G 3PH SYNC
Three-phase synchronous generator
A three-phase synchronous generator supplies a documented AC source associated with its mechanical prime mover and excitation system.
SLD / Schematic
Symbols · G 3~ ASG
Three-phase induction generator
A squirrel-cage asynchronous machine driven above synchronous speed so that it delivers power into a three-phase network.
In plain English
What does Three-phase induction generator mean?
An induction generator is an asynchronous machine driven slightly faster than synchronous speed by a turbine or engine. It exports active power but needs reactive power from the network or from capacitors to establish its magnetic field, so it cannot normally hold voltage and frequency on its own.
A simple example
The symbol is a machine circle with G, a three-phase AC mark and often the letters ASG or a squirrel-cage indication to separate it from a synchronous generator. It is found in small hydro, older wind turbines and some biogas or heat recovery sets connected in parallel with a stronger supply.
What the drawings help you do
The symbol does not tell you whether the machine can run isolated with self-excitation capacitors, or what happens to its output when the network trips. Islanded operation and reverse power or loss-of-mains protection have to be read from the protection and control drawings.
This particular reference
A squirrel-cage asynchronous machine driven above synchronous speed so that it delivers power into a three-phase network. An induction generator draws its magnetising current from the network; a synchronous generator has its own field and can regulate voltage.
- AC
- Alternating current: electricity whose direction changes periodically.
- Phase
- One of the related AC waveforms in a power system.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
Read the source: Three-phase motor symbol variants · IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams
SLD / Schematic · G 3~ ASG
What it represents
An induction generator is an asynchronous machine driven slightly faster than synchronous speed by a turbine or engine. It exports active power but needs reactive power from the network or from capacitors to establish its magnetic field, so it cannot normally hold voltage and frequency on its own.
The symbol is a machine circle with G, a three-phase AC mark and often the letters ASG or a squirrel-cage indication to separate it from a synchronous generator. It is found in small hydro, older wind turbines and some biogas or heat recovery sets connected in parallel with a stronger supply.
The symbol does not tell you whether the machine can run isolated with self-excitation capacitors, or what happens to its output when the network trips. Islanded operation and reverse power or loss-of-mains protection have to be read from the protection and control drawings.
How to read it
- Look for excitation capacitors near the machine terminals.
- Check loss-of-mains protection, since the machine may self-excite on capacitors if islanded.
Information to show or reference
- State rating, voltage and rated slip.
- Show capacitor compensation and its switching.
- Reference loss-of-mains protection.
A distinction that matters
An induction generator draws its magnetising current from the network; a synchronous generator has its own field and can regulate voltage.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Three-phase motor symbol variants
Public three-phase induction machine symbol family; the generator mark is added in this original illustration.
IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams
Graphic-symbol standards context for rotating machines.
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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