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Effect of Transformer on the Performance of Short Circuit Impedance
Release time: 2018-03-10 Click times: 1128 times

When the transformer is running at full load, the level of the short-circuit impedance has a certain effect on the level of the secondary-side output voltage. The short-circuit impedance is small, the voltage drop is small, the short-circuit resistance is large, and the voltage drop is large. When the transformer load is short-circuited, the short-circuit resistance is small, the short-circuit current is large, and the transformer is subjected to a large electric force. The short-circuit resistance is large, the short-circuit current is small, and the electric force that the transformer bears is small.

The so-called short-circuit impedance is the resistance formed by the short circuit of electrical appliances, such as eddy current. The short-circuit impedance of a transformer refers to the equivalent series impedance Zk = Rk + jXk between a pair of windings and between the terminals of a winding at the rated frequency and the reference temperature. Because its value must be determined through load test in addition to calculation, it is customarily called it short-circuit voltage or impedance voltage.

We have all learned physics. Current-carrying conductors in a magnetic field will be subject to mechanical forces. Therefore, when a current is passed through the transformer windings, electromagnetic currents will be generated in the windings due to the effect of the current and the leakage magnetic field. , Its size depends on the magnetic flux density of the magnetic leakage field multiplied by the wire current, and we all know that the left direction is determined by the left direction. When the transformer is operating under normal load, the force acting on the conductor is relatively small, but when a short-circuit occurs, the maximum short-circuit current will be 25 to 30 or greater of the rated current. However, According to the calculation of the formula, the electromagnetic force generated between the windings in the short circuit is proportional to the square of the short circuit current, so the mechanical force in the short circuit will be basically more than a few hundred times the normal operating force, and the speed of this force is very high. Quick, in such a short time it is too late for the circuit breaker to cut off the circuit.

Transformer short-circuit impedance is also called impedance voltage. It is defined in the transformer industry as follows: When the secondary winding of a transformer is short-circuited (steady state), the voltage applied to the primary winding through the rated current is called the impedance voltage Uz. Usually Uz is expressed as a percentage of the rated voltage, that is, uz = (Uz / U1n) * 100%

In short, under the action of a large short-circuit electromagnetic force, many parts of the transformer's windings may be damaged. So when designing a transformer, the manufacturer must study the transformer's ability to withstand the short-circuit electric force and the windings under short-circuit conditions. To verify the mechanical strength, in order to ensure the normal operation and use of the transformer, we must consider the force of the transformer.

When the transformer is running at full load, the level of the short-circuit impedance has a certain effect on the level of the secondary-side output voltage. The short-circuit impedance is small, the voltage drop is small, the short-circuit resistance is large, and the voltage drop is large. When the transformer load is short-circuited, the short-circuit resistance is small, the short-circuit current is large, and the transformer is subjected to a large electric force. The short-circuit resistance is large, the short-circuit current is small, and the electric force that the transformer bears is small.

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