Advantages & Disadvantages of Delta - Delta Connected Transformer


The delta – delta transformer is applicable where large current requires on low voltage supply and continuity of supply is possible in spite of one phase fails.


  • No phase displacement between primary winding and secondary winding

Advantages & Disadvantages of Star - Star Connected Transformer

The Star – Star connection is applicable for low current, high voltage applications.


  • As the phase voltage is 1/ √ 3 to that of line voltage, number of turns per phase and amount of insulation is reduced that proportional.
  • No phase shift between primary voltage and secondary voltage.


What is All day efficiency of the transformer?



  • The performance of the Distribution Transformer cannot be judged by ordinary efficiency. 
  • As the primary winding of the transformer is energized throughout the day ( 24 hours ) , iron loss occurs continuously whether the transformer is loaded or unloaded. 


Direct Loading Test of Single Phase Transformer

  • The circuit diagram for the direct loading test is shown in the figure. 
  • As the transformer is loaded, this test is known as direct test. The rated voltage is given to transformer primary side with the help of single phase auto-transformer and secondary side is loaded. 
  • The load is increased step-by-step till ammeter A2 shows the full load secondary current. Note down the reading of wattmeter, voltmeters and and ammeters.


Low Smoke Zero Halogen ( LSZH ) Cable


  • The LSZH cables are designed to avoid emission of toxic fumes and propagation of fire in public places and industrial facilities in the case of fire.



  • Tin plated annealed copper
  • Silver plated annealed copper


Back To Back Test ( Temperature Rise Test ) of Single Phase Transformer


Main objective

  • The main objective of this test is to determine efficiency at any load, regulation and temperature rise of the transformer.
  •  If the high-capacity transformer is loaded for long time, temperature rise is known but it is very difficult to arrange suitable load for that transformer and also large amount of wastage of energy.


AC Power Transmission Systems ( Single Line Diagram of AC Power Transmission )

Generating station

  • The electrical power is generated in the thermal / hydro / nuclear power station. 
  • The generation of 11 kV is done by alternator. 
  • The generated power is transmitted to different areas which are far away from generating station.