The X/R ratio compares the inductive reactance of the network seen from a fault point with its resistance. A high value, common near generators and large transformers where it can exceed 30, means a slowly decaying DC component and a first peak of fault current up to about 2.7 times the symmetrical RMS value. Breaker ratings assume a test X/R, so equipment in high X/R locations may need derating, and CT saturation becomes more likely.
X/R at the generator bus comes out at 42, check the breaker's DC component rating before you sign off the study.
Also heard as
- X over R
Related terms
Fault current
Abnormally high current that flows when insulation fails and a short circuit or earth fault forms.
Breaking capacity
Highest fault current a circuit breaker or fuse can interrupt safely at its rated voltage.
CT
Current transformer: an instrument transformer that scales large primary currents down to a standard secondary.