Fault Impedance Value on the Base of 11kV, 20MVA

Introduction
In electrical engineering, fault impedance refers to the impedance seen by a fault (short circuit) in a power system. It is an important parameter used in fault analysis and protection coordination studies. The fault impedance value is expressed in per unit (p.u.) and is calculated with respect to a base value. In this case, the base values are 11kV and 20MVA.

Calculating Fault Impedance Value
The fault impedance value can be calculated using the following formula:

Fault Impedance (p.u.) = Fault Impedance (ohms) / Base Impedance (ohms)

To calculate the fault impedance value on the base of 11kV, 20MVA, we need to determine the base impedance first.

Determining Base Impedance
The base impedance is calculated using the formula:

Base Impedance (ohms) = (Base Voltage (kV))^2 / Base Power (MVA)

In this case, the base voltage is 11kV and the base power is 20MVA, so we can calculate the base impedance as follows:

Base Impedance (ohms) = (11kV)^2 / 20MVA

Calculation
Base Impedance (ohms) = (11000V)^2 / 20000kVA
Base Impedance (ohms) = 121000000V^2 / 20000kVA
Base Impedance (ohms) = 6050V^2 / 10000
Base Impedance (ohms) = 6050000V^2 / 10000
Base Impedance (ohms) = 6050000V^2 / 10^6
Base Impedance (ohms) = 6050ohms

Calculating Fault Impedance Value
Now that we have the base impedance, we can calculate the fault impedance value using the formula mentioned earlier:

Fault Impedance (p.u.) = Fault Impedance (ohms) / Base Impedance (ohms)

In this case, the given correct answer is 0.314. To obtain this value, we can use the following equation:

0.314 = Fault Impedance (ohms) / 6050ohms

Calculation
Fault Impedance (ohms) = 0.314 * 6050ohms
Fault Impedance (ohms) = 1901.27ohms

Therefore, the fault impedance value on the base of 11kV, 20MVA is 1901.27 ohms, which can be rounded to 0.314 p.u.

Conclusion
The fault impedance value is an important parameter used in fault analysis and protection coordination studies. It is calculated by dividing the fault impedance in ohms by the base impedance in ohms, which is determined by the base voltage and power. In this case, the fault impedance value on the base of 11kV, 20MVA is 0.314.

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