Power Systems Objective Questions & Answers – Set 9

Y bus matrix is a sparse matrix, containing more number of zero elements. So that faster calculation is possible. The Y bus matrix is used for the load flow studies. Z bus algorithm or matrix is used for the fault analysis. Inverse of Y bus matrix gives the Z bus matrix, But Z matrix is a full matrix even though Y bus is a sparse matrix. More time is required for inverse of Z bus matrix if the size of the matrix is more than three.

If the fault is very nearer to the generator, the fault current is

Making current is a------------ value?

Operator "a" rotates a vector

A transmission line has (2 + j4)Ω impedance, 100 MVA and base voltage is 10 KV. Find the per unit impedance value of transmission line?

Three generators rated 100 MVA, 11 kV have an impedance of 0.15 pu each. If in the same plant, these generators are being replaced by a single equivalent generator, the effective impedance of equivalent generator will be

The angular moment of 10 MVA generator is 0.2. Find the new value of angular moment for 20 MVA base?

If in a line, resistance and reactance are found to be equal and regulation is zero, then load will have

The draw back of NR method as compare to Gauss-Seidel method is/are?

A generator has reactances of sub transient (X")= 0.5 pu, transient (X') = 0.8 pu and synchronous reactance (X) = 5 pu. The voltages at these reactances are 1.2 V, 1.1 V and 1 V respectively. Find the corresponding sub transient fault current in pu?

Breaking current is a ------------------ value?

The charging current of a 400 kV line is more than that of a 220 kV line of the same length?

For a 500 Hz frequency excitation, a 100 km long power line will be modelled as

When series reactor is used in generating stations, the fault current magnitude is

The per unit impedance Z(pu) is given by

Fault calculations using computer are usually done by

Per unit of any quantity is defined as

A 10 MVA generator has reactance of 0.2 pu. Find the new reactance value for 50 MVA base?

Which of the following method is/are more reliable?

A transmission line has impedance of (0.005 + j0.05) pu. Find the line at which maximum value of negative DC off set current is produced, if it is applied with V_m cosωt?

The per unit impedance of a circuit element is 0.30. If the base kV and base MVA are halved, then the new value of the per unit impedance of the circuit element will be

A 20 MVA generator has inertia constant of 0.5 pu. Find new value for 50 MVA base?

The voltage and current instantaneous values are given as 5 sin (ωt + 30°) pu and 2 sin (ωt - 15°) pu respectively. Find the per unit active power?

Find the relation between sub transient (X"), transient (X') and synchronous reactance (X) ?

The load current in short circuit calculations are neglected because

A transmission line has impedance of (0.005 + j0.05) pu. Find the line at which maximum value of negative DC off set current is produced, if it is applied with V_m sinωt?

Advantage/s of per unit system as compare to absolute system?

The voltage regulation of a line at full load 0.8 power factor is 11. A long transmission line under no load conditions, for a good voltage profile needs

A generator has a rating of 10 MVA, 5 kV has a reactance of 0.02 pu. Find the reactance at a new base values of 50 MVA, 10 kV?

The per unit value of a 2 ohm resistor at 100 MVA and 10 kV base voltage is