1. A 100-kVA distribution transformer has a maximum efficiency of 98 % at 50 % full-load and unity power factor. Determine its iron losses and full-load copper losses. The transformer undergoes a daily load cycle as follows : Load Power factor Load duration 100 kVA 1.0 8 hrs 50 kVA 0.8 6 hrs No load 10 hrs Determine its all-day efficiency. (Electrical Engineering, MS Univ. Baroda 1979)

1. A 100-kVA distribution transformer has a maximum efficiency of 98 % at 50 % full-load and unity power factor. Determine its iron losses and full-load copper losses. The transformer undergoes a daily load cycle as follows : Load Power factor Load duration 100 kVA 1.0 8 hrs 50 kVA 0.8 6 hrs No load 10 hrs Determine its all-day efficiency. (Electrical Engineering, MS Univ. Baroda 1979)

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 3.57P: A two-winding single-phase transformer rated 60kVA,240/1200V,60Hz, has an efficiency of 0.96 when...

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A single-phase 100-kVA,2400/240-volt,60-Hz distribution transformer is used as a step-down transformer. The load, which is connected to the 240-volt secondary winding, absorbs 60 kVA at 0.8 power factor lagging and is at 230 volts. Assuming an ideal transformer, calculate the following: (a) primary voltage, (b) load impedance, (c) load impedance referred to the primary, and (d) the real and reactive power supplied to the primary winding.
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.
The transformer of Problem 3.16 is supplying a rated load of 50 kVA at a rated secondary voltage of 240 V and at 0.8 posr factor lagging. Neglect the transformer exciting current. (a) Determine the input terminal voltage of the transformer on the high-voltage side. (b) Sketch the corresponding phasor diagram. (c) If the transformer is used as a step-down transformer at the load end of a feeder whose impedance is 0.5+j2.0, find the voltage VS and the power factor at the sending end of the feeder.
The motors M1andM2 of Problem 3.45 have inputs of 120 and 60 MW, respectively, at 13.2 kV, and both operate at unity power factor. Determine the generator terminal voltage and voltage regulation of the line. Neglect transformer phase shifts.
1) A single-phase 100-kVA, 2,400/240 V, 60-Hz distribution transformer is used as a step-down transformer. The load, which is connected to the 240 V secondary winding, absorbs 80 kVA at 0.8 power factor lagging and is at 230 V. Assuming an ideal transformer, calculate the following: (a) primary voltage;(b) load impedance;(c) load impedance referred to the primary;(d) the active and reactive power supplied to the primary winding.
A simple power system is shown in this Fig. The generator (480 V, 10 kVA) is connected to an ideal step-up transformer (1:10), a transmission line (R=20 Ohm and X=60 Ohm), step down transformer (20:1) and a load with magnitude Z=10 Ohm and angle =30 degree the base values for this system are chosen to be 480 V and 10 kVA at the generator. Calculate the per-unit impedance of the load. Select one: a. 1736 (45 degree) Ohm b. 36 (90 degree) Ohm c. 1.736 (30 degree) Ohm d. None of the above
In a three-phase step-down transformer with 150 kVA, 2080/208 V 60 Hz Y / Y connected R1 = 0.45 ohm, X1 = 2.2 ohm, R2 = 4.5 mohm, X2 = 22 mohm, Rc = 10 kohm, Xm = 8 kohms. When installed at 120 kVA, 90 kW back power factor, if the voltage at the load ends is at its nominal value, a) Primary side terminal voltage b) Yield (efficiency) c) Calculate the voltage regulation value?
A 2,300/240-V, 60-Hz, 4.6-kVA transformer isdesigned to have an induced emf of 2.5 V/turn.Assuming an ideal transformer, finda. The numbers of high-side turns Nh and low-sideturns Nl .b. The rated current of the high-voltage side Ih.c. The transformer ratio when the device is used as astep-up transformer.
2) A three -phase transformer of 90 kVA, 13200/480 V (line to line), with connection Delta-Delta, has a resistance of 1.3% and a reactance of 8.2% per unit. a) Calculate the phase impedance of the transformer referred to the high side strain. b) Calculate the phase impedance of the transformer referred to the low side strain. c) Calculate the transformer voltage regulation into nominal conditions with F.P.0,8 in delay.
A.1. A gas likely to be used in an inert-gas system of a power transformer isA. oxygen.B. hydrogen.C. air.D. nitrogen.A.2. In the design of transformer windings, creepage between conductors and core yokes is prevented byproviding,A. keep-back distance.B. vertical oil ducts.C. separation sticks.D. bushing terminals.
A Transformer with 10:1 ratio and rated at 50-kVA, 2400/240-V, 50-Hz is used to step down the voltage of a distribution system. The low-tension voltage is to be kept constant, if the transformer has: R = 2.2 0, R2 = 0.014 Q, X, = 4.1 0, X2 = 0.03 0, then, a. What load impedance connected to low-tension side will be loading the transformer fully. b. Calculate the equivalent resistance as referred to primary. c. Calculate the equivalent reactance as referred to primary. d. Calculate the equivalent impedance as referred to primary. e. Calculate the total Cu loss.
A 20-kVA 8000/277-V distribution transformer has the following resistances and reactance: RP = 32 Ω RS = 0.05Ω X P = 45Ω XS = 0.06Ω RC = 250 kΩ X M = 30 kΩ The excitation branch impedances are given referred to the high-voltage side of the transformer. (a) Find the equivalent circuit of this transformer referred to the high-voltage side. (b) Find the per-unit equivalent circuit of this transformer. (c) Assume that this transformer is supplying rated load at 277 V and 0.8 PF lagging. What is this transformer’s input voltage? What is its voltage regulation? (d) What is the transformer’s efficiency under the conditions of part (c)?