MKEP1623
Q1.
A three phase, 275kV, 50 Hz, 120 km transmission line has the following parameters:
Series impedance, 𝑍 = 0.042 + 𝑗0.35 Ω /km
Shunt susceptance, 𝑌 = 𝑗5 × 10−6 S /km
a) The load at receiving-end at full load is 250 MW at 0.87 lagging power factor at 95% of
the rated voltage. Determine the sending end voltage and sending end current at full load.
(15 marks)
b) Determine the efficiency of the transmission line at full load.
(5 marks)
Q2.
A 275kV transmission line has the following parameters:
𝐴 = 0.93 ∠ 3.8°
𝐵 = 182 ∠ 72°
a) The sending end voltage is 275kV. If three loads are connected in parallel at the receiving
end of the line;
 Load 1: 0.5 MVar
 Load 2: 20 MW (at 0.85 power factor lagging)
 Load 3: 17.2 MW, 1 MVar
what type and rating of compensation equipment required to keep the voltage at the
receiving end 275kV?
(13 marks)
b) If the power factor of load 2 is improved into 0.95 power factor lagging, briefly discuss
the expected impact on the voltage at the receiving end with compensation equipment in
Q2(a) remain connected. Support your answer with relevant calculations.
(5 marks)
Q3.
Figure below shows an overhead sub transmission line with a span of 760ft between tower
A and Tower B. The weight of the conductor is 5000 lb/mi. The height of Tower B is 85ft.
with the level of Tower A 40 ft. higher than Tower B. The minimum clearance above
ground is 80ft. Assuming the tension along the conductor is uniform and the tension of the
conductor is set at 10,000 lb. Determine the minimum height of Tower A in order for the
conductor to meet the minimum clearance above ground. The diameter of the overhead line
is 1.1 in. and radial thickness of ice is 0.25 in., in a wind that exerts a pressure of 8.5 lb/ft2
(note: 1 mile = 5280 feet).
Tower B
Tower A
85 ft.
40 ft.
(12 marks)
1. ABCD parameter of Medium Transmission Line Model
1
(1 + 𝑌𝑍)
2
[
1
𝑌 (1 + 𝑌𝑍)
4
𝑍
1
(1 + 𝑌𝑍)
2
]
2. Effect of ice
𝑤𝑖 = 1.25𝑡𝑖 (𝑑𝑐 + 𝑡𝑖 )
𝑙𝑏⁄
𝑓𝑡.
1
(𝑑 + 2𝑡𝑖 )𝑝
12 𝑐
𝑙𝑏⁄
𝑓𝑡.
Effect of wind
𝑃=
Where;
𝑤𝑖 : weight of ice per unit length
𝑡𝑖 : radial thickness of ice in in.
𝑑𝐶 : diameter of conductor in in.
𝑃: horizontal wind force
𝑝: wind pressure in pounds per square feet
3.
3|𝑉𝑆 ||𝑉𝑅 |
3|𝐴||𝑉𝑅 |2
𝑃𝑅 =
cos(𝛽 − 𝛿) −
cos(𝛽 − 𝛼)
|𝐵|
|𝐵|
3|𝑉𝑆 ||𝑉𝑅 |
3|𝐴||𝑉𝑅 |2
𝑄𝑅 =
sin(𝛽 − 𝛿) −
sin(𝛽 − 𝛼)
|𝐵|
|𝐵|