Description : Why to calculate equivalent impedance referred to primary or secondary side?
Last Answer : Equivalent impedance is essential to be calculated because the electrical power transformer is an electric power system equipment, for estimating different parameters of electric power system ... referred to primary or equivalent circuit of transformer referred to secondary sides respectively.
Description : Give equivalent resistance, reactance and impedance referred to secondary circuit.
Last Answer : Req = R2 +R1' = R2+ R1'/a² Xeq = X2 +X1' = X2+ X1'/a² Zeq = Z2 + Z1' = Z2+ Z1'/a² where a=T1/T2
Description : Give equivalent resistance, reactance and impedance referred to primary circuit.
Last Answer : Req = R1 +R2' = R1+a² R2' Xeq = X1 +X2' = X1+a² X2' Zeq = Z1 +Z2' = Z1+a² Z2' where a=T1/T2
Description : 28.In a two winding transformer, the emf /turn in secondary winding is always......the induced emf power turn in primary A. equal to k times B. equal to 1/k times C. equal D. greater than
Last Answer : C. equal
Description : 57 In a transformer the resistance between its primary and secondary is A. Zero B. 1Ω C. 1000 Ω D. Infinite
Last Answer : D. Infinite
Description : In a transformer the resistance between its primary and secondary should be?
Last Answer : In a transformer the resistance between its primary and secondary should be infinity.
Description : A certain transformer has 200 turns in the primary winding, 50 turns in the secondary winding and 120 volts applied to the primary. What is the voltage across the secondary? (A) 30 Volts (B) 480 Volts (C) 120 Volts (D) 60 Volts
Last Answer : A certain transformer has 200 turns in the primary winding, 50 turns in the secondary winding and 120 volts applied to the primary. What is the voltage across the secondary? (A) 30 Volts (B) 480 Volts (C) 120 Volts (D) 60 Volts
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 : A 230 V/460 V single-phase transformer operating at 20 A and unity power factor has primary referred resistance of 0.2 Ω and reactance of 0.5 Ω. The approximate primary induced emf is (A) 216 V (B) 226 V (C) 234 V (D) 236 V
Last Answer : A 230 V/460 V single-phase transformer operating at 20 A and unity power factor has primary referred resistance of 0.2 Ω and reactance of 0.5 Ω. The approximate primary induced emf is 226 V
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 : What current flows in the transformer primary when its secondary is open?
Last Answer : A. When the secondary is open, there is no current in the secondary of the transformer. The primary takes a small current I0) from the source called no-load current which has a magnetizing ... ) producing the magnetic flux and a working component (I0 cosθ0) supplying real power for iron losses.
Description : In a Tap changing transformer on which side is the tap connected, primary side or secondary side?
Last Answer : A. Tapings are always connected to high voltage winding side, because of low current. If we connect tapings to low voltage side, sparks will produce while tap changing operation due to high current.
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 : 59.An ideal transformer has infinite values of primary and secondary inductances. The statement is A. True B. False
Last Answer : B. False
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 : 38] In a transformer the energy is conveyed from primary to secondary? A. Through cooling coil B. Through air C. By the flux D. None of the above
Last Answer : C. By the flux
Description : 6 In a two winding transformer, the primary and secondary induced emf E1 & E2 are always A. equal in magnitude B. anti phase with each other C. in phase with each other D. determined by load on transformer secondary
Last Answer : C. In phase with each other
Description : The frequency of the secondary voltage of a transformer will be..... A. less than frequency of the primary voltage B. equal to the primary voltage C. greater than the frequency of the primary voltage D. much greater than the frequency of the primary voltage
Last Answer : B. Equal to the primary voltage
Description : 12] Which is not the basic element of the transformer? A. core B. primary winding C. secondary winding D. mutual flux
Last Answer : D. Mutual flux
Description : During short circuit test iron losses are negligible because A. The current on secondary side is negligible B. The voltage on secondary side does not vary C. The voltage applied on primary side is low D. Full-load current is not supplied to the transformer
Last Answer : C) the voltage applied on primary side is low
Last Answer : An ideal transformer has infinite values of primary and secondary inductances. The statement is false.
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 : [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 : Does the transformer draw any current when its secondary is open?
Last Answer : Yes, no-load primary current.
Description : Does the transformer draw any current when secondary is open ? Why ?
Last Answer : Yes,it (primary) will draw the current from the main supply in order to magnetize the core and to supply iron and copper losses on no load . There will not be any current in the secondary since secondary is open
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 : Increasing the number of turns of wire on the secondary of a transformer will (A) Decrease the secondary current (B) Increase the primary current (C) Have no effect on the secondary current (D) Increase the secondary current
Last Answer : Increasing the number of turns of wire on the secondary of a transformer will Decrease the secondary current
Description : When secondary of a current transformer is open-circuited its iron core will be?
