Electric Motor Control
10th Edition
ISBN: 9781133702818
Author: Herman
Publisher: CENGAGE L
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Chapter 26, Problem 6SQ
To determine
Explain how the starter provides smooth acceleration and a gradual increase of torque.
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(B)- Indicate whether the following statements are true or false and correct the false statements
I-A d.c. shunt motor is running with certain load. The effect of adding an external
resistance in armature circuit is to increase the motor speed F Constant speed
2- A de series motor develops a torque of 30 N.m at 4 A of load current. if the current
is increased to 6 A, the torque developed will be 67.5 N.m T
3-If the two field Windings are wound in such a manner that the fluxes produced by the
two always help each other, the motor is called cumulatively compound F
4-The speed of d.c series motor is decreased if the armature current is increased T
5- To solve the Commutation Problem in large machines, this can be achieved by increasing
the brush width.
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In (Rm. Ps)
A full load current of 50 A is generated by a 250 V d.c. shunt motor with a 0.5 ohm armature resistance. When a 1 ohm resistance is connected in series with the armature, what is the ratio of stalling torque to full load torque?
Q2 A DC shunt motor is connected to a 220 V supply. Figurel below shows the time/current
characteristics with a resistance starter. If armature resistance is 0.12 0,
a) What is the maximum current that is flowing in the armature at the instant of starting?
b) What is the minimum current in the armature?
c) How many sections does this starter resistance have? Show your work.
d) Calculate the required starter resistance required to limit the current to the maximum
value.
270
162
13
t.
Chapter 26 Solutions
Electric Motor Control
Ch. 26 - What is the purpose of inserting resistance in the...Ch. 26 - Why is the power not interrupted when the motor...Ch. 26 - If the starter is to function properly and a...Ch. 26 - How may additional steps of acceleration be added?Ch. 26 - What is meant by the low or poor starting economy...Ch. 26 - Prob. 6SQ
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, electrical-engineering and related others by exploring similar questions and additional content below.Similar questions
- Q2 A DC shunt motor is connected to a 220 V supply. Figurel below shows the time/current characteristics with a resistance starter. If armature resistance is 0.12 0, a) What is the maximum current that is flowing in the armature at the instant of starting? b) What is the minimum current in the armature? c) How many sections does this starter resistance have? Show your work. d) Calculate the required starter resistance required to limit the current to the maximum value. 270 162 t2 tsarrow_forwardWhat types of motors contain brushes and a commutator? What is the function of these parts?arrow_forwardA 500 V shunt motor running at 720 rpm takes an armature current of 50 A. The equivalent armature resistance is 0.4 ohm. What resistance must be placed in series with the armature to reduce the speed to 540 rpm while maintaining the same torque?arrow_forward
- An induction motor develops rated torque with a slip of 3.5% when the rotor is cold. If the rotor resistance is 20% higher when the motor is at normal running temperature, at what slip it will develop rated torque?arrow_forwardAt full load, when the DC shunt motor is supplied by 110 V dc source, the armature current is 20 A keeping the speed of the motor at 500 rpm. If the flux of the motor is weakened by 10%, the armature current drops to 15 A. By how much is the torque decreased?arrow_forwardbläs 5 The input power to a 220 V lap wound shunt D.C motor runs is 11 kW , the speed is 1150 rpm takes 5 A at no load „shunt field resistance is 110 Q and armature resistance is 0.5Q Find a- The speed of motor at this load b-The speed if connected resistance (25 Q) in series with field resistance when the armature torque is constant and the flux is proportional to field current .assume the information in branch a is normal condition.c-Maximum efficiency before and after adding (R .add)arrow_forward
- 2. A 110 V shunt motor has a field resistance of 55 ohms and armature resistance of 0.1 ohm. The motor takes 20 A of current at 1000 rpm while developing full load torque. What is the motor speed when this motor develops 70% of the full load torque.arrow_forwardA 120 V shunt motor has an armature equivalent of 0.5 ohm and a field resistance of 60 ohm. At full load, the motor takes 10 A and the speed is 1000 rpm. At what speed must this motor maybe driven as a generator to deliver 10 A to an external load at 120 V?arrow_forward1. A 100 v dc series motors run at 400 rpm when taking a current of 55 Amp. Armature resistance is 0.03 ohm, field resistance is 0.03 ohm. If the load torque remains the same. What is the input current when the field is shunted by a resistor of 0.02 ohm? 2. A four-pole lap wound 500 V shunt motor takes a full-load armature current of 50A, the full-load speed being 800 r.p.m. There are 440 armature conductors and armature resistance is 0.3 ohm, contact drop brush = 1 V.Find the useful flux per pole.arrow_forward
- A 240 V shunt motor has an armature current of 15 A when running at 800 rpm against full-load torque. The armature resistance is 0.6 ohm. What resistance must be inserted in series with the armature to reduce the speed to 400 rpm at the same torque? What will be the speed if the load torque is halved with this resistance in the circuit? Assume the flux to remain constant throughout.arrow_forwardA 400 V series motor has a field resistance of 0.2 ohm and an armature resistance of0.1 ohm. The motortakes 30 A of currentat 1000 rpm while developing full load torque. What is the motorspeed when this motor develops 60% of full load torque?arrow_forwardQ1: A // A shunt D.C motor runs at 500 rpm takes 40 A.The shunt field 225 2 .If the mechanical power developed in armature 8000 W. The friction and iron losses 800 W fim 1- Useful and total torque. 2- The armature current when the speed reduced by 10% from initial speed. Q1: B Why the d.c motor called " a self-regulating machine ?arrow_forward
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