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IEEE C37.118.2 Reference

A quick reference for the IEEE C37.118.2 synchrophasor protocol as implemented in this tool. For the full specification, see docs/reference/README.md.

Protocol Overview

IEEE C37.118.2 defines the communication protocol for synchrophasor measurement systems. It specifies frame formats for exchanging configuration, data, header, and command information between PMUs (Phasor Measurement Units) and PDCs (Phasor Data Concentrators).

A typical TCP session from a microPMU:

[CFG-2 frame] → [Data frame] → [Data frame] → ... → [CFG-2 retransmit] → [Data frame] → ...

The CFG-2 frame describes the stream layout (phasor count, names, data types, encoding). Data frames follow at the configured reporting rate. Real PMUs periodically retransmit CFG-2; this tool supports that via --cfg2-interval.

Frame Types

Type Code SYNC Byte 1 Description
Data 0 0x02 Measurement data
Header 1 0x12 Human-readable ASCII header
CFG-1 2 0x22 Configuration (capabilities)
CFG-2 3 0x32 Configuration (current operating)
Command 4 0x42 Control commands
CFG-3 5 0x52 Extended configuration

SYNC byte 0 is always 0xAA. Byte 1 = (frame_type << 4) | version. Current version = 2.

Common Header (14 bytes)

Every frame starts with this header:

Offset  Bytes  Field      Description
0       2      SYNC       0xAA + frame type/version
2       2      FRAMESIZE  Total frame length including CRC
4       2      IDCODE     PMU/PDC stream identifier (1–65534)
6       4      SOC        Seconds since 1970-01-01 UTC
10      4      FRACSEC    Fractional second + time quality

All multi-byte fields are big-endian (network byte order).

FRACSEC Layout

Bits 31–24: Time quality flags (8 bits)
Bits 23–0:  Fractional second (24 bits)

Fractional second = fraction / TIME_BASE (TIME_BASE from CFG-2, typically 1,000,000).

CRC-16/IBM-3740

Every frame ends with a 2-byte CRC computed over all preceding bytes in the frame.

Parameter Value
Polynomial 0x1021
Initial value 0xFFFF
Reflect input No
Reflect output No
Final XOR 0x0000

Canonical test vector: CRC of ASCII "123456789" = 0x29B1

Warning: Some online references and the bundled crc16_ccitt_reference.html describe CRC-CCITT with init=0x0000. That is a different algorithm. Always use init=0xFFFF per the IEEE standard.

CFG-2 Frame

Configuration Frame 2 describes the current operating configuration of a PMU.

Key fields after the common header:

Field Bytes Description
TIME_BASE 4 Resolution of FRACSEC (typically 1,000,000)
NUM_PMU 2 Number of PMU blocks in this frame

Per-PMU block:

Field Bytes Description
STN 16 Station name (null-padded, not space-padded)
IDCODE 2 PMU data stream ID
FORMAT 2 Data format flags (see below)
PHNMR 2 Number of phasors
ANNMR 2 Number of analog values
DGNMR 2 Number of digital status words
CHNAM 16×N Channel names (16 bytes each, null-padded)
PHUNIT 4×PHNMR Phasor conversion factors
ANUNIT 4×ANNMR Analog conversion factors
DGUNIT 4×DGNMR Digital channel masks
FNOM 2 Nominal frequency (0 = 60 Hz, 1 = 50 Hz)
CFGCNT 2 Configuration change count

Trailing fields (after all PMU blocks):

Field Bytes Description
DATA_RATE 2 Reporting rate (positive = fps)
CRC 2 CRC-16 checksum

FORMAT Word

Bit 3: Frequency/ROCOF format (0 = int16, 1 = float32)
Bit 2: Analog format (0 = int16, 1 = float32)
Bit 1: Phasor format (0 = int16, 1 = float32)
Bit 0: Phasor notation (0 = rectangular, 1 = polar)

PHUNIT

Bits 31–24: Phasor type (0 = voltage, 1 = current)
Bits 23–0:  Scale factor (ignored for float32)

Data Frame

Data frames carry the actual measurement data.

