Transformer FAQ
What is transformer impedance voltage and why does it matter?
Impedance voltage affects fault current, voltage regulation, load sharing and the ability of transformers to operate in parallel.
Direct answer
Transformer impedance voltage, often expressed as a percentage, represents the voltage required to circulate rated current when one winding is short-circuited under specified test conditions. A higher percentage generally limits short-circuit current more strongly but can increase voltage drop. The required value must be coordinated with the system study and any parallel transformers.
System effect
Impedance influences prospective fault current and voltage drop under load. It is therefore both a transformer parameter and a power-system coordination parameter.
Parallel operation
Transformers intended to operate in parallel require compatible voltage ratios, vector groups and impedance values so that load is shared appropriately.
What to provide
Provide the required percentage impedance, MVA base, tolerance, short-circuit level, loading duty and details of any existing transformer that must operate in parallel.
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