Description : A 50 KVA transformer has iron loss 2 kW on full load. Calculate its iron loss at 75% of full load.
Last Answer : Iron loss is dependent on voltage and independent of load. Hence iron loss at 75% of Load = Iron loss at full load = 2 kW
Description : [23] Transformers are rated in KVA instead of KW because A. load power factor is often not known B. KVA is fixed whereas KW depends on load power factor C. Total transformer loss depends on volt ampere D. It has become customary
Last Answer : C. Total transformer loss depends on volt ampere
Description : 5 The efficiency of a transformer is maximum when A. It runs at half full load B. it runs at full load C. its Cu loss equal iron loss D. it runs over load
Last Answer : C. Its cu loss equal iron loss
Description : Why are motor ratings given in KW and that of alternator and transformer given in KVA?
Last Answer : kW is the output mechanical power of a motor and is expressed in kW. kVA is the net (apparent) power input to the transformer. This input power is the output + losses. kW = kVA x system power factor
Description : The transformer ratings are usually expressed in terms of A. Volts B. Amperes C. kW D. kVA
Last Answer : D) KVA
Description : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is
Last Answer : A 40 kVA transformer has a core loss of 400 W and a full load copper loss of 800 W. The proportion of full load at maximum efficiency is 0.707
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 building intended to be used for commercial purpose will be required to follow Energy conservation building code under Energy Conservation Act, 2001 provided its a) connected load is 120 kW and above b) ... and above c) connected load is100 kW and above or contract demand is 120 kVA and above
Last Answer : c) connected load is100 kW and above or contract demand is 120 kVA and above
Description : Why are generators rated in kVA not in kW ?
Last Answer : Because It's rating of generator kva is apparent power. Kw is active power which we use. And one is kvar reactive power.
Description : The apparent power drawn by an A.C. circuit is 10 kVA and active power is 8 kW. The reactive power in the circuit is?
Last Answer : The apparent power drawn by an A.C. circuit is 10 kVA and active power is 8 kW. The reactive power in the circuit is 6 kVAR.
Description : KVA of an Auto-transformer of V1/V2 = 220/150 for a load of 100KVA is: a. 100KVA b. 50KVA c. 33.3KVA d. 20KVA
Last Answer : KVA of an Auto-transformer of V1/V2 = 220/150 for a load of 100KVA is: a. 100KVA b. 50KVA c. 33.3KVA d. 20KVA
Description : What should be kVA rating of each transformer in V-V bank when three phase balanced load is 40 kVA ? (A) 19 (B) 28 (C) 37 (D) 23
Last Answer : What should be kVA rating of each transformer in V-V bank when three phase balanced load is 40 kVA ? (A) 19 (B) 28 (C) 37 (D) 23
Description : The kVA rating required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV will be: A. 4 kVA B. 0.25 kVA C. 16 kVA D. 8 kVA
Last Answer : The kVA rating required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV will be: 16 kVA
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 : The rotor power output of a 3-phase induction motor is 15 KW and corresponding slip is 4%. The rotor copper loss will be (A) 600 W. (B) 625 W (C) 650 W (D) 700 W
Last Answer : Ans: B Rotor copper losses = rotor input- rotor output and output = (1-s) input ∴ Input = output/(1-s) = 15000 /1-0.04 = 15625 ∴ loss = 15625 -1500 = 625 watt
Description : [53] The iron loss of the transformer is negligible during short circuit test because A. The entire input is just sufficient to meet Cu losses only B. Flux produced is a small fraction of the normal flux C. Iron core becomes fully saturated D. Supply frequency is held constant
Last Answer : B. Flux produced is a small fraction of the normal flux
Description : A 10 kVA, 400 V/200 V single phase transformer with 10% impedance draws a steady short-circuit line current of (a) 250A (b) 50 A (c) 150 A (d) 350 A
Last Answer : A 10 kVA, 400 V/200 V single phase transformer with 10% impedance draws a steady short-circuit line current of 250A
Description : Why are Alternators rated in kVA and not in kW?
Last Answer : The continuous power rating of any machine is generally defined as the power the machine or apparatus can deliver for a continuous period so that the losses incurred in the machine gives rise to a ... generator , the Alternators have only their apparent power in VA/kVA/MVA as their power rating.
