Found 1006 Articles for Electronics & Electrical

DC Motor Voltage EquationConsider a DC shunt motor as shown in the figure.Let, $$\mathrm{V\:=\:Applied\:DC\:voltage}$$$$\mathrm{E_{b}\:=\:Back\:EMF}$$$$\mathrm{R-{a} \:=\:Resistance\:of\:the\:armature\:circuit}$$$$\mathrm{I_{a}\:=\:Armature\:current}$$By applying the KVL in the armature circuit, we get, $$\mathrm{V\:=\:E_{b}\:+\:I_{a}R_{a} … (1)}$$The expression in eqn. (1) is known as the voltage equation of the DC motor.Power Equation of DC MotorIf the eqn. (1) is multiplied by Ia on both sides, we obtain, $$\mathrm{VI_{a}\:=\:E_{b}I_{a}\:+\:I_a^2R_{a}\:.... (2)}$$The eqn. (2) is known as the power equation of DC motor. The mechanical losses are neglected.Where, $$\mathrm{VI_{a}\:=\:Input\:electrical\:power\:to\:the\:armature}$$$$\mathrm{E_{b}I_{a}\:=\:Electromechanical\:power\:developed\:by\:armature}$$$$\mathrm{I_a^2R_{a}\:=\:Electric\:power\:wasted\:in\:the\:armature\:Cu\:losses}$$Condition for Maximum Mechanical PowerThe mechanical power developed by the motor (neglect mechanical losses) is given by, $$\mathrm{P_{m}\:=\:E_{b}I_{a}}$$$$\mathrm{⇒\:P_{m}\:= VI_{a}I_a^2R_{a}}$$Since, the V and Ra are constant ... Read More

A DC motor is an electromechanical energy conversion device, which converts electrical energy input into the mechanical energy output.The operation of the DC motor is based on the principle that when a current carrying conductor is placed in a magnetic field, a mechanical force acts on the conductor. The magnitude of the force is given by, $$\mathrm{F\:=\:BIl\:Newtons}$$The direction of this is given by the Fleming's left hand rule.Construction of a DC MotorHere is the schematic diagram of a DC MotorA DC motor consists of six main parts, which are as followsYokeThe outer frame of a DC motor is a hollow ... Read More

DC GeneratorA DC generator is an electromechanical energy conversion device that converts mechanical power into DC electrical power through the process of electromagnetic induction.A DC generator operates on the principle of electromagnetic induction i.e. when the magnetic flux linking a conductor changes, an EMF is induced in the conductor. A DC generator has a field winding and an armature winding.The EMF induced in the armature winding of a DC generator is alternating one and is converted into direct voltage using a commutator mounted on the shaft of the generator. The armature winding of DC Generator is placed on the rotor ... Read More

Critical Field Resistance of DC Shunt GeneratorThe critical field resistance (RC) of a DC shunt generator is defined as the maximum field circuit resistance with which the shunt generator would just excite.The voltage build-up in a shunt generator depends upon field circuit resistance. If the field circuit resistance is R1, then the generator will build-up a voltage V0 (see the E0 versus If curve). If the field circuit resistance is increased to R2, then the generator will build-up a voltage V0 slightly less than V0. As the resistance of the field circuit is increased, the slope of the field resistance ... Read More

When the transformer is in operation, heat is generated due to copper losses in the windings and iron losses in the core. The removal of heat from the transformer is known as cooling of the transformer.Transformer Cooling MethodsFor the dry type transformersAir Natural (AN) CoolingAir Forced (AF) or Air Blast (AB) CoolingFor oil immersed type transformersOil Natural Air Natural (ONAN) CoolingOil Natural Air Forced (ONAF) CoolingOil Forced Air Forced (OFAF) CoolingOil Forced Water Forced (OFWF) CoolingAir Natural (AN) CoolingThe air natural (AN) cooling is used in dry type, self-cooled transformers. In this method, the natural circulation of surrounding air is ... Read More

The transformers are designed such that it approaches the characteristics of an ideal transformer. For this, following design considerations are incorporatedThe core is made of magnetic materials (like silicon steel) which have high permeability and low hysteresis loss. Also, the core is made laminated to reduce the eddy current loss. Therefore, by doing these the iron losses or core losses can be reduced considerably and hence the no-load current.Instead of placing primary winding on one limb and the secondary winding on the other limb, in practice, the one half of each winding is wound on one limb and the other ... Read More

In DC machines, there are mainly three methods to obtain good commutation. They areResistance CommutationVoltage CommutationCompensating WindingsResistance CommutationIn the resistance commutation method of improving commutation, the high resistance carbon brushes are used. This increases the resistance between the contact of commutator segments and brushes. This high contact resistance has the tendency to force the current in the short-circuited coils to reverse according to commutation requirements and then increase in the reverse direction.Voltage CommutationIn voltage commutation method, the arrangements are made to induce a voltage in the coil undergoing commutation, which will neutralise the reactance voltage. This induced voltage is in ... Read More

The performance of a DC motor is given by the relation among the armature current, torque and speed. These relations are given graphically in the form of curves, which are called as characteristics of DC motors. These characteristics show the behaviour of the DC motor under different load conditions.Following are the three important characteristics of a DC motorTorque and Armature Current CharacteristicsIt is the graph plotted between the armature torque (τa) and the armature current (Ia) of a DC motor. It is also known as electrical characteristics of the DC motor.Speed and Armature Current CharacteristicsIt is the graph plotted between ... Read More

Characteristics of DC GeneratorsThe speed of a DC generator is made constant by the prime mover. Under such conditions, the performance of the generator is given by the relation among the excitation, terminal voltage and load. These relations are given graphically in the form of curves, which are called as characteristics of DC generators. These characteristics show the behaviour of the DC generator under different load conditions.The following are the main characteristics of a DC generatorOpen Circuit Characteristics or Magnetisation CurveThis is the graph plotted between the generated EMF at no-load (E0) and the field current (If) at a given ... Read More

Since the armature of a DC motor rotates in a magnetic field, an emf is induced in the conductors of the armature due to electromagnetic induction (as in a generator). This induced emf acts in the opposite direction to the applied voltage (according to Lenz’s law) and hence is known as back emf or counter emf. It is denoted by Eb and is given by, $$\mathrm{E_{b}=\frac{NP\varphi Z}{60A}}$$The magnitude of the back emf is always less than the magnitude of the applied voltage. But under normal operating conditions the difference of these two is small.ExplanationConsider a DC shunt motor as shown ... Read More