Before we start discussing about the no-load condition of a transformer, it is important to first understand that what is meant by no-load.

Transformer At No-Load

Phasor Diagram At No-Load

NO-LOAD PHASOR DIAGRAM OF A PRACTICAL TRANSFORMER.

The transformer is the most important electrical machine which transfers electrical power. If you do not know how a Transformer works then you can read our article Working of a Simple transformer.
Today we are going to know the Three Reasons Why Transformer Ratings in KVA, not KW or KVAR.








The three reasons why transformer ratings in KVA given below,

Why Transformer Ratings in KVA.

This is the Three Reasons Why Transformer Ratings in KVA.


Read Also:

• Can DC Motor run on AC supply and Vice-Versa? Full Explanation.
• Use Step Down Transformer in different ways.
• Why Transformer cannot run on DC supply?

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Why Transformer Cannot work on DC Supply?

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Use Step Down Transformer in different ways.

In this post, you will learn the Use of Step Down Transformer in different ways.

(1) Have you known, how a Step-down transformer can be used as an Auto Transformer?

Yes, you can use a Step Down Transformer as an Auto Transformer very easily. The circuit diagram is given below. See the circuit diagram carefully and make the circuit properly. The connection of the terminal of the two winding is to be made as the circuit diagram.

As Step Up auto Transformer:

                                   

As Step Down Auto Transformer:

(2) Let's know how a Step-Down Transformer can be used as Step Up Transformer?

You can use a Step-Down Transformer as a Step Up Transformer very easily using low voltage side as the primary side and high voltage side as the secondary side. But remember that only AC supply is to be given. The voltage can be applied up to the rated voltage.

(3) How a Step Down Transformer can be used as a Current Transformer?

Use the low voltage coil of the Transformer as the primary coil and connect in series with the circuit whose current is to be measured. Connect an ammeter to the high voltage side. By calculating the ratio of the transformer you will measure current.




Read Also:

• Working of a Simple transformer?
• Why the Transformer cannot work on DC?
• How EMF induced? Types of Induced EMF.

Thank you for visiting the website. keep visiting for more updates.

Working of a simple transformer.

What is a Transformer?

A transformer is a stationary electrical device or machine. A transformer can not convert electrical energy into another energy, it only transforms electrical energy from one circuit to another circuit at one voltage level to another voltage level. That's why it's named Transformer. Obviously Transformer work in AC cannot work in DC. The transformer does not change frequency and power. The transformer has no rotating part that's why it is called a stationary device or machine.

Hii "Electrical Engineers", lets check that how much you know about the transformers. We are having MCQ which are based on Transformers having one correct option. So let's start.
If you are having any doubt regarding the questions or you are not reaching the answer, then feel free to comment or you can ask me on my facebook page.


Answers to the questions are given at the last.

Q.1  Which of the following losses are not present in the transformer ?
       
      a. Copper loss                                b. Stray loss
      c. Core loss                                    d. None of the above.


Q.2 What is the condition for the maximum efficiency of a transformer for a given power ?

      a. Core loss should be zero.
      
      b. Copper loss should be zero.
  
      c. Total losses of transformer should be zero.

      d. Copper loss of transformer should be equal to the core loss in transformer.

Q.3 Transformer core is laminated in order to reduce ?
     
      a. Eddy current loss                          b. Heat loss

      c. Core loss                                      d. All of the above

Q.4 Transformer has zero voltage regulation at

      a. Unity power factor                         b. Leading power factor

      c. Lagging power factor                      d. Depends upon nature of load

Q.5 The copper loss at half load is 300 W. What will be the copper loss at full load ?

