A 250 V, 10 hp series motor is mechanically coupled to a fan and draws 30 A and runs at 500 rpm when connected to a 220 V supply with no external resistance connected to the armature circuit (i.e., Radd = 0). The torque required by the fan is proportional to the square of the speed. 0.5 Q and R, = 0.3 Q. By neglecting the armature reaction and rotational loss, it is required to: Ra= =

A 250 V, 10 hp series motor is mechanically coupled to a fan and draws 30 A and runs at 500 rpm when connected to a 220 V supply with no external resistance connected to the armature circuit (i.e., Radd = 0). The torque required by the fan is proportional to the square of the speed. 0.5 Q and R, = 0.3 Q. By neglecting the armature reaction and rotational loss, it is required to: Ra= =

Introductory Circuit Analysis (13th Edition)

13th Edition

ISBN:9780133923605

Author:Robert L. Boylestad

Publisher:Robert L. Boylestad

Chapter1: Introduction

Section: Chapter Questions

Problem 1P: Visit your local library (at school or home) and describe the extent to which it provides literature...

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A separately-excited d.c motor has an armature resistance of 1.1Ω and the excitation circuit is connected to a fixed d.c source, such that k = 1.4V/rad/s. The mechanical losses are negligible. The motor is supplied from a constant 170V d.c source and loaded with a rated torque of 26 Nm. I t is required to reduce the speed of the motor by inserting resistance in the armature circuit or by reducing the armature voltage. How much resistance should be added in series with the armature of the motor, in order that the steady-state speed is half of the rated speed at the full load torque? How much must the applied armature voltage be reduced in order to achieve the same speed in part (i) for the same load? Determine which of the two methods is more efficient.
A 120V dc shunt motor has an armature resistance of 0.25Ω is drawing 50A. If a fixed loss of 200W was measured and neglecting the shunt field, what is the copper loss (in watts)? (meaning no shunt field used)
A three-phase, 460-V, 60-Hz, ten-pole, star-connected cylindrical rotor synchronous motor has a synchronous reactance of Xs = 0.8 Ω per phase, and the armature resistance is negligible. The load torque, which is proportional to the speed squared, is TL = 1250 Nm at 720 rpm. The power factor is maintained at 0.8 lagging by field control, and the voltage-to-frequency ratio is kept constant at the rated value. If the inverter frequency is 45 Hz and the motor speed is 540 rpm, calculate the i) input voltage, Va; ii) armature current, Ia; iii) excitation voltage, Vf; iv) torque angle, δ; and v) pull-out torque, Tp.
a shunt-wound motor runs at 600 r.p.m from a 230 V supply when taking a line current of 50 A. its armature and Field resistance are 0.4 ohms and 104.5 ohms respectively. Neglecting the effects of armature reaction and allowing 2 V brush drop, calculate (a) the no-load speed if the no-load line current is 5 A. (b) the resistance to be placed in armature circuit in order to reduce the speed to 500 r.p.m when motor is taking a line current of 50 A . (c) the percentage reduction in the flux per pole in order that the speed maybe 750 r.p.m when the armature is 30 A with no added resistance in the armature circuit.
(A shunt DC motor has a total resistance value for all conditions as Ra=2ohm and under full load conditions (nominal load) armature current is la = 10 A. The nominal terminal Voltage for the motoris Vi=300 V and total value for field circuit resistance for all conditions is Rf=150 ohm Under full load conditions (nominal load), find the internal generated Voltage (EA), excitation circuit current(field current) (II), (total supply current flow, from electrical source) line current (IL), electrical input power (Pin) supplied from the source. Be careful about your solutions to be written readable andwrite the answers as it was shown below inside boxes.)EA-IH (IL) =Pin =
250V, 15A, 1100 rpm separately excited dc motor with armature resistance (Ra) equal to 2 ohms. Calculate back emf developed in the motor when it operates on half of the full load. (Assume rotational losses are neglected)
1.1. A 3-phase, 10 MVA, Salient Pole, Synchronous Motor is run off an 11 kV supply at 50Hz. The machine has Xd = 0.8 pu and Xq = 0.4 pu (using the Machine Rating as the base). Neglect the rotational losses and Armature resistance. Calculate 1.1.1. The maximum input power with no field excitation. 1.1.2. The armature current (in per unit) and power factor for this condition.
A 208V, 45hp, 0.8pf leading, Y- connected 60Hz cylindrical rotor synchronous motor has a synchronous reactance of 2.5Ω and a negligible armature resistance. Its friction and windage losses are 1.5kW. Initially, the shaft is supplying an 11kW load at 0.8 power factor (leading).a) Sketch the phasor diagram of this motor, and find the values of Ia, and Ea.b) Assume that the shaft load is now increased to 36kW. Sketch the behaviour of the phasor diagram in response to this change.c) Find Ia, and Eaf after the load change. What is the new power factor of the machine?d) Calculate the percentage change of the rotor excitation current (If) that would bring the power factor to the unity.
A separately excited DC motor is rotated at 1000rpm, The variation of armature terminal voltage as a function of field current is measured under no-load conditions and tabulated below: IF 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 VT 0 30 60 85 102 115 124 130 134 The field winding supply VF=24V and the field resistance is adjustable. The armature winding resistance RA=0.2? and the armature terminal voltage VT=130V. a. Calculate the field current if the motor is operated with no-load at 1000 rpm b. The motor drives a load at 1200 rpm. Calculate the armature voltage at 1200 rpm if the field resistance RF=60? c. Calculate the torque for the above condition d. The motor supplies a mechanical load of 4000W at 1450rpm. The mechanical rotational losses are 160W, calculate the efficiency
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The full load slip of a 4-pole, 60Hz, 440V (line-to-line) three phase induction motor is 0.05. (i). What is the speed of the rotating stating? What is the frequency (in Hz) of the rotor current? (ii). When the output power of the motor is 90 hp at a speed of 1732 rmp, rotational losses (which include frictional and core losses) are 10,100W, while copper losses for both the rotor and stator total 3700W. Determine the motor efficiency and line current, assuming the motor has a 0.8pf lagging under the conditions.