A current transformer is an instrument that uses the principle of electromagnetic induction to convert a large current on the primary side into a small current on the secondary side. A current transformer consists of a closed iron core and windings. Its primary winding has several turns, strung on the current line that needs to be measured.
Therefore, all the current of the line often flows, and the number of turns of the secondary winding is relatively large. It is connected in series with the measuring instrument and the protection circuit. When the current transformer is working, its secondary circuit is always in a closed state, so the impedance of the instrument series coil and the protection circuit is very small, and the working state of the current transformer is close to a short circuit. The current transformer converts the large current on the primary side into a small current on the secondary side for measurement, and the secondary side cannot be opened.
The structure of a current transformer is very similar to that of a normal transformer. The iron core of the current transformer is composed of silicon steel laminations. A current transformer (CT) basically has one or more turns of a primary coil of a large cross-sectional area. In some cases, the strip carrying the high current may act as the primary. It is in series with the line carrying the high current.
What it does is:
Measuring CT:
Current transformers used in metering and indicating circuits are often referred to as measuring CTs. They have a lower saturation point. In the event of a fault, the iron core saturates and the secondary current does not damage the measurement equipment connected to it.
Protect CT:
The current transformer used in conjunction with the protection device is called a protection CT. The purpose is to detect the fault current in the system and pass the signal to the relay. Since it operates at a higher current value than its rated value, its core has a high saturation point.
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