Assignment

Problem 1

A 150 MVA, 24 kV, 123% three-phase synchronous generator operates with an induced voltage that is twice the rated line-to-neutral voltage.

Calculate the three-phase steady-state short circuit current.

Problem 2

A 250 MVA, 24 kV, 125% three-phase synchronous generator supplies a large network. The network voltage is 27 kV. The generator operates with an induced voltage, which is twice the rated line-to-neutral voltage. The phase angle between the network voltage and induced voltage is 56 degrees.

Calculate the network real and reactive powers.

Problem 3

A three-phase 60 Hz synchronous generator rated at 15 MVA and 2.2 kV has a synchronous reactance per phase of 13 Ω and spins at 1800 rpm.

(a) Calculate the induced voltage versus load function if the terminal voltage is the rated value and the power factor is 0.8 lagging. Calculate the induced voltage at the rated load and at open circuit conditions.

(b) Calculate and plot the stator short circuit current for variable load conditions if the short circuit occurs across the machine terminals. Use the induced voltage function calculated in part (a).

(c) Determine the short circuit current at both the open circuit condition and at rated load.

Problem 4

A synchronous generator supplies a network through two transformers and a transmission line, as drawn in Figure 8.70.
Figure 8.70 One-line diagram for Problem 8.12.

The generator is rated at 380 MVA and 22 kV with a reactance of 1.2 p.u. The identical transformers are rated at 480 MVA with primary and secondary voltages of 22 kV and 340 kV, respectively, and a 15% reactance. The transmission line is 45 mi long with an impedance of 0.07+j0.5 Ω/mi. The transmission line capacitances are neglected. The network voltage is 21 kV.

(a) Determine the transmission line, generator, and transformer parameters. Draw the equivalent circuit.

(b) Compute the generator excitation (induced) voltage at rated load. Assume that the terminal voltage is the same as the rated voltage, and the power factor is 0.88 lagging.

(c) Calculate the power transmitted to the network if the absolute value of the excitation voltage is the same as the value found in part (b), and the angle between the network and generator excitation voltage varies. Plot the transmitted power versus power angle, and determine the power angle at 350 MW.

Book: Electrical Energy conversion and Transport, 2nd Edition