Description : Which of the following statements are true? i) reactive current is necessary to build up the flux for the magnetic field of inductive devices ii) some portion of reactive current is converted into work iii) the cosine of angle ... called power factor a) i & iv b) ii & iii c) i & iii d) iii & iv
Last Answer : a) i & iv
Description : A 50 Hz, 4 pole turboalternator rated at 20 MVA. 13.2 KV has an inertia constant H = 4 KW sec/KVA. The K.E. stored in the rotor at synchronous speed is
Last Answer : A 50 Hz, 4 pole turboalternator rated at 20 MVA. 13.2 KV has an inertia constant H = 4 KW sec/KVA. The K.E. stored in the rotor at synchronous speed is 80 MJ
Description : What is difference between KW and KVA?
Last Answer : kW is kilowatt and kVA is kilovolt ampere. kW is unit of real power and kVA is unit of Apparent power.
Description : A transformer has maximum efficiency at 3/4 full load. The ratio of its iron losses and full load copper loss is : - a) 16/9 b) 4 / 3 c) 3/4 d) 9 /16
Last Answer : A transformer has maximum efficiency at 3/4 full load. The ratio of its iron losses and full load copper loss is : - 9 /16
Description : In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is :
Last Answer : In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is : 0.075
Description : When two transformer of different kVA rating are connected in parallel they share the load in proportion to their respective kVA rating only when their:
Last Answer : When two transformer of different kVA rating are connected in parallel they share the load in proportion to their respective kVA rating only when their: P u impedance are equal
Description : At full -load of a transformer, the iron loss and copper loss are 3000 W and 4000 W respectively. Then total loss at maximum efficiency is : (A) 7000 W (B) 6000 W (C) 8000 W (D) 4000 W
Last Answer : At full -load of a transformer, the iron loss and copper loss are 3000 W and 4000 W respectively. Then total loss at maximum efficiency is : 6000 W
Description : A 220/440 V, 50 Hz, 5 KVA, single phase transformer operates on 220V, 40Hz supply with secondary winding open circuited. Then (A) Both eddy current and hysteresis losses decreases. (B) Both ... same but hysteresis loss increases. (D) Eddy current loss increases but hysteresis loss remains the same.
Last Answer : (A) Both eddy current and hysteresis losses decreases.
Description : A 3-phase, 11 kv, 50 Hz, 200 kW load has a power factor of 0.8 lag. A delta connected 3-phase capacitor is used to improve the power factor to unity. The capacitance perphase of the capacitor in micro-farads is?
Last Answer : A 3-phase, 11 kv, 50 Hz, 200 kW load has a power factor of 0.8 lag. A delta connected 3-phase capacitor is used to improve the power factor to unity. The capacitance perphase of the capacitor in micro-farads is 1.316.
Description : A consumer finds that after running 10 kVA equipment on full load for six hours, his energy consumption was 48 kWH. It can be concluded that (A) The load factor of consumer for the day was unity. (B ... (C) The equipment was drawing only reactive power. (D) The power factor of equipment was 0.8.
Last Answer : A consumer finds that after running 10 kVA equipment on full load for six hours, his energy consumption was 48 kWH. It can be concluded that The power factor of equipment was 0.8.
Description : The kVA rating of Three-phase transformer with Voltage = 200V and Current = 100A will be : (A) 34.64 kVA (B) 75 kVA (C) 20 kVA (D) None of the above
Last Answer : The kVA rating of Three-phase transformer with Voltage = 200V and Current = 100A will be : 34.64 kVA
Description : A 1100 kVA, 11 kV/1.1 kV conventional two-winding transformer is connected as a 12.1 kV/11 kV step-down auto-transformer. The rating of the auto-transformer is (A) 1000 kVA (B) 1100 kVA (C) 11000 kVA (D) 12100 kVA
Last Answer : A 1100 kVA, 11 kV/1.1 kV conventional two-winding transformer is connected as a 12.1 kV/11 kV step-down auto-transformer. The rating of the auto-transformer is 12100 kVA
Description : A single phase transformer rated at 3000 kVA, 69 kV 4.16 kV, 60 Hz has a total internal impedance Zp of 127 ohm, referred to the primary side. Calculate the primary current if the secondary is accidentally short circuited. (A) 43.5 A (B) 543 A (C) 9006 A (D) 721 A
Last Answer : 543A
Description : Transformer generally rated in KVA
Last Answer : The power of transformer is apparent power because it has no power factor and it is the product of voltage and current.
