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Q1. Two Three phase generators supply a three phase load through seprate three phase lines. The

load absorbs 30KW at 0.8 lagging power factor. The line impedance per phase between

generator G1 and the load is 1.4+j1.6Ω . If generator G1 supplies 15KW at 0.8 Lagging power

factor with terminal voltage of 460V line to line .Determine:

a) The voltage at load terminals.

b) The voltage at terminals of generator G2.

c) The real and reactive power supplied by generator G2.

The Islamic University of Gaza

Faculty of Engineering

Electrical Engineering Department

Electric Machinary

HW#1 ( Chapter 1)

Eng. Haya Ashraf Swedan

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Q2. Three loads are connected to 208V three phase source as shown. One is a three phase motor

connected Y-connected and running such that the line current 25A and the power factor is

0.8lagging.The second is a single phase motor connected between lines a and b which takes a

current of 8A at power factor of 0.707 lagging. The third is a single Phase connected between

lines b and c ,taking a current of 10A at power factor of 0.8 leading .Using Vab as refrence,

Determine:

a) The voltage of terminals of three motors.

b) The line currents.

c) The total input power.

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Q3.Three Phase balanced, Three Phase loads are connected in Parallel:

Load1 : Y , Z=300+J100Ω/Ph

Load2 : ∆ , Z=5400-J2700Ω/Ph

Load3 : S=112.32+J95.04Ω/Ph

Z(line)=1+j10Ω/Ph . The magnitude of the line to neutral voltage of the end of the load is 7.2KV

Calculate:

a) Total load current

b) Voltage of generator terminal

c) Complex power supplied by generator.

d) Efficiency.

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Q4.Three Phase ,50Hz generator supplies power to load through transmission line of series

impedance 50+j500Ω/Ph , the load consume 50KW of 11KV with P.F 0.8 lag , three phase

capacitor 0.5µF are connected star across the load .Find:

a) The current supplies by the generator.

b) The voltage of the generator terminal.

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Q5. Balance inductive delta load is connected to 550v,60HZ ,three phase supply ,the line current

is 90A and the total power is 10KW ,a delta connected capacitive bank of 40µF is connected in

parallel. Determine:

a) The magnitude of the resulting current

b) Power factor

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Q6. Three Phase , Three loads are connected in Parallel as :

Load1 : 120KVA ,0.6 (P.f Lead)

Load2 : 180KVA ,0.8 (P.f Lag)

Load3 : 100.8KW + j5.6KVAR

Z(line)=1+j8Ω Vload=240v

a) Draw the power triangle for each load

b) Equivalent load per phase

c) Supply current

d) Complex Power of source

e) Loss complex power

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Q7.The two Balanced system shown in are interconnected through lines having per phase

impedance =1+j2Ω . If =10∟KV rms and If =10∟KV rms.Find

a) State which system is the source and which is load

b) Waht is the power supplied by the source and the power absorbed by the load

c) Show the total power generated equals the total power absorbed

0 6

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Q8.The output of the balanced three phase source shown in figure is 78KVA at 0.8leading power

factor .If the line voltage at the source is 208√3 V .Fimd

a) The the magnitude of line voltage at the load

b) The total complex power at the terminals of the load

c) The effiecency of the transmision line

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Q9.The figure shown represents a one lone digram of simple three phase power system with

single 480Vgenerator and three loads.Assume that the transmision lines in this power system are

lossess and load1 is Y-connected while load2 and load3 delta-connected.

a) Calculate the complex power supplied by the generator when the switch is open

b) What is the total line current when the switch is open

c) Calculate the complex power supplied by the generator when the switch is closed

d) What is the total line current when the switch is closed

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Q10.The one-line diagram below shows a small 3-phase , 480V industrial distribution system.

The power system supplies a constant line voltage of 480V, and the impedance of 10Ω and phase

angle of 30. Load2 is Y-connected with a phase impedance of 5Ω and a phase angle -36.87.

a) Find the overall power factor of the distribution system

b) Sketch the power triangle of each load

c) Find the total line current supplied to the distribution system

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Q11. Three balanced three phase loads are connected in parallel .Load1 is Y-connected with

impedance of 400+j300Ω\ϕ .load2 is ∆-connected with impedance of 2400+j1800Ω\ϕ and load3

is 172.8+2203KVA.The loads are fed from a distribution line with impedance of 2+j16 Ω\ϕ . The

magnitude of the line to line voltage at the load end of the line is 24√3KV.

a) Sketch the single phase equivalent circuit of the system

b) Calculate the total complex power at the sending end of the line

c) What is the efficiency of distribution line?

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Q12.A balanced three phase source is supplying 1800KVA at 0.96leading power factor to two

balanced Y-connected loads through a distribution line. The distribution line has negligible

impedance.Load1 =192+J1464KVA. The line voltage at the load terminals is 6400√3V

a) Sketch the power triangle of the source,Load1 and load2

b) Sketch the single phase equivalent circuit of the system

c) Determine the impedance of load1

d) Determine the impedance of load2

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Q13.A certain load draws a current of 10A at a lagging power factor of 0.5 from 120V ,60Hz

source. The electric supply company imposes a penalty if the power factor drops below 0.8.What

size capacitor must be used just to a void the penalty?

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Q14.An electric heater takes 1000W at unity power factor from 120V,60Hz supply. When a

single phase motor is connected a cross the supply, The power factor of total load becomes 0.8

lagging .If the power requirement of the motor is 1750W, what is its power factor?

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Q15.A balanced ∆-load consisting of pure resistance of 15Ω\ϕ is in a parallel with balanced Y-

connected having phase of 8+j6Ω .Identical impedance of 2+j5Ω are in each of the three lines

connected the combined loads to a 110V three phase supply. Find the current drawn from the

supply and line voltage at the combined loads.

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Q16.

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Q17