Question 1 1. A transformer has a A connected primary and a star connected secondary, working on 50 Hz supply. The line voltages on primary and secondary sides are 6.6 KV and 400 V respectively. The line current on the primary side is 8 A and the secondary side has a balanced load of 0.6 p.f. lagging. Find (a) output of the transformer (b) the line current on the secondary side. (Ans. (a) 54.857 kW (b) 132 A) 2. A scott connected transformer set supplies two electric furnaces at 110 V each from a 3 phase, 4400 V system. If the furnace connected to teaser transformer secondary takes 270 kW and other one connected to main transformer secondary takes 450 kW at unity p.f.. find the line currents taken from the three phases mains. (Ans.: 108.2486 A, 108.2486 A, 70.9364 A) 3. Explain the choice of connection of 3 phase transformers. 4. What are instrument transformers? State its advantages and disadvantages. 5. Explain the working of current transformer. 6. Explain the construction and working of potential transformer. 7. Compare C.T. and P.T.

Question 1 1. A transformer has a A connected primary and a star connected secondary, working on 50 Hz supply. The line voltages on primary and secondary sides are 6.6 KV and 400 V respectively. The line current on the primary side is 8 A and the secondary side has a balanced load of 0.6 p.f. lagging. Find (a) output of the transformer (b) the line current on the secondary side. (Ans. (a) 54.857 kW (b) 132 A) 2. A scott connected transformer set supplies two electric furnaces at 110 V each from a 3 phase, 4400 V system. If the furnace connected to teaser transformer secondary takes 270 kW and other one connected to main transformer secondary takes 450 kW at unity p.f.. find the line currents taken from the three phases mains. (Ans.: 108.2486 A, 108.2486 A, 70.9364 A) 3. Explain the choice of connection of 3 phase transformers. 4. What are instrument transformers? State its advantages and disadvantages. 5. Explain the working of current transformer. 6. Explain the construction and working of potential transformer. 7. Compare C.T. and P.T.

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

See similar textbooks

Similar questions

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.
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.
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.
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 23/230-kV step-up transformer feeds a three-phase transmission line, which in turn supplies a 150-MVA,0.8 lagging power factor load through a step-down 230/23-kV transformer. The impedance of the line and transformers at 230kVis18+j60. Determine the tap setting for each transformer to maintain the voltage at the load at 23 kV.
(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 50-kVA,2400/240-volt,60-Hz distribution transformer is used as a step-down transformer at the load end of a 2400-volt feeder whose series impedance is (1.0+j2.0) ohm. The equivalent series impedance of the transformer is (1.0+j2.5) ohms referred to the high-voltage (primary) side. The transformer is delivering rated load at a 0.8 power factor lagging and at a rated secondary voltage. Neglecting the transformer exciting current, determine (a) the voltage at the transformer primary terminals, (b) the voltage at the sending end of the feeder, and (c) the real and reactive power delivered to the sending end of the feeder.
An ideal transformer has no real or reactive power loss. (a) True (b) False
For the transformer in Problem 3.10. The open-circuit test with 11.5 kV applied results in a power input of 65 kW and a current of 30 A. Compute the values for GcandBm in siemens referred to the high-voltage winding. Compute the efficiency of the transformer for a load of 10 MW at 0.8 p.f. lagging at rated voltage.
A single-phase transformer, with primary turns of 500, is delivering full-load of 80 kW at a lagging power factor of 0.8 from a 220 V, 50 Hz supply. The current delivered to the load is 227 A. i. Estimate the peak magnetizing ﬂux, Φmax in the transformer. ii. What is the turns ratio of the transformer? iii. Determine the load impedance. iv. Determine the current drawn from the supply. v. Assume the core and copper losses are 800 W and 3200 W respectively. Detemine the input power and eﬃciency of the transformer. vi. If the load impedance on the transformer is doubled, what will be eﬀect on the core and copper losses? What is the eﬃciency at this operating condition?