Effect of utility X R ratios on system | Information by Electrical . . . The second effect of X R is that circuit breakers are rated at a maximum X R ratio and if the fault X R is higher, then the fault duty has to be adjusted to compare with the breaker rating This adjustment is needed because fault current is higher initially, with a dc component that decreases with time (asymmetric vs symmetric fault)
X R ratio for transformers | Information by Electrical Professionals . . . Question How does unit size effect X R? Picture two scenarios 1 115kv to 34 5kv Dyn1 120MVA unit 2 3 115kv to 34 5kv Dyn1 40MVA units run in parallel In general, would I have the same X R for both scenarios or would #2 be higher in resistance while being lower in reactance? If so how
Utility X R Ratio | Information by Electrical Professionals for . . . It is calculated at the point of a fault A high X R means a long DC offset A very high X R can result in the short circuit current sine wave being so offset that the current never reaches zero during the 3-8 cycles the breaker is trying to open Some breakers' interrupting ratings have to be reduced for high X R faults
Calculating Transformer X R from kW Losses Calculating X R ratio from loss data is an accepted practice Which loss figure you use is probably not going to make that much difference for short circuit calculations For larger transformer, the winding resistance is probably provided directly
Determining P. U. Impedance and X R from Transformer % Impedence Value However, you can use a couple approximations The first is by looking in IEEE Std 141 (Red Book) Chapter 6 that has a graph of typical X R ratios of transformers based on IEEE C37 010 From the graph, a typical 1250KVA transformer has an X R of approx 7 This is a unitless number With this you can determine the X and R components of Z as follows:
Calculating SUbstation X R Ratio | Information by Electrical . . . The utility has given me positive and zero sequence impedance values but did not have the X R ratios of the substation handy The impedance values are in the form of "z = 5 + j3 93 ohms" Could anyone offer me guidance in arriving at the X R ratio from these values - I have not been successful in finding a formula Thank You!
Finding X R ratio using the sequence impedance The X R ratio on the primary side of a utility owned transformer will not have much impact on your secondary side values Try running your analysis with several assumptions and compare the results at your service entrance equipment I remember using starting values of 8 for a POCO and 20 for a generator
X R RATIO and Equivalent Pf % | Information by Electrical . . . Or how a PF 0 2 equals an X R RATIO 4 9 These are published values for testing LV Breakers The 6 6 X R and equals 15 % PF I have searched the internet and can not find how this conversion is calculated Can anyone post the formula for this conversion Why is it nearly impossible to find the listed X R ratios of Induction motors
X R ratio | Information by Electrical Professionals for Electrical . . . Power Factor=Cos(Tan^-1(X R)) Looking at this equation, the value inside the fist set of parenthesses represents the angle between the voltage and current waveform Therefore looking at this in reverse you can prove that the X R ratio is the Tangent of the phase angle between the voltage and current waveforms