Electrical Transformers and Rotating Machines
4th Edition
ISBN: 9781305494817
Author: Stephen L. Herman
Publisher: Cengage Learning
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Chapter 7, Problem 6RQ
A delta connection has 30 A of current flowing through each phase winding. How much current is flowing through each of the lines supplying power to the load?
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2. Read the following Vernier caliper measurements. (The scales have been
enlarged for easier reading.) The Vernier caliper is calibrated in metric units.
(a)
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4 5
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(b)
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Explain why on the interval 0<x<1000 mm and 1000<x<2000mm, Mt is equal to positive 160 Nm, but at x= 0mm and x=1000mm Mt is equal to -160 Nm (negative value!). What is the reason for the sign change of Mt?
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Gears
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A pair of helical gears consist of a 20 teeth pinion meshing with a 100 teeth gear. The pinion rotates at
Ta
720 r.p.m. The normal pressure angle is 20° while the helix angle is 25°. The face width is 40 mm and
the normal module is 4 mm. The pinion as well as gear are made of steel having ultimate strength of
600 MPa and heat treated to a surface hardness of 300 B.H.N. The service factor and factor of safety
are 1.5 and 2 respectively. Assume that the velocity factor accounts for the dynamic load and calculate
the power transmitting capacity of the gears.
[Ans. 8.6 kW
Chapter 7 Solutions
Electrical Transformers and Rotating Machines
Ch. 7 - Prob. 1RQCh. 7 - Prob. 2RQCh. 7 - A wye-connected load has a voltage of 480 V...Ch. 7 - A wye-connected load has a phase current of 25 A....Ch. 7 - Prob. 5RQCh. 7 - A delta connection has 30 A of current flowing...Ch. 7 - A three-phase load has a phase voltage of 240 V...Ch. 7 - If the load in question 7 is connected in a wye,...Ch. 7 - An alternator with a line voltage of 2400 V...Ch. 7 - Prob. 10RQ
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- 4. A single stage helical gear reducer is to receive power from a 1440 r.p.m., 25 kW induction motor. The gear tooth profile is involute full depth with 20° normal pressure angle. The helix angle is 23°, number of teeth on pinion is 20 and the gear ratio is 3. Both the gears are made of steel with allowable beam stress of 90 MPa and hardness 250 B.H.N. (a) Design the gears for 20% overload carrying capacity from standpoint of bending strength and wear, (b) If the incremental dynamic load of 8 kN is estimated in tangential plane, what will be the safe power transmitted by the pair at the same speed?arrow_forwardDetermine the stress in each section of the bar shown in Fig. when subjected to an axial tensile load shown in Fig. The central section is 30 mm hollow square cross- section; the other portions are of circular section, their diameters being indicated What will be the total deformation of the bar? For the bar material E = 210GPa. 20mi О 30mm 30mmm 2.6 15mm 30kN 1 2 10kN - 20kN 3 -329 91mm 100mm 371mmarrow_forwardCalculate the load that will make point A move to the left by 6mm, E=228GPa. The diameters of the rods are as shown in fig. below. 2P- PA 80mm B 200mm 2P 0.9m 1.3m.arrow_forward
- If the rods are made from a square section with the dimension as shown. Calculate the load that will make point A move to the left by 6mm, E=228GPa. 2P- P A 80mm B 200mm 2P 0.9m 1.3marrow_forward3. 9. 10. The centrifugal tension in belts (a) increases power transmitted (b) decreases power transmitted (c) have no effect on the power transmitted (d) increases power transmitted upto a certain speed and then decreases When the belt is stationary, it is subjected to some tension, known as initial tension. The value of this tension is equal to the (a) tension in the tight side of the belt (b) tension in the slack side of the belt (c) sum of the tensions in the tight side and slack side of the belt (d) average tension of the tight side and slack side of the belt The relation between the pitch of the chain (p) and pitch circle diameter of the sprocket (d) is given by 60° (a) p=d sin (c) p=d sin (120° T where T Number of teeth on the sprocket. 