1- A 3-phase 400KVA, 11000/416 transformer is delta-connected on the primary and star connected on the secondary. The primary resistance / phase is 4.3 2 and secondary resistance/phase is 0.0022. if the iron loss is 990 watts. Determine the full load copper losses. 2- A three-phase transformer has 3300/400 V, D/Y connected and working on 50Hz. The line current on the primary side is 12A and secondary has a balanced load at 0.8 lagging p.f. Determine the, i) Secondary phase voltage ii) Line current iii) Output power 4 * Remember For 中 3phase Tr 1-Connected system connected system. A- * 34 = 3 V I 2... COS = S34 зиф 9 = FL = √3 3 P3 = 3 * Zba = 3 Ye baze 3+ * Any given Power is 3phase * Any Jiven voltage I S Lone が is chosen base Upase S chosen Power: P oltage according to Rating of Tr. ording For A-D sr 人一人 3ph Tr the same as the problem. For A-1 3ph T to Vp/Vs Ratio a Vp/Vs a = Vē ·For A-D 3ph Tr √3

1- A 3-phase 400KVA, 11000/416 transformer is delta-connected on the primary and star connected on the secondary. The primary resistance / phase is 4.3 2 and secondary resistance/phase is 0.0022. if the iron loss is 990 watts. Determine the full load copper losses. 2- A three-phase transformer has 3300/400 V, D/Y connected and working on 50Hz. The line current on the primary side is 12A and secondary has a balanced load at 0.8 lagging p.f. Determine the, i) Secondary phase voltage ii) Line current iii) Output power 4 * Remember For 中 3phase Tr 1-Connected system connected system. A- * 34 = 3 V I 2... COS = S34 зиф 9 = FL = √3 3 P3 = 3 * Zba = 3 Ye baze 3+ * Any given Power is 3phase * Any Jiven voltage I S Lone が is chosen base Upase S chosen Power: P oltage according to Rating of Tr. ording For A-D sr 人一人 3ph Tr the same as the problem. For A-1 3ph T to Vp/Vs Ratio a Vp/Vs a = Vē ·For A-D 3ph Tr √3

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.54P: An infinite bus, which is a constant voltage source, is connected to the primary of the...

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A two-winding single-phase transformer rated 60kVA,240/1200V,60Hz, has an efficiency of 0.96 when operated at rated load, 0.8 power factor lagging. This transformer is to be utilized as a 1440/1200-V step-down autotransformer in a power distribution system. (a) Find the permissible kVA rating of the autotransformer if the winding currents and voltages are not to exceed the ratings as a two-winding transformer. Assume an ideal transformer. (b) Determine the efficiency of the autotransformer with the kVA loading of part (a) and 0.8 power factor leading.
An open-delta three-phase transformer system has one transformer center-tapped to provide a neutral for single-phase voltages. If the voltage from line to center tap is 277 V, what is the high-leg voltage?
The ratings of a three-phase three-winding transformer are Primary(1): Y connected 66kV,15MVA Secondary (2): Y connected, 13.2kV,10MVA Tertiary (3): A connected, 2.3kV,5MVA Neglecting winding resistances and exciting current, the per-unit leakage reactances are X12=0.08 on a 15-MVA,66-kV base X13=0.10 on a 15-MVA,66-kV base X23=0.09 on a 10-MVA,13.2-kV base (a) Determine the per-unit reactances X1,X2,X3 of the equivalent circuit on a 15-MVA,66-kV base at the primary terminals. (b) Purely resistive loads of 7.5 MW at 13.2 kV and 5 MW at 2.3kV are connected to the secondary and tertiary sides of the transformer, respectively. Draw the per- unit impedance diagram, showing the per-unit impedances on a 15-MVA,66-kV base at the primary terminals.
A single-phase, 50-kVA,2400/240-V,60-Hz distribution transformer has the following parameters: Resistance of the 2400-V winding: R1=0.75 Resistance of the 240-V winding: R2=0.0075 Leakage reactance of the 2400-V winding: X1=1.0 Leakage reactance of the 240-V winding: X2=0.01 Exciting admittance on the 240-V side =0.003j0.02S (a) Draw the equivalent circuit referred to the high-voltage side of the transformer. (b) Draw the equivalent circuit referred to the low-voltage side of the transformer. Show the numerical values of impedances on the equivalent circuits.
(a) An ideal single-phase two-winding transformer with turns ratio at=N1/N2 is connected with a series impedance Z2 across winding 2. If one wants to replace Z2, with a series impedance Z1 across winding 1 and keep the terminal behavior of the two circuits to be identical, find Z1 in terms of Z2. (b) Would the above result be true if instead of a series impedance there is a shunt impedance? (c) Can one refer a ladder network on the secondary (2) side to the primary (1) side simply by multiplying every impedance byat2 ?
A single-phase step-down transformer is rated 13MVA,66kV/11.5kV. With the 11.5 kV winding short-circuited, rated current flows when the voltage applied to the primary is 5.5 kV. The power input is read as 100 kW. Determine Req1andXeq1 in ohms referred to the high-voltage winding.
Rework Example 3.12 for a+10 tap, providing a 10 increase for the high-voltage winding.
Rework Problem 3.14 if the transformer is delivering rated load at rated secondary voltage and at (a) unity power factor, (b) 0.8 power factor leading. Compare the results with those of Problem 3.14. -
For an ideal transformer, the efficiency is (a) 0 (b) 100 (c) 50
A three phase transformer is used for ancillary services in a thermal power plant. It shows the following nameplate data: 30 MVA, 20/6.6 kV, and an impedance of 8%. The transformer has 21 taps to change the tap ratio in 1% increments. Neglect the transformer resistance. a) If the voltage at the high side is 18.5 kV, determine the tap ratio that must be used under a full load condition at unity power factor. b) What is the number of the actual tap? Assume you start counting from the lowest possible tap.
The single-phaseequivalent circuit parameters appearing on the high voltage (primary) windings side of the three-phase, 60 Hz 6600/1100 Y/△-connected transformer are given below. Find the transformer efficiencywhen a 5 ohm delta-connected resistive load is connected to the low voltage (secondary) windings of this transformer and the nominal voltage is applied to the high voltage windings. Total iron losses of three phases will be taken as 2500 W.
A 50Hz, single phase transformer has a ratio of N2:N1 = 0.2. On full-load, the secondary current is 200A. The resistance and reactance of the primary winding are 0.8 ohm and 4 ohm respectively. The corresponding values for the secondary winding are 0.04 ohm and 0.1 ohm. If the secondary is short circuited, what voltage must be applied to the primary to produce full-load current? What will be the copper loss?