elctrical transformers basic concept,working principle,parts,history and types

Posted by : admin Tuesday 4 November 2014

1. Define Electrical Transformers:

A transformer is an electrical device, Transfers energy between two or more circuits through electromagnetic induction.
2. History of Transformers:
A wide range of transformer designs is encountered in electronic and electric power applications. Since the invention in 1885 of the first constant potential transformer, transformers have become essential for the AC transmission, distribution, and utilization of electrical energy.
3. Parts of transformers:

3.1) BUCHHOLZ RELAY: it is a very sensitive gas and oil operated instrument which safely detect the formation of gas or sudden pressure inside the oil transformer.
3.2) CONSERVATOR: it is used to provide adequate space for the expansion of oil when transformer is loaded or when ambient temperature changes.
3.3) SILICA GEL BREATHER: it sucks the moisture from the air which is taken by transformer so that dry air is taken by transformer.
3.4) DOUBLE DIAPHRAGM EXPLOSION VENT: it is used to discharge excess pressure in the atmosphere when excess pressure is developed inside the transformer during loading.
3.5) OIL LEVEL INDICATOR: it is used to show the oil level in the transformer.
3.6) WINDING AND OIL TEMPERATURE INDICATOR: used to show the temperature of transformer winding and Oil winding.
3.7) RADIATORS: these are used for cooling of the transformer oil.
4. Basic working principles:

A transformer can be defined as a static device which helps in the transformation of electric power in one circuit to electric power of the same frequency in another circuit. The voltage can be raised or lowered in a circuit, but with a proportional increase or decrease in the current ratings.

The main principle of operation of a transformer is mutual inductance between two circuits which is linked by a common magnetic flux. A basic transformer consists of two coils that are electrically separate and inductive, but are magnetically linked through a path of reluctance.

5. Transformer Construction (single-phase)

Where:
V_P - is the Primary Voltage
V_S - is the Secondary Voltage
N_P - is the Number of Primary Windings
N_S - is the Number of Secondary Windings
Φ (phi) - is the Flux Linkage

Notice that the two coil windings are not electrically connected but are only linked magnetically. A single-phase transformer can operate to either increase or decrease the voltage applied to the primary winding. When a transformer is used to “increase” the voltage on its secondary winding with respect to the primary, it is called a Step-up transformer. When it is used to “decrease” the voltage on the secondary winding with respect to the primary it is called a Step-down transformer.

5.1) Transformers turns ratio

5.2) Transformer Efficiency

6. Types of transformer

6.1) Autotransformer: Transformer in which part of the winding is common to both primary and secondary circuits.

6.2) Capacitor voltage transformer: Transformer in which capacitor divider is used to reduce high voltage before application to the primary winding.

6.3) Distribution transformer, power transformer: International standards make a distinction in terms of distribution transformers being used to distribute energy from transmission lines and networks for local consumption and power transformers being used to transfer electric energy between the generator and distribution primary circuits.

6.4) Phase angle regulating transformer: A specialized transformer used to control the flow of real power on three-phase electricity transmission networks.

6.5) Scott-T transformer: Transformer used for phase transformation from three-phase to two-phase and vice versa.

6.6) Poly phase transformer: Any transformer with more than one phase.

6.7) Grounding transformer: Transformer used for grounding three-phase circuits to create a neutral in a three wire system, using a wye-delta transformer or more commonly, a zigzag grounding winding.

6.8) Leakage transformer: Transformer that has loosely coupled windings.

6.9) Resonant transformer: Transformer that uses resonance to generate a high secondary voltage.

6.10) Audio transformer: Transformer used in audio equipment.

6.11) Output transformer: Transformer used to match the output of a valve amplifier to its load.

6.12) Instrument transformer: Potential or current transformer used to accurately and safely represent voltage, current or phase position of high voltage or high power circuits.