Last Answer : A transformer cannot raise or lower the voltage of a D.C. supply because Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero.
Description : A dc shunt generator has a speed of 800 rpm when delivering 20 A to the load at the terminal voltage of 220V. If the same machine is run as a motor it takes a line current of 20A from 220V supply. The speed of ... . (B) more than 800 rpm. (C) less than 800 rpm. (D) both higher or lower than 800 rpm.
Last Answer : (C) less than 800 rpm.
Description : If the centrifugal switch or relay used for cutting out the starting winding of a split-phase induction motor fails to open once the motor is in operation, the _____________. A. motor will overspeed B ... C. motor will immediately stall under load D. motor torque will be above normal at rated speed
Last Answer : Answer: B
Description : If a three-phase induction motor is operated under a light load and it develops an open in one of its supply lines, the motor will _____________. A. continue to run, but will vibrate and have reduced ... speed up due to the reduced number of poles C. run cooler due to reduced current flow D. stop
Last Answer : Answer: A
Description : Centrifugal pumps as compared to reciprocating pumps (A) Run at a lower speed for the same discharge (B) Do not need priming (C) Deliver fluid with pulsating/fluctuating discharge (D) Can be run with discharge line valve closed for a short interval
Last Answer : (D) Can be run with discharge line valve closed for a short interval
Description : 52 A transformer has 1000 primary turns, connected to 250V ac supply. To get 400V secondary voltage the no of secondary turns should be A. 1600 B. 250 C. 400 D. 1250
Last Answer : A. 1600
Description : The inrush current of a transformer at no load is maximum if the supply voltage is switched on (1) at peak voltage value (2) at zero voltage value (3) at half voltage value (4) at 0.866 time voltage value
Last Answer : At 0.866 time voltage value
Last Answer : When a given transformer is run at its rated voltage but reduced frequency, its core flux density is increased.
Description : If a three-phase induction motor malfunctions and drops to a single-phase (one supply line open) ____________. A. the motor will continue to run if it is not heavily loaded B. more torque will be ... be able to be restarted D. the motor will immediately stop and can only be restarted at no load
Description : 51 A transformer has negative voltage regulation when its load power factor is A. Zero B. Unity C. Leading D. Lagging
Last Answer : C. leading
Description : A transformer has negative voltage regulation when its load power factor is (1) Zero (2) Unity (3) Leading (4) Lagging
Last Answer : 0
Description : 44] The highest voltage for transmitting electrical power in India is A. 33kV B. 66kV C. 132kV D. 400kV
Last Answer : D. 400kv
Description : 25 A step up transformer increases A. voltage B. current C. power D. frequency
Last Answer : A. Voltage
Description : 16.step-up transformer increases A. voltage B. current C. power D. frequency
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 : A salient pole synchronous motor is running at no load. Its field current is switched off. The motor will (A) come to stop. (B) continue to run at synchronous speed. (C) continue to run at ... more than the synchronous speed. (D) continue to run at a speed slightly less than the synchronous speed.
Last Answer : (B) continue to run at synchronous speed.
Description : If a unloaded shunt motor's field were weakened by rheostat resistance or by an open circuit, the motor would _________. A. overspeed due to reduced CEMF B. stop because of low flux C. continue to run at base speed D. slow down and overheat
Description : Reduced voltage applied to a motor during the starting period will _____________. A. result in decreased acceleration time only B. lower the starting current and increase accelerating time C. cause a greater starting torque D. increase the starting current and pump capacity
Description : What happen when Transformer is given DC supply ?
Last Answer : When DC supply is given to the transformer primary winding no back emf is induced in the transformer. Importance of Back emf is that it limits the current drawn by the machine. In the absence ... in burning down of primary winding. So when dc supply is given to transformer primary windings will burn
Description : What is the supply rated o/p if two single phase transformer connect to give three phase o/p from a three phase I/p?
Last Answer : A. Each transformer is only capable of supplying 86.6%of its o/p rating
Description : What will happen if DC supply is given on the primary of a transformer?
Last Answer : A. Mainly transformer has high inductance and low resistance. In case of DC supply there is no inductance, only resistance will act in the electrical circuit. So, high electrical current will flow through primary side of the transformer. Due to this the coil and insulation will burn out.
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 : An AC supply of 230 V is applied to a half-wave rectifier circuit through a transformer having primary to secondary turn’s ratio 12:1. The peak inverse voltage is A) 8.62 V B) 12 V C) 19.17 V D) 27.11 V
Last Answer : An AC supply of 230 V is applied to a half-wave rectifier circuit through a transformer having primary to secondary turn’s ratio 12:1. The peak inverse voltage is A) 8.62 V B) 12 V C) 19.17 V D) 27.11 V
Description : What will happen if the primary of a transformer is connected to D.C. supply? (A) Transformer will operate with low efficiency (B) Transformer will operate with high efficiency (C) No effect (D) Transformer may start to smoke and burn
Last Answer : What will happen if the primary of a transformer is connected to D.C. supply? (A) Transformer will operate with low efficiency (B) Transformer will operate with high efficiency (C) No effect (D) Transformer may start to smoke and burn
Last Answer : If the supply frequency to the transformer is increased, the iron loss will increase.
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 : Why does a transformer only work with an AC supply?
Last Answer : The transformer work depends on the induction as main principle ,for that AC is the right means
Description : why transformer don't work on DC supply?
Last Answer : A DC current does not produce a changing magnetic field which is capable of inducing current on the secondary windings of a transformer through mutual induction process.
