Symbols of current transformers (CT)
1. Basic symbol overview
The symbols of current transformers (CT or new national standard TA) have the following two main forms in different drawings:
Primary system diagram: circles represent secondary windings, and vertical lines represent primary windings (through-type primary windings are replaced by actual lines). The number of circles corresponds to the number of windings (e.g. two circles represent double windings).
Secondary schematic diagram: inductor-like symbols (two semicircles) are used to represent secondary windings, and the primary windings are still represented by straight lines.
2. Symbol classification and meaning
According to the structure and function, the symbols can be divided into the following types:
Ordinary CT: rectangle (iron core) + coil (winding).
Through-type CT: a straight line passes through the rectangular core (representing the primary conductor).
Multi-winding CT: multiple coils (e.g. double windings are represented by two circles, and the overlap or not distinguishes whether they share the core).
Special markings: The symbol is often marked with the ratio (such as 100/5), accuracy level (such as 0.5 or 10P10) and the number of turns (such as "5 times through the core").
3. Comparison between the old and new standards
The old national standard symbol used "LH" (the first letter of the pinyin for "liuhu"), and now it is internationally used as "CT" or "TA".
The latest national standard (GB/T 4728.6-2000) has detailed regulations on symbols, including graphical representations of cores, windings and ratios.
4. Application scenario examples
Single-winding CT: used for simple measurement, the symbol is a circle or an inductance graphic.
Dual-winding CT: commonly used in measurement + protection combinations (such as 0.5-level metering winding + P-level protection winding).
Multi-winding CT: three windings may be used for metering, measurement and protection respectively.