Electrical Laws

Ohm's Law Coulomb's Law Kirchoff's Law Faraday's Law Ampere's Law Joule's Law Lenz's Law Biot Savart Law

Electrical Theorems

Thevenin Theorem Nortons Theorem Super Position Theorem Reciprocity Theorem Compensation Theorem Maximum Power Transfer Millmans Theorem Tellegans Theorem

Electrical Rules

Flemings Left Hand Rule Flemings Right Hand Rule Cork Screw Rule

Electrical Network

Network Terminologies

Electrical Terms

Electrical Terms Materials Capacitors Resistors Inductor Self Inductance Mutual Inductance Magnetic Flux Magnetic Characteristics EMF MMF Permeability Sources Reluctance Torque

Electrical Transformer

Transformers How Transformer Works Transformer Classifications Types Transformers Core Type Transformers Ideal Transformers Parallel Operation Transformer Cooling Transformer Forces Transformer Losses Transformer Testing Transformer Bushing Transformer Windings

Types of Transformer

Auto Transformer Current Transformer Potential Transformer Rectifier Transformer Converter Transformer

AC Motor

Stator and Rotor Three Phase Induction Motor Induction Motor Transformer

AC Generator

AC Generators Alternator Stator Construction Alternator Rotor Construction Alternator - Parallel Operation Synchronizing AC Alternator Losses in Alternator

DC Motors

DC Motors Commutator Braking of Electric Motors Dynamic Rheostatic Braking Regenerative Braking Plugging Braking Speed Control DC Motor Losses DC Motors

Types Of DC Motor

DC Motors Types DC Series Motors DC Shunt Motors DC Compound Motor Brushless DC Motors Permanent Magnet DC Motor

Starter For DC Motors

Starters DC Motors

DC Generator

DC Generator Types DC Generators Sparking DC Generators Why Generator Overloading Losses DC Generators

Parallel Operation

PO - DC Generator Series DC Generator Shunt DC Generator Compound DC Generator
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Speed Control of DC Motors

We can control a DC motor by following methods,

  • Voltage Control Method
  • Armature Control Method
  • Field Control Method

Voltage Control Method

By changing the supply voltage V, the speed can be changed. As supply voltage can only be reduced, speed of a dc motor N can also be reduced from its rated value by this method.

Armature Control Method

By putting an extra variable resistance like rheostat in the armature circuit, the speed of a dc motor can be reduced to a desired value. It is clear from the above equation, a speed of a dc motor can only be reduced by reducing the values in the numerator.

Field Control Method

By varying the field flux Φ, speed of a dc motor can be changed. Field current produces the flux Φ, and hence this method is called the field control method. This is simply by putting a variable resistance in the field circuit, field current can be reduced, and hence flux produced can be reduced. When flux is reduced, speed is increased. Thus, by the field control method the speed of the dc motor can only be increased.

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