## Why Are Transformers Rated in kVA, and not in kW?

Manish Kumar Saini

Updated on 16-Aug-2021 12:46:33

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, ... Read More

## What is a Three Winding Transformer?

Manish Kumar Saini

Updated on 16-Aug-2021 12:45:26

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 ... Read More

## What is Delta-Delta Connection of Transformer?

Manish Kumar Saini

Updated on 16-Aug-2021 12:33:13

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 ... Read More

## Why Don't Transformers Work on DC Supply?

Manish Kumar Saini

Updated on 16-Aug-2021 12:19:40

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 ... Read More

## Four Quadrant Operation of DC Motor – Motoring and Breaking Operation

Manish Kumar Saini

Updated on 16-Aug-2021 11:26:47

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 ... Read More

## Working Principle of a Three-Point Starter

Manish Kumar Saini

Updated on 16-Aug-2021 11:25:04

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 ... Read More

## Open Circuit Characteristics of a DC Generator

Manish Kumar Saini

Updated on 16-Aug-2021 11:22:26

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 ... Read More

## Losses in DC Machine – Iron Loss, Copper Loss and Mechanical Losses

Manish Kumar Saini

Updated on 16-Aug-2021 11:18:48

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 ... Read More

## Working Principle of Four-Point Starter

Manish Kumar Saini

Updated on 16-Aug-2021 11:13:26

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 ... Read More

## Efficiency of DC Generator & Condition for Maximum Efficiency with Examples

Manish Kumar Saini

Updated on 16-Aug-2021 10:51:47

Efficiency of DC GeneratorThe efficiency of a DC generator is defined as the ratio of mechanical input power to the output electrical power.$$\mathrm{Efficiency, \:\eta\:=\frac{Electrical\:Power\:Output(P_{o})}{ Mechanical\:Power\:Input(P_{i})}}$$ExplanationConsider the power flow diagram of a DC generator (see the figure), here the power is represented in three stages asBy referring the power flow diagram, ... Read More