Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Textbook Question
Chapter 11, Problem 6SQ
In Figure 11–10, assume that both motors are running. What would be the action of the circuit if the overload contact connected in series with coil 1M should open?
- a. Both motors will continue to run.
- b. Both motors will stop running.
- c. Pump motor 1 will continue to operate and pump motor 2 will stop running.
- d. Pump motor 1 will stop running and pump motor 2 will continue to operate.
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QUESTION 5 ✓
A 100 kVA, 7200 -480 V 50 Hz single phase transformer has the following parameters all given
in ohms:
RLS = 0.00800 RHS = 1.96 RfеHS = 53.2
XLS = 0.01510 XHS=4.55 XMHS=7800
This transformer is operated in step-down mode and delivers 75% of its rated power to a load that
has a power factor of 0.93 lagging.
a) Draw the equivalent circuit model of the transformer with the equivalent series Z's referred to
the high voltage side (3 Marks)
b) Find the total Zin of the transformer at the high side (3 Marks)
c) Find input Z of the transformer with the load disconnected (3 Marks)
d) Find input voltage at 75% of the load required to maintain the rated load voltage (3 Marks)
e) Find an exciting current with the load disconnected (3 Marks).
60 Marks
2- Sketch the circuits in the Block 1, Block 2
and Black 3, Then show the type of every
circuit
Iov
Vout
Block!
Vouts
20
t
Vout 2
t
lovT
Block 2
-lov
P-50HZ
25
*Vout 3
Block 3-2
2.2V 22V
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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