How to tackle Electrical Machines (Transformers) and important topics for GATE?

Dear Engineer's,

In this post, I will discuss how to tackle the most important subject of Electrical Engineering which is Electrical Machines and trust me guys, by the end of this post you will understand how to cover Electrical Machines course in the least possible time.

Electrical Machines is the most important topic for Electrical Engineers not only from GATE perspective but also for understanding as you are not a complete Electrical Engineer unless you have a good grasp of Machines concepts.

In GATE exam if they focus on core subjects then Electrical Machines will easily have weight-age of more than 10 marks.

The problem with machines is not the complexity of concepts but rather the impact of the problem on one’s mind. 

People usually presume that machines question would be tough and this presumption is based on the language of the question generally which is more complex than the question itself.

Whenever you are starting Electrical Machines, you need to be well aware of the pre-requisite concepts which is the basic of Electromagnetic Theory and some basics of Electrical Material. 

These concepts will help you understand the working of each machine in detail and you will also be able to understand why some particular material is used in the construction of Electrical Machines. 

Though this may not directly come in handy in GATE exam it will give you an edge in the interview.

First, we will cover each topic in Electrical Machines and the concepts required for GATE from that topic and then I will tell you some problem-solving tips.

The subject will be classified into 4 categories

1. Transformers

2. DC Machines

3. Induction Machines

4. Synchronous Machines

In this post I'll share how to prepare and some important topics of Transformers. Further I'll provide day by day on remaining categories. 

Transformers

This is the beginning of Electrical Machines course and is a good platform to get acquainted with the basics of machines.

This chapter will start with the basics of Transformers such as Construction and Working Principle. In construction, you should be clear about the differences in Core Type and Shell Type Transformers and where they are used. Then you can move onto the concept of Ideal Transformer and one by one removing the idealities we can realize a practical transformer.

Transformers

Then by removing each non-ideality, you should understand how the phasor diagram of the Transformer is modified like by introducing the core loss, magnetizing current, leakage flux, etc. based on these phasor diagrams you can draw the equivalent circuit of Transformer.

The next important concepts are the concepts of Voltage Regulation and efficiency.

Generally the biggest confusion in the Voltage Regulation Concept is whether it should be calculated with respect to No-load Voltage or Full-Load Voltage, I would suggest that you calculate both as either of them may be used and you mark the option based on that but if question is numerical type we generally calculate with respect to rated voltage.

Then in the concept of Efficiency, you must be very well aware of the computation of various losses in Transformers in absolute values as well as pu values. The concept of maximum efficiency both with respect to load as well as power factor is important.

Also, one of the most commonly asked concepts is the core losses which are Hysteresis and Eddy Current Losses so practice few problems on that where we are given total core losses and we need to calculate individual Hysteresis and Eddy Current Losses.

In the case of three phase transformers, you have to understand how to draw the phasor diagram and calculate the phase difference between the line voltages on both sides. The questions nowadays are very common on this topic and are mostly based on connections and phase shift. You have to cover mainly for connections which are: Star-Star, Star-Delta, Delta-Star, Delta-Delta.

The next concept is the auto-transformer which I believe is the easiest as the entire question just depends on the ratio of low voltage to the high voltage rating of auto-transformer and we can scale each and every quantity of two winding transformers based on that. Generally, it would give you the parameters of two-winding transformers and will ask you corresponding parameters of Auto-transformer and when an Auto-Transformer is realized using the two-winding transformer.

The last concept would be Parallel Operation of Transformers in which you have to understand how to find the load sharing between the two transformers when a load is given and how to find the maximum load that can be supplied by the parallel connection. The concepts of Harmonics is good for understanding but is not required from the GATE point of view.

So totally you have to remember 5-8 concepts for Transformers and then you can solve almost all problems based on Transformers.

I hope this could be very helpful for preparing TRANSFORMERS, in the next article I'll share how to prepare for Induction Machines, stay connected. Feel free to ask your queries in comment box.

Thanks & Regards
Nani

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