-Select the correct answer for the alternatives given. -which of the following does not change in transformer a)-current b)-voltage c)- frequency d)-all of the above 2- The full-load copper loss and iron loss of transformer are 6400w and 5000w respectively. The copper loss and iron loss at half load will be respectively. . a)-(3200 w and 2500 w) b)-(1600 w and 1250 w), c)-(1600 w and 5000w d)- (3200 w and 1250 w) 3-A d.c. shunt motor is running with certain load. The effect of adding an external resistance in field circuit is to a)-reduce the motor speed b) increase the motor speed; c)- stop the motor d)- reduce the armature current of the motor 4- The emf induced in the windings of a transformer will a-lag the core flux by 90°. b)-be in-phase with the core flux c)- lead the core flux by 90° d)-be independent of the core flux 5-In a 4-pole, 25kw,200v wave wound dc shunt generator the current in each parallel path will be a)- (62.5A) " b)- (125A). c)- (250A) d)- (31.5A)

-Select the correct answer for the alternatives given. -which of the following does not change in transformer a)-current b)-voltage c)- frequency d)-all of the above 2- The full-load copper loss and iron loss of transformer are 6400w and 5000w respectively. The copper loss and iron loss at half load will be respectively. . a)-(3200 w and 2500 w) b)-(1600 w and 1250 w), c)-(1600 w and 5000w d)- (3200 w and 1250 w) 3-A d.c. shunt motor is running with certain load. The effect of adding an external resistance in field circuit is to a)-reduce the motor speed b) increase the motor speed; c)- stop the motor d)- reduce the armature current of the motor 4- The emf induced in the windings of a transformer will a-lag the core flux by 90°. b)-be in-phase with the core flux c)- lead the core flux by 90° d)-be independent of the core flux 5-In a 4-pole, 25kw,200v wave wound dc shunt generator the current in each parallel path will be a)- (62.5A) " b)- (125A). c)- (250A) d)- (31.5A)

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 3.9P

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Similar questions

For 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) No
A bank of three single-phase transformers, each rated 30MVA,38.1/3.81kV, are connected in Y- with a balanced load of three 1, Y-connected resistors. Choosing a base of 90MVA,66kV for the high-voltage side of the three-phase transformer. spify the base for the low-voltage side. Compute the per-unit resistance of the load on the base for the low-voltage side. Also, determine the load resistance in ohms referred to the high-voltage side and the per-unit value on the chosen base.
The ideal transformer windings are eliminated from the per-unit equivalent circuit of a transformer. (a) True (b) False
Three single-phase, two-winding transformers, each rated 450MVA,20kV/288.7kV, with leakage reactance Xeq=0.10perunit, are connected to form a three-phase bank. The high-voltage windings are connected in Y with a solidly grounded neutral. Draw the per-unit equivalent circuit if the low-voltage windings are connected (a) in with American standard phase shift or (b) in Y with an open neutral. Use the transformer ratings as base quantities. Winding resistances and exciting current are neglected.
For developing per-unit equivalent circuits of single-phase three-winding transformer, a common Sbase is selected for all three windings and voltage bases are selected in proportion to the rated voltage of the windings (a) True (b) False
An ideal transformer has no real or reactive power loss. (a) True (b) False
In per-unit equivalent circuits of practical three-phase transformers, under balanced thr-phase operation, in which of the following connect ions would a phase-shifting transformer come up? (a) Y-Y (b) Y- (c) -
For an ideal 2-winding transformer, the ampere-turns of the primary winding, N1I1 is equal to the ampere-turns of the secondary winding, N2I2 (a) True (b) False
Three single-phase two-winding transformers, each rated 25MVA,54.2/5.42kV, are connected to form a three-phase Y- bank with a balanced Y-connected resistive load of 0.6 per phase on the low-voltage side. By choosing a base of 75 MVA (three phase) and 94 kV (line-to-line) for the high-voltage side of the transformer bank, specify the base quantities for the low-voltage side. Determine the per-unit resistance of the load on the base for the low-voltage side. Then determine the load resistance RL in ohms referred to the high-voltage side and the per-unit value of this load resistance on the chosen base.
With the American Standard notation, in either a Y-or-Y transformer, positive- sequen quantities on the high-voltage side shall lead their corresponding quantities on the low-voltage side by 30. (a) True (b) False
The ratings of a three-phase, three-winding transformer are Primary: Y connected, 66kV,15MVA Secondary: Y connected, 13.2kV,10MVA Tertiary: connected, 2.3kV,5MVA Neglecting resistances and exciting current, the leakage reactances are: XPS=0.09 per unit on a 15-MVA,66-kV base XPT=0.08 per unit on a 15-MVA,66-kV base XST=0.05 per unit on a 10-MVA,13.2-kV base Determine the per-unit reactances of the per-phase equivalent circuit using a base of 15 MVA and 66 kV for the primary.
The per-unit equivalent circuit of two transformers Ta and Tb connected in parallel, with the same nominal voltage ratio and the same reactan of 0.1 per unit on the same base, is shown in Figure 3.43. Transformer Tb has a voltage-magnitude step-up toward the load of 1.05 times that of Ta (that is, the tap on the secondary winding of Tb is set to 1.05). The load is represented by 0.8+j0.6 per unit at a voltage V2=1.0/0 per unit. Determine the complex power in per unit transmitted to the load through each transformer, comment on how the transformers share the real and reactive powers.