CT
Current transformer
A current-measurement transformer used with metering and protection equipment.
SLD / Schematic
Functional block · CRCB
CT ratio-correction calculation block
Functional block · Substations
An independently authored application reference. The drawing shows the named function or circuit relationship; use the project legend and selected equipment documentation for its drafting form and connections.
Browse this installation focusIn plain English
What this block does
Converts a measured current quantity to the common basis used by the selected protection calculation.
A simple example
In a substation protection panel, separate CT cores can supply metering and protection circuits with different duties. A test boundary must preserve the secondary arrangement required by the selected CT and test device. For this reference, the drawing identifies “Measured current and ratio data” at the input and “Ratio-corrected current” at the output. Software correction does not change the physical CT ratio.
What the drawings help you do
Start at the named input: Measured current and ratio data. Identify its source device or document and the state represented on the drawing. Follow the named output: Ratio-corrected current. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Input
- Measured current and ratio data
- Output
- Ratio-corrected current
- Application reference
- An explanation of a named drawing function or circuit relationship; the project documents define the equipment and its connections.
Read the source: Indoor current and voltage transformers
Schematic · CRCB
What it represents
Converts a measured current quantity to the common basis used by the selected protection calculation. A current-transformer secondary arrangement carries a measuring current from a defined primary location to metering or protection inputs. Core identity, polarity and the connected circuit determine the measurement's meaning.
In a substation protection panel, separate CT cores can supply metering and protection circuits with different duties. A test boundary must preserve the secondary arrangement required by the selected CT and test device. For this reference, the drawing identifies “Measured current and ratio data” at the input and “Ratio-corrected current” at the output. Software correction does not change the physical CT ratio.
Trace every secondary connection and the assigned earthing point against the actual connection diagram. These illustrations explain circuit roles and never prescribe a live CT switching or disconnection procedure. The functional block is an independent explanation of this named application. Equipment-specific ratings, terminal connections and operating conditions must be established in the project documentation.
How to read it
- Start at the named input: Measured current and ratio data. Identify its source device or document and the state represented on the drawing.
- Follow the named output: Ratio-corrected current. Cross-reference its destination and separate the command from confirmation that the equipment responded.
- Software correction does not change the physical CT ratio.
- Trace every secondary connection and the assigned earthing point against the actual connection diagram. These illustrations explain circuit roles and never prescribe a live CT switching or disconnection procedure.
Information to show or reference
- Label the source and connection reference for measured current and ratio data.
- Identify the destination and defined state of ratio-corrected current.
- Record the equipment or control-document revision supporting this functional block.
- Check this application limit in the project design: Software correction does not change the physical CT ratio.
A distinction that matters
Software correction does not change the physical CT ratio. This reference describes the named application; it does not establish a new IEC graphical symbol, an ANSI device-function number or an exact manufacturer connection diagram.
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 technical context for current-transformer secondary arrangements. Current and voltage measurement transformers and their secondary interfaces. The application text and educational graphic are independently authored; the publisher does not certify this representation.
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. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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