90° (b) p=d sin T 180° (d) p=d sin Tarrow_forwardOBJECTIVE TYPE QUESTIONS 1. The maximum fluctuation of energy is the 2. (a) sum of maximum and minimum energies (b) difference between the maximum and minimum energies (c) ratio of the maximum energy and minimum energy (d) ratio of the mean resisting torque to the work done per cycle In a turning moment diagram, the variations of energy above and below the mean resisting torque line is called (a) fluctuation of energy (b) maximum fluctuation of energy (c) coefficient of fluctuation of energy (d) none of the above Chapter 16: Turning Moment Diagrams and Flywheel 611 The ratio of the maximum fluctuation of speed to the mean speed is called 3. (a) fluctuation of speed (c) coefficient of fluctuation of speed 4. (b) maximum fluctuation of speed (a) none of these The ratio of the maximum fluctuation of energy to the.......... is called coefficient of fluctuation of energy. (a) minimum fluctuation of energy (b) work done per cycle The maximum fluctuation of energy in a flywheel is equal to 5.…arrow_forward
- OBJECTIVE TYPE QUESTIONS 1. The velocity ratio of two pulleys connected by an open belt or crossed belt is 2. (a) directly proportional to their diameters (b) inversely proportional to their diameters (c) directly proportional to the square of their diameters (d) inversely proportional to the square of their diameters Two pulleys of diameters d, and d, and at distance x apart are connected by means of an open belt drive. The length of the belt is (a)(d+d₁)+2x+ (d₁+d₂)² 4x (b)(d₁-d₂)+2x+ (d₁-d₂)² 4x (c)(d₁+d₂)+ +2x+ (d₁-d₂)² 4x (d)(d-d₂)+2x+ (d₁ +d₂)² 4x 3. In a cone pulley, if the sum of radii of the pulleys on the driving and driven shafts is constant, then (a) open belt drive is recommended (b) cross belt drive is recommended (c) both open belt drive and cross belt drive are recommended (d) the drive is recommended depending upon the torque transmitted Due to slip of the belt, the velocity ratio of the belt drive 4. (a) decreases 5. (b) increases (c) does not change When two pulleys…arrow_forwardQ3: (10 MARKS) A piston with a weight of 29.4 N is supported by a spring and dashpot. A dashpot of damping coefficient c = 275 N.s/m acts in parallel with the spring of stiffness k = 2400 N/m. A fluctuating pressure p = 960 sin 30t N/m² acts on the piston, whose top surface area is 0.05 m². Determine the steady-state displacement as a function of time and the maximum force transmitted to the base. P=Po sin cot Warrow_forward9. Design a spur gear drive required to transmit 45 kW at a pinion speed of 800 r.p.m. The velocity ratio is 3.5 : 1. The teeth are 20° full-depth involute with 18 teeth on the pinion. Both the pinion and gear are made of steel with a maximum safe static stress of 180 MPa. Assume a safe stress of 40 MPa for the material of the shaft and key. 10. Design a pair of spur gears with stub teeth to transmit 55 kW from a 175 mm pinion running at 2500 r.p.m. to a gear running at 1500 r.p.m. Both the gears are made of steel having B.H.N. 260. Approximate the pitch by means of Lewis equation and then adjust the dimensions to keep within the limits set by the dynamic load and wear equation.arrow_forward
- 7. A motor shaft rotating at 1440 r.p.m. has to transmit 15 kW to a low speed shaft rotating at 500 r.p.m. The teeth are 20° involute with 25 teeth on the pinion. Both the pinion and gear are made of cast iron with a maximum safe stress of 56 MPa. A safe stress of 35 MPa may be taken for the shaft on which the gear is mounted. Design and sketch the spur gear drive to suit the above conditions. The starting torque may be assumed as 1,25 times the running torque. Ruins 20 LW at 100 nm to another shaft running approxiarrow_forward6. A two stage reduction drive is to be designed to transmit 2 kW; the input speed being 960 r.p.m. and overall reduction ratio being 9. The drive consists of straight tooth spur gears only, the shafts being spaced 200 mm apart, the input and output shafts being co-axial.arrow_forward2 A metal block of mass m = 10 kg is sliding along a frictionless surface with an initial speed Vo, as indicated below. The block then slides above an electromagnetic brake that applies a force FEB to the block, opposing its motion. The magnitude of the electromagnetic force varies quadratically with the distance moved along the brake (x): 10 FEB = kx², with k = 5 N m² V₁ = 8 m/s m = 10 kg FEB Frictionless surface Electromagnetic brake ⇒x Determine how far the block slides along the electromagnetic brake before stopping, in m.arrow_forward
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