Voltage transformer and current transformer have the same point. They all use the working principle of electricity magnetism electricity. As shown in Figure 1 below.Both voltage transformer and current transformer are components for measurement and protection in power supply system.Common voltage transformers are reduced to the rated voltage of the instrument to provide working voltage for the circuit; Its symbol is represented by TV; Its output voltage is connected in parallel with the instrument. See the figure below for its physical map.
This configuration of high-voltage voltage transformer is mainly used for measurement and protection of voltage level of 10kV and above; The high-voltage winding of the voltage transformer is connected in parallel with the tested circuit, and the low-voltage winding is connected in parallel with the voltage coil of the measuring instrument. Due to the large internal impedance of the voltage coil, when the voltage transformer works, it is equivalent to a no-load transformer, so its secondary side cannot be short circuited, otherwise the winding coil will be burned.Its working principle is shown in the figure below.Current transformer provides rated 1 5A current with different ampere turn ratio for instruments and watt hour meters. It is represented by the symbol TA, and its physical diagram is shown in the figure below.
Because the number of coils on the primary side of the current transformer is small and all are in series, its current depends on the line load current and has nothing to do with the secondary side load. Because the impedance of the current coil connected to the secondary side is very small, the current transformer is equivalent to a short-circuit transformer when it works normally. Therefore, the actual current value in the line is very large, so its secondary side cannot be open circuit during normal operation; Short circuit at secondary side of voltage transformer; One terminal on the secondary side of both of them is a protective grounding terminal, which must be protected and grounded according to the safety regulations during installation.
The same point: they are all transformers. The primary side is connected with the measured circuit, and the secondary side is connected with instruments or control elements. They are generally used for the measurement and control of AC circuitsdifference:The primary side of the current transformer is connected in series in the measured circuit, and the voltage induced by the secondary side changes with the current of the primary side;
The primary side of the voltage transformer is connected in parallel with the measured circuit, and the voltage induced by the secondary side changes with the terminal voltage of the primary sideThe key is the current transformer. The secondary side cannot open circuit, and the secondary side open circuit is equivalent to infinite impedance. According to the principle of mutual inductance, the resistance reflected to the primary side is infinite. When the current at the primary side is large, a large voltage drop will be generated at the primary side, which is very easy to burn the transformer. Therefore, when there is no measuring instrument at the secondary side of the current mutual inductor, the secondary side should also be short circuited with wires.In the same point, they all obtain monitoring data at the secondary side through electromagnetic induction. The difference is that the monitoring objects are different, one is voltage and the other is current.
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