Last Answer : When secondary of a current transformer is open-circuited its iron core will be hot because of heavy iron losses taking place in it due to high flux density.
Description : The secondary of a current transformer is always short-circuited under operating conditions because it?
Last Answer : The secondary of a current transformer is always short-circuited under operating conditions because it avoids core saturation and high voltage induction.
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 : 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 : 21.The ordinary two winding transformer's primary and secondary windings always have A. different no of turns B. same size of copper wire C. a common magnetic circuit D. separate magnetic circuits
Last Answer : C. A common magnetic circuit
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 : 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 : Primary winding of a transformer could either be a low voltage or high voltage winding.
Description : 68 The path of a magnetic flux in a transformer should have A. High resistance B. High reluctance C. Low resistance D. Low reluctance
Last Answer : D. Low reluctance
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 : 13) In an ideal transformer A. windings have no resistance B. core has no losses C. core has infinite permeability D. all of the above
Last Answer : D. All of the above
Description : 64)During the short-circuit test on a small transformer the frequency is increased from 50-200Hz. The copper losses will increase by a factor of A. 16 B. 4 C. 1 D. 1/4
Last Answer : A) 16
Description : What would happen if a power transformer designed for operation on 50 Hz (frequency) were connected to a 500 Hz (frequency) source of the same voltage: (A) Eddy Current and Hysteresis losses will be ... Current will be too much high (C) Transformer may start to smoke and burn (D) No effect
Last Answer : What would happen if a power transformer designed for operation on 50 Hz (frequency) were connected to a 500 Hz (frequency) source of the same voltage: (A) Eddy Current and Hysteresis losses will be ... will be too much high (C) Transformer may start to smoke and burn (D) No effect
Description : A transformer at 25 Hz develops 20 W hysteresis loss and 50 W eddy current loss. If the applied voltage and frequency are doubled, the new core losses are (A) 140 W (B) 180 W (C) 240 W (D) 480 W
Last Answer : A transformer at 25 Hz develops 20 W hysteresis loss and 50 W eddy current loss. If the applied voltage and frequency are doubled, the new core losses are 240 W
Description : A transformer has a turns ratio of two to one. If a 100 ohm resistor is connected on the high side, its resistance as measured on the low side would be: w) 25 ohms x) 50 ohms y) 100 ohms z) 400 ohms
Last Answer : ANSWER: W -- 25 OHMS
Description : N resistors of each of resistance R when connected in series offer an equivalent resistance of 50 ohm and when reconnected in parallel the effective resistance is 2 ohm the value of R is
Last Answer : 25 ohms
Description : 62)The no-load current drawn by transformer is usually........percent of the full-load current? A. 0.2 to 0.5 % B. 2 to 5% C. 12 to 15 % D. 20 to 30 %
Last Answer : B) 2 to 5%
Description : Material used for construction of transformer core is usually A. 0.4mm to 0.5 mm B. 4mm to 5 mm C. 14mm to 15 mm D. 25mm to 40 mm
Last Answer : d) 25mm to 40mm
Description : The temperature coefficient of copper is `0.004^(@)C^(-1)`. Find the resistance of a 5 m long copper wire of diameter 0.2 mm at `100^(@)C`, if the res
Last Answer : The temperature coefficient of copper is `0.004^(@)C^(-1)`. Find the resistance of a 5 m long copper wire of ... `0^(@)C` is `1.7xx10^(-8) Omega` m.
Description : A 1:5 step-up transformer has 120V across the primary and 600 ohms resistance across the secondary. Assuming 100% efficiency, the primary current equals (A) 0.2 Amp. (B) 5 Amps. (C) 10 Amps. (D) 20 Amps.
Last Answer : I1= V1 /R1 = 120/600 = 0.2 (η = 100%, losses are zero ∴V1 = VR = I1R1)
Description : If a wire conductor of 0.2 ohm resistance is doubled in length, its resistance becomes?
Last Answer : If a wire conductor of 0.2 ohm resistance is doubled in length, its resistance becomes 0.4 ohm.
Description : A cannon of weight 10 tonnes fires a shell of 50 kg with a muzzle velocity of 900 m/sec at an angle of 30?. The time taken for the shell to emerge from the barrel is 0.004 sec. The velocity of the cannon would be a.3.9 m/sec b.7.8 m/sec c.8.95 m/sec d.1.95 m/sec e.5.85 m/sec
Last Answer : a. 3.9 m/sec