Description : 49 The open circuit test is carried out in a transformer to find the A. Cu loss B. Core loss C. Total loss D. Insulation resistance
Last Answer : B. Core loss
Description : 48.During light loads, the transformer efficiency is low because A. Secondary output is low B. Transformer losses are high C. Fixed loss is high in proportion to the output D. Cu loss is small
Last Answer : C. Fixed loss is high in proportion to the output
Description : A 400/200 volts transformer has pu impedance of 0.05. The HV side voltage required to circulate full load current during short circuit test is
Last Answer : A 400/200 volts transformer has pu impedance of 0.05. The HV side voltage required to circulate full load current during short circuit test is 20 V
Description : The rotor power output of a 3 -phase induction motor is 15 kW and the corresponding slip is 4%. The rotor copper losses will be: (A) 600 W (B) 625 W (C) 650 W (D) 700 W
Last Answer : The rotor power output of a 3 -phase induction motor is 15 kW and the corresponding slip is 4%. The rotor copper losses will be: 625 W
Description : In an actual transformer the iron loss remains practically constant from no load to full load because?
Last Answer : In an actual transformer the iron loss remains practically constant from no load to full load because core flux remains practically constant.
Description : Match each of the reaction given in Column I with the corresponding product(s) given in Column II. `{:("Column I","Column II"),(A. "Cu+dil. HNO"_(3),p
Last Answer : Match each of the reaction given in Column I with the corresponding product(s) given in Column II. `{:("Column I"," ... (,t. "Zn"("NO"_(3))_(2)):}`
Description : A 150 kW electric motor has an efficiency of 92 %, when it operates at full load. Calculate the losses in the machine. (A) 92 kW (B) 150 kW (C) 163 kW (D) 13 kW
Last Answer : efficiency -output /input * 100 150/0.92----------163(input) losses-----(163--150) ---------13kw.
Description : 55 When a 400Hz transformer is operated at 50Hz its KVA rating is A. Reduced to 1/8 B. Increased 8 times C. Unaffected D. Increased 64 times
Last Answer : A. Reduced to 1/8
Description : The maximum demand of consumer is 2 kW and his daily energy consumption is 20 units. Its Load Factor is (1) 10.15% (2) 41.6 % (3) 50 % (4) 60%
Last Answer : Total maximum demand of energy in a day = 2kw*24= 48 units Consumer consumption is 20 units . Load factor = (number of units utilizing)/(total max. demand) = 20/48 = 41.6%
Description : What is the maximum current allowed to be drawn from the secondary of a 2 KVA step-down transformer with a turns ratio of four to one if connected across a 440 volt line? A. 1.1 amps B. 4.5 amps C. 18.1 amps D. 22.7 amps
Last Answer : Answer: C
Description : What is the maximum allowable primary current of a 2 KVA step-down transformer with a four to one turns ratio if connected across a 440 volt line? A. 1.1 amps B. 4.5 amps C. 18.1 amps D. 27.7 amps
Last Answer : Answer: B
Description : Why we do 2 types of earthing on transformer i.e.: body earthing & neutral earthing, what is function. I am going to install a 5oo kva transformer & 380 kva DG set what should the earthing value?
Last Answer : The two types of earthing are Familiar as Equipment earthing and system earthing. In Equipment earthing: body (non conducting part) of the equipment should be earthed to safeguard the human ... earthing will be further classified into directly earthed, Impedance earthing, resistive (NGRs) earthing.
Description : For which of the following ratings of the transformer differential protection is recommended ? (a) above 30 kVA. (b) equal to and above 5 MVA (c) equal to and above 25 MVA (d) none of the above
Last Answer : (b) equal to and above 5 MVA
Description : 4] In operating a 400hz transformer at 50Hz A. Only voltage is reduced in the same proportion as the frequency B. Only KVA rating is reduced in the same proportion as the frequency C. Both voltage and KVA rating are reduced in the same proportion as frequency D. None of the above
Last Answer : B. Only KVA rating is reduced in the same proportion as the frequency
Description : Why Transformer rating is given in kVA?
Last Answer : Because of core losses and iron losses as core losses are measured in amps and cu losses in voltage ....this is definatly reason for the rating Or kVA is the unit for apparent power. Apparent ... shift between voltage and current). So a transformer has to be rated (and selected) by apparent power.
Description : Define kVA rating of transformer.
Last Answer : kVA rating of transformer is defined as the product of voltage (V) and current (I) on primary side of transformer or secondary side of transformer divided by 1000. On both side the VA rating remains ... Mathematically kVA rating is given by, kVA rating of transformer = V1I1/1000 =V2I2/1000
Description : A 400V/100 V, 10 KVA two-winding transformer is reconnected as an auto-transformer across a suitable voltage source. The maximum rating of such an arrangement could be A) 50 KVA B) 15 KVA C) 12.5 KVA D) 8.75 KVA
Last Answer : A 400V/100 V, 10 KVA two-winding transformer is reconnected as an auto-transformer across a suitable voltage source. The maximum rating of such an arrangement could be 50 KVA