Three phase step-up transformer installed at power house, just before commencement of transmission line, have:

1 Answer

Answer :

Three phase step-up transformer installed at power house, just before commencement of transmission line, have: star delta connections

Related questions

Description : In a step-up or step-down transformer, electrical power is transferred from one circuit to another without change in

Last Answer : In a step-up or step-down transformer, electrical power is transferred from one circuit to another without change in frequency

Description : A three-phase, three-stack, variable reluctance step motor has 20 poles on each rotor and stator stack. The step angle of this step motor is  (A) 3o (B) 6o (C) 9o (D) 18o

Last Answer : A three-phase, three-stack, variable reluctance step motor has 20 poles on each rotor and stator stack. The step angle of this step motor is  6o

Last Answer : The purpose of providing iron core in a step-up transformer is to decrease the magnitude of magnetizing current.

Description : Why phasing out and polarity test is carried out on three phase transformer?

Last Answer : The phasing out test is carried out to identify the windings (primary and secondary) of corresponding phase of the three phase transformer. The polarity test is carried out to identify the ... identical polarity of the primary and secondary windings of each phase of the three phase transformer.

Description : Which three-phase connection can be used in a transformer to introduce a phase difference of 30o between its output and corresponding input line voltages  (A) Star-Star (B) Star-Delta (C) Delta-Delta (D) Delta-Zigzag

Last Answer : Which three-phase connection can be used in a transformer to introduce a phase difference of 30o between its output and corresponding input line voltages  (A) Star-Star (B) Star-Delta (C) Delta-Delta (D) Delta-Zigzag

Description : A simple phase transformer has a maximum efficiency of 90% at full load and unity power factor. Efficiency at half load at the same power factor is  (A) 86.7% (B) 88.26% (C) 88.9% (D) 87.8%

Last Answer : A simple phase transformer has a maximum efficiency of 90% at full load and unity power factor. Efficiency at half load at the same power factor is 87.8%

Description : In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of?

Last Answer : In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of less than 15A.

Description : Which of the following devices will receive voltage surge first travelling on the transmission line ? (a) Lightning arresters (b) Relays (c) Step-down transformer (d) Switchgear

Last Answer : (a) Lightning arresters

Description : A generator is connected through a 20 MVA, 13.8/138 kV step down transformer, to a transmission line. At the receiving end of the line a load is supplied through a step down transformer of 10 MVA, 138/69 kV rating. A 0.72 ... load (in per unit) in generator will be (A) 36 (B) 1.44 (C) 0.72 (D) 0.18

Last Answer : A generator is connected through a 20 MVA, 13.8/138 kV step down transformer, to a transmission line. At the receiving end of the line a load is supplied through a step down transformer of 10 MVA, 138/ ... MVA and 69 kV in load circuit, the value of the load (in per unit) in generator will be 36 

Description : Explain direct loading test on single phase transformer with neat circuit diagram. 

Last Answer : Direct loading test on single phase transformer with neat circuit diagram:   Direct loading test on transformer is carried out to calculate the losses, efficiency and voltage regulation of the ... voltage.  Efficiency and regulation can be calculated by using following formulae:   

Description : Single phase transformer

Last Answer : Single phase Transformer Transformer

Description : Explain construction and working of single phase Auto transformer.

Last Answer : Construction of single phase auto transformer: (i) It has only one winding wound on a laminated circular magnetic core. (ii) The core is made of silicon steel stampings. (iii) The two terminals of the ... help of handle. 5) The same transformer can be used as step-up or step down auto-transformer

Description : A single-phase transformer has a turns ratio of 1 :2 and is connected to a purely resistive load as shown in the figure. The magnetizing current drawn is 1A, and the secondary current is 1A. Ifcore losses and ... reactances are neglected, the primary current is  A)1.41A B)2A C) 2.24A D)3A

Last Answer : A single-phase transformer has a turns ratio of 1 :2 and is connected to a purely resistive load as shown in the figure. The magnetizing current drawn is 1A, and the secondary current is 1A. Ifcore losses and leakage reactances are neglected, the primary current is 2.24A

Description : A 500 kVA, 3-phase transformer has iron losses of 300 W and full load copper losses of 600 W. The percentage load at which the transformer is expected to have maximum efficiency is  (A) 50.0% (B) 70.7% (C) 141.4% (D) 200.0%

Last Answer : A 500 kVA, 3-phase transformer has iron losses of 300 W and full load copper losses of 600 W. The percentage load at which the transformer is expected to have maximum efficiency is 70.7%

Description : A single-phase, 50 kVA, 250 V/500 V two winding transformer has an efficiency of 95% at full load, unity power factor. If it is re-configured as a 500 V/750 V auto-transformer, its efficiency at its new rated load at unity power factor will be  (A) 95.752% (B) 97.851% (C) 98.276% (D) 99.241%

