Understand the difference.

Compare the meaning, drawing context and source references of two entries. A similar graphic or shared abbreviation does not establish equivalence.

PD

Symbols

Partial discharge sensor

Partial discharge sensors detect small electrical discharges inside insulation before it fails. Common types include transient earth voltage sensors on metal-clad switchgear, UHF antennas in gas-insulated equipment and high-frequency CTs on cable earth straps, each feeding a monitoring unit that records and trends the activity.

Drawing use

SLD / Schematic

Application

Metering & protection

Reference family

Manufacturer

A distinction that matters

A partial discharge sensor assesses insulation condition; an insulation monitoring relay measures insulation resistance of an unearthed system.

Full referenceAdd to legend

IMD

Symbols

Insulation monitoring relay

An insulation monitoring relay is connected between the conductors of an unearthed (IT) system and earth, and injects a measuring signal to determine insulation resistance. It warns when insulation falls below its setting so a first fault can be located before a second fault causes a trip.

Drawing use

Schematic / SLD

Application

Metering & protection

Reference family

IEC / Manufacturer

A distinction that matters

An insulation monitoring relay measures insulation resistance of an unearthed system; a residual current monitor measures leakage current in an earthed system.

Full referenceAdd to legend

Original educational previews. Follow the source references on each full entry for the appropriate standard or selected product.