A DC series motor having a resistance of 0.4 o and runs at 2000 rpm when connected to 250 V supply and drawing a current of 20 A. (i) What resistance must be added in order to limit the speed to 4000 rpm when armature current is 5A? Assume flux varies linearly. (ii) What resistance must be added to limit the speed to 1000 rpm when armature current is 30 A? Assume that the flux at 30 A is 20% more than that at 20A. (iii) At

A DC series motor having a resistance of 0.4 o and runs at 2000 rpm when connected to 250 V supply and drawing a current of 20 A. (i) What resistance must be added in order to limit the speed to 4000 rpm when armature current is 5A? Assume flux varies linearly. (ii) What resistance must be added to limit the speed to 1000 rpm when armature current is 30 A? Assume that the flux at 30 A is 20% more than that at 20A. (iii) At

Delmar's Standard Textbook Of Electricity

7th Edition

ISBN:9781337900348

Author:Stephen L. Herman

Publisher:Stephen L. Herman

Chapter5: Resistors

Section: Chapter Questions

Problem 1PA

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A 240-V series motor has an armature resistanceof 0.42Ω and a series-field resistance of0.18Ω . If the speed is 500 r/min when the current is36 A, what will be the motor speed when the loadreduces the line current to 21 A? (Assume a 3-Vbrush drop and that the flux is proportional to thecurrent.)
A 220-V shunt motor has an armature resistanceof 0.32 Ω and a field resistance of 110Ω . At no loadthe armature current is 6 A and the speed is1,800 r/min. Assume that the flux does not vary withload, and calculatea. The speed of the motor when the line current is62 A (assume a 2-V brush drop).b. The speed regulation of the motor.
A DC series motor having a resistance of 0.4 ꭥ and runs at 2000 rpm when connected to 250 V supply and drawing a current of 20 A. (i) What resistance must be added in order to limit the speed to 4000 rpm when armature current is 5A? Assume flux varies linearly. (ii) What resistance must be added to limit the speed to 1000 rpm when armature current is 30 A? Assume that the flux at 30 A is 20% more than that at 20A. (iii) At what speed the motor will run if it is connected directly to 250 V supply when the load is such that the current drawn is 30 A?
A dc series motor operates at its full rated load at 1500 rpm. The line condition are 125 V and 10 A. The motor has an armature circuit resistance, including the commutating field, of 1.25 ohms and a series field resistance of 0.425 ohms . Assuming that the field flux changes linearly with field current, what will be the motor speed if the load is such that the line current drops to 6.25 A?
A 6-pole, 500-V wave-connected shunt motor has 1200 armatureconductors and useful flux/pole of 20 mWb. The armature and fieldresistance are 0.5 ohm and 250 ohms respectively. What will be the (a)speed and (b) torque developed by the motor when it draws 20 A from thesupply mains? If stray power losses amount to 900 W, find (c) useful torque(d) output in kW and (e) efficiency at this load.
On full load a 500-volt series motor takes 100-Amp and runs at 840 rpm. The armature resistance of 0.1-ohm, field resistance 0.04-ohm. Find the speed when developing haft full load toque but with a 0.08-ohm diverter resistance parallel with the series field winding. Assume flux proportion to the field current.
A separately excited D.C motor is rated for a full load torque of 100Nm. For an applied voltage of 240V and for flux (φ) per pole of 30 mWb, the no-load and full load speeds of the motor are 1595 r.p.m and 1195 r.p.m respectively. (a) Find the armature resistance (b) If the applied voltage and the flux per pole are reduced to 200V and 20mWb respectively, Find the corresponding full load speed.
A 240 V shunt motor has an armature current of 15 A when running at 800 rpm against full-load torque. The armature resistance is 0.6 ohm. What resistance must be inserted in series with the armature to reduce the speed to 400 rpm at the same torque? What will be the speed if the load torque is halved with this resistance in the circuit? Assume the flux to remain constant throughout.
(use 2-decimal digits for solutions) A 6-pole, 500-V. wave-connected shunt motor has 1200 armature conductors anduseful flux/pole of 20 mWb. The armature and field resistances are 0.5 Ω and 250Ω respectively. What will be the speed and torque developed by the motor when itdraws 20 A. from the supply mains? If the magnetic and mechanical losses amountto 900 W., find (a) useful torque, (b) output in kW, and (c) efficiency at this load.
a dc shunt motor runs at 900 r.p.m from a 460 V supply when taking an armature current of 25 A. Calculate the speed at which it will run from a 230 V supy when taking an armature current of 15 A . The resistance of the armature circuit is 0.8 ohms . Assume the flux per pole at 230 V to have decreased to 75 % of its value at 460 V .
The armature winding of a 4-pole, 250-V DC shunt motor is lap connected. There are 130 slots, each slot containing 8 conductors. The flux per pole is 30 mWb and the current taken by the motor is 35-A. The resistance of armature and field circuit are 0.25 and 150 ohms respectively. If the rotational losses amount to 750W. Determine the (a) gross torque in N-m, (b) useful torque in N-m and (c) the efficiency.
A shunt motor is rotating at 1500 rpm and is powered by a 120V voltage source. The current line resistance is 51-A and the shunt field resistance is 120ohm. If the armature resistance is 0.12ohm, Determine: a) the armature current, b) the back emf (E), c) the total power that is supplied to the motor, d) the power absorbed by the armature, e) power dissipated in the armature. You have to answer all subpart not only first three subpart Either dislike is ready