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LevelPE — Electrical & Computer
SubjectPE — Electrical & Computer
Year2025 BS
Exam sessionModel questions
Full marks80
Time allowed480 minutes
Questions10, all with step-by-step solutions
A

Electrical & Computer Engineering

Select the best answer.

10 questions·1 mark each
1Multiple choice1 mark

Synchronous generator: S=100MVAS = 100\,\text{MVA}, pf=0.85\text{pf} = 0.85 lagging. Real power:

P=S×pfP = S \times \text{pf}
  • a

    70MW70\,\text{MW}

  • b

    85MW85\,\text{MW}

  • c

    100MW100\,\text{MW}

  • d

    117.6MW117.6\,\text{MW}

Correct answer: b

85MW85\,\text{MW}

P=100×0.85=85MWP = 100 \times 0.85 = 85\,\text{MW}
power-generation
2Multiple choice1 mark

345 kV line, Zc=300ΩZ_c = 300\,\Omega. Surge impedance loading:

SIL=V2/Zc\text{SIL} = V^2/Z_c
  • a

    199MW199\,\text{MW}

  • b

    297MW297\,\text{MW}

  • c

    397MW397\,\text{MW}

  • d

    500MW500\,\text{MW}

Correct answer: c

397MW397\,\text{MW}

SIL=(345,000)2300=3.967×108W397MW\text{SIL} = \frac{(345{,}000)^2}{300} = 3.967 \times 10^8\,\text{W} \approx 397\,\text{MW}
transmission
3Multiple choice1 mark

Transformer: 500kVA500\,\text{kVA}, 13.2kV/480V13.2\,\text{kV}/480\,\text{V}. Primary current:

I1=S/V1I_1 = S/V_1
  • a

    18.9A18.9\,\text{A}

  • b

    37.9A37.9\,\text{A}

  • c

    75.8A75.8\,\text{A}

  • d

    1,042A1{,}042\,\text{A}

Correct answer: b

37.9A37.9\,\text{A}

I1=500,000/13,200=37.9AI_1 = 500{,}000 / 13{,}200 = 37.9\,\text{A}
distribution
4Multiple choice1 mark

Three-phase fault: If=10kAI_f = 10\,\text{kA}, VLL=13.8kVV_{LL} = 13.8\,\text{kV}. Fault MVA:

MVAfault=3×VLL×If\text{MVA}_{fault} = \sqrt{3} \times V_{LL} \times I_f
  • a

    138MVA138\,\text{MVA}

  • b

    239MVA239\,\text{MVA}

  • c

    345MVA345\,\text{MVA}

  • d

    414MVA414\,\text{MVA}

Correct answer: b

239MVA239\,\text{MVA}

MVA=1.732×13,800×10,000=239MVA\text{MVA} = 1.732 \times 13{,}800 \times 10{,}000 = 239\,\text{MVA}
protection
5Multiple choice1 mark

Induction motor: Ns=1,800rpmN_s = 1{,}800\,\text{rpm}, s=3%s = 3\%. Rotor speed:

Nr=Ns(1s)N_r = N_s(1 - s)
  • a

    1,710rpm1{,}710\,\text{rpm}

  • b

    1,746rpm1{,}746\,\text{rpm}

  • c

    1,764rpm1{,}764\,\text{rpm}

  • d

    1,800rpm1{,}800\,\text{rpm}

Correct answer: b

1,746rpm1{,}746\,\text{rpm}

Nr=1800×0.97=1,746rpmN_r = 1800 \times 0.97 = 1{,}746\,\text{rpm}
motor-drives
6Multiple choice1 mark

CT ratio 600:5, primary current 450 A. Secondary current:

I2=I1×5/600I_2 = I_1 \times 5/600
  • a

    2.50A2.50\,\text{A}

  • b

    3.75A3.75\,\text{A}

  • c

    5.00A5.00\,\text{A}

  • d

    7.50A7.50\,\text{A}

Correct answer: b

3.75A3.75\,\text{A}

I2=450×5/600=3.75AI_2 = 450 \times 5/600 = 3.75\,\text{A}
instrumentation
7Multiple choice1 mark

Wind turbine: D=80mD = 80\,\text{m}, v=12m/sv = 12\,\text{m/s}, ρ=1.225\rho = 1.225, Cp=0.40C_p = 0.40:

P=12ρAv3CpP = \frac{1}{2}\rho A v^3 C_p
  • a

    853kW853\,\text{kW}

  • b

    1,066kW1{,}066\,\text{kW}

  • c

    1,706kW1{,}706\,\text{kW}

  • d

    2,133kW2{,}133\,\text{kW}

Correct answer: c

1,706kW1{,}706\,\text{kW}

A=π(80)2/4=5,026.5m2A = \pi(80)^2/4 = 5{,}026.5\,\text{m}^2 P=0.5×1.225×5026.5×1728×0.401,706kWP = 0.5 \times 1.225 \times 5026.5 \times 1728 \times 0.40 \approx 1{,}706\,\text{kW}
power-generation
8Multiple choice1 mark

Transformer pu impedance base change: Zpu=0.10Z_{pu} = 0.10 at 50 MVA. New base 100 MVA, same voltage:

Znew=Zold×Snew/SoldZ_{new} = Z_{old} \times S_{new}/S_{old}
  • a

    0.10pu0.10\,\text{pu}

  • b

    0.20pu0.20\,\text{pu}

  • c

    0.05pu0.05\,\text{pu}

  • d

    0.40pu0.40\,\text{pu}

Correct answer: b

0.20pu0.20\,\text{pu}

Znew=0.10×100/50=0.20puZ_{new} = 0.10 \times 100/50 = 0.20\,\text{pu}
transmission
9Multiple choice1 mark

Distance relay: line ZL=10+j40ΩZ_L = 10 + j40\,\Omega, Zone 1 at 80%. Reach impedance:

  • a

    8+j32Ω8 + j32\,\Omega

  • b

    10+j40Ω10 + j40\,\Omega

  • c

    12+j48Ω12 + j48\,\Omega

  • d

    5+j20Ω5 + j20\,\Omega

Correct answer: a

8+j32Ω8 + j32\,\Omega

Z1=0.80(10+j40)=8+j32ΩZ_1 = 0.80(10 + j40) = 8 + j32\,\Omega
protection
10Multiple choice1 mark

VFD: motor rated 60 Hz / 460 V, operating at 40 Hz. Constant V/Hz voltage:

V=Vrated×f/fratedV = V_{rated} \times f/f_{rated}
  • a

    230V230\,\text{V}

  • b

    307V307\,\text{V}

  • c

    345V345\,\text{V}

  • d

    460V460\,\text{V}

Correct answer: b

307V307\,\text{V}

V=460×40/60=307VV = 460 \times 40/60 = 307\,\text{V}

Constant V/Hz maintains constant flux.

motor-drives

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The PE — Electrical & Computer PE — Electrical & Computer 2025 paper carries 80 full marks and is meant to be completed in 480 minutes, across 10 questions.
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