A 3-phase, 125hp, 460V rms (line-to-line), 60Hz, 0.85 PF leading, 4-pole star-connectedsynchronous motor has Ls = 3.5mH with negligible Rs. The speed of this motor is controlledover the range from 300 to 1800 rpm.a) Determine the range of supply frequency variation.b) Determine the excitation voltage at the rated condition.c) Determine the maximum power the motor can deliver at:Rated speedLowest speedI.II.

Answered: A 3-phase, 125hp, 460V rms…

Introductory Circuit Analysis (13th Edition)

13th Edition

ISBN:9780133923605

Author:Robert L. Boylestad

Publisher:Robert L. Boylestad

Chapter1: Introduction

Section: Chapter Questions

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L-1). The 3-phase wound-rotor induction motor has .... . a) high starting torque b) low starting current c) both "a" and "b" d) neither "a" nor "b" L-2). The 3-phase wound-rotor induction.........a) motor has a wire wound rotor b) motor's rotor can be connected to an external resistive load by way of slip rings and brushes c) motor requires more maintenance than the 3-phase squirrel-cage induction motor d) all of the above L-3). The 3-phase wound-rotor induction motor's rotor circuit's resistance should be adjusted so it is__________ during starting. a) low b) high c) either "a" or "b" d) neither "a" nor "b" L-4). Will a 3-phase wound-rotor induction motor start with no external circuit connected to its rotor leads? a) yes b) no
A single-phase, 120 V, 60 Hz, four-pole, split-phase induction motor has the following standstill impedances:Main winding: Zm =5+j6.25Auxiliary winding: Za =8+j6a) Determine the value of capacitance to be added in series with the auxiliary winding to obtainmaximum starting torque.b) Compare the starting torques and starting current with and without the added capacitance in theauxiliary winding circuit when operated from a 120V, 60Hz supply
18. A single-phase, 120 V, 60 Hz, four-pole, split-phase induction motor has the following standstill impedances: Main winding: Zm =5+j6.25 Auxiliary winding: Za =8+j6 a) Determine the value of capacitance to be added in series with the auxiliary winding to obtain maximum starting torque. b) Compare the starting torques and starting current with and without the added capacitance in the auxiliary winding circuit when operated from a 120V, 60HZ supply.
A 48kW, 600V, 1500 rpm separately excited dc motor is controlled by single phase semi-controlled converter. The resistance of the armature is 192 and of the field is 1450. The field circuit is controlled by a single phase fully controlled converter and its firing angle is set to 20. The AC supply voltage to the armature and field converters is a single phase 220V, 60 Hz. The voltage constant is 0.946 V/A rad/s. If the armature converter firing angle is 45 and the speed is 1200 rpm; calculate the armature current and the developed torque.
QA.2 a) b) c) d) A 480 V permanent-magnet excited DC motor has armature resistance of 1.5 . When driving a load of constant load torque at rated speed of 1200 rpm, the armature takes rated 20 A. Speed is controlled by armature voltage variation, and armature is supplied from a three-phase fully controllable bridge rectifier. Available AC voltage is three-phase 415 V, 50 Hz, interfacing transformer is not used, and armature current is continuous. The machine operates at rated speed with rated load. Determine rectifier output voltage and thyristor firing angle. Determine the rated motor torque and power. The machine operates at 25% of the rated speed with 75% of the rated load. Determine rectifier output voltage and the thyristor firing angle. A three-phase rectifier can operate with different load types at the output. One possibility is placement of a capacitor across the output. Explain when this is done and why?
A 3 phase, 1500 rpm, 2200 V, star connected synchronous motor has an impedance of 0.4+j90 per phase. At some excitation 2900 V is induced in the armature. Find the maximum torque developed by motor before the motor breaks out of synchronism. Also find the load angle this time.
A value of magnetizing current in a 3-phase induction motor * gives power factor smaller .. larger smaller. .poor large . better O large...poor O
Derive the torque equation for a three phase induction motor, with the help of torque speed characteristics curve briefly explain how an induction motor can operate in stable region.
(b) A 2 pole 220 V, 100A, and 850 rpm separately excited DC motor has an armature resistance of 0.15 0. Two field coils are connected in parallel and used to drive a load with the torque of TL = 400 – 0.2N, Nm Where N is the motor speed in rpm. Armature voltage control and two field windings connected in series are used in speed control below and above the rated, respectively. (i) Calculate the motor armature current and speed when the armature voltage is reduced to 110VV. (ii) Examine the motor speed and current when field coils are connected in series.
Q5- Adjust a fire angle for a three-phase full-wave semi-controlled converter to feed the separately exciter DC motor to get a load torque can be reached to 750 rpm. When the supply voltage of converter is 150 volts per-phase and the absorbed current through the armature 40A with resistance 0.2 a and a constant back emf 0.4v/rpm. Then find the maximum speed for motor assume the previous parameters values are a constant.
A four-pole, single-phase, 120 V, 60 Hz induction motor gave the following standstill impedances when tested at rated frequency:Main winding : Zm =1.5+j4 ohmsAuxiliary winding : Za =3+j6 ohmsa) Determine the value of external resistance to be inserted in series with the auxiliary winding to obtain maximum starting torque as a resistor split-phase motor.b) Determine the value of the capacitor to be inserted in series with the auxiliary winding to obtain maximum starting torque as a capacitor-start motor.c) Determine the value of the capacitor to be inserted in series with the auxiliary winding to obtain maximum starting torque per ampere of the starting current as a capacitor-start motor.d) Compare the starting torques and starting currents in parts (a), (b), and (c) expressed as per unit of the starting torque without any external element in the auxiliary circuit, when operated at 120V, 60Hz.
A four-pole induction motor drives a load at 2405 rpm. This is to be accomplished by using an electronic converter to convert a 400V dc source into a set of three-phase ac voltages. a) Find the frequency required for the ac voltages assuming that the slip is 4 percent. The load requires 2hp. b) If the dc-to-ac converter has a power efficiency of 93 percent and the motor has a power efficiency of 80 percent, estimate the current taken from the dc source.

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