Transformer

Introduction to Electrical Transformer

What is a Transformer?

In Very Simple words.

Transformer is a device which:

1. Transfer Electrical power from one electrical circuit to another Electrical circuit.
2. It’s working without changing the frequency.
3. Work through on electric induction.
4. When, both circuits take effect of mutual induction.
5. Can’t step up or step down the level of DC voltage or DC Current.
6. Can step up or step down the level of AC voltage or AC Current.
   

                                    1500 kVA Transformer by Siemens | Electrical pattarai

Without transformers the electrical energy generated at generating stations won’t probably be sufficient enough to power up a city. Just imagine that there are no transformers.How many power plants do you think have to be set up in order to power up a city? It’s not easy to set up a power plant. It is expensive.
Numerous power plant have to be set up in order to have sufficient power. Transformers help by amplifying the Transformer output (stepping up or down the level of voltage or current).

When the number of turns of the secondary coil is greater than that of primary coil, such a transformer is known as step up transformer.

Likewise when the number of turns of coil of primary coil is greater than that of secondary transformer, such a transformer is known as step down transformer.

Construction of a Transformer | Parts of  a Transformer

Parts of a Transformer

1	Oil filter valve	17	Oil drain valve
2	Conservator	18	Jacking boss
3	Buchholz relay	19	Stopper
4	Oil filter valve	20	Foundation bolt
5	Pressure-relief vent	21	Grounding terminal
6	High-voltage bushing	22	Skid base
7	Low-voltage bushing	23	Coil
8	Suspension lug	24	Coil pressure plate
9	B C T Terminal	25	Core
10	Tank	26	Terminal box for protective devices
11	De-energized tap changer	27	Rating plate
12	Tap changer handle	28	Dial thermometer
13	Fastener for core and coil	29	Radiator
14	Lifting hook for core and coil	30	Manhole
15	End frame	31	Lifting hook
16	Coil pressure bolt	32	Dial type oil level gauge

Types of Transformers

There are two basic Types of Transformers

1. Single Phase Transformer
2. Three Phase Transformer

Below are the more types of transformer derived via different functions and operation etc.

Types of Transformers w.r.t Cores

• Core Type Transformer
• Shell Type Transformer
• Berry Type Transformer

Types of Transformer w.r.t uses

• Large Power Transformer
• Distribution Transformer
• Small Power Transformer
• Sign Lighting Transformer
• Control & Signalling Transformer
• Gaseous Discharge Lamp Transformer
• Bell Ringing Transformer
• Instrument Transformer
• Constant Current Transformer
• Series Transformer for Street Lighting

Types of Transformer w.r.t Cooling

• Self Air Cooled or Dry Type Transformer
• Air Blast-Cooled Dry Type
• Oil Immersed, Self Cooled (OISC) or ONAN (Oil natural, Air natural)
• Oil Immersed, Combination of Self Cooled and Air blast (ONAN)
• Oil Immersed, Water Cooled (OW)
• Oil Immersed, Forced Oil Cooled
• Oil Immersed, Combination of Self Cooled and Water Cooled (ONAN+OW)
• Oil Forced, Air forced Cooled (OFAC)
• Forced Oil, Water Cooled (FOWC)
• Forced Oil, Self Cooled (OFAN)

Types of  Instrument Transformer

• Current Transformer
• Potential Transformer
• Constant Current Transformer
• Rotating Core Transformer or Induction regulator
• Auto Transformer

Operating & Working Principle of a Transformer

Transformer is a static device (and doesn’t contain on rotating parts, hence no friction losses), which convert electrical power from one circuit to another without changing its frequency. it Step up (or Step down) the level of AC Voltage and Current.

Transformer works on the principle of mutual induction of two coils or Faraday Law’s Of Electromagnetic induction. When current in the primary coil is changed the flux linked to the secondary coil also changes. Consequently an EMF is induced in the secondary coil due to Faraday law’s of electromagnetic induction.

The transformer is based on two principles: first, that an electric current can produce a magnetic field (electromagnetism), and, second that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.

A simple transformer has a soft iron or silicon steel core and windings placed on it(iron core). Both the core and the windings are insulated from each other. The winding connected to the main supply is called the primary and the winding connected to the load circuit is called the secondary.

Winding (coil) connected to higher voltage is known as high voltage winding while the winding connected to low voltage is known as low voltage winding. In case of a step up transformer, the primary coil (winding) is the low voltage winding, the number of turns of the windings of the secondary is more than that of the primary. Vice versa for step down transformer

Limitation of the Transformer

To understand the main points, we have to discuss some basic terms related to transformer operation. So lets back to basic for a while.

A transformer is an AC machine that steps up or steps down an alternating voltage or current. A transformer being an AC machine however cannot step up or down a DC voltage or DC current. It sounds a bit weird though. You might be thinking “so are there not DC transformers?”

To answer the two questions whether there are or there are not DC transformers and know “why transformer cannot step up or step down a DC voltage” it’s necessary we know how electric current and magnetic field interact with each other in transformer operation.