Assignment Task

The performance of a 275-kV transmission line (TL) is to be studied with regard to power flow analysis. The line may be assumed to be fed from an ‘infinite’ generator (the Grid) and terminated with a lumped load with fixed real and reactive power. The following system data applies: -

System Bases

2000 MVA, 50 Hz, 275 kV Infinite Generator (Grid) 275 kV, 50 Hz, 3-ph, 100,000 MVA Fault level 3-ph & 1-ph, X/R ratio =10, Voltage set at 1.0 p.u.

Busbars

275 kV, 50 Hz, 100,000 MVA Fault level, voltage limit is 1 p.u. +8%, -15%

Transmission Line

275 kV, 3-ph, 50-Hz, R = 0.0081 Ohms/km, L = 0.51 mH/km, C = 0.0078 µF/km,  with the maximum current Summer/Winter/Spring/Autumn = 850 A.

Question

i. Calculate, the receiving end current, the sending end (voltage, current and power) using the line models discussed in the lecture notes. The load parameters are as  follows; 325 MVA, 0.91 pf lagging, 50 Hz, 275 kV for the following transmission line  lengths;

1. 25 km (short line)
2. 35 km (long line)

Then, create and run load flow model of the above system in ERACS (pay extra attention to parameters to be considered in each model). Outline any assumptions made in representing the system. c. Compare your calculation with the simulation results.

ii. For only the simulation study conducted in Part (I), calculate the transmission system performance indicators, i.e. voltage regulation and line efficiency, for both line lengths, pay attention to the used formulas.

III. For the system described above (Grid, Long Transmission Line), calculate the surge impedance loading (SIL), verify by running appropriate simulation, the power system performance under SIL condition, consult your lecture notes

iv. For the system described above (Grid, Long Transmission Line), add a stepdown power transformer (275 kV/33 kV, 110 MVA) at the end of the long line that is specified in Part (I), keep the line parameters (r, L, C) unchanged.

v. Investigate the maximum unity power factor load that can be connected to the secondary side of the transformer without violating the system constraints, show evidences of constraints’ violation.