Chapter 12 Transformers, Industrial Electricity, 8th Edition, by Michael Brumbach, published by Delmar/Cenage Learning

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Electrical Power and Control, 2nd Edition, Edition, 2004, by Timothy L. Skvarenina and William E. Dewitt, from Pearson/Prentice Hall, ISBN 0-13-113045-5

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References

• Transformer Basics• Winding, Current, and Voltage Relationship• Transformer Operation and Loading• Transformer Construction• Types of Transformers• Transformer Connections• Transformers with Loads

Topics of Discussion

Transformer Basics

Primary side, Secondary side, Iron Core•

Single-phase, Three-phase transformer○

Step-down, Step-up transformer○

Types•

; EP primary-side voltage, ES secondary-side voltage, Np number of turns on primary-side windings, NS

number of turns on secondary-side

○

; EP primary-side voltage, ES secondary-side voltage, IS secondary-side current, IP primary-side current○

Winding Turns, Voltage and Current Relationships•

Idea transformer, neglecting all losses○

Pp = Ep*Ip = Ps = Es*Is ○

Rating: VA, KVA, MVA; primary voltage, secondary voltage, etc•

High-voltage coil (HV) denoted by the letter H; Low-voltage coil (LV) denoted by the letter X•

; VH high-side voltage, VX low-side voltage, NH number of turns on high-side windings, NX number of

Voltage ratio relationship:•

Lecture 11 - Transformers (Part I)Sunday, July 20, 2014 9:46 AM

ECE 211 Lectures Page 1

Pp = Ep*Ip = Ps = Es*Is ○

High-voltage coil (HV) denoted by the letter H; Low-voltage coil (LV) denoted by the letter X•

; VH high-side voltage, VX low-side voltage, NH number of turns on high-side windings, NX number of

turns on low-side

○

Voltage ratio relationship:•

Ampere turns relationship: IH NH = IX NX•Volt-Amp Rating: VH IH = VX IX •H1, H2: X1: X2 have the same simultaneous polarity (current entering these terminals will produce flux in the same direction); also using black dots to denote the polarity

Step down voltage from 120V to 12V•If Np = 400, what is the Ns?•

Example 1. A transformer has the following rating:

Solution:

Use the formula:

Example 2. If the transformer in Example 1 supplies a load current of 5A, how much is Ip? Solution:

Use the formula:

○ Faraday’s Law Erms = 4.44 f NΦmax = 4.44 f N Bmax Ac

○ Voltage : Turn Ratio Ep/Es = Np/Ns = a

○ Transformer Parallel Operation

• Ideal Transformer Operation

No load○

Under load○

Transformer Loading•

Exciting current: B = Φ/A and H = NI/L○

Exciting power: |So| = Erms Iorms = (4.44fNAcBmax) x Lc Hrms/N = 4.44fNAcBmax Lc Hrms○

Inrush Current○

Exciting Current•

Transformer Operation and Loading

High-permeance (low-reluctuance) material to minimize the magnetizing current○

To keep eddy current losses down, the core is made of laminations○

Typically, for 60 Hz operation, silicon steel laminations with thicknesses of 0.010” to 0.020” are used

○

Core Material•

Transformer Construction

ECE 211 Lectures Page 2

used Conductors: Copper or Aluminum•

Core Configuration: core type and shell type•

Between the coils and the transformer tank○

Insulation•

In the Barrel Winding: LV coil is surrounded by HV coil => reduce insulation requirements between the coil and core

○

Barrel windings plus Core type design: half of the primary and secondary windings are placed on each leg of the core to maximize the mutual coupling and reduced leakage flux.

○

Pancake Winding○

Coil types: Barrel and Pancake•

Coil Markings•

Transformer Noise (120 Hz vibration sound)•

Control transformer•Power transformer•K-Factor rated transformer (nonlinear loads)•Auto-transformer•Isolation transformer•

Current transformer (CT)○

Potential transformer (PT)○

Instrumentation transformers•

Types of Transformers

Series Connection - Increase voltage level•Parallel Connection - Increase current or wattage rating•

High-side 1 x 120V/ 1 x Low side 12 or 24 V○

High-side 2 x 240V / 1 x Low side 120 V (Figure 12-30)○

High-side 2 x 240V/ 2 x Low side 120V (Figure 12-32B)○

High-side 2 x 240V/ 2 x 120V, 1 x 240 V (Figure 12-32C)○

Single phase transformers•

Transformer Connections

ECE 211 Lectures Page 3

Delta-Delta: Δ-Δ○

Delta-Wye: Δ-Y○

Wye-Wye: Y-Y○

Wye-Delta: Y-Δ○

Three-phase transformers

ELine = Ephase•ILine = √3*Iphase•Rating = 3*Ephase*Iphase = √3*ELine*ILine•

Delta Δ Connection

ELine = √3Ephase•ILine = *Iphase•Rating = 3*Ephase*Iphase = √3*ELine*ILine•

Wye Y Connection

ECE 211 Lectures Page 4

GE Industrial Solutions: Transformers, http://www.geindustrial.com/cwc/Dispatcher?REQUEST=PRODUCTS&famid=42

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GE Instrumentation Transformers: http://site.ge-energy.com/prod_serv/products/metering/en/inst_transform.htm

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GE Silicones: http://www.gesilicones.com/silicones/americas/business/industries/electrical/motors/•Transformers, Schneider Electric, http://products.schneider-electric.us/products-services/products/transformers/•MV Transformers, Schneider Electric - http://www2.schneider-electric.com/corporate/en/products-services/energy-distribution/energy-distribution-intermediate.page?f=NNM1%3AMV+Transformers

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Voltage Regulators: http://ustpower.com/•Transformer and Regulators: http://www.electricalpowertransformer.com/•

Web Site References

ECE 211 Lectures Page 5