Found 1006 Articles for Electronics & Electrical

Transformers are always rated in kVA instead of kW. Let's see why it is so.Reason 1The first reason is the power loss in the transformer. As, the copper loss or I2R loss depends on the current and the iron or core loss depends upon the voltage of the transformer. Thus, the total losses in a transformer depend upon volt-ampere (VA) only and not on the power factor of the load. That is why the transformer rating is given in kVA and not in kW.Reason 2At the time of designing a transformer, the manufacturer does not know which kind of load ... Read More

The transformers may also be constructed with a third winding in addition to the primary and secondary windings. This third winding is known as tertiary winding. The primary winding has the highest voltage rating, the tertiary winding has the lowest voltage rating and the secondary winding has the intermediate voltage rating. Also, the kVA ratings of the three windings of the 3-winding transformer are usually unequal. The figure shows the schematic diagram of a 3-winding transformer.The tertiary winding is always connected in delta. The primary advantage of the delta connected tertiary winding is that it suppresses any harmonic components that ... Read More

The Scott-T connection is a method of connecting two 1-phase transformers to perform the 3- phase to 2-phase conversion and vice-versa. In the Scott connection, the two 1-phase transformers are connected electrically (not magnetically), where one transformer is known as main transformer and the other is called as auxiliary or teaser transformer.The connection diagram of the Scott connection is shown in the figure. The main transformer is the centre tapped transformer at point D and is connected across the lines Y and B of the 3- phase side. Thus, the primary of the main transformer is YB and the secondary ... Read More

The delta-delta connection of the primary and secondary windings of a three-phase transformer is shown in the figure. Here, the secondary winding r1r2 corresponds to the primary winding R1R2, and the terminals R1 and r1 have same polarity. Also, the polarity of terminal 𝐫 connecting the r1 and b2 is the same as that of R connecting R1 and B2.The phasor diagram is drawn for the usual case of lagging power factor load. Here, the magnetising current and voltage drops in the impedances have been neglected. Under balanced condition, the line currents are √3 times of the phase currents and ... Read More

Transformers do not work on DC supply. Let us see why.The transformer works on the principle of mutual inductance i.e. current in one winding must change uniformly to induce the EMF in the other. When a DC voltage V is applied to the primary of a transformer, the primary will draw a constant current or direct current and hence, the magnetic flux produced in the core is also constant. As a result of it, there is not mutual inductance between the primary and secondary windings so no EMF will be induced in the primary and secondary windings because, $$\mathrm{EMF, \:𝑒 ... Read More

The three-point starter is mainly used for starting shunt and compound motors.Schematic Diagram of Three Point StarterThe circuit diagram of the three-point starter is shown in the figure. It is called three-point starter because it has three terminals viz. L, Z and A. It consists of a graded starting resistance to limit the starting current and is connected in series with the armature of the motor. The tapping points of the starting resistance are taken out to a number of studs.The three terminals L, Z and A of the starter are connected to the positive terminal, the shunt field terminal ... Read More

The open circuit characteristics (O.C.C) or magnetization characteristics is the curve that shows the relationship between the generated EMF at no-load (E0) and the field current (If) at constant speed. It is also known as no-load saturation curve. Its shape practically the same for all types of DC generator whether separately excited or self-excited.ExplanationIn order to determine the open circuit characteristics of a DC generator, the field winding is disconnected from the machine and is excited by an external DC source. The generator is run at its normal speed. The field current (If) is increased gradually from zero and the ... Read More

The losses in DC machine (generator or motor) may be divided into three categories as −Iron or Core LossesCopper LossesMechanical LossesThe losses in DC machines appear in the form of heat and hence increases the temperature of the machine. Also, the losses reduces the efficiency of the machine.Iron or Core LossesThe iron losses occur in the armature core of the DC machine since the armature core is subjected to the magnetic field reversal i.e. changing magnetic field. The core losses are of two types viz.Hysteresis LossEddy Current LossHysteresis LossThe armature core of DC machine is subjected to magnetic field reversal ... Read More

The four-point starter is used to overcome the drawbacks of the 3-point starter.Schematic Diagram of Four Point StarterThe circuit diagram of the four-point starter is shown in the figure. It consists of a graded starting resistance to limit the starting current and is connected in series with the armature of the motor. The tapping points of the starting resistance are taken out to a number of studs. It is called 4-point starter because it has 4 terminals viz. L, N, F and A.The one end of the armature coil is connected to the terminal A and of the shunt field ... Read More

A DC motor operates in two modes – motoring and breaking.In motoring operation, it converts electrical energy into the mechanical energy, which assists its motion.In breaking operation, it converts mechanical energy into electrical energy, thus works as a generator and opposes its motion.The motor can provide motoring and breaking operations in both forward and reverse directions. Therefore, a DC motor can operate in both directions of rotation and of producing both motoring and breaking, hence it is known as four quadrant operation of DC motor.The power developed by the motor is given by the product of angular speed and the ... Read More