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TRANSFORMERS. MARK LEAKEY KOK WAI, WONG WAN HAZLIN ZAINI. Reference : http://www.osha.gov/SLTC/etools/electric_power/images/transformer2.jpg. DEFINITION. Device used to transfer energy from primary winding to secondary winding by electromagnetic induction.

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transformers

TRANSFORMERS

MARK LEAKEY

KOK WAI, WONG

WAN HAZLIN ZAINI

Reference : http://www.osha.gov/SLTC/etools/electric_power/images/transformer2.jpg

definition
DEFINITION
  • Device used to transfer energy from primary winding to secondary winding by electromagnetic induction.
  • Based on Faraday’s Law of induction

Where:-

ε– EMF (V)

ΦB– Magnetic flux (Wb)

transformer uses
TRANSFORMER USES
  • Impedance matching
  • Electrical Isolation
  • AC power transmission
      • STEP-UP Transformer
      • STEP-DOWN Transformer
history
HISTORY
  • 1831 – Michael Faraday invented the Induction Ring.
  • 1881 – Lucien Gaulard and John Gibbs exhibited a device called secondary generator.
  • 1885 – William Stanley developed the fist commercially used practical device while working for Westinghouse Electric Company in US.
induction theory
INDUCTION THEORY
  • Transformers behaviour is based on Faraday’s Law of Induction

Where:-

ε– EMF (V)

N – No of turns of wire

ΦB– Magnetic flux (Wb)

induction theory1
INDUCTION THEORY

Reference: http://www.tpub.com/doeelecscience/electrical%20science2_files/image1053.jpg

transformer models
TRANSFORMER MODELS

Ideal Transformer

Np = No of windings on the primary Ns = No of windings on the secondary

ip = Current into the primary is = Current out from the secondary

Vp = Voltage across the primary Vs = Voltage across the secondary

primary and secondary relationship
Primary and Secondary Relationship

VP = NP = a = iS

VS NS iP

Note; a < 1 = Step up transformer

a > 1 = Step down transformer

Voltage and current angles are NOT affected hence, θP = θS = θ

losses
LOSSES
  • Transformers have losses and these losses must come into consideration.
      • Copper losses (I^2 R)
      • Leakage Flux losses
      • Core losses
          • Eddy currents
          • Hysteresis losses
real transformer losses
REAL TRANSFORMER LOSSES
  • Copper losses (I^2 R)
  • Leakage Flux losses
  • Core losses
      • Eddy currents
      • Hysteresis losses
equivalent circuit
EQUIVALENT CIRCUIT

Approximate Transformer Model referred to the primary side

types

IH

ISE

VSE

NSE

IL

VH

VL

NC

TYPES

Auto-Transformer

  • Used to change a desirable voltage by only a small amount. For example: 120/132 V
types1
TYPES

Three Phase Transformers

  • Three phase transformers
  • can be constructed in two
  • different ways i.e. :-
  • A three phase bank consists of three single phase transformers.
  • Three windings wrapped around a common core.

Reference : Electric Machinery and Power System Fundamentals, Stephen J. Chapman

three phase transformer connections
THREE PHASE TRANSFORMER CONNECTIONS

Delta – wye (Δ – Y)

  • Delta – delta (Δ – Δ)

Wye – delta (Y- Δ)

  • Wye – wye (Y – Y)

Reference : Electric Machinery and Power System Fundamentals, Stephen J. Chapman

types2
TYPES
  • Two types of special purpose transformers used in power systems for taking measurements.
    • Potential Transformer
    • Current Transformer

Reference : Electric Machinery and Power System Fundamentals, Stephen J. Chapman

efficiency
EFFICIENCY
  • Efficiency (η) is the ratio of the power out to the power in of a transformer.
    • η in an Ideal transformer, no power losses
      • PIN = VPIP cos θP
      • POUT = VSIS cos θS
      • PIN = POUT = VPIP cos θP = VSIS cos θS
      • SOUT = SIN = VPIP = VSIS
      • ηIdeal = 100%
efficiency for a single phase real transformer
Efficiency for a single phase real transformer
  • As mentioned previously, losses occur in a real transformer and these losses must be taken into count.
  • Hence, ηReal = POUT x 100%

PIN

= POUT x 100%

POUT + PLOSS

= VSIS cos θS_________

VSIS cos θS + i2R + (VP/a)2

RC

voltage regulation
VOLTAGE REGULATION
  • Voltage regulation (VR) is the ability of a system to provide near constant voltage over a wide range of load conditions. Also it compares the VO at no load to VO at full load.
  • An Ideal transformer has a voltage regulation,
  • VR = 0%

Reference : http://en.wikipedia.org/wiki/Voltage_regulation