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Training - 1 Transformer Basics
Principle of operation Electrical transformer is a static electrical machine which transforms electrical power from one circuit to another circuit, without changing the frequency. Working Principle Of Transformer Thebasic principle behind working of a transformeris the phenomenon of mutual induction between two windings linked by common magnetic flux. Basically a transformer consists of two inductive coils; primary winding and secondary winding. The coils are electrically separated but magnetically linked to each other. When, primary winding is connected to a source of alternating voltage, alternatingmagnetic flux is produced around the winding. The core provides magnetic path for the flux, to get linked with the secondary winding. As the flux produced is alternating (the direction of it is continuously changing), EMF gets induced in the secondary winding according toFaraday's law of electromagnetic induction. If the secondary winding is closed circuit, then mutually induced current flows through it, and hence the electrical energy is transferred from one circuit (primary) to another circuit (secondary). Mutual induction is the principle that current running through a conductor will generate a magnetic field, and a changing magnetic field will induce current in another conductor
Type of Transformer • (A) On the basis of their purpose • Step up transformer: Voltage increases (with subsequent decrease in current) at secondary. • Step down transformer: Voltage decreases (with subsequent increase in current) at secondary. • (B) On the basis of type of supply • Single phase transformer • Three phase transformer • (C) On the basis of their use • Power transformer: Used in transmission network, high rating • Distribution transformer: Used in distribution network, comparatively lower rating than that of power transformers. • Instrument transformer: Used in relay and protection purpose in different instruments in industries • Current transformer (CT) • Potential transformer (PT) • (D) On the basis of cooling • Dry Type • Oil Type • (D) On the basis of cooling employed (Oil Type) • Oil Natural Air Natural • Oil Natural Air Forced • Oil Forced Air Forced • Oil Forced Water Forced • (E) On the Basis of Construction • Shell Type • Core Type
Component of Transformer These are the basic components of a transformer:- Laminated core Windings Transformer oil Tap changer Oil Conservator Breather Cooling tubes Buchholz Relay Explosion vent
Test of Transformer • Winding Resistance Test • Transformer Ratio Test • Transformer vector Group Test • Short Circuit Test • Open Circuit Test • Measurement of Insulation Resistance Test • Dielectric Test • Temperature Rise Test • Measurement of Harmonics of No-Load Current • Measurement of Zero Sequence Impedance
What cause transformerfailure? • Cooling system failure • Phase to phase and Phase to Ground Fault • Turn to Turn Fault • Transformer Overload • Insulation Breakdown • Over heating due to over excitation • Oil contamination and leakage
What cause transformerfailure? • Winding failures51% • Tap changer failures19% • Bushings failures9% • Terminal board failures6% • Core failures2% • Miscellaneous failures13%
What cause transformerfailure? • Bushing • Bushings deterioration come from: • General aging • Contamination • Cracking • Internal moisture • Winding • Insulation deterioration come from: • Moisture • Vibration • Overheating • Voltage surge
TransformerFaults • Internal faults • Winding Failure • Winding inter-turn faults • Core Fault • 4. Over fluxing. • External faults • Overloads • Overvoltage • Over heating • External system short circuits.
Transformer Protection • Electrical • Bias Differential Protection (87) • Over Voltage (59) • Under Voltage (27) • Neutral Unbalance (64R) • Restricted Earth Fault (64REF) • 6.Back up O/C & E/F (50/51/67) • Mechanical • Buchholzrelay • Explosion Vent • Pressurerelief • Temperatureprotection
