Engineering Q&A
Explain concept of back emf in DC machine. State how it governs armature current. 
in DC machine by
retagged by

1 Answer

0 like 0 dislike

Back emf: When the armature of DC machine rotates under the influence of driving torque, the armature conductors move in the magnetic field and cut it and hence emf is induced in them. The induced emf acts in opposite direction to the applied voltage as per Lenz‟s law. Hence known as back or counter emf Eb.


Significance of back emf:

image


i) If the motor is suddenly loaded, the first effect is to cause the armature to slow down. Therefore the speed of armature is reduced. Hence back emf falls. This allows a larger current flow through armature means increased driving torque, thus the driving torque increases as motor slows down.


ii) If load on motor is decreased, the driving torque is momentarily in excess so armature is accelerated and armature speed increases, which increases back emf and causes armature current to decrease. 

It follows therefore that back emf in DC motor regulates the flow of armature current i.e. it automatically changes the armature current to meet load requirements.

by

Related questions

1 answer
asked Nov 13, 2019 in DC machine by Purushotham | 120 views
1 answer
1 answer
asked Mar 20, 2018 in DC generator by anonymous1 | 34 views
0 answers
2 answers
1 answer
1 answer
2 answers
Welcome to electronics2electrical.com, where students and teachers can ask and answer any question. Get help and answers to any engineering problem including Electrical, electronics, mechanical, telecommunication, instrumentation, computer, mathematics, physics etc. Get answers to questions. Help is always 100% free!

Most popular tags

power motor dc circuit transformer voltage current system used phase resistance factor ac load synchronous induction energy electric generator electrical series frequency capacitor between plant line speed transmission use meter type advantages difference single mosfet control function instrument problem magnetic diode amplifier high bjt machine unit source motors and diagram winding shunt field parallel define electricity torque value maximum time relay types arduino supply digital armature applications thyristor working transformers wave on flow operation three coil material instruments state ratio signal emf effect formula efficiency theorem method disadvantages starting microprocessor network test operating direction controlled different logic transistor single-phase scr loss temperature connected rc law force inductance compare measure station wire low conductor principle wattmeter full characteristics measuring constant measurement breaker losses device converter bridge linear materials nuclear matrix flux drive resistivity of machines angle switch free rectifier protection core circuits battery solar gain thermal loop generators open negative analog number lines friction basic reactance short gate pole inverter the conservation diesel iron resistors capacitance engineering using direct main electronic electronics a steam induced relays hysteresis universal transducer computer feedback range distribution work secondary igbt algebra pmmc plants factors capacitors dielectric controller regulation systems design air fault components rotor cable starter oscillator eddy alternator application semiconductor ammeter rl average forces damping rlc connection zener electromagnetic biasing minimum insulation pressure balanced permanent moving errors running copper self analysis impedance stability quality start ideal curve over commutation is 3-phase arc permeability peak bias error fuzzy commutator conductors superposition density mechanical rotation construction measured electrons charge memory inductive two transfer explain fuse methods off back three-phase tariff locomotive installation welding heating rms surge rating generation potentiometer coupled shaded rate capacity storage adc excitation active pure resistor harmonics reluctance microcontroller voltmeter inductor internal 8085 cro reaction insulating overhead hydro resonance traction definition breakers earth

9,199 questions

7,946 answers

158 comments

3,292 users

9,199 questions
7,946 answers
158 comments
3,292 users