Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Chapter 7, Problem 3SQ
What are the advantages of a
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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]
Q4. A 415V, three phase, 50 Hz 4 pole, star connected induction motor ruins at 24 rev/s on
full load. The rotor resistance and reactance per phase are 0.35 ohms and rotor respectively
and the effective rotor stator turns ratio is 0.85:1 calculate:
a. The synchronous speed
b. The slip.
c. The full load torque.
d. The power output if mechanical losses amount to 770 W
e. The maximum torque
f. The speed at which maximum torque occurs
g. The starting torque
h. Direct on-line starting
i. Star delta starting
[20]
Chapter 7 Solutions
Electric Motor Control
Ch. 7 - What are control relays?Ch. 7 - What are typical uses for control relays?Ch. 7 - What are the advantages of a mechanically held...Ch. 7 - Why are mechanically held relays energy-saving...Ch. 7 - Why does the coil (CR) in Figure 719 drop out when...Ch. 7 - Which device is used to connect the load to the...Ch. 7 - Which device is used to connect the load to the...Ch. 7 - What is optoisolation?Ch. 7 - What type of device is used to suppress voltage...
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- 3. The per unit values of positive, negative and zero sequence reactances of a network at fault are 0.08, 0.07 and 0.05 respectively. Determine the fault current if fault is line-to-line-to-ground. [j 16 p.u.]arrow_forwardFor the network shown in Figure B2, the switch is closed on to position I when t = 0 and then moved to position 2 when t = 100 ms. 1V 50 R₁ R₂ 200 10 mH Figure B2 a) i. What is the value of the time constant when charging (position I)? ii. Determine the current equation when charging (position I) [I mark] [2 marks] b) Determine the value of the charging current at 1.5 ms. [3 marks] i. What is the value of the time constant when discharging? [2 marks] ii. Determine current equation when discharging (remember switch is moved to position 2 when t = 100 ms) [3 marks] c) Determine the current in the inductor when t = 102.5 ms (remember switch is moved to position 2 when t = 100 ms) [4 marks]arrow_forwardNEED HANDWRITTEN SOLUTION PLEASE DO NOT USE AIarrow_forward
- NEED HANDWRITTEN SOLUTION PLEASE DO NOT USE AIarrow_forward1) What is the value of the current through the battery when the switches SW1, SW2, and SW3 are OPEN?arrow_forwardIn the circuit of the figure, ε = 12.2 V, R = 7.34 Ω and L = 5.48 H. The battery is connected at t = 0. Determine: a) The amount of energy delivered by the battery during the first 2.00 s. b) The amount of energy stored in the magnetic field of the inductor. c) The amount of energy dissipated in the resistor.arrow_forward
- 4) For the sinusoidal signal m(t) = 2 sin(1000πt + 0.0557), shown down, is sampled, quantized and then encoded using the PCM technique. If a uniform quantizer, with 8 levels and a dynamic range [-2, 2], is used (a) Calculate the first 4 quantized samples and the ciated quantization errors. (b) Calculate the maximum quantization error (c) Calculate the signal-to-quantization- noise ratio. (d) Calculate the resultant bit rate. italicio (e) If it is required to increase the signal-to-quantization-noise ratio by 6 dB, how many quantization levels should be used in this case? What is the ratio between the new bit rate and the previous bit rate? msecarrow_forwardThe current of a 90.0 mH inductor changes with time in the form I=1.00t2 - 6.00t (in SI units). Determine the magnitude of the induced fem at a) t=1.00 s b) At what time will the fem equal zero?arrow_forwardA coil of 200 turns and 4 cm2 of section, is rotating in a magnetic field of 0.5 T. a) What must be its angular frequency to generate a maximum fem (εm) of 10 V?b) What is the value of εm if it rotates at 60 rev/s?arrow_forward
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