Σ kWh
Summation energy meter
Integrating device that adds energy from several meters or circuits to give one total register.
SLD / Schematic
Symbols · ΣCT
Summation current transformer
Auxiliary CT with several primary windings that adds the secondary currents of other CTs into one output.
In plain English
What does Summation current transformer mean?
A summation CT has several primary windings, each fed from the secondary of a main CT, and one secondary winding that carries their sum. It lets one meter or relay see the total current of several feeders, or in some relay designs combines three phase currents into a single weighted quantity.
A simple example
All main CTs feeding a summation CT must have the same ratio, and their polarity must be consistent, otherwise currents cancel instead of adding. The symbol shows the summing arrangement but the burden it adds to each main CT has to be checked separately.
What the drawings help you do
Check that every feeding CT has the same ratio. Verify polarity of each primary winding. A summation CT adds currents before measurement; a summation energy meter adds energy after measurement.
This particular reference
Auxiliary CT with several primary windings that adds the secondary currents of other CTs into one output. A summation CT adds currents before measurement; a summation energy meter adds energy after measurement.
- Winding
- A coil of conductor inside an electrical machine or transformer.
- Coil
- A wound conductor that can produce a magnetic field when energised.
- Phase
- One of the related AC waveforms in a power system.
Read the source: Current transformer symbol variants · Indoor current and voltage transformers
Schematic / SLD · ΣCT
What it represents
A summation CT has several primary windings, each fed from the secondary of a main CT, and one secondary winding that carries their sum. It lets one meter or relay see the total current of several feeders, or in some relay designs combines three phase currents into a single weighted quantity.
All main CTs feeding a summation CT must have the same ratio, and their polarity must be consistent, otherwise currents cancel instead of adding. The symbol shows the summing arrangement but the burden it adds to each main CT has to be checked separately.
How to read it
- Check that every feeding CT has the same ratio.
- Verify polarity of each primary winding.
Information to show or reference
- List feeding CTs
- Show polarity marks
- Check burden on main CTs
A distinction that matters
A summation CT adds currents before measurement; a summation energy meter adds energy after measurement.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Current transformer symbol variants
Public AutoCAD Electrical current transformer family used for context; this variant is independently drawn.
Indoor current and voltage transformers
Public manufacturer overview of indoor current and voltage instrument transformers.
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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