Delmar's Standard Textbook Of Electricity
7th Edition
ISBN: 9781337900348
Author: Stephen L. Herman
Publisher: Cengage Learning
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Textbook Question
Chapter 28, Problem 10RQ
Referring to the transformer connection in Question 9, if the center tap of the primary is connected to a neutral conductor on the incoming power, will it permit the secondary voltages to be balanced when single-phase loads are added?
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A three-phase transformer bank has the primary and secondary windings connected in a wye configuration. The secondary center tap is being used as a neutral to supply single-phase loads. Will connecting the center tap connection of the secondary to the center tap connection of the primary permit the secondary voltage to stay in balance when a single-phase load is added to the secondary?
A fault occurs at point F of the system in the figure. Calculate the sub-transient current in phase c of machine 1, assuming that the currents before the fault are zero. Both machines have a nominal capacity of 1200 kVA, 480 V, with reactances X”=X2= 11% and X0 = 3.5%. The nominal capacity of each three-phase transformer is 1200 kVA, 480 V Δ/ 2400 V and with reactances X1=X2=X0= 6%. Transmission line reactances are X1=X2=22% and X0 = 35% on a 1200 kVA, 2400 V basis. Neutral grounding reactor reactances are 8% on a kVA and kV basis. of the machines.
a) Calculate the fault current if a ground fault occurs in phase a,
b) The fault current if it is a line-to-line fault
c) the voltage in phase b and c for the line-to-ground fault in phase a .
Subject: Electrical ApparatusA certain single-phase transformer with full load copper loss and core-loss is loaded at full load. Does power factor of the load affect the power loss of a transformer? Why?
Chapter 28 Solutions
Delmar's Standard Textbook Of Electricity
Ch. 28 - How many transformers are needed to make an...Ch. 28 - Two transformers rated at 100 kVA each are...Ch. 28 - How does the NEC specify that the high leg of a...Ch. 28 - An open-delta three-phase transformer system has...Ch. 28 - If a single-phase load is connected across the two...Ch. 28 - A three-phase transformer connection has a...Ch. 28 - A three-phase transformer connection has a...Ch. 28 - A three-phase transformer bank has the secondary...Ch. 28 - A three-phase transformer bank has the primary and...Ch. 28 - Referring to the transformer connection in...
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- Three single-phase two-winding transformers, each rated 3kVA,220/110volts,60Hz, with a 0.10 per-unit leakage reactance, are connected as a three-phase extended autotransformer bank, as shown in Figure 3.36(c). The low-voltage winding has a 110 volt rating. (a) Draw the positive-sequence phasor diagram and show that the high-voltage winding has a 479.5 volt rating. (b) A three-phase load connected to the low-voltage terminals absorbs 6 kW at 110 volts and at 0.8 power factor lagging. Draw the per-unit impedance diagram and calculate the voltage and current at the high-voltage terminals. Assume positive-sequence operation.arrow_forwardFor a short-circuit test on a 2-winding transformer, with one winding shorted, can you apply the rated voltage on the other winding? (a) Yes (b) Noarrow_forwardA certain single-phase transformer with full-load copper loss and core loss is loaded at full load. Does power factor of the load affect the power loss of a transformer? Why?arrow_forward
- During routine tests of a three phase transformer, measurements of DC resistance between windingterminals is noted down. What kind of information can be obtained from the values so noted?arrow_forward1-Why the transformer core made from lamination plates? 2- Why core losses remain almost constant at any load? 3- Why O.C.T. is generally performed on L.V. side (not at H.V. side)?arrow_forwardThe equivalent circuit impedances of a 20-kVA, 8000/240-V, 60-Hz transformer are to be determined. The open-circuit test and the short- circuit test were performed on the primary side of the transformer, and the following data were taken: Open-circuit test (on primary) Short-circuit test (on primary) Voc = 8000 V Ve = 489 V Ioc = 0.214 A Isc = 2.5 A Poc = 400 W Pyc = 240 W Find the impedances of the approximate equivalent circuit referred to the primary side, and sketch the circuit.arrow_forward
- The equivalent circuit impedances of a 20-kVA, 8000/240-V, 60-Hz transformer are to be determined. The open-circuit test and the short- circuit test were performed on the primary side of the transformer, and the following data were taken: Open-circuit test (on primary) Short-circuit test (on primary) 8000 V V= 489 V I0.214 A 2.5 A P= 400 W P= 240 W Find the impedances of the approximate equivalent circuit referred to the primary side, and sketch the circuit.arrow_forward3-phase 50-kVA 31,5/0,4-KVLL distribution transformers are connected in A-Y. Open-circuit test was performed on the high-voltage side of this transformer bank, and the following data were recorded: Vline,oc=480 V, Iline,oc=4.10 A, Poc = 945 W Short-circuit test was performed on the low-voltage side of this transformer bank, and the following data were recorded: Vline,sc = 808 V, Iline,sc = 3.11 A, Psc = 912 W (a) Find the voltage regulation of this transformer bank at the rated load and 0.85 power factor lag. (b) Draw a phasor diagram of this transformer at 0.85 power factor leading. A 20 Hp, 440-V, 0.85-PF-lagging Y-connected synchronous motor has an armature resistance of 0.22 2 and a synchronous reactance of 3.0 2. Its efficiency at full load is 92% (1 Hp=746 watt). (a) What is the input power to the motor at rated conditions? (b) What is the line current of the motor at rated conditions? (c) What is the internal generated voltage EA of this motor at rated conditions? A 3-phase…arrow_forwardHow many transformers are needed to make an open-delta connection? 2. Two transformers rated at 100 kVA each are connected in an open-delta connection. What is the total output power that can be supplied by this bank? 3. How does the NEC specify that the high leg of a four-wire delta connection be marked? 4. 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? 5. If a single-phase load is connected across the two line conductors and neutral of the transformer in Question 4 and one line has a current of 80 A and the other line has a current of 68 A, how much current is flowing in the neutral conductor? 6. A three-phase transformer connection has a delta-connected secondary, and one of the transformers has been center-tapped to form a neutral conductor. The phase-to-neutral value of the center-tapped secondary winding…arrow_forward
- In the single-phase, three- winding, transformer, the primary current is equal to lo at the condition of ints there is no load on tertiary windings the current in secondary windings equal to zero the resistances (R1, R2, and R3) in transformer windings are equal the inductances (L1, L2, and L3) in transformer windings are equal.arrow_forward1- When loaded the transformer : a- Chang of flux will be constant just during the load. during the no-load. c- Chang of flux will be constant during load and no-load. d- Chang of flux will be variable during the load and no-load. b- Chang of flux will be constant just 2- When transformer is open circuit a- the phase shift between voltage and current is bigger than ninety degrees. shift between voltage and current is zero. c- the phase shift between voltage and current is equal ninety degrees. d- the phase shift between voltage and current is less than ninety degrees. b- the phase 3- In practical transformer: a- V E: c- V, E: d- V,> E, , V;< E,arrow_forwardDuring short-circuit test of a transformer, which winding must be short-circuited? Why?arrow_forward
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