Last Answer : A

Description : A single-phase transformer has no-load loss of 64 W, as obtained from an open circuit test. When a short-circuit test is performed on it with 90% of the rated currents flowing in its both LV and HV windings, ... .0% of the rated current (C) 80.0% of the rated current (D) 88.8% of the rated current

Last Answer : A single-phase transformer has no-load loss of 64 W, as obtained from an open circuit test. When a short-circuit test is performed on it with 90% of the rated currents flowing in its both ... measured loss is 81 W. The transformer has maximum efficiency when operated at 80.0% of the rated current

Description : The hysteresis and eddy current losses of a single phase transformer working on 200 V, 50 Hz supply are Ph and Pe respectively. The percentage decrease in these when operated on a 160 V, 40 Hz supply are   (a) 32, 36 (b) 20, 36 (c) 25, 50 (d) 40, 80 

Last Answer : The hysteresis and eddy current losses of a single phase transformer working on 200 V, 50 Hz supply are Ph and Pe respectively. The percentage decrease in these when operated on a 160 V, 40 Hz supply are 20, 36

Last Answer :  Sandwich type winding is used in 3 phase shell-type transformer.

Last Answer : A Buchholz relay can be installed on oil cooled transformers.

Description : A single-phase, 230 V, 50 Hz ac mains fed step down transformer (4:1) is supplying power to a half-wave uncontrolled ac-dc converter used for charging a battery (12 V dc) with the series current limiting resistor being 19.04 Ohm. The charging current is  (A) 2.43 A (B) 1.65 A (C) 1.22 A (D) 1.0 A

Last Answer : A single-phase, 230 V, 50 Hz ac mains fed step down transformer (4:1) is supplying power to a half-wave uncontrolled ac-dc converter used for charging a battery (12 V dc) with the series current limiting resistor being 19.04 Ohm. The charging current is 1.0 A

Description : In a power transformer, the fundamental frequency of the hum arising due to magnetostriction is  (a) equal to the line frequency (b) double the line frequency (c) 4 times the line frequency (d) not related to the line frequency

Last Answer : In a power transformer, the fundamental frequency of the hum arising due to magnetostriction is double the line frequency

Last Answer : The efficiency of a power transformer is of the order of 98 percent.

Last Answer : A common method of cooling a power transformer is oil cooling.

Last Answer : The power transformer is a constant main flux device.

Last Answer : In a power or distribution transformer about 10 percent end turns are heavily insulated to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns.

Description : The maximum load that a power transformer can carry is limited by its?

Last Answer : The maximum load that a power transformer can carry is limited by its voltage ratio.

Description : The president of India addresses both Houses of Parliament assembled together at the commencement of the first session – (1) of each year (2) After each general election to the House of the People (3) Both 1 and 2 (4) Neither 1 nor 2

Last Answer : -(3) Both 1 and 2 Explanation: Article 87(1) of the Constitution provides: "At the commencement of the first session after each general election to the House of the People and at the ... shall address both Houses of Parliament assembled together and inform Parliament of the causes of its summons."

Description : When does a pilot apply the limitations of the MEL? a. At parking before commencement of taxi b. Prior to take-off c. At any time in flight d. Any time up to coming to a complete stop and applying the parking brake

Last Answer : d. Any time up to coming to a complete stop and applying the parking brake

Description : A three phase transmission line delivers a load of 5 MW at 0.8 power factor lagging. Resistance of each conductor is 0.5 ohm / km. Receiving end voltage is 33 kV. If the line loss is not to exceed 10%, determine the length of the line.  (A) 7 km (B) 27.9 km (C) 56.8 km (D) 13.9 km

Last Answer : B

Description : Explain with the neat circuit diagram only the scott connection scheme for conversion of three phase supply to two phase supply. Name one application of the same.

Last Answer : Three-phase to Two-phase Transformation (Scott Connection of Transformers): Working: i) Scott connection can be used for three-phase to two-phase conversion using two single-phase transformers ... a 3-phase system with a two-phase system with the flow of power in either direction. 

Description : What is the meaning of Indian State in the Constitution— (A) Any territory recognized by President of India (B) Any territory before commencement of Indian Constitution by the British ruler (C) Any territory which government of the Dominion of India recognised (D) B & C

Last Answer : (D) B & C

Description : In an election, electioneering has to be stopped in a Constituency— (A) 24 hours before the poll commences (B) 24 hours before the closing hour of polling (C) 48 hours before the hour of commencement of polling (D) 48 hours before the closing hour of polling

Last Answer : (D) 48 hours before the closing hour of polling

Description : What is the meaning of Indian State in the Constitution— (A) Any territory recognized by President of India (B) Any territory before commencement of Indian Constitution by the British ruler (C) Any territory which government of the Dominion of India recognised (D) B & C

Last Answer : (D) B & C

Description : In an election, electioneering has to be stopped in a Constituency— (A) 24 hours before the poll commences (B) 24 hours before the closing hour of polling (C) 48 hours before the hour of commencement of polling (D) 48 hours before the closing hour of polling

Last Answer : (D) 48 hours before the closing hour of polling

Description : Contracts made after incorporation but before the grant of Certificate of commencement of Business _________ A. Provisional contracts B. Pre incorporation contracts C. Preliminary contracts D. Both (b) & (c)

Last Answer : A. Provisional contracts

Description : An activity which must be completed before commencement of one or more other activities is called................................. a. Successor activity b. Predecessor activity c. Dummy activity d. None of these

Last Answer : b. Predecessor activity

Description : A 20m chain was found to be 6cm too long after chaining a distance of 1059m. It was found to be 9cm too short after chaining at the end 1985m. If the chain was correct before commencement of work find the true distance.