Description : Which of the following conditions will occur if the solenoid coil burns out on a cargo winch with an electrical brake? A. The brake will be set by spring force. B. The motor will overspeed and burn ... the cargo boom will fall. D. Nothing will happen; the winch will continue to operate as usual.
Description : Which of the following problems will most likely occur if the starting winding of a split-phase induction motor failed to cutout once the motor was in continuous operation? A. The motor will overspeed. B. The ... reduced speed. C. A time delay will stop the motor. D. The winding will burn out.
Last Answer : Answer: D
Description : What is the recommended technique to counter the loss of airspeed and resultant lift from wind shear? a. Maintain, or increase, pitch attitude and accept the lower-than-normal airspeed ... shaker, and apply maximum power d. Accelerate the aircraft to prevent a stall by sacrificing altitude
Last Answer : c. Avoid overstressing aircraft, pitch to stick shaker, and apply maximum power
Description : A single phase transformer has resistance and reactance of 0.2 pu and 0.6 pu respectively. Its pu voltage regulation at 0.8 pf lagging would he
Last Answer : A single phase transformer has resistance and reactance of 0.2 pu and 0.6 pu respectively. Its pu voltage regulation at 0.8 pf lagging would he 0.52
Description : To reverse the direction of rotation of a three-phase AC induction motor, do one of the following: w) reverse any two of the three-phase connections x) change the frequency of the applied AC power y) operate the motor below the stall torque at very high slip z) none of the above
Last Answer : ANSWER: W -- REVERSE ANY TWO OF THE THREE-PHASE CONNECTIONS
Description : What effects are produced by change in voltage?
Last Answer : a) Iron loss.........varies approximately as V2. b) Cu loss.........it also varies as V2 but decreases with an increase in voltage if constant kVA output is assumed. c ... ..for constant kVA output, iron temperatures increase whereas Cu temperatures decrease with increase in voltages and vice-versa.
Description : What is voltage ratio of a transformer?
Last Answer : A. Voltage ratio is the ratio of the voltage between the line terminals of one winding to that between the line terminals of another winding at no load.
Description : If we give 2334 A, 540V on Primary side of 1.125 MVA step up transformer, then what will be the Secondary Current, If Secondary Voltage=11 KV?
Last Answer : A. As we know the Voltage & current relation for transformer-V1/V2 = I2/I1 We Know, VI= 540 V; V2=11KV or 11000 V; I1= 2334 Amps. By putting these value on Relation540/11000= I2/2334 So,I2 = 114.5 Amps
Description : In transformers, why the low voltage winding is placed near the core?
Last Answer : The winding & Core are both made of metals and so an insulation have to be placed in between them, the thickness of insulation depends on the voltage rating of the winding. In order to reduce the insulation requirement the low voltage winding place near the core.
Description : What will happen if transformer in parallel connection have different voltage ratio?
Last Answer : Two transformers in Parallel should have the same primary and secondary voltage ratings. Any error in the voltage ratio would cause heavy circulating currents to flow between the transformers. ... in overloading of one transformer. This circulating current will result in increased copper losses.
Description : Why the open circuit test on a transformer is conducted at rated voltage?
Last Answer : A:The open circuit on a transformer is conducted at a rated voltage because core loss depends upon the voltage. This open circuit test gives only core loss or iron loss of the transformer.
Description : What are the necessary tests to determine the efficiency, voltage regulation, and temperature rise of winding & insulation of transformer?
Last Answer : 1.Direct loading test 2.Open circuit test 3. Short circuit test 4. Sumpner's or back to back test
Description : What are the factors affecting voltage regulation?
Last Answer : Load current Equivalent resistance Equivalent reactance power factor
Description : What is the condition for maximum voltage regulation?
Last Answer : It occurs when load is inductive and power factor is lagging.
Description : What is the condition for zero voltage regulation?
Last Answer : Negative sign indicates zero voltage regulation. It occurs when load is capacitive and power factor is leading.
Description : What is voltage transformation ratio or turn ratio?
Last Answer : It is expressed as ratio of the primary and secondary voltages of transformer. or It is expressed as ratio of the primary and secondary turns of transformer. E1/ E2= T1/T2 = K
Description : 66 While conducting short-circuit test on a transformer the following side is short circuited A. High voltage side B. low voltage side C. primary side D. secondary side
Last Answer : B. Low voltage side
Description : 56 Which of the following does not change in a transformer? A. Current B. Voltage C. Frequency D. All of the above
Last Answer : C. Frequency
Description : 47 Cross over windings are used in A. Low voltage side of high kVA rating transformers B. Current transformers C. High voltage side of high kVA rating transformers D. High voltage side of low kVA rating transformers
Last Answer : D. High voltage side of low kVA rating transformers
Description : 30 In performing the short circuit test of a transformer A. high voltage is usually short circuited B. low voltage side is usually short circuited C. any side is short circuited with preference D. none of the above
Last Answer : B. Low voltage side is usually short circuited
Description : 29.In transformer terminology, the ratio 20:1 indicates that A. there are 20 turns on primary one turn on secondary B. secondary voltage is 1/20th of the primary C. primary current is 20 times greater than the secondary current D. for every 0 turns on primary, there is one turn on secondary
Last Answer : A. there are 20 turns on primary one turn on secondary
Description : 19 Transformer cores are built up from laminations rather than from solid metal so that A. Oil penetrates the core more easily B. Eddy current loss is reduced C. Less lamination is required for the windings D. Turn ratio is higher than voltage ratio
Last Answer : B. Eddy current loss is reduced