The general mutual-inductance watt-hour meter and the high-voltage watt-hour meter of the three-phase watt-hour meter must be connected to a current transformer or a voltage transformer. This article mainly introduces you in detail what are voltage transformers and current transformers and What is the difference between these two transformers.
1. Voltage transformer
The working principle of electromagnetic voltage transformer is the same as that of transformer. The characteristics of the voltage transformer are: (1) The volume is not large, close to a small-volume transformer; (2) The secondary side load of the voltage transformer is relatively stable, and the characteristic impedance of the working voltage coil of the connected detection instrument and relay is very large. , So in normal operation, the voltage transformer is close to the no-load condition. The ratio of the rated voltage of the primary and secondary electromagnetic coils of the voltage transformer is called the ratio of the rated voltage of the voltage transformer. That is: kn=U1n/U2n where the rated voltage of the primary electromagnetic coil U1n is the rated voltage of the power network, and it has been standardized (such as 10, 35, 110, 220, 330, 500 kV, etc.), and the secondary working voltage U2n is unified It is defined as 100 (or 57.7) volts, so kn is also standardized.
2. Current transformer
A current transformer is a current conversion device. It can convert high-voltage and low-voltage large currents into small currents with lower working voltage to provide instrument panels and relay protection devices and separate the instrument panels and protection equipment from the high-voltage power circuit. The secondary side current of the current transformer is 5A or 1A, which promotes the safe and convenient application of detection instruments and relay protection devices, and also makes it standardized in production.
The secondary circuit of the current transformer is not allowed to be open. When the current transformer is in operation, its secondary circuit is closed from beginning to end, but because the characteristic impedance of the series winding of the detection instrument and the protection device is not large, the current transformer’s working condition is close to the short-circuit fault condition, caused by the primary current Most of the magnetizing force is compensated by the secondary current, the total magnetic flux density is not large, and the secondary winding potential is also small. When the current transformer is open, the characteristic impedance of the secondary circuit is infinite, and the current is equivalent to zero.
The primary current completely becomes the excitation current, causing a very high potential in the secondary winding, which seriously threatens the safety of the staff and leads to the dashboard , Relay protection equipment, current transformer secondary insulation layer is destroyed. The secondary circuit of the current transformer must be grounded to prevent the primary insulation layer from penetrating and the secondary stringing high voltage, threatening the safety of the staff and destroying the equipment.[/vc_column_text][/vc_column][/vc_row]