     a. 1200 W       b. 300 W          c. 900 W            d. 600 W

Q.6 The desirable properties of transformer core are

     a. low permeability and low hysteresis loss 

     b. high permeability and high hysteresis loss

     c. high permeability and low hysteresis loss

     d. low permeability and high hysteresis loss

Q.7 Originally the color of silica gel is ______ and after absorbing the moisture it turns _______

     a. Yellow , Blue                                     b. Pink , Blue

     c. Blue , Yellow                                     d. Blue , Pink

Q.8 A transformer has hysteresis of 30 W at 240 V , 60 Hz. Find the hysteresis loss at 200 V -50 Hz ?
      
      a. 20 W             b. 25 W            c. 30 W               d. 35 W

Q.9 The value of Steinmetz constant lies between

     a. 1.5 - 2.5                                            b. 1.0-2.0

     c. 0.5 - 1.5                                            d.  0 - 1.5

Q.10 The saving in conductor material if auto-transformer is used in place of ordinary two winding transformer(where W =weight of copper in ordinary transformer) is

     a. W/K               b. W/(K-1)            c. W/(1-K)           d. K*W

(Take K= Secondary Voltage/Primary Voltage)

Hii guys in this post we will study about the SUMPNER'S TEST on a transformer. It is also called Regenerative test or Back-to-Back test.

Please read the whole article carefully for understanding it properly

Main objective of the Sumper's test is to check the tranformer efficiency , maximum temperature rise. It is also used to measure the losses in the large transformers.  This method is advantageous for large  transformers because for full load test on large transformers, it would be expensive as a large amount of energy will get wasted during the test. Therefore, large transformers can be tested by SUMPNER'S TEST.


Sumpners test requires requires two identical transformers. Given figure shows the circuit diagram for back-to-back test (Sumpner's test).


The primary winding of the  two transformers are connected in parallel and is supplied at rated voltage and frequency. As seen in the figure, a Voltmeter, an ammeter and wattmeter are connected to the input.

The secondary of the transformers are connected in series in phase opposition and voltmeter is connected across them. The range of the voltmeter is twice the voltage of secondary winding. Phase opposition of the winding is checked by this voltmeter. If voltmeter reads 0, it means they are in phase opposition , because both windings have equal voltages but in opposite direction due to which overall voltage in the secondary circuit become 0.
Now if the supply is given to the primary circuit, then the total voltage in secondary circuit will be 0, as discussed above.
There will be no current in the secondary winding and it will behave as secondary is open circuited. Only No-load current will flow in the primary circuit which is measured by the ammeter on the primary side.
Hence , wattmeter on the primary side will read the total Iron losses of the both transformers.


Now, a small voltage is injected in the secondary cicuit with the help of regulating transformer (see the figure). The magnitude of the voltage is adjusted till the ammeter on the secondary side reads the full-load secondary current. This produces the full load copper losses of the both transformers. Thus wattmeter on the secondary side reads the total Full-load copper losses.

Thus with the help of this method we have founded the both losses in the transformer. We have loaded the transformer to the full load but the power taken from the supply is just that it will be only sufficient to supply the losses of both transformers.

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Hello friends, in this article we will study about an ideal transformer, its properties and phasor diagram.

PROPERTIES OF AN IDEAL TRANSFORMER.

Ideal transformer is an imaginary transformer which has following properties:

1. Primary and secondary winding of an ideal transformer has negligible resistance.

2. The core of an ideal transformer has infinite permeability so negligible mmf is required to setup the flux in the core.

3. The entire flux produced in the ideal transformer is confined only to the core and links with the two windings only. Hence, its leakage flux and leakage inductance is zero.

4. There are no losses in the transformer due to resistance , hysteresis and eddy current.
    Thus, the efficiency of an ideal transformer is 100%.
Practical transformer does not have such properties.

PHASOR DIAGRAM OF AN IDEAL TRANSFORMER AT NO LOAD.

Given figure shows the phasor diagram of an ideal transformer.

Since the transformer is on no load, so the current in the secondary winding is zero i.e. I2 = 0
Here ,V1 = Primary Supply Voltage.
           E1 = Primary Induced Emf.
           I1  = Primary Current.
           �  =  Mutual flux.
          V2 =  Secondary Output Voltage.
          E2 = Secondary Induced Emf.
          

