# Displacement power-factor supervision

Canonical URL: https://eloragrid.ai/protection-functions/55d-displacement-power-factor-supervision
Publisher: Elora Grid
Updated: 2026-10-13
Lookup label: 55D
Drawing use: SLD, Schematic
Reference families: IEEE / ANSI, Manufacturer

Supervises displacement power factor as defined by the relay's fundamental-frequency measurements.

## What it represents

Supervises displacement power factor as defined by the relay's fundamental-frequency measurements.
The drafting record should connect this function to the current and voltage inputs and displacement-angle reference, then trace the displacement power-factor output or control interface. Keep the complete designation and equipment tag together so that the SLD, relay logic and terminal schedule describe the same implementation.
The cited mapping is a public manufacturer example (Eaton E-Series function mapping). Suffixes are not universal equivalences across products, and this reference supplies neither a protection setting nor certification of the selected scheme.

## How to read it

- Identify the current and voltage inputs and displacement-angle reference.
- Trace the displacement power-factor output or control interface.

## Information to show or reference

- Label the current and voltage inputs and displacement-angle reference.
- Cross-reference the displacement power-factor output or control interface.
- Retain the complete suffix, selected device tag and manufacturer manual revision.

## Important distinction

55D is not interchangeable with the apparent power-factor element 55A when the waveform contains harmonics.

## Facts

- Function designation: 55D
- Base function: 55 — Power factor protection
- Published mapping: Eaton E-Series function mapping
- Suffix scope: Application or manufacturer specific; check the complete drawing legend and selected device manual.

## Public references

- [E-Series protective relays: public family comparison brochure](https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/protective-relays-and-predictive-devices/e-series-protective-relays-br026001en.pdf) — Eaton. Public primary-source function or application mapping used to identify this designation; wording and drafting notes are original.
- [IEEE C37.2-2022: power-system device function numbers](https://ieeexplore.ieee.org/document/9984140) — IEEE. Device-number and suffix convention. This page is not a reproduction of the full licensed standard.

## 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.