Effect of transformer on the performance of short-circuit impedance
Release time:
2023-11-17
When the transformer is running at full load, the short-circuit impedance has a certain influence on the output voltage of the secondary side. The short-circuit impedance is small, the voltage drop is small, the short-circuit impedance is large, and the voltage drop is large. When the transformer load is short-circuited, the short-circuit impedance is small, the short-circuit current is large, and the electric force of the transformer is large. The short-circuit impedance is large, the short-circuit current is small, and the electric force borne by the transformer 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 the transformer refers to the equivalent series impedance Zk = Rk jXk between the terminals of a certain winding in a pair of windings at the rated frequency and the reference temperature. Since its value is determined by load tests in addition to calculations, it is customary to call it short-circuit voltage or impedance voltage.
We have all learned physical knowledge. The current-carrying conductor in a magnetic field will bear the action of mechanical force. Therefore, when current passes through the transformer winding, but because of the action of current and leakage magnetic field, electromagnetic mechanical force will be generated in the winding. Its magnitude depends on the multiplication of magnetic flux density of magnetic leakage field and conductor current. We also know that the direction of departure is determined by the left hand. When the transformer is running under normal load, the force acting under the wire is relatively small, but when a sudden short circuit occurs, because the maximum short-circuit current will be 25 to 30 of the rated current or more, however, according to the formula, the electromagnetic force generated between the windings during short circuit is proportional to the square of the short-circuit current, therefore, the mechanical force during short circuit will be basically the force during normal operation will be greater than several hundred times, and the speed of this force is very fast, in such a short time, the short circuit breaker is too late to cut off the circuit.
Transformer short-circuit impedance is also called impedance voltage, which is defined in the transformer industry as follows: when the transformer secondary winding is short-circuited (steady state), the primary winding flows through the rated current and the applied voltage is called 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 huge short-circuit electromagnetic force, many parts in the winding of the transformer may be damaged, so when the manufacturer designs the transformer, it is necessary to study the tolerance of the transformer in the short-circuit electrodynamic force and the mechanical strength of the winding under the short-circuit condition. In order to ensure the normal operation and use of the transformer, we must consider the stress problem of the transformer.
When the transformer is running at full load, the short-circuit impedance has a certain influence on the output voltage of the secondary side. The short-circuit impedance is small, the voltage drop is small, the short-circuit impedance is large, and the voltage drop is large. When the transformer load is short-circuited, the short-circuit impedance is small, the short-circuit current is large, and the electric force of the transformer is large. The short-circuit impedance is large, the short-circuit current is small, and the electric force borne by the transformer is small.