Explanation
 Since the ideal transformer has zero impedance of primary and secondary winding,so voltage induced in the primary winding E1  is equal to the applied voltage V1. But by LENZ'S LAW, E1 is equal and opposite to the V1.

The current I1 drawn from the supply is sufficient to produce an alternating flux � in the core. This current is also called magnetizing current because it magnetizes the core and sets up flux in the core.
So, the current I1 and flux � are in the same phase.

Primary current I1 lags behind the supply voltage V1 by 90 degree.
Since emf induced in primary winding E1 and secondary winding E2  are induced by the same mutual flux, � . So, E1 and E2 are in same direction.

Since the ideal transformer has zero impedance of secondary winding so emf induced in secondary winding E2 and  secondary output voltage V2 will be equal in magnitude and in same direction.

Hello friends, welcome to "beingelectricalengineer". In this article, we will study about the basics and introduction to Transformers.

WHAT IS TRANSFORMER ?

A transformer is a static device which consists of two stationary electrical circuits connected to each other by a common magnetic circuit for the purpose of transferring electrical energy between them.
This transfer of electrical energy takes place without the change in frequency.
Transformer works on the principle of Electromagnetic Induction. Electromagnetic Induction is one of the basic law of Electrical Engineering. You can read about Electromagnetic Induction.

Also Read - Electromagnetic Induction

CONSTRUCTION & WORKING PRINCIPLE  OF TRANSFORMER.

A simple transformer consists of two coils wounded on a core as shown in the figure.

There is no electrical connection between these two coils.

When an alternating voltage source V is applied to the coil 1, an alternating current I1 flows in it. This alternating current produces an alternating magnetic flux in the core. This alternating flux links with the turns  T1 of the coil1 and induces an emf E1 by self-induction.
Thus, all the flux produced by the coil1 also links with the turns T2 of the coil2 and thereby inducing an emf E2 by mutual induction.
If load is connected to the coil2, then an alternating current I2 will flow through it and hence electrical energy will delivered to the load without change in frequency.

Coil1 which receives the electrical energy from the source of a.c supply is called primary winding.

Coil2 which is connected to the load and delivers the energy to the load is called secondary winding.

Note that the transformer can only work with the alternating source. It cannot be used for transferring electrical energy in DC form because transformer works on the principle of Electromagnetic Induction and it requires that current should be alternating in nature. So, transformer cannot work on DC.

EMF EQUATION OF THE TRANSFORMER.

As we have studied that an emf is induced in both the coils or windings. So the magnitude of the emf can be calculated from the emf equation of the transformer which is ;

E = 4.44* � * f * T

Where , E = Magnitude of emf induced.
             � = Maximum flux in webers.
             f  = Frequency in Hertz.
             T = Number of turns in the coil.

With the help of the emf equation, emf induced in the primary as well as secondary winding can be calculated by providing the suitable number of turns.
It shows that winding having higher number number of turns will have higher voltage and hence it is called high voltage  (hv) winding.
Winding having lower number number of turns will also have lower voltage is called low voltage (lv) winding.

TRANSFORMATION RATIO.

The ratio of emf induced in the primary winding to the emf induced in the secondary winding is called transformation ratio. It is denoted by 'k'.

k = E1/E2 = T1/T2;

Transformation ratio can also be defined as the ratio of number of turns of primary winding and number of turns of secondary winding. It is also called turn ratio.


STEP-UP & STEP-DOWN TRANSFORMER.

Transformer in which the secondary voltage is greater than the primary voltage is called step-up transformer.
Step-up transformer has turn ratio smaller than 1.

Transformer in which the secondary voltage is smaller than the primary voltage is called step-down transformer.
Step-down transformer has turn ratio greater than 1.

Transformer having secondary voltage equal to the primary voltage is called isolation transformer or one-to-one transformer.
Such transformer has turn ratio equal to 1.

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