CT
Current transformer
A current-measurement transformer used with metering and protection equipment.
SLD / Schematic
Symbols · CT
Wound-primary current transformer
CT with a primary winding of several turns, used for low primary currents where a bar primary gives too little accuracy.
In plain English
What does Wound-primary current transformer mean?
A wound-primary CT has a primary winding of more than one turn rather than a single bar or conductor through a window. This is needed at low primary currents, where a single turn would not produce enough magnetising ampere-turns for accurate metering, and it is common in MV metering units.
A simple example
The wound primary has a lower short-time withstand than a bar primary, so its thermal and dynamic ratings need checking against the fault level. The symbol shows the winding but not those ratings, which belong in the CT schedule.
What the drawings help you do
Check the short-time thermal rating against the fault level. Read primary terminals P1 and P2 for polarity. A wound-primary CT has a multi-turn primary; a window or bar CT uses the circuit conductor as a single-turn primary.
This particular reference
CT with a primary winding of several turns, used for low primary currents where a bar primary gives too little accuracy. A wound-primary CT has a multi-turn primary; a window or bar CT uses the circuit conductor as a single-turn primary.
- Winding
- A coil of conductor inside an electrical machine or transformer.
- Rating
- A value stating the conditions for which equipment is specified.
- Schematic
- A drawing showing function and connections rather than physical appearance.
Read the source: Indoor current and voltage transformers · Current transformer symbol variants
SLD / Schematic · CT
What it represents
A wound-primary CT has a primary winding of more than one turn rather than a single bar or conductor through a window. This is needed at low primary currents, where a single turn would not produce enough magnetising ampere-turns for accurate metering, and it is common in MV metering units.
The wound primary has a lower short-time withstand than a bar primary, so its thermal and dynamic ratings need checking against the fault level. The symbol shows the winding but not those ratings, which belong in the CT schedule.
How to read it
- Check the short-time thermal rating against the fault level.
- Read primary terminals P1 and P2 for polarity.
Information to show or reference
- State ratio and class
- Give short-time rating
- Show polarity marks
A distinction that matters
A wound-primary CT has a multi-turn primary; a window or bar CT uses the circuit conductor as a single-turn primary.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Indoor current and voltage transformers
Public manufacturer overview of indoor current and voltage instrument transformers.
Current transformer symbol variants
Public AutoCAD Electrical current transformer family used for context; this variant is independently drawn.
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.
Explore related references
CT
ANSI/IEEE current transformer with conductor indication symbol
IEEE-library CT form that shows the primary conductor passing through the core, as with window and bar-type CTs.
IEEE / ANSI
CT/VT
Combined instrument transformer
Single unit housing a current transformer and voltage transformer for each phase, typical of MV and HV metering points.
SLD / Schematic
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