X/R Ratio
The ratio of reactance to resistance in a transformer determining fault current decay and DC offset characteristics.
X/R ratio = reactance (X) / resistance (R) in impedance. Determines transient behavior during faults): DC offset decay rate and peak asymmetrical current.
High X/R (large power transformers, 20-50+): fault current predominantly reactive, slow DC decay, peak 2.0-2.7x RMS symmetrical. Affects circuit breaker duty and protection coordination.
For breaker selection, X/R determines required asymmetrical capability. IEEE C37 provides correction factors.
QDTB provides X/R data for all products for proper protection coordination.
Related Products
Related Terms
Impedance (%Z)
Total opposition to current flow in a transformer as a percentage, determining fault current and voltage regulation.
Fault Current
The extremely high current during a short circuit that transformers must withstand mechanically.
Leakage Reactance
Reactance from magnetic flux not linking both windings, a major component of transformer impedance.
Winding Resistance
The DC resistance of transformer windings, measured for loss calculation and connection quality verification.
More Terms Starting with “X”
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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