1. Definition and significance of short circuit impedance

Transformer is one of the most widely used power equipment in power system. Its function is to transform voltage, reduce voltage loss and undertake various tasks such as overcurrent protection. In practical applications, a short-circuit fault may occur when the transformer fails. If the short-circuit impedance of the transformer is small, the current it will withstand will be very large when the fault occurs, which will cause irreversible damage to the structure, performance and safety of the equipment. Therefore, in transformer design, it is generally required that its short-circuit impedance be high enough to ensure that it has good over-current protection capability and arc-resistant capability.

2. Calculation method of short circuit impedance

The short-circuit impedance of the transformer can be measured experimentally or calculated. The formula for calculating the short-circuit resistance is:

Zk=Uk/Ik

Among them, Zk represents the short-circuit impedance, Uk and Ik represent the voltage and current during the short-circuit test of the transformer, respectively. For a single-phase transformer, a drop-down resistor can be added to one of the windings to make it a series circuit, and then a power supply and an ammeter are connected to both ends of the other winding to measure the secondary side current and short-circuit test voltage, thereby calculating The short-circuit resistance value of the transformer.

3. Factors Affecting Short Circuit Impedance

The short-circuit impedance value of a transformer is closely related to its iron core cross-sectional area, winding structure, magnetic leakage coefficient, winding resistance and other factors. Generally speaking, the larger the short-circuit impedance value of the transformer, the more stable its performance and can withstand higher over-current impact, but its cost and volume will also increase.

Four. Summary

The short-circuit impedance of a transformer is an important parameter to measure its performance against overcurrent shocks, and the calculation of the short-circuit impedance can be done by experiment or calculation. The main factors affecting the short-circuit impedance include the structure of the transformer, magnetic flux leakage coefficient and resistance, etc. Generally speaking, the higher the short-circuit impedance of the transformer, the better, so as to ensure that the structure and performance of the equipment will not be affected too much in the event of a fault.

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