What is the significance of x r ratio?

What is the significance of x r ratio?

Why is the X/R ratio important? Its importance is that it affects the level of short circuit current a circuit breaker is required to interrupt. When a short circuit occurs, the rms value of the symmetrical fault current is determined by the system source voltage and the total system impedance to the point of fault.

What is XR ratio of transformer?

The X/R ratio of a transformer is simply the imaginary part of its impedance divided by the real part of its impedance. When used in conjunction with the X/R ratio above the transformer’s primary, it’s used to calculate the maximum, asymmetric, secondary fault current capability.

In which of the following system is the X R ratio greater than one?

The ratio of X to R is greater than one for the transmission line and distribution line. In underground distribution networks (cables) the X/R ratio is very small and maybe smaller than 1.

What is the ratio of AC & DC component when fault occurs?

Before the fault, only AC voltages and currents are present, but immediately after the fault, both AC and DC currents are present. initially average about 50 – 60\% of the AC current flow the instant after the fault occurs. The total initial current is therefore typically 1.5 or 1.6 times the AC component alone.

What is Z in transformer?

The percentage impedance of a transformer (Z\%) is the voltage drop on full load due to the winding resistance and leakage reactance expressed as a percentage of the rated voltage. The ratio of voltage applied to circulate full load current to the primary voltage is the percentage impedance of the transformer.

How is XR ratio calculated?

The X/R ratio is the amount of reactance X divided by the amount of resistance R which also happens to be the Tangent of an angle created by reactance and resistance in a circuit. When calculating short circuit currents, there are usually many impedances that must be added together.

What is typical XR ratio of transmission line?

According to IEEE Std. 242, a 1500 kVA transformer with a secondary voltage < 600 Volts and a primary voltage of up to 15,000 Volts, the suggested X/R ratio is 7.0.

What causes DC offset in power systems?

When the voltage is zero in an inductive circuit, the current must be maximum. Therefore the maximum DC offset occurs when the voltage is zero. Remember that when the A-Phase voltage is zero, the other two phases will not be at zero, so different phases will react to the same fault differently.

How do you increase short circuit ratio?

For the same value of Tph Excitation voltage is directly proportional to the field flux per pole. Hence, the short circuit ratio is directly proportional to the air gap reluctance or air gap length. If the length of the air gap is increased, the SCR can be increased.

Why are modern alternators designed with high short circuit ratio?

High value of short circuit ratio gives improved voltage regulation. Thus the terminal voltage is practically constant during the load variation. It also results in better stability limit due to increased value of synchronizing power.