# Phasor measurement unit

Canonical URL: https://eloragrid.ai/symbols/phasor-measurement-unit
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: PMU
Drawing use: SLD, Schematic
Reference families: IEEE / ANSI, Manufacturer

Device that measures voltage and current phasors with precise time stamps so angles can be compared across a network.

## In plain English

### What does Phasor measurement unit mean?

A phasor measurement unit samples voltages and currents and calculates magnitude and phase angle referenced to an absolute time source, normally GPS. Data from many PMUs can then be compared to see angle differences across a network, oscillations and islanding.

### A simple example

On a single-line diagram the PMU is drawn with its CT and VT inputs and a time input. The symbol does not show reporting rate, the communications path to a data concentrator or the measurement class, which together determine whether the data suits protection, control or monitoring.

### What the drawings help you do

Check the time synchronisation input. Trace CT and VT inputs to the measuring point. A PMU reports time-aligned phasors; a phase-angle meter shows a local angle between two inputs.

### This particular reference

Device that measures voltage and current phasors with precise time stamps so angles can be compared across a network. A PMU reports time-aligned phasors; a phase-angle meter shows a local angle between two inputs.

### Terms

- Phase: One of the related AC waveforms in a power system.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- Rating: A value stating the conditions for which equipment is specified.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [SEL 2022 Product and Solution Guide: published protection function tables](https://selinc.com/api/download/136012)
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/)


## What it represents

A phasor measurement unit samples voltages and currents and calculates magnitude and phase angle referenced to an absolute time source, normally GPS. Data from many PMUs can then be compared to see angle differences across a network, oscillations and islanding.
On a single-line diagram the PMU is drawn with its CT and VT inputs and a time input. The symbol does not show reporting rate, the communications path to a data concentrator or the measurement class, which together determine whether the data suits protection, control or monitoring.

## How to read it

- Check the time synchronisation input.
- Trace CT and VT inputs to the measuring point.

## Information to show or reference

- Show time source
- State reporting rate
- Reference data concentrator link

## Important distinction

A PMU reports time-aligned phasors; a phase-angle meter shows a local angle between two inputs.

## Facts

- Output: Time-stamped voltage and current phasors
- Time source: Usually GPS-derived
- Preview: Functional illustration of the device role; not a product footprint or certified standard graphic

## Public references

- [SEL 2022 Product and Solution Guide: published protection function tables](https://selinc.com/api/download/136012) — Schweitzer Engineering Laboratories. Public product guide covering synchrophasor-capable devices.
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/) — IEEE Standards Association. IEEE standards context; the PMU block is a functional illustration only.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.