In order to accurately measure the power consumption in high-voltage and high-current AC circuits, voltage transformers and current transformers are generally used to convert high voltage into low voltage and large current into small current, and configure a moderate meter to use voltage Transformers to carry out accurate measurements. For example, the current, working voltage, output power, frequency and electromagnetic energy measurement and verification in the high-voltage power supply system are all measured by voltage transformers. In addition, voltage transformers are also equipment that cannot be lacked in the power supply system’s relay protection devices, data signal labels and other levels.
The key structure and principle of voltage transformer is similar to that of current transformer. The primary winding coil of the voltage transformer has many turns and is connected to the high voltage side under test, while the secondary winding has a small number of smashes, and the secondary load is relatively stable. The accurate measurement when connected to high impedance is only for meters and automotive relays. The working voltage winding, therefore, when everything is in normal operation, the voltage transformer is close to the full load condition. The rated current of the primary and secondary windings of the voltage transformer is called the rated value transformation ratio of the voltage transformer.
The volume of the voltage transformer is small, and its load is generally very small and stable. Therefore, the primary side of the voltage transformer can be regarded as a constant voltage source, and most of it will not be harmed by the secondary load. The transformer is different. Its primary working voltage is greatly affected by the secondary load. The impedance of the operating voltage electromagnetic coil of the detection instrument and the automobile relay connected to the secondary side is very large. When everything is in normal operation, the voltage transformer is basically operating under full load.
Current transformer is a kind of current transformer, the principle of current transformer. Only its secondary winding is only connected in series with the current winding of the instrument panel and automobile relay.
The primary winding of the current transformer is connected in series in the power circuit and the number of turns of the coil is very small. The current in the primary winding is completely based on the load current of the power circuit under test, which is not related to the size of the secondary current. The transformer is the reverse, the size of the primary current changes with the transformation of the secondary current.
The instrument panel connected to the secondary winding of the current transformer and the current winding of the automobile relay have little impedance, so it operates close to a short-circuit fault under all normal conditions. Generally, the low-voltage side of the transformer is not allowed to operate under short-circuit faults.
The primary working voltage of the transformer determines the main magnetic flux in the transformer core, and the main magnetic flux determines the secondary potential difference. Therefore, the secondary working voltage will not change, and the secondary potential difference will basically not change. The current transformer is not the case, when the impedance in the secondary circuit changes, it will also harm the secondary potential difference. Under a certain value of the primary current effect, the size of the magnetic induction secondary current is determined by the impedance in the secondary circuit. When the secondary impedance is large, the secondary current is small, and the primary current used to balance the secondary current is small, and the excitation current As it increases, the secondary potential difference becomes higher. On the contrary, the secondary impedance hour, the secondary current of magnetic induction exceeds the part of the primary current used to balance the secondary current, the excitation current decreases, and the secondary potential difference is also low.
Most of the magnetic flux caused by the primary current of the current transformer is balanced by the secondary current. If the secondary leads, the primary current will be used for the excitation current, so that the transformer core will be saturated, high voltage will be induced in the secondary magnetic field and the transformer core will over-temperature. Therefore, the secondary current transformer is not allowed to lead the way.
