Understanding Motor Controls
4th Edition
ISBN: 9781337798686
Author: Stephen L. Herman
Publisher: Delmar Cengage Learning
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Textbook Question
Chapter 4, Problem 15RQ
A three-phase motor nameplate indicates a full load current of 362 amperes. The nameplate indicates that the heaters are to be sized for 125% of motor full load current. Current transformers with a ratio of 600:5 are used to reduce the motor current. Using the chart shown in Figure 4–7B, determine the size of overload heaters needed to protect this motor.
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Question 5
The blower requires 20 kW to run at 350 rpm. The power is
transmitted by a v-belt shown in Figure 4 from an electric motor. The
diameter of the machine pulley is 650 mm and that of the motor
pulley is 330 mm. The centre distance between the pulleys is 1.2 m.
The contact angle of the belt is 150°. The safe pull in each belt is
900 N and the mass of the belt is 0.46 kg per meter length. The
coefficient of friction between the belt and the pulley is 0.25. The
belt should not exceed the speed of 1 800 m/min.
X1 = 16 mm
H= 6 mm
B
X2 = 7 mm
Figure 4: Cross sectional view of the v-belt
5.1. Calculate the velocity of the belt in m/s.
Determine the length of the belt.
Calculate the belt tensions.
5.2.
5.3.
Question 2
Beli vifth
Slack side
Motor
(imprut)
Tight side
Beli thickpess\
Centre distance
Figure 2
Figure 2 shows an open flat belt drive connected to a motor and a pulley. The
motor transmits 20 kw to the connect pulley of 450 mm diameter and is rotating
at 850 r/min to a second pulley rotating at 400 r/min. The distance between
pulley centres is approximately 2 m. The belt is 6 mm thick and has a density of
970 kg/m. The maximum stress in the belt is not to exceed 2,7 MPa. The
coefficient of friction for both pulleys is 0,3.
Determine:
2.1. The diameter of the second pulley.
2.2. The length of the belt.
3.3. The width of the belt taking centrifugal tension into account.
In a given DC motor, the output power is 45 HP, and the copper losses are 2.005 KW.
If the rotational losses is one tenth of the output power,
find the converted power and the efficiency of the motor.
Select one:
O a. None
O b. Pcony = 33.57 KW and % efficiency = 89.2 %
%3D
O C. Pcony = 39 KW and % efficiency = 75.8 %
O d. Peony = 36.927 KW and % efficiency = 86.2 %.
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Chapter 4 Solutions
Understanding Motor Controls
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, mechanical-engineering and related others by exploring similar questions and additional content below.Similar questions
- A 480-volt three-phase load is rated at 34.5 kVA. It is to be supplied with variable three-phase voltage. Because the load is continuous, the transformers ratings are to be increased by 1.25% of the rated load. Three variable autotransformers are used to supply this load. Refer to Table 4-2 and determine the standard size of each transformer that should be used to make this connection.arrow_forwardA large motor has a full load current rating of 425 amperes. Current transformers with a ratio of 600:5 are used to reduce the current to the overload heaters. What should be the full load current rating of the overload heaters?arrow_forwardName three factors that determine the amount of induced voltage.arrow_forward
- Power-consuming devices are wired in _____(series orparallel).arrow_forwardRefer to the transformer shown in Figure 5-13 to answer the following questions. The transformer shown in Figure 5-13 is supplying 325 volt amperes to a load. The primary voltage is 240 volts. What is the primary current? Figure 5-13 Autotransformer practice problems.arrow_forwardIf the load in question 7 is connected in a wye, what would be the line voltage and line current supplying the load?arrow_forward
- Refer to the transformer shown in Figure 5-13 to answer the following questions. What is the turns ratio of the winding between points B and E as compared to the winding between points D and E? Figure 5-13 Autotransformer practice problems.arrow_forwardA 3 kVA motor operates from a 240 V supply at 50 Hz and has a power factor of 0.6. Determine the active power Select one: 1800 W Non of the Answers 1900 W 2000 Warrow_forwardIf the load in question 7 was supplied by two autotransformers connected in open delta, what would be the minimum standard size transformers that could be used to supply this load?arrow_forward
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