Everyone knows that voltage transformers cannot be short-circuited, and current transformers cannot be open-circuited. Once the voltage transformers are short-circuited or the current transformers are open-circuited, they will destroy the voltage transformers or cause risks.
In terms of structural design, we all know that both voltage transformers and current transformers are all transformers, but the main parameters are different. So why are the same transformers, but one cannot be short-circuited and the other cannot be open-circuited?
When everything is in normal operation, the secondary magnet electromagnetic coil of the voltage transformer is equivalent to an open circuit, and the characteristic impedance ZL is very large. If the secondary circuit is short-circuited, the characteristic impedance ZL is quickly reduced to almost zero. It will cause a large amount of short-circuit current, which will destroy the secondary industrial equipment and even threaten the safety of life. The voltage transformer can be installed with a knife switch on the secondary side to protect itself from being damaged by a short circuit on the secondary side. If possible, a knife switch should also be installed on the primary side to protect the high-voltage power network from jeopardizing the safety performance of the primary system software due to the failure of the high-voltage magnet coil or power line of the voltage transformer.
When the current transformer is working normally, the characteristic impedance ZL is not too large, which is equivalent to the operation of the secondary magnet electromagnetic coil under short-circuit conditions. The magnetic flux potential caused by the secondary current has a degaussing effect on the magnetic potential caused by the primary current. The current of the excitation regulator is very small, the total magnetic flux in the inductance coil is not too large, and the current in the induction coil of the secondary winding is not large. more than tens of volts. If the secondary side is open circuit, the secondary current is equal to zero, the demagnetization effect will disappear, but the ε1 of the primary magnet electromagnetic coil will remain unchanged, and the primary current will completely become the excitation regulator current, resulting in a sharp increase in the magnetic flux Φ in the inductor coil. , the inductance coil is extremely saturated, and the number of coil turns of the secondary winding is quite large, which will cause a very high (even thousands of volts) working voltage on both sides of the secondary winding, which is not only very likely Destroy the insulating sleeve of the secondary winding, and will obviously damage the safety of life. Therefore, the open circuit of the secondary side of the current transformer must not be allowed.
In principle, voltage transformers and current transformers are all transformers. Voltage transformers focus on the change of working voltage, and current transformers focus on the change of current. As for why it is the same transformer, the current transformer cannot operate in open circuit, and the voltage transformer cannot operate in short circuit? The reason is here.
During normal operation, ε1 and ε2 remain unchanged. The primary side of the voltage transformer is connected in the distribution line, the working voltage is relatively high, and the current is very small. During normal operation, the alternating current on the secondary side is also very small, almost 0. In the secondary circuit, it is caused by the infinite characteristic impedance of the open circuit. a relatively balanced one. When the characteristic impedance of the secondary side is rapidly reduced to a short circuit, since ε2 remains unchanged, the amount of secondary current will expand rapidly and destroy the secondary magnet electromagnetic coil.
In the same way, during normal operation, ε1 and ε2 remain unchanged. The primary side of the current transformer is connected to each other in the distribution line, the current is relatively high, the working voltage is very small, and the voltage of the secondary side is also very small during normal operation, almost zero, and the short circuit in the secondary circuit is infinitely small. Impedance equalizes. When the characteristic impedance of the secondary circuit rapidly expands to an open circuit, the secondary current rapidly drops to 0, and the primary current is all converted into the current of the excitation regulator, causing the magnetic flux to rapidly expand to saturation and destroy the voltage transformer.
Therefore, the same transformers are used differently, and the results will be different.
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