Notes from Toppers

The Basics of Transformers

NCERT Reference: Chapter 13, Electromagnetism, Class 12 NCERT Physics textbook.

Notes:

  • A transformer is an electrical device that transfers electrical energy from one circuit to another through electromagnetic induction.
  • It consists of two or more coils of wire wound around a laminated iron core.
  • The primary coil is connected to the AC power source, and the secondary coil is connected to the load.
  • When an alternating current flows through the primary coil, it creates a changing magnetic field in the core.
  • This changing magnetic field induces an alternating current in the secondary coil, which is proportional to the number of turns in each coil.
  • Transformers can be used to step up or step down voltage, isolate circuits, and provide impedance matching.

Transformer Theory

NCERT Reference: Chapter 13, Electromagnetism, Class 12 NCERT Physics textbook.

Notes:

  • The EMF equation of a transformer is given by: Es=NsNpEp where Es is the secondary voltage, Epis the primary voltage, Ns is the number of turns in the secondary coil, and Np is the number of turns in the primary coil.
  • The turns ratio of a transformer is the ratio of the number of turns in the secondary coil to the number of turns in the primary coil.
  • The current transformation ratio of a transformer is the inverse of the turns ratio.
  • The power transfer ratio of a transformer is equal to the product of the turns ratio and the current transformation ratio.
  • The losses in a transformer include copper loss, iron loss, hysteresis loss, and eddy current loss.
  • The efficiency of a transformer is defined as the ratio of the output power to the input power.
  • The regulation of a transformer is defined as the change in the secondary voltage when the load current changes from no load to full load.

Transformer Design

NCERT Reference: Chapter 13, Electromagnetism, Class 12 NCERT Physics textbook.

Notes:

  • The design considerations for a transformer include the materials used, the core design, and the winding design.
  • The core of a transformer is made of laminated iron to reduce eddy current losses.
  • The windings are made of copper wire, and the number of turns in each coil is determined by the desired voltage transformation ratio.
  • The thermal design of a transformer is important to ensure that the transformer does not overheat.
  • Cooling methods for transformers include oil-filled and dry-type.

Transformer Testing

NCERT Reference: Chapter 13, Electromagnetism, Class 12 NCERT Physics textbook.

Notes:

  • Transformer testing is performed to ensure that the transformer meets the desired specifications.
  • The no-load test is performed to measure the open-circuit voltage and the exciting current.
  • The short-circuit test is performed to measure the short-circuit current and the impedance of the transformer.
  • The open-circuit test is performed to measure the core loss.
  • The efficiency and regulation of a transformer are determined by performing a series of tests.

Applications of Transformers

NCERT Reference: Chapter 13, Electromagnetism, Class 12 NCERT Physics textbook.

Notes:

  • Transformers are used in a wide variety of applications, including power distribution and transmission, isolation of circuits, voltage regulation, impedance matching, and autotransformers.
  • Instrument transformers, such as current transformers and potential transformers, are used to measure current and voltage in electrical circuits.