if Number of PMU is 2, the phasor output value will be [Ph1 mag, Ph1 ang, Ph2 mag, Ph1 ang].

Regarding the PMU Server Phasor representation, whether the Phasors are represented in rectangular or polar mode, the output values will be magnitude and angle, where angle is in degrees.

FREQ, DFREQ, Phasor and Analog output values are always of floating point type. Digital signal output are represented with integer.

Additional terminal labeled RDY will output 0 if client is not connected to the server and 1 if the connection is established.

Command terminal, labeled CMD, is used to trigger the sending of request frames. The command is sent when the signal value is changed and the following values are used:
  • 0 - idle state where no command is sent
  • 1 - command to connect with the server
  • 2 - send the request for Configuration 2 frame
  • 3 - send the request to Stop sending data
  • 4 - send the request to Start sending data

If Auto start option is enabled in PMU Receive component, the client will automatically send commands 1, 2 and 4.

When the simulation is started, the client must first receive the Configuration 2 frame to successfully receive the Data frames. Otherwise, the Data frames are ignored.

PMU Receive example

The example illustrates the client that receives messages send by the PMU Server from the example Figure 7.

Figure 10. PMU Receive example

Bus Split component can be used to split values between PMU Station like illustrated for Phasor output.

Virtual HIL support

Virtual HIL currently does not support this protocol. When using a Virtual HIL environment (e.g. when running the model on a local computer), inputs to this component will be discarded and outputs from this component will be zeroed.