ELECTRICITY FOR TRADES
3rd Edition
ISBN: 9780078118630
Author: Petruzella
Publisher: RENT MCG
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Chapter 7.2, Problem 9RQ
The current through and the voltage drop across a precision resistor are measured and found to be 8 mA and 1.5 V, respectively. What is the resistance value of the resistor?
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2- Sketch the circuits in the Block 1, Block 2
and Black 3, Then show the type of every
circuit
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2. A 3-phase, 75 MVA, 11-8 kV star-connected alternator with a solidly earthed neutral point has the fol-
lowing p.u. impedances based on rated phase voltage and rated phase current :
Positive phase sequence impedance
Negative phase sequence impedance
Zero phase sequence impedance
=
j 2 p.u.
=
j 0.16 p.u.
=
j 0.08 p.u.
Determine the steady-state fault current for the following: (i) 3-phase symmetrical short-circuit (ii) one
line-to-earth fault (iii) two line-to-earth fault. The generated e.m.f. per phase is equal to the rated voltage.
[(i)1840 A (ii) 4920 A (iii) 3580 A]
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Q1. With the help of a well-drawn diagram, explain concept map of an electromechanical
system modelling.
[20]
Q2. Separately-excited generator develops a no load emf of 150V at an armature spend of 20
rev/s and a flux per pole of 0.1 Wb. determine the generated emf when
a. The spend increases to 25rev/s and the pole flux remains unchanged.
b. The speed remains at 20 rev/s and the pole flux is decreased to 0.08Wb.
c. The speed increases to 24 rev/s and the pole flux is decreased to 0.07 Wb
Write short notes on the following term
a. Copper loss
b. Iron loss
c. Friction and Windage losses.
[20]
Chapter 7 Solutions
ELECTRICITY FOR TRADES
Ch. 7.1 - What is the base unit and symbol used for...Ch. 7.1 - Write the metric prefix and symbol used to...Ch. 7.1 - Convert each of the following: a. 2,500 to...Ch. 7.2 - State Ohms law.Ch. 7.2 - List the three formulas associated with Ohms law.Ch. 7.2 - Calculate the unknown value for each circuit (a)...Ch. 7.2 - A pilot lamp with 12 volts applied to it draws a...Ch. 7.2 - A resistor has a resistance of 220 . The current...Ch. 7.2 - An electric soldering iron with a 40- heating...Ch. 7.2 - A baseboard heater draws a current of 8 A when...
Ch. 7.2 - A sensor module has an internal resistance of...Ch. 7.2 - The current through and the voltage drop across a...Ch. 7.2 - The heating element for an electric floor heating...Ch. 7.2 - How much power is lost in the form of heat when 25...Ch. 7.2 - The voltage drop across a 330- resistor is...Ch. 7.2 - A digital multimeter display indicates a reading...Ch. 7.2 - Calculate the unknown value for each circuit (a)...Ch. 7.2 - Assume that applying 120 volts to a resistive load...Ch. 7.2 - The voltage drop across a 10-W, 330- resistor is...Ch. 7.2 - The cold resistance of a tungsten lamp filament is...Ch. 7.2 - An electric baseboard heater is rated for 1200 W...Ch. 7.2 - A lamp dimmer switch is rated for 5 A at 120 V....Ch. 7.2 - A 400-W 4- public address speaker is to be fused...
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