Meaning
Internal opposition to current flow within a transformer is expressed as a percentage of the rated voltage required to produce full-load current under short-circuit conditions. This transformer impedance determines the maximum fault current that can pass through the device and influences the voltage regulation of the electrical system. It is a fundamental factor in the design of protection schemes and the selection of downstream circuit breakers.
Current Limitation
High impedance values restrict the amount of energy that flows during a short circuit.
Parallel Operation
Connecting two transformers to the same load requires their impedance values to be nearly identical. If they are mismatched, the unit with the lower impedance will carry a disproportionate share of the current and may overheat. Engineers verify these ratings on the nameplate before commissioning a new substation.
Efficiency Impact
Losses within the windings and the core are related to the impedance of the unit. A transformer with very low impedance might be more efficient but requires more expensive protection gear to handle potential faults. A demonstrated rate of performance under full load provides the final check on the system design.
Correct specification of this value prevents mechanical damage to the transformer core during a sudden surge in demand.
