Ratings of Transformer.

Rating — Those numerical values assigned to the quantities which define The Operation Of The Transformer In The Conditions Specified In Is 2026 (Part 2) and on which the manufacturer’s guarantees and the tests are based.   - © BIS 2011

  • Rated Quantities — Quantities (Voltage, Current,Etc), The Numerical Values Of Which Define The Rating.

       Notes .
           1. For Transformers Having Tappings, Rated Quantities Are Related To The Principal Tapping ,              Unless Otherwise Specified.Corresponding Quantities With Analogous Meaning, Related To Other Specific Tappings, Are Called Tapping Quantities.

           2 .Voltages And Currents Are Always Expressed By Their R.M.S. Values, Unless Otherwise                    Specified.

  • Rated Voltage Of A Winding (Ur) — The Voltage Assigned To Be Applied, Or Developed At No-Load, Between The Terminals Of An Untapped Winding, Or Of A Tapped Winding Connected On The Principal Tapping . For A Three-Phase Winding It Is The Voltage between Line Terminals

              1. The Rated Voltages Of All Windings Appear Simultaneously At No-Load When The                            Voltage Applied To One Of Them Has Its Rated Value.
             2. For Single-Phase Transformers Intended To Be Connected In Star To Form A Three-Phase                  Bank, The Rated Voltage Is Indicated As Phase-To-Phase Voltage, Divided By 3, For           Example Ur = 400 3 Kv.
             3 For The Series Winding Of A Three-Phase Booster Transformer Which Is Designed As An                  Open Winding . The Rated Voltage Is Indicated As If The Winding Were Connected In    Star,For Example Ur = 23 3 Kv.

  • Rated Voltage Ratio — The Ratio Of The Rated Voltage Of A Winding To The Rated Voltage Of Another Winding Associated With A Lower Or Equal      Rated Voltage.
  • Rated Frequency (Fr) — The Frequency At Which The Transformer Is Designed To Operate.
  • Rated Power (Sr) — A Conventional Value Of Apparent Power Assigned To A Winding Which, Together With The Rated Voltage Of The Winding, Determines Its Rated Current.

               1. Both Windings Of A Two-Winding Transformer Have The Same Rated Power Which By                    Definition Is The Rated Power Of The Whole Transformer.
               2. For A Multi-Winding Transformer, Half The Arithmetic Sum Of The Rated Power                              Values Of All Windings (Separate Windings, Not Auto-Connected) Gives A Rough     Estimate Of Its Physical Size As Compared With A Two-Winding Transformer.

  • Rated Current (Ir) — The Current Flowing Througha Line Terminal Of A Winding Which Is Derived From Rated Power Sr And Rated Voltage Ur For The Winding.

                    1.For A Three-Phase Winding The Rated Current Ir Is Given By:
                    2. For Single-Phase Transformer Windings Intended To Be Connected In Delta To 
            Form A Three-Phase Bank The Rated Current Is Indicated As Line Current Divided By 3 , 
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