Transformer Operation and Applications: A Guide for Electrical Engineering Students, Slides of Electrical Engineering

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Learning & Development - Technical Training Engineering Development & Skills-Based Training Team

AC MACHINES: TRANSFORMER

October 1, 2011 Matatag Room, Lineman’s Training Camp

Course Outline

• (^) understand the principle of operation of a transformer
• (^) understand the term “rating” of a transformer
• use V 1 /V 2 = N 1 /N 2 = I 2 /I 1 in calculations on transformers
• (^) describe losses in transformers and calculate efficiency
• (^) describe an autotransformer, its advantages / disadvantages and uses
• (^) describe an isolating transformer, stating uses
• (^) describe a three-phase transformer
• (^) describe a current and voltage transformers

ADVANTAGES OF TRANSFORMER

1. Easy to increase or decrease an alternating voltage through transformers in AC transmission and distribution
2. Losses in transformers are generally low thus efficiency is high

3. Their efficiencies commonly range from

90% to 99% at full load.

4. Being static, they have long life and stable

FARADAY’S LAW

PRINCIPLE OF OPERATION

First law: Whenever the flux linking a coil or current changes, an emf is induced in it. Second law: The magnitude of the induced emf is proportional to the rate of change of flux linkages. Where: е = induced emf (volts) N = number of turns dФ/dt = rate of change in flux (webers per second)

Basic principle

PRINCIPLE OF OPERATION

TRANSFORMER

Leakage Flux

The flux that does not follow the intended path in a magnetic circuit.

General Equation:

TRANSFORMATION RATIO

Where: E p

& E

s = Primary and secondary induced voltage N p

& N

s = Primary and secondary number of winding turns. I p

& I

s = Primary and secondary current a = Transformation Ratio

MAJOR PARTS OF TRANSFORMER

Laminated Core – carries the magnetic lines and

usually made up of steel or silicon steel.

Coils

 Primary Windings

Where the voltage source connected.

 Secondary Windings

Where the load is connected and maybe

composed of several windings where several

loads of different voltages can be connected.

Shell type (Cut View)

CLASSIFICATIONS OF

TRANSFORMER

Shell type (Exploded View)

CLASSIFICATIONS OF

TRANSFORMER

According to Purpose to Which Used:

 (^) Transmission Transformer  (^) Distribution Type Transformer  (^) Power Transformer  (^) Instrument Transformer  (^) Regulating Transformer

CLASSIFICATIONS OF

TRANSFORMER

According to method of cooling:

Self -cooled transformer

Forced air - cooled transformer

Oil self - cooled transformer

Forced oil-cooled transformer

CLASSIFICATIONS OF

TRANSFORMER

Voltage Regulation (% VR) – percentage rise in

the voltage at the terminals of a transformer

when the load is removed.

Where: VNL = no load terminal voltage VFL = full load terminal voltage

VOLTAGE REGULATION OF

TRANSFORMER

Efficiency – ratio of output power (power drawn by

the load )to the input power (power generated by

the load)

Where: Po= Watts output Pin= Watts input = (Watts output + Losses)

EFFICIENCY OF TRANSFORMER