Dula \u0394 Y Connection Current ratio of each phase of the transformer a I \u00d8S I\u00d8P

# Dula δ y connection current ratio of each phase of

This preview shows page 179 - 200 out of 487 pages.

Flaviano D. Dula Δ -Y Connection Current ratio of each phase of the transformer a = I ØS /I ØP Line - to – current ratio of the 3Ø transformer a T = I S /I P = I ØS /(√3I ØP ) = I S /(I P /√3 ) = (√3I S )/I P
Three-Phase Transformer
Flaviano D. Dula Problem 70 Three 10:1 transformers are connected Δ-Y for stepping up the 2300- volts 3-Ø source. Calculate the secondary line voltage. Ans. V S = 39.84kV
Flaviano D. Dula Solution V P = 2300V V ØP V P /a √3V P a Primaries Secondaries ∆ - Y step-up transformer = V S
Flaviano D. Dula Solution V S √3 V P a √3(2300) 1/10 = = 39.84 kV Answer Or a V ØP V ØS = V P V S / √3 Ratio of transformation of each transformer: a V S √3 V P a then = = =
Flaviano D. Dula Problem 71 A 2000-kW, 2400-V, 75% power factor load is to be supplied from a 34,500 -volt, 3Ø line through a single bank transformers. Give the secondary/primary line currents in amperes for the Y-Y connections. REE April 2006 A.50/200 B. 48/650 C. 60/800 D. 642/45
Flaviano D. Dula Solution I P P load √3 V P cosθ P = 2000kW √3(34.5kV)(0.75) = 44.626A Answer Primary line current: I P =
Flaviano D. Dula Solution I S P load √3 V S cosθ = 2000kW √3(2.4kV)(0.75) = 641.5A Answer Secondary line current: I S I S = aI P = (34500/2400) x 44.626A = 641.5A or =
Flaviano D. Dula Problem 72 A 13.8-kV/480-V, 10-MVA 3-Ø transformers has 5% impedance. What is the impedance in ohms referred to primary? REE March 1998 A. 0.952Ω B. 0.03Ω C. 5.125Ω D. 9.01Ω
Flaviano D. Dula Solution Per Unit Quantity = Actual Quantity Base Quantity Z p.u. = Z actual Z base Z e (V base ) 2 /S base = = Z e S base (V base ) 2 or Per unit impedance: Z p.u.
Flaviano D. Dula Solution Z p.u. Z e I rated V rated = Z e S rated (V rated ) 2 %Z Z(MVA) (kV) 2 Percent impedance: %Z Per unit impedance: Z p.u = Multiply each by V rated = X 100%
Flaviano D. Dula Solution herefore, the impedance in ohms referred to primar Z P %Z(kV L ) 2 (MVA ) x 100% (0.05) ( 13.8 ) 2 10 = 0.952 Ω Note: Z actual = Z p.u . Z base , Z base = (kV) 2 /MVA Actual impedance = =
Flaviano D. Dula Problem 73 A transformer rated 2000-kVA, 34500/240- volts has 5.75% impedance. What is the per- unit impedance? REE April 2004 A. 0.0635 B. 0.0656 C. 0.0575 D. 34.2
Flaviano D. Dula Solution Z p.u. = %Z/100 = 5.75% / 100 = 0.0575 Answer Per unit impedance: Z p.u
Flaviano D. Dula Problem 74 A Y- Δ transformation is used to take power from a 3-phase supply at a line voltage of 13,200-volts and deliver a 3-Ø load at a line voltage of 480-volts. The total load is 2500-kVA. At rated load: determine: (i) ratio of transformation a , (ii) high and low sides line and phase currents, (iii) the transformer coil (or winding) voltages, (iv) kVA rating of each transformer, and (v) bank or overall ratio.
Flaviano D. Dula Solution V P = 13200V V P 3 I P I ØS = a I ØP a ( √3I P ) = I S V P a√3 Primaries Secondaries I ØP = I P 2500 kVA Load, 480V (3Ø) = V S V ØP =
Flaviano D. Dula Solution (i) a V ØP V ØS = V P /√3 V S = 13200/√ 3 480 = 15.877 Answer = Ratio of transformation of each transformer or phase transformation ratio: a Y P S
Flaviano D. Dula Solution (ii) High or primary rated line current: I P I P S Load √3V P 2500 x 1000VA √3 x 13200V = = 109.35A Answer = Y P
Flaviano D. Dula Solution Low or secondary rated line current: I S I S S Load √3V S 2,500 , 000VA √3 x 480V = = 3007.03A Answer a(√ 3 I P ) = 13200/√3 480 (√3 x 2500 x 1000 √3 x 13200 ) = 3007.03A or = = Y-Δ s
Flaviano D. Dula Solution = I ØS a I ØP = I P = 109.35A and and high or primary rated phase current: I ØP I ØP S Load 3V ØP 2,500 , 000 3(13200/√3) = = 109.35A Answer Note: Y-connection: I L = I Ø or = Y P

#### You've reached the end of your free preview.

Want to read all 487 pages?

• Fall '19
• Flaviano D. Dula

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern