Understanding Motor Controls
4th Edition
ISBN: 9781337798686
Author: Stephen L. Herman
Publisher: Delmar Cengage Learning
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Chapter 4, Problem 14RQ
To determine
The size of the overload heater that should be used to protect the 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.
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 %.
!!
n dunlay I AP-wound armature which
A 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 W
Chapter 4 Solutions
Understanding Motor Controls
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- 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.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
- 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.arrow_forwardTwo transformers rated at 100 kVA each are connected in an open-delta connection. What is the total output power that can be supplied by this bank?arrow_forwardWhat is one special problem with dry-type transformers used in unit substations?arrow_forward
- A 10 kVA transformer has a primary voltage rating of 240 volts and a secondary voltage rating of 480 volts. The transformer is connected to a circuit protected by a 100 ampere circuit breaker. The secondary is protected by a 25-ampere fuse. Does the primary require separate overcurrent protection?arrow_forward5. The operation factor of a unit is 80% and its use factor is 50%. If the load factor and reserve-over-peak are 42% and 3000 kW, respectively, the average load is kW.arrow_forwardPower-consuming devices are wired in _____(series orparallel).arrow_forward
- Refer 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_forwardWhat are common efficiencies for transformers?arrow_forward10. The output voltage of a turbine is 224 V at no load and 218 V at full load. How much is the copper loss in the transformer if the current is 1000 A at full load, assuming that the entire copper loss materializes inside the transformer?arrow_forward
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