AC THEORY


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�� To ensure the neutral current is zero

Question 1

What is the reason for balancing the load across the three phases

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�� IL

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��Question 2

In an RL Parallel circuit what is the lagging component

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�� Fit p.f. correction capacitors across the load

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��Question 3

What can be done to improve the power factor of an industrial installation

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�� 3488.37 VA

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��Question 4

If the true power is 3kW and the power factor is 0.86 what is the apparent power.

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�� 48.81 degrees

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��Question 5

If R=7 ohms�and Xc=8 ohms what is the phase angle

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�� 0.919

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��Question 6

If the phase angle is 23.185 degrees what is the power factor

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�� 106.10 ohms

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��Question 7

What is the Ohmic value (or capacitive reactance) of a 30 micro Farad Capacitor

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�� 25 kVAr

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��Question 8

If the apparent power is 50 kVA and the phase angle is 30 degrees what is the value of the reactive component

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�� IL=Ip

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��Question 9

In a star connected system what is the relationship between Line Current and Phase Current

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�� 45 degrees

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��Question 10

If the true power was 500 watts and the apparent power was 707.106 VA what would the phase angle be

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�� V (Volts)

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��Question 11

In an RLC Parallel circuit which quantitiy remains constant

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�� VL

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��Question 12

In an RL Series circuit what is the lagging component

Feedback:

In an RL Series circuit what is the lagging component

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�� 0.636

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��Question 13

If R=7 and Z=11 what is the power factor

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�� Ohms

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��Question 14

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What does the ratio W/VA produce:

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�� To improve the power factor

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��Question 15

What is the purpose of the capacitor across the terminals of a fluorescent fitting used for:

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�� 0.707

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��Question 16

If the true power was 500 watts and the apparent power was 707.106 VA what would the power factor be

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�� Unity

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��Question 17

When W=VA what is the p.f

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�� 1390 micro farads

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��Question 18

An RL circuit connected to a 50Hz supply consists of a 5 ohm resistor in series with an inductor of� 7.29mH. What size capacitor would you need to connect across the supply to correct the phase shift

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�� VA (Volt Amps)

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��Question 19

On a power triangle what does the hypotenuse represent:

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�� 120

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��Question 20

By how many degrees are the three phases separated

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�� One third the power (p/3)

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��Question 21

What is the relationship between the power dissipated in a star connected system to that of a delta connected system

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�� IL>Ip

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��Question 22

In a delta connected system what is the relationship between Line Current and Phase Current

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�� 9.42 ohms

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��Question 23

What is the Ohmic value (or inductive reactance) of a 30 milli Henry (30mH) inductor

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�� 1

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��Question 24

When R=Z what is the p.f

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�� Z

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��Question 25

On an impedance triangle what does the hypotenuse represent:

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�� 54.31 degrees

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��Question 26

If R=7 and Z=12 what is the phase angle

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�� PowerFactor

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��Question 27

What does the ratio of R/Z produce:

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�� XL = 2.29�ohms, p.f. = 0.909,�phase angle = 24.59 degrees

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��Question 28

An RL circuit connected to a 50Hz supply consists of a 5 ohm resistor in series with an inductor of� 7.29mH.

What is the Ohmic value of the inductor, The power factor and the phase angle

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�� 7.3mH

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��Question 29

In a series RL circuit�the value of R is 4 ohms and the phase angle is 30 degrees what is the� value of the inductor

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�� I (Amps)

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��Question 30

In an RLC Series circuit which quantity remains constant



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