Impedance (Z)
Total opposition to AC current combining resistance and reactance as Z = sqrt(R^2 + X^2).
Impedance (Z) combines resistance (R) and reactance (X): Z = R + jX, |Z| = sqrt(R^2 + X^2).
As %Z of rated voltage: determines fault current (Ifault = Irated x 100/%Z), regulation, parallel load sharing. For large power transformers, %X >> %R.
X/R ratio affects fault asymmetry and breaker requirements. Determined by short-circuit measurement at factory. One of most important nameplate parameters.
QDTB designs and verifies impedance precisely. See %Z and short-circuit impedance for related concepts.
Related Products
Related Terms
Impedance (%Z)
Total opposition to current flow in a transformer as a percentage, determining fault current and voltage regulation.
Short-Circuit Impedance (%Zsc)
Transformer impedance measured with one winding short-circuited, determining fault current and regulation.
X/R Ratio
The ratio of reactance to resistance in a transformer determining fault current decay and DC offset characteristics.
Leakage Reactance
Reactance from magnetic flux not linking both windings, a major component of transformer impedance.
More in “Performance Parameters”
Core Loss
Power dissipated in the transformer magnetic core due to hysteresis and eddy currents, also called iron loss or no-load loss.
Copper Loss
Power lost as heat in transformer windings due to electrical resistance, proportional to the square of load current.
Efficiency Class (IE1-IE4)
International classification for transformer energy efficiency, IE1 (standard) to IE4 (premium) with progressively lower losses.
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