The transformer short-circuit impedance is also called impedance voltage. In the transformer industry, it is defined as follows: when the transformer secondary winding is short circuited (steady state), the voltage applied by the primary winding flowing the rated current is called impedance voltage Uz. Uz is usually expressed as a percentage of the rated voltage, that is, uz=(Uz/U1n) * 100%
When the transformer operates with full load, the level of short circuit impedance has a certain impact on the level of secondary side output voltage. 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 that the transformer bears is large. The short circuit impedance is large, the short circuit current is small, and the electric force borne by the transformer is small.
(1) The greater the impedance voltage of the transformer, the smaller the short-circuit current flowing through the transformer when the secondary side of the transformer is short circuited, and the smaller the impact on the transformer. Therefore, the current owner requires the minimum short-circuit impedance value in the transformer manufacturing process, but increasing the transformer impedance voltage has higher requirements for the manufacturing process;
(2) The greater the impedance voltage of the transformer is, the greater the voltage change amplitude at the load side of the transformer is when the load changes, and the voltage stability is poor;
(3) The greater the impedance voltage of the transformer, the greater the reactive power consumed by the transformer winding under the same load.
The percentage of short-circuit impedance of the transformer is numerically equal to the mass percentage of short-circuit protection voltage inside the transformer. It refers to the percentage of the ratio of the voltage applied by the primary winding to the rated output voltage level when the secondary winding passes through the rated working current of the system when the transformer is short circuited by the secondary winding.
The percentage of the transformer short-circuit impedance value is an important parameter of the transformer, which reflects the internal impedance of the transformer, that is, the impedance voltage drop of the transformer itself when the transformer is operating under rated load. It is also of great significance for the sudden short circuit at the secondary side of the transformer, how much short circuit current will be generated, the manufacturing price of the transformer and the parallel operation of the transformer.
