What are the losses in transformer?

In power transmission from primary and secondary, there are losses in the transformer which are bases on load of the transformer i.e. No-load losses and Load Losses.

2)      Pt = PNL + PLL


          Pt       = Total Losses in the transformer

          PN L  = No-load losses in the transformer

          PLL   = Load losses in the transformer.

No load losses:

1)      Hysteresis losses in the core lamination

2)      Eddy current losses in the core lamination

3)      Dielectric losses in the transformer components during excitation.

4)      I2R losses due to no-load current in the primary and secondary windings.

Load losses:

1)      Primary winding copper loss (I12R1)

2)      Secondary winding copper loss (I22R2)

What is a three phase transformer?

The three phase transformer consists of three primaries and three secondary winding with the same magnetic coupling as in the normal transformer. Where as in this transformer the power transmitted is much more compared to single phase transformer. It consists three iron core legs on which the windings are mounted. These can be delta connected or star connected winding depending up on their application.

 What is single phase transformer?

Single phase transformer is a normal transformer with one primary and one secondary winding which are magnetically coupled. This is normally used for distribution purposes primarily household where the loads are single phase loads. It consists of two terminals phase and neutral. The power transmission is less and construction and size of single phase transformer is less compared to three phase transformer.

 Differences between single phase and three phase transformer?

Parameter Single phase Three phase
Windings One set of primary and secondary windings Three sets of primary and secondary windings which are connected in Delta or Star arrangement.
Power transmission Less because of one phase Power transmission is high as the three phases combinely transmits high power
Application Distribution purpose Transmission lines and power generating stations
Cost Less high
Size Less high


Advantages of three phase systems

  • Three phase motors for a given horsepower are smaller in physical size compared to single phase.
  • Smaller conductors are required to carry the same amount of power compared to single phase.
  • Three phase motors are self-starting while single phase motors require an auxiliary start winding.
  • Three phase motors have better power factor compared to single phase motor.
  • Rectified Three phase signal gives less ripple factor compared single phase rectifier.  
  • Requires less copper compared to single phase to transmit the same power.
  • High efficiency compared to single phase motor.

What is transformer regulation?

Transformer regulation is defined as the percentage change in output voltage from no-load to full load with respect to full load. It can also measured with respected to no-load voltage where as in the first case it is called as regulation up and in second case it is called as regulation down.

% regulation = No-load Voltage – Full load voltage/ full load voltage * 100;

Under no load condition the induced voltage E2 is presented at the output terminals and when the transformer is loaded due to drop across the reactance it changes to V2. So the expression for transformer regulation is

% regulation = (E2 –V2)/V2 * 100.

What is transformer impedance?

The impedance of the transformer is the combination of resistance and reactance of the primary and secondary winding coils.

Z1= R1+X1

Z2= R2+X2

Due to this impedance there will be voltage drop in the both primary and secondary windings.

What are the name plate details of transformer?

The following details shows the typical name plate details of a transformer

Power rating (1000 KVA) : It indicates that the transformer is able to supply 1000 KVA of load without any problem.

H.V rating (21KV): This is the maximum high voltage side voltage with it can withstand. If the applied voltage is higher than 10% of rated voltage then transformer core saturation may occur.

L.V rating (6.6KV): This is the rated secondary line voltage of the transformer.

 Frequency (60Hz): The rated frequency of the transformer with it can operated. The transformer can be operated above the rated frequency but it cannot be operated below.

%impedance: It indicates the amount of voltage drop from the no-load current to full load current.

 Tap voltages: This parameter specifies the rated voltage for each tap that the transformer can provide.

Type of transformer: power transformer, distribution transformer, instrumentation transformer etc.

 Winding connection diagram: This diagram shows the primary and secondary winding connection diagram.

Cooling class (ONAF): This indicates of type of cooling used in transformer. For example ONAF indicates that it is Oil Natural and Air Forced type cooling.

Rated temperature (600): The maximum rated temperature that the transformer can be operated without any heating.

In-addition to the above the name plate also contains about weight of the transformer, volume of the oil, type of insulating material etc.

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