Electrical Transformers and Rotating Machines
4th Edition
ISBN: 9781305494817
Author: Stephen L. Herman
Publisher: Cengage Learning
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Question
Chapter 15, Problem 20RQ
To determine
The efficiency of the motor.
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Students have asked these similar questions
A (21 HP, 3-Phase, 380 volts) motor with an efficiency of 95% is operating at a load
factor of 0.63. What is the input current (Amperes) when the power factor is 89%? (1
HP = 0.75 kW)
Question 2 Calculate the amount of DC current required for the magnetic circuit given below to generate a
flux density of 1.0 T in the airgap. The details are
Number of turns, N = 400
The core is made up of steel, the B-H characteristic has been given below
The magnetic core length, le = 500 mm
The airgap length, Ig = 2 mm
The cross-sectional area of the core, Ag = 100 mm²
Neglect leakage and fringing.
Core
Cross-sectional
i(1)
area
as
Air gap
Magnetic path
length
Figure 1
2.0
1.8
B-H Curves for Various Metals
Steel
1.6
1.4
Magnetic
Saturation
1.2
1.0
0.8
Iron
근 0.4
Air
0.2
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Magnetic Field Strength - H (A/m)
Figure 2
Flux Density - B (T)
In a given DC motor, the output power is 20 HP, and the copper losses are 1.1 KW. If the motor is operating at 87 % efficiency, find the converted power and the rotational losses. Select one:
a. Pconv = 16.05 KW and Prot = 1.13 KW
b. Pconv = 17.15 KW and Prot = 3.11 KW
c. Pconv = 14.92 KW and Prot = 1.35 KW
d. None
Chapter 15 Solutions
Electrical Transformers and Rotating Machines
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- A motor develops 189 ft-lb of torque at 1745 RPM. What is the horse-power output of the motor?arrow_forwardAssume that a primary current of 75 amperes flows through the windings of the transformer in question 4. How much current will flow in the secondary winding?arrow_forwardA current transformer has 4 turns of wire in its primary winding. How many turns of wire are needed in the secondary winding to produce a current of 2 amperes when a current of 60 amperes flows in the primary winding?arrow_forward
- If the secondary of the transformer in question 5 supplies a current of 9.6 amperes to a load, what is the primary current? (Disregard excitation current.)arrow_forwardA motor develops 225 ft-lb of torque at 860 RPM. What is the horsepower output of the motor?arrow_forwardThe working current has a power of 100 kW and a power factor of 0.50. After a capacitor of 75 KVAR is installed, what does the power factor become? A 0.84 B 0.71 C 0.63 D 0.78 E 0.92arrow_forward
- If a single-phase load is connected across the two line conductors and neutral of the transformer in question #2, and one line has a current of 80 amps and the other line has a current of 68 amps, how much current is flowing in the neutral conductor?arrow_forwardA current transformer has a ratio of 600:5. If three loops of wire are wound through the transformer core, how much primary current is required to produce 5 amperes of current in the secondary winding?arrow_forwardA motor works when it is connected to AC. By mistake you connect it to DC, but you see it also works with DC. What kind of motor is it?arrow_forward
- 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 Warrow_forwardQuestion 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_forward
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