Last Answer : Given : Line ABC, AB=1059m, AC=1985m  L= 20m, No error at start, 0.06m too long at B,  0.09m too short  Find : True distance of AC = ? Solution : For part AB L = Length of chain= 20 m e = Average ... Total true distance of AC = True distance of (AB + BC)  = 1060.59 m + 922.52 m  = 1983.11 m

Description : A 20 m chain was found to be 10 cm too short after chaining 1000 m It was found to be 20 cm too short after chaining 1800 m. If the chain was correct before commencement of the work find the true distance.  

Last Answer : Average error in chain for 1000 m length = (0 + 10) / 2 = 5 cm = 0.05 m too short True length up to 1000 m = (20 - 0.05) x 1000 / 20 = 997.5 m. Average error in chain from 1000 m to 1800 m length = (10 ... 1800 m length = (20 - 0.15) x 800 / 20 = 794.0 m. True distance = 997.5 + 794 = 1791.5 m.

Description : Can I use a step up transformer at my house?

Last Answer : Yes you can use a step up trnasformer if you wish.You will not see any benefits from doing so.

Description : Explain the effect of Harmonics on the Transformer.

Last Answer : Effect of Harmonics on the Transformer:  1. Core loss: Harmonic voltage increases the hysteresis and eddy current losses in the lamination. The amount of the core loss depends on ... small core vibrations.  5. Saturation problem: Sometimes additional harmonic voltage causes core saturation.

Description : List two special feature of welding transformer.

Last Answer : Special features of welding transformer: i) It is a step down transformer that reduces the source voltage to a voltage desired according to the demands of the welding process. ii) Having large primary turns and less ... V ii) Secondary voltage - 40 to 60 V iii) Secondary current - 200 to 600 A

Description : State two applications of isolation transformer

Last Answer : Applications of isolation transformer: i) Isolates the load equipment from supply ground: ii) Reduction of voltage spikes iii) It acts as a decoupling device. iv) Protects loads from harmonic distortion.

Description : State why a transformer always have an efficiency of more than 90%.

Last Answer : As transformer is static device with no moving parts, the losses due to friction & windage are completely absent. Hence transformer has efficiency of more than 90%.

Description : Equivalent circuit of transformer

Last Answer : Equivalent Circuit Diagram of Transformer Referred to Primary: V1 -Primary Input voltage I1 - Input Current I0- Exciting current/ No load current Im- Magnetizing component ... equivalent of secondary terminal voltage ZL- Load impedance ZL ′- Primary equivalent of load impedance

Description : What is the use of transformer?

Last Answer : The use of transformer  is to do lower or raise  the voltage or currents in an electrical  circuit.  That's quite so simple. 

Description : Write about transformer on DC.

Last Answer : Transformer on DC : Transformer cannot work on DC. Transformer works on electromagnetic induction principle. Electromagnetic induction principle means when flux linking with coil changes and EMF induced in it ... winding insulation will burn. https://youtu.be/TVp_0fIfxqY

Description : State and justify which of the following two transformers is better:  Transformer A = 4% voltage regulation  Transformer B = 6% voltage regulation

Last Answer : Transformer A with 4% voltage regulation is better.  Justification: Voltage regulation refers to the percentage change in secondary voltage when load is changed from no-load to full-load with primary voltage ... 4% voltage regulation, which is less as compared to 6% of transformer B, it is better.

Description : State any four characteristics of core type transformer.

Last Answer : Characteristics of core type transformer: i) It has one window. ii) It has one magnetic circuit. iii) Core surrounds the winding. iv) Average length of core is more. v) Area of cross ... Better cooling for winding. vii) Mechnical strength is comparatively less. viii) Repair and maintenance is easy.

Description :  If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, then: A) both hysteresis loss and eddy current loss in the core will increase B) ... current loss will increase D) hysteresis loss will decrease but eddy current loss will remain unchanged

Last Answer :  If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, then: hysteresis loss will decrease but eddy current loss will remain unchanged

Description : Full load copper loss in a transformer is 1600 watts. At half load the copper loss will be: A) 6400 watt B) 1600 watt C) 800 watt D) 400 watt

Last Answer :  Full load cupper loss in a transformer is 1600 watts. At half load the cupper loss will be: 400 watt