Why Should One End of the Current Transformer Be Grounded? Let's Find Out

When it comes to current transformers, everyone must be familiar with them. Its main function is to convert high values into low values, which is suitable for measuring instruments and relays. A commonly used secondary current rating is 5A. So, the question is: why should one end of the current transformer be grounded? Let's find out together

(1) Secondary windings of current and voltage transformers

The secondary winding of the current transformer and the voltage transformer should be grounded during operation to prevent the high voltage from being connected to the low voltage through the transformer after the transformer insulation is broken down, which will hurt the instrument and the operating personnel. Grounding the secondary point of the transformer will not affect the normal operation of the equipment, but also ensure the safety of personnel and equipment.

To ensure safety, the secondary side of the current transformer must be grounded, and it plays a protective role when the secondary side of the current transformer is in danger of high voltage to ensure the safety of people and equipment.

(2) What is the function of the current transformer?

In the production process, the operation status of each primary piece of equipment in the system is monitored to ensure the safe operation of the power system. The current transformer usually converts the large current of the primary loop into a small secondary current proportional to it, and finally outputs the small current on the secondary side to the secondary instrument, relay protection, and automatic device for use. Therefore, the current transformer is an AC current source for electrical control, regulation, measurement and protection components, and is also a hub for the connection between the electrical secondary circuit and the primary circuit.

(3) Why is the current transformer grounded?

It is to ensure safety, one is equipment safety, and the other is personal safety. Because there is distributed capacitance between the primary winding and the secondary winding of the current transformer and between the secondary winding and the ground. Then the partial pressure of this distributed capacitance causes the secondary winding to generate a higher voltage to the ground. Also, the insulation between the primary winding and the secondary winding is damaged for some reason. Then the high voltage of the primary circuit will be directly added to the secondary circuit, which is very harmful to the secondary equipment and personal safety.

Therefore, the secondary side of the current transformer must be grounded, and the secondary circuit has only one grounding point, and multiple grounding points are not allowed.

(4) Why can't the secondary side of the current transformer be open?

Because the secondary circuit of the current transformer is open, then the secondary current disappears, and the demagnetization effect also disappears, which will cause a high magnetic density in the iron core. And because the number of turns of the secondary side winding is much larger than the number of turns of the primary side winding, once the secondary side is open, a very high voltage will also appear. Sometimes as high as several thousand volts, thus endangering not only secondary equipment but also personal safety.