Transformer questions and answers

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Today we will discuss about, 

Why a transformer core is laminated?
Why transformer is a constant flux machine? 
Why transformer burns?
Why transformer is used?
Which oil used in transformer?
Main losses of the transformer?

So let's go to learn.  

Why a transformer core is laminated?

  1. The main reason of laminated core is the Eddy current losses. 
  2. The Eddy current losses are the losses occurs due to circulating current flow through the core. 
  3. To reduce the Eddy current losses, the core is made up of a number of laminations. 
  4. When we use a laminated core the resistance of the core increases, which decreases the flow of circulating current and reduce the Eddy current loss. 

Why transformer is a constant flux machine?

Let's understand it from the working of transformer.

  • First of all we apply the input voltage to the primary winding of the transformer.
  • Due to this input voltage V a current I flow through the primary winding. 
  • This current I will produce a mmf (N×I) in the primary winding which will further produce the main flux Φ. 
  • Due to this main flux Φ a self induced emf E will produce in the primary winding which will oppose the applied input voltage V. 
  • The main flux Φ link to the secondary winding through the core and if the secondary winding is close (connected to load) then a current I" will flow through it. 
  • This current I" will further produce a mmf (N"×I") which will further produce the flux Φ" in the core. 
  • This flux Φ" will oppose the main flux Φ and decrease its effect. 
  • As now, main flux Φ reduces, the self induced emf E also reduces. (Because E = dΦ / dt) 
  • Now the E decreases means the opposition to apply input voltage V will also reduce. (Because E is in opposition to the input voltage.) 
  • The V get less opposition as compared to before, therefore now more current will flow through the primary winding. And known as I'.
  • As this I' will also produce its own mmf' (N×I') and flux Φ'.
  • This flux Φ' is equal and in opposition to the flux produced by the secondary winding Φ" therefore these both flux cancels out each other and only main flux flow through the core and remains constant all the time. 
Therefore the transformer is called a constant flux machine. 

Why transformer burns?

There are various reasons behind the burning of the transformer but the most common reasons are: -
  • Overloaded-
If the transformer is loads more than its capacity, then the transformer will burn. So for avoiding of burning of transformer, we use a different rating transformer for different loads. 
  • DC supply: -
We all know that the transformer does not work on the DC supply. If we connect the DC supply to the transformer, the heat from the primary winding will increase with the time (because flux produce will not vary and remains constant.) and burn the winding. 
Therefore the transformer always use of AC supply. 

  • Poor cooling: -
This is also one reason of the burning of the transformer. If the transformer is not provided with better cooling then this will increase the temperature of the windings and burn it. 

Why transformer is used?

  • There are various uses of a transformer, but the main use of the transformer is to step up or step down the voltage. (Without change in frequency).
  • The power transformer is used to step up the voltage at the power plant and the distribution transformer is used to step down the voltage at the substations. 

Which oil used in transformer?

The oil used in transformer is known as mineral oil. The mineral oil further classified into two types: -
  • Nepthanic oil
  • Paraffinic oil

Main losses of the transformer?

There are mainly two types of losses occurs in the transformer: -
  • Iron losses 
  • Copper losses

The iron losses are the losses which occur in the core of the transformer whereas the copper losses are the losses which occurs in the windings of the transformers. 

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