SFC
Static frequency converter
A rectifier and inverter in one unit that converts AC at one frequency to AC at another, such as 50 Hz to 60 Hz.
SLD
Symbols · MG
Motor-generator set
A motor mechanically coupled to a generator, used to isolate, change frequency or convert between AC and DC.
In plain English
What does Motor-generator set mean?
A motor-generator set is an electric motor driving a generator on a common shaft. It provides complete electrical isolation, conversion of frequency or voltage, or AC to DC conversion, and its rotating mass rides through short disturbances. Some sets add a flywheel or an engine on the same shaft for backup.
A simple example
Drawings show two machine circles, one marked M and one marked G, joined by a mechanical coupling line. The motor input and generator output are on separate circuits, each with its own protection and earthing.
What the drawings help you do
Efficiency is lower than a static converter and the rotating machines need maintenance, so motor-generator sets are now mainly found in legacy, test or special-purpose installations. The symbol does not show speed, coupling arrangement or ride-through time.
This particular reference
A motor mechanically coupled to a generator, used to isolate, change frequency or convert between AC and DC. A motor-generator set converts through rotating machines; a static frequency converter uses power electronics.
- DC
- Direct current: electricity flowing in one direction.
- AC
- Alternating current: electricity whose direction changes periodically.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
Read the source: IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams · Generator symbol variants
SLD / Schematic · MG
What it represents
A motor-generator set is an electric motor driving a generator on a common shaft. It provides complete electrical isolation, conversion of frequency or voltage, or AC to DC conversion, and its rotating mass rides through short disturbances. Some sets add a flywheel or an engine on the same shaft for backup.
Drawings show two machine circles, one marked M and one marked G, joined by a mechanical coupling line. The motor input and generator output are on separate circuits, each with its own protection and earthing.
Efficiency is lower than a static converter and the rotating machines need maintenance, so motor-generator sets are now mainly found in legacy, test or special-purpose installations. The symbol does not show speed, coupling arrangement or ride-through time.
How to read it
- The coupling line shows a mechanical link, not an electrical one.
- Earthing of the generator output is independent of the motor supply.
Information to show or reference
- State motor and generator ratings.
- Show output earthing and protection.
- Reference flywheel or engine if fitted.
A distinction that matters
A motor-generator set converts through rotating machines; a static frequency converter uses power electronics.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams
Graphic-symbol standards context for rotating machines.
Generator symbol variants
Public generator symbol family context.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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SLD
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SLD / Schematic
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