What is the difference between a voltage transformer and a current transformer? Aren't they both transformers? Don't they both have a primary side and a secondary side?

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What is the difference between a voltage transformer and a current transformer? Aren't they both transformers? Don't they both have a primary side and a secondary side? [Copy link]

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The same is true for collecting input voltage data. Figure 2 uses a voltage transformer to collect data, and Figure 4 uses a current transformer to collect data.

What is the difference between a voltage transformer and a current transformer? Aren't they both transformers? Don't they both have a primary and a secondary? Don't they both have to induce voltage from the secondary? Are current transformers cheaper than voltage transformers?

maychang

"What is the difference between a voltage transformer and a current transformer? Aren't they both transformers? Don't they both have a primary side and a secondary side? Don't they both induce voltage from the secondary side?"

Yes, they are all mutual inductors, they all have primary and secondary sides, and even iron cores and windings.

The secondary side of the voltage transformer induces voltage, but the secondary side of the current transformer outputs current. The voltage across the secondary side of the current transformer is not allowed to exceed a certain value, or the secondary side load resistance is specified not to exceed a certain value. For example, the power industry usually specifies that the secondary side resistance of the current transformer shall not exceed 4 ohms.

maychang

"What is the difference between a voltage transformer and a current transformer? Aren't they both transformers? Don't they both have a primary side and a secondary side? Don't they both induce voltage from the secondary side?"

The secondary side of the voltage transformer must not be short-circuited, and the secondary side of the current transformer must not be open-circuited.

chunyang

It is recommended that you dismantle one voltage transformer and one current transformer respectively to see if there are any major differences in structure first.

wei152

The current transformer is equivalent to a current source, which converts a large current into a standard 5A or 1A. There is a main insulation requirement between high voltage and low voltage. The voltage transformer is equivalent to a voltage source, which converts a high voltage into a standard 100V or 100: root 3.

injoinic11

Excuse me, why is it said that the currents at both ends of the primary and secondary sides of a current-type voltage transformer are equal? Isn't the voltage equal?

maychang

injoinic11 posted on 2024-3-12 17:57 Excuse me, why is it said that the currents at both ends of the primary and secondary sides of a current-type voltage transformer are equal? Isn't the voltage equal?

[Why is it said that the currents at both ends of the primary and secondary sides of the current type voltage transformer are equal? Isn't the voltage equal?]

The current on the primary and secondary sides of this type of transformer is equal, and the voltage is also equal.

injoinic11

maychang posted on 2024-3-12 18:36 [Why is it said that the current at both ends of the primary and secondary sides of the current type voltage transformer are equal? Isn't the voltage equal?] The current at the primary and secondary sides of this transformer is equal, and the voltage is equal.

Thanks for the answer. I don't understand why the currents are equal. I've thought about it these past two days, and I don't know if it's right: equal currents should be an approximation. Only when the inductance of the transformer is large enough, the frequency of the measured signal is large enough, and the load resistance is small enough, can the currents be considered approximately equal. For a transformer, the inductance has been determined. In order to ensure that the currents at both ends are equal, the specification generally has a limit on the load resistance. When the load resistance is too large, the currents at both ends are not obviously equal, and there is a phase shift. When the signal frequency is too small, similar problems will also exist.

maychang

injoinic11 posted on 2024-3-14 16:08 Thanks for the answer. I don’t understand the reason why the currents are equal. I have thought about it these two days. I don’t know if it is right: the equal currents should be an approximation. When they are mutually...

Yes, it is an approximation. Not only is the primary and secondary currents equal, it is an approximation, but the primary and secondary voltages are also equal.

However, the condition "the frequency of the measured signal is large enough" needs to be changed to "the frequency range of the measured signal is appropriate", because the error will increase if the frequency is too high, and the error will also increase if the frequency is too low.

injoinic11

maychang posted on 2024-3-14 16:15 Yes, it is an approximation. Not only is the primary and secondary currents equal, but the primary and secondary voltages are also equal. However, "the measured signal...

Thank you very much, very helpful.