ct in electrical symbols refers to current transformer (Current transformer abbreviated CT).
The current transformer consists of a closed core and windings. It has a small number of turns on the primary winding and is strung in the line of the current to be measured.
The current transformer principle is based on the principle of electromagnetic induction. Current transformer is composed of a closed core and winding. Its primary winding turns are few, strung in the line of the current to be measured, so it is often all the current flow through the line, the secondary winding turns are more, connected in series in the measurement instrumentation and protection circuit, the current transformer in the work, its secondary circuit is always closed, so the measurement instrumentation and the protection circuit of the series coil of the impedance is very small, the current transformer's working condition is close to a short-circuit.
Extended information:
Principle of operation
In the power generation, substation, transmission, Distribution and use of electricity in the line current size, from a few amps to tens of thousands of amps. In order to facilitate the measurement, protection and control needs to be converted to a more uniform current, in addition to the line voltage is generally higher such as direct measurement is very dangerous. Current transformers play a role in current conversion and electrical isolation.
For pointer type ammeter, the secondary current of the current transformer is mostly ampere level (such as 5A, etc.). For digital instrumentation, the sampled signal is generally milliampere level (0-5V, 4-20mA, etc.). Miniature current transformer secondary current for milliampere level, mainly play a large transformer and sampling between the bridge role.
The miniature current transformer is also called "instrumental current transformer". ("Instrumental current transformer" has a layer of meaning is used in the laboratory more current ratio precision current transformer, generally used to expand the instrument range.)
Current transformers and transformers are similar to the principle of electromagnetic induction is also based on the work of the transformer transformer is the voltage and current transformer transformer is the current just. Current transformer connected to the measured current winding (turns for N1), known as the primary winding (or primary winding, primary winding); connected to the measuring instrument winding (turns for N2) known as the secondary winding (or secondary winding, secondary winding).
Current transformer primary winding current I1 and secondary winding I2 current ratio, called the actual current ratio K. Current transformer in the rated current when the work of the current ratio is called the current transformer rated current ratio, expressed in Kn.
Kn=I1n/I2n
Current transformer (Current transformer abbreviated as CT) is the role of the larger value of the primary current through a certain ratio converted to a smaller value of the secondary current, used for protection, measurement and other purposes. Such as the ratio of 400/5 current transformer, the actual 400A current can be transformed into 5A current.
Baidu Encyclopedia - Current Transformer