The secondary side of the current transformer cannot be open-circuited

First, we need to understand the basic working principle of the current transformer. The current transformer is a special transformer that is mainly used to convert high current into low current for measurement and protection equipment. Its primary side is connected to the high current circuit, while the secondary side outputs a smaller current. This conversion is based on the principle of electromagnetic induction, that is, the magnetic field generated by the current on the primary side will be induced to the secondary side, thereby generating a secondary current.
When the secondary side of the current transformer is open-circuited, it means that no current flows through the secondary side. In this case, since the primary current still exists, it will continue to generate a magnetic field. However, since there is no current on the secondary side to balance this magnetic field, the magnetic field will become very strong, which may cause the core inside the current transformer to saturate. Core saturation will greatly affect the performance of the current transformer and may even damage the equipment.
In addition, the secondary side open circuit will also generate high voltage. Due to the principle of electromagnetic induction, when the magnetic field changes, a voltage will be generated on the secondary side. Under normal circumstances, this voltage is limited by the current on the secondary side. However, when the secondary side is open-circuited, there is no current to limit this voltage, so the voltage may rise to a very high level. This high voltage may not only damage the current transformer itself, but also other equipment connected to the secondary side, and even pose a threat to personnel safety.
To illustrate this point, suppose a current transformer is used to monitor high currents in a power system. If its secondary side is accidentally opened, thousands of volts may be generated due to the above reasons. Such high voltage is enough to break through the insulation material and cause fire or electric shock accidents. Therefore, in order to ensure the normal operation of the current transformer and the safety and stability of the system, the secondary side must be avoided.