Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Textbook Question
Chapter 40, Problem 4SQ
When the rotor and stator fields lock into step, why may the reading of the AC ammeter decrease?
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Q4.
a)
Consider a transmission line modelled as a four-terminal network with an
unknown configuration. You are provided with the following measured
parameters at the operating frequency:
Open-circuit voltage ratio: 0.9521°
• Short-circuit impedance: 40+j80
• Open-circuit admittance: -j2 × 10-4 S
Use the four terminal equations and the provided measurements to
mathematically derive the A, B, C, and D parameters of the network and
explain their physical significance. Show your work and formulas used in
the derivation.
Q1.
Consider a single-phase step-down transformer with primary and
secondary turns of 600 and 100 respectively and a primary voltage of
11 kV.
(i) An open circuit test was conducted on the transformer and the primary
current was measured as:
I₁ = 2.20 A
Use these results to calculate the magnetising reactance in the equivalent
circuit (X) given that Rm, representing the core loss, has a value of 21 km.
(ii) The remaining equivalent circuit parameters are as follows:
R₁ = 40, X₁ = 25 N, R₂ = 0.4 N, X₂ = 0.3 N
Draw the complete simplified equivalent circuit, by referring series
components on the primary side to the secondary, giving all component
values.
(iii) The transformer is connected, on its secondary side, to a load of 10
at a power factor of 1. Calculate the voltage across the load.
(iv) Calculate the efficiency of the transformer when operating at the load
given in part (iii).
b)
A 132 kV supply feeds a line of reactance 15 which is connected to a 100
MVA, 132/33 kV transformer of 0.08 p.u. reactance as shown in the
Figure 2. The transformer feeds a 33 kV line of reactance 8 Q, which, in
turn, is connected to a 75 MVA, 33/11 KV transformer of 0.12 p.u.
reactance. The transformer supplies an 11 KV substation from which a local
11 kV feeder of 4 Q reactance is supplied.
T1
T2
132 kV
33 kV
11 kV
Fault
X
CB
Relay
Figure 2. Network for Q4 b).
(i) Given the system base of 100 MVA, compute the total equivalent
reactance of the radial circuit in per unit (p.u.).
(ii) Determine the three-phase fault current at the load end of the 11 kV
feeder, assuming a fault impedance of 0.05 Q. Calculate the fault
current in Amperes.
(iii) The 11 kV feeder connects to a protective overcurrent relay via 200/5 A
current transformers. This relay has a standard normally inverse IDMT
characteristic, with a setting current of 3 A and a time multiplier setting
of 0.4. Calculate the…
Chapter 40 Solutions
Electric Motor Control
Ch. 40 - What are the two basic functions of synchronous...Ch. 40 - Prob. 2SQCh. 40 - If all of the control circuits are ACand DC is not...Ch. 40 - When the rotor and stator fields lock into step,...Ch. 40 - Prob. 5SQCh. 40 - Prob. 6SQCh. 40 - In Figure 402, approximately what is the...Ch. 40 - Why are the AC ammeter and DC meter necessary in...Ch. 40 - Prob. 9SQ
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