ECE4762011_Lect9 - ECE 476 POWER SYSTEM ANALYSIS Lecture 9...

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Lecture 9 Transformers, Per Unit Professor Tom Overbye Department of Electrical and Computer Engineering ECE 476 POWER SYSTEM ANALYSIS
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2 Announcements Be reading Chapter 3 HW 3 is 4.32, 4.41, 5.1, 5.14. Due September 22 in class.
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3 Transformer Equivalent Circuit Using the previous relationships, we can derive an equivalent circuit model for the real transformer ' 2 ' 2 2 1 2 ' 2 ' 2 2 1 2 This model is further simplified by referring all impedances to the primary side r e e a r r r r x a x x x x = = + = = +
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4 Simplified Equivalent Circuit
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5 Calculation of Model Parameters The parameters of the model are determined based upon nameplate data: gives the rated voltages and power open circuit test: rated voltage is applied to primary with secondary open; measure the primary current and losses (the test may also be done applying the voltage to the secondary, calculating the values, then referring the values back to the primary side). short circuit test: with secondary shorted, apply voltage to primary to get rated current to flow; measure voltage and losses.
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6 Transformer Example Example: A single phase, 100 MVA, 200/80 kV transformer has the following test data: open circuit: 20 amps, with 10 kW losses short circuit: 30 kV, with 500 kW losses Determine the model parameters.
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7 Transformer Example, cont’d e 2 sc e 2 2 e 2 e 100 30 500 , R 60 200 500 P 500 kW R 2 , Hence X 60 2 60 200 4 10 200 R 10,000 10,000 20 sc e e sc c e m m MVA kV I A jX kV A R I kV R M kW kV jX jX X A = = + = = = = = = - = = = + + = = = From the short circuit test From the open circuit test
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8 Residential Distribution Transformers Single phase transformers are commonly used in residential distribution systems. Most distribution systems are 4 wire, with a multi-grounded, common neutral.
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9 Per Unit Calculations A key problem in analyzing power systems is the large number of transformers. It would be very difficult to continually have to refer impedances to the different sides of the transformers This problem is avoided by a normalization of all variables. This normalization is known as per unit analysis. actual quantity quantity in per unit base value of quantity =
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10 Per Unit Conversion Procedure, 1 φ 1. Pick a 1 φ VA base for the entire system, S B 2. Pick a voltage base for each different voltage level, V B . Voltage bases are related by transformer turns ratios. Voltages are line to neutral. 3.
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This note was uploaded on 11/17/2011 for the course ECE 476 taught by Professor Overbye,t during the Fall '08 term at University of Illinois, Urbana Champaign.

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ECE4762011_Lect9 - ECE 476 POWER SYSTEM ANALYSIS Lecture 9...

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