What is base kVA and short circuit kVA?

The product of normal system voltage and short-circuit current at the point of fault expressed in kVA is known as Short Circuit kVA. Let. V = normal phase voltage in volts. I = full-load current in amperes at base kVA. \%X = percentage reactance of the system on base kVA upto the fault point.

How do I choose a base kVA?

Transformer Rating is 2.5 MVA and Transformer Impedance is 6\%. \% Reactance at Base KVA = (Base KVA x \% impedance at Rated KVA) / Rated KVA. \% Reactance at Base KVA = (2.5X6)/2.5. \% Reactance at Base KVA =6\%

What is the importance of short circuit calculation in power system?

Short circuit study is used to determine the available fault current or short circuit current at each point in the system. Based on that study, power system engineers can easily determine the required interrupting capacity of the circuit breakers which forms the basis of designing a proper relaying system.

What is the advantage of expressing Reactances in percentage values?

Percentage reactance values remain unchanged as they are referred though transformers, unlike ohmic reactances which become multiplied or divided by the square of transformation ratio. This makes the procedure simple and permits quick calculations.

What is the relation between base kVA rated kVA?

ADVERTISEMENTS: A base kVA may be chosen in the following manner: (i) Equal to the kVA rating of the largest unit connected in the network. (ii) Equal to the sum of the kVA ratings of all the units connected in the network.

How do you calculate short circuit?

The formula is I = V/R. When there is a short circuit the resistance becomes very small, and that means the current becomes very large. If the resistance was zero, then the calculated fault current would go to infinity.

What is the importance of per unit system?

For the analysis of electrical machines or electrical machine system, different values are required, thus, per unit system provides the value for voltage, current, power, impendence, and admittance. The Per Unit System also makes the calculation easier as all the values are taken in the same unit.

What is the significance of short circuit?

A short circuit (sometimes abbreviated to short or s/c) is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit.

What is meant by short circuit also write significance of short circuit in electrical circuit?

A short circuit is a problem in an electrical circuit where two or more wires that are not supposed to come in contact with each other touch. A short circuit can result in a very high current flowing through the circuit. A “short circuit” also happens when there is a bypass of electrical current.

What is the need for base values?

What is the need for base values? The components or various sections of power system may operate at different voltage and power levels. Hence for analysis purpose a base value is chosen for voltage, power, current and impedance.

What is a base KVA?

Voltage in equations (KV) is the secondary transformer voltage, line to line. Base KVA is 10,000 in all examples. Only those components actually in the system have to be included, each component must have an X and an R value. Neutral size is assumed to be the same size as the phase conductors.

What does base KVA mean?

The unit KVA (kilovolt amperes) is a measure of the power in an electrical circuit. For most residential applications, the voltage and current in AC circuits are in phase, and the KVA power is equal to the kilowatts (KW).

How do you calculate three phase short circuit kVA?

Thus three phase short circuit kVA is obtained by dividing the Base kVA by percentage impedance.

What is base kVA?

Ans: As the various equipment used in the power system have different KVA rating with different percentage reactances so for easy calculation it is necessary to find the percentage reactances of all equipment on a common KVA rating. This common KVA rating is known as base KVA. 10.

How do you calculate SCA for short circuits?

Short Circuit Calculations Only one calculation needs to be done for most 3 phase systems. This is for the per unit method. 3 Phase I SCA = KVA Base √3 KVLL total PUZ KVA Base = 10,000 Single Phase Two separate calculations must be done for single phase systems. I SCA = KVA Base ( KV line to line ) (total PUZ)

How to calculate the short circuit current at the HV terminal?

As we need to calculate the short circuit current at the HV terminal of the transformer, therefore first of all we need to calculate the total impedance of the system up to the HV terminal of transformer. But for finding the percentage impedance we need to select a base kVA rating.