Fault Analysis

What is the purpose of fault calculation in a power system?

• To estimate the current flowing immediately after a fault occurs

• To determine the settings of the relays that control the circuit breakers

• To analyze the types of faults that can occur in a power system

• To calculate the impedance of transformers during a fault

What are the types of faults that can occur in a power system?

• Shunt faults and series faults

• Symmetrical faults and unsymmetrical faults

• Positive sequence faults and negative sequence faults

• Zero sequence faults and double line to ground faults

What are the sequence components of a three-phase system?

• Positive sequence components, negative sequence components, and zero sequence components

• Symmetrical components, asymmetrical components, and balanced components

• Primary components, secondary components, and tertiary components

• Real components, reactive components, and apparent components

What is the purpose of sequence networks in fault analysis?

• To calculate the fault current during a symmetrical fault

• To determine the impedance of transformers during a fault

• To analyze the types of faults that can occur in a power system

• To resolve unbalanced system vectors into balanced system vectors

What is the difference between a symmetrical fault and an unsymmetrical fault?

• A symmetrical fault has equal fault currents in the lines with 120 degrees phase displacement, while an unsymmetrical fault has unequal fault currents with unequal phase displacement

• A symmetrical fault occurs during a short circuit, while an unsymmetrical fault occurs during an open circuit

• A symmetrical fault occurs in the transmission lines, while an unsymmetrical fault occurs in the distribution lines

• A symmetrical fault can be resolved into positive, negative, and zero sequence components, while an unsymmetrical fault cannot

What is the equivalent circuit of a generator during a line-to-ground fault?

• Open circuit

• Short circuit

• Series circuit

• Parallel circuit

What is the short circuit MVA of four generators connected in parallel with a rating of 100 MVA each and a sequence impedance of 0.12 pu?

• 3333.33 MVA

• 400 MVA

• 250 MVA

• 5000 MVA

What is the per unit impedance of the neutral grounding for a generator if the fault current of a line-to-line fault is the same as that of a line-to-ground fault?

• 0.01 pu

• 0.03 pu

• 0.05 pu

• 0.10 pu

What is the magnitude of the fault current in kA for a B-phase to ground fault in a 125 MVA, three-phase, 15.5 kV star grounded generator with positive, negative, and zero sequence impedances of j0.1 pu, j0.05 pu, and j0.01 pu respectively?

• 10 kA

• 20 kA

• 30 kA

• 40 kA

What is the reactance of a series reactor connected to an alternator to reduce the sub-transient current from 20 pu to 5 pu?

• 0.25 pu

• 0.50 pu

• 0.75 pu

• 1.00 pu