After the common header:

Field Bytes Description
STAT 2 Status word
PHASORS varies Phasor values (see encoding)
FREQ 2 or 4 Frequency deviation
DFREQ 2 or 4 Rate of change of frequency
ANALOG varies Analog channel values
DIGITAL varies Digital status words
CRC 2 CRC-16 checksum

Phasor Encoding

Float32 polar (default):

  • Magnitude: 4 bytes (IEEE 754 float, in engineering units)
  • Angle: 4 bytes (IEEE 754 float, in radians)
  • 8 bytes per phasor × 8 phasors = 64 bytes

Int16 polar:

  • Magnitude: 2 bytes (signed, scaled by PHUNIT)
  • Angle: 2 bytes (signed, ~0.0001 rad/LSB)
  • 4 bytes per phasor × 8 phasors = 32 bytes

STAT Word (16 bits)

Bits 15–14: Data error (00=good, 01=PMU error, 10=test mode, 11=PMU error no data)
Bit  13:    PMU sync (0=in sync, 1=out of sync)
Bit  12:    Data sorting (0=by timestamp, 1=by arrival)
Bit  11:    PMU trigger detected
Bit  10:    Configuration change pending
Bit   9:    Data modified indicator
Bits 8–6:   Time quality (locked status)
Bits 5–4:   Unlocked time (seconds since GPS lock)
Bits 3–0:   Trigger reason (manual, mag low/high, angle diff, freq, df/dt, digital, user-defined)

Frequency

  • Float32: deviation from nominal in Hz (e.g., 0.05 means 60.05 Hz on a 60 Hz system)
  • Int16: deviation in millihertz (value × 0.001 = Hz deviation)

ROCOF (Rate of Change of Frequency)

  • Float32: Hz/s
  • Int16: centihertz per second (value × 0.01 = Hz/s)

MicroPMU vs. Transmission PMU

The tool supports the full IEEE C37.118.2 parameter space, but the LBNL data sources and default synthetic configuration target microPMU (distribution-level) characteristics:

Attribute MicroPMU Transmission PMU
Reporting rate 120 Hz 30–60 Hz
Voltage level 120–480 V (secondary), 4–35 kV (primary) 69–765 kV
Typical install Distribution feeder, PV site Substation
Captured events Cap switching, motor starts, PV transients System oscillations, islanding

This Implementation

  • Configurable phasor count (1-16, default 8): VA, VB, VC, V+ (voltage), IA, IB, IC, I+ (current)
  • Positive sequence (V+, I+) derived via Fortescue transformation
  • Configurable analog channels (0-N, with substation preset: temperature, tap position, MW, MVAR)
  • Configurable digital words (0-N, with breaker preset: breaker status + relay flags)
  • Multi-PMU aggregated streams (1-256 PMUs per config frame)
  • Default encoding: float32 polar (90 bytes/frame for 8 phasors)
  • Independent encoding per type: phasor, analog, and frequency can each be float32 or int16
  • Polar or rectangular phasor notation
  • Nominal frequency: 50 Hz or 60 Hz (configurable)
  • Configurable TIME_BASE (default 1,000,000; supports 1,048,576 and other values)
  • StatWord transitions: sync loss, config change, data quality degradation, trigger events
  • TimeQuality transitions: GPS unlock/relock ramps, leap second flags
  • Timing anomalies: frame gaps, duplicate timestamps, timing jitter
  • Invalid measurement frames: NaN/zero phasor override with PmuErrorNoData status
  • Periodic CFG-2 retransmission (configurable interval)
  • Corpus generator for diverse test datasets across the full parameter space

Reference Documents

See docs/reference/README.md for links to the IEEE standard, overview papers, and other reference materials.