Description : Define balanced and unbalanced load in three phase circuit.

**Answer** : Balanced Load: When all the imedances of 3 phases are equal in magnitude and of same nature then load is said to be balanced. Unbalanced Load: When all the imedances of 3 phases are not equal in magnitude and of different nature then load is said to be unbalanced.

Description : State any four applications of three phase circuits.

**Answer** : The application of three phase circuits are 1. Three phase circuit is used for power transmission over long distances. 2. Three phase circuit can produce rotating magnetic field 3. Three phase ... three phase Motors and Transformers. 4. Three phase circuit is used for power converters circuits.

Description : List any two methods of reactive power measurement in 3 phase circuit.

**Answer** : Methods of reactive power measurement in 3 phase circuit: (i) Two single phase wattmeter method (ii) One single phase wattmeter method

Description : Explain with neat circuit diagrams the procedures to perform no load and blocked rotor tests on three phase induction motor.

Description : List different starting methods of three phase synchronous motor. Explain any one of them.

**Answer** : Different Starting Methods of Three Phase Synchronous Motor: As synchronous motor is not self starting, different methods of starting are as follows: 1) By using an Induction (Pony) motor 2) ... . The rotor gets pulled into synchronism and starts running at constant speed as a synchronous motor.

Description : Explain the need and steps to conduct the reduced voltage running up test on the three phase induction motor.

Description : Explain three phase half wave controller or three phase unidirectional controller.

**Answer** : Three phase half wave controller or unidirectional controller:

Description : Explain Three Phase Bidirectional Delta Connected Controller.

**Answer** : Three Phase Bidirectional Delta Connected Controller:

Description : Explain three phase bridge inverter.

**Answer** : Three phase bridge inverter: Three phase bridge inverter converts DC voltage input to three-phase variable frequency variable voltage output. DC voltage source can be a DC source or output of the rectifier. ... in proper sequence. The switch may be thyristor or IGBT etc.

Description : Explain three phase full wave controller.

**Answer** : Three phase full wave controller: Three phase full wave controller is also called as the three-phase bidirectional controller. Let the load is star connected so at each phase there are antiparallel connected SCRs. ... conduct at the same time and the third phase will be open.

Description : Why is a capacitor used in a single phase motor and not in three phase motor ?

**Answer** : In 1-phase induction motor capacitor work is generate the auxiliary winding current than excite the main winding to rotor starts rotate. After rotor start rotating about 75% of their speed than auxiliary ... emf to start the motor.so,in 3-phase induction motor is self start induction motor.

Description : When a V-V three phase transformer system is converted into a Δ-Δ system, increase in capacity of the system is (A) 86.6% (B) 50% (C) 57.7% (D) 73.2%

**Answer** : When a V-V three phase transformer system is converted into a Δ-Δ system, increase in capacity of the system is 73.2%

Description : In a three-phase supply floating neutral is undesirable because it way give rise to?

**Answer** : In a three-phase supply floating neutral is undesirable because it way give rise to unequal line voltages across the load.

Description : Why is a three phase denoted by R, Y, B ?

**Answer** : phase 1 ,R =Red colour cable terminal, phase 2 Y=Yellow colour terminal cable,Phase 3 B=Blue colour cable terminal, N =Neutral. For identification.

Description : State advantages of three phase over single phase.

**Answer** : Advantages of 3-phase system over 1-phase system: - 1. More output: For the same size, output of poly-phase machines is always higher than single phase machines. 2. Smaller size: For ... are self- starting: The three phase ac motors are self starting, while single phase induction motor are not.

Description : The slip of 400 V, three phase, 4 -pole induction motor when rotating at 1440 rpm is

**Answer** : The slip of 400 V, three phase, 4 -pole induction motor when rotating at 1440 rpm is 4 percent

Description : Three phase synchronous motor will have how many sliprings?

**Answer** : Three phase synchronous motor will have two sliprings.

Description : How is a three phase cage induction motor self starting?

**Answer** : Any type of induction motor is self starting. Because the reason for torqe production require two flux displaced by some angle theta.If theta is constant with time then torqe will be constant;if ... torqe also pulsating. In induction motor this angle theta is not pulsating.so it is self starting

Description : What is a three phase connection?

**Answer** : RYB, 440 volt/phase

Description : three phase to single phase cycloconverter

**Answer** : three phase to single phase cycloconverter

Description : how can we reverse the direction of rotation of three phase induction motor ?

**Answer** : The direction of rotation of three phase induction motor can be reversed by plugging i.e by changing any two out of three phases of the supply to the stator of the Induction motor terminal.

Description : List three important characteristics of an electric circuit.

Description : Consider a circuit with three parallel branches connected across a DC supply. What is the ratio of the branch currents I1 : I2 : I3 if the branch resistances are in the ratio of 2 : 3 : 4 respectively? A) 2 : 3 : 4 B) 6 : 4 : 3 C) 4 : 3 : 2 D) None of these

**Answer** : Consider a circuit with three parallel branches connected across a DC supply. What is the ratio of the branch currents I1 : I2 : I3 if the branch resistances are in the ratio of 2 : 3 : 4 respectively? A) 2 : 3 : 4 B) 6 : 4 : 3 C) 4 : 3 : 2 D) None of these

Description : Explain the procedure to perform Short Circuit test on single phase transformer with circuit diagram.

Description : The power consumed in a circuit element will be least when the phase difference between the current and voltage is?

**Answer** : The power consumed in a circuit element will be least when the phase difference between the current and voltage is 90°.

Description : The product of apparent power and cosine of the phase angle between circuit voltage and current is?

**Answer** : In parllpar reasonans RLC circuit the current is

Description : With a neat sketch explain working of 1 phase dynamometer type power factor meter.

**Answer** : Working of 1 phase dynamometer type power factor meter : The current coil is connected in series with load. Two pressure coils marked as A and B are connected across the supply terminals ... becomes stationary and the pointer shows steady deflection corresponding to the power factor of the load.

Description : In a 3-phase converter circuit during commutation when one SCR in one phase is turned on to turn-off an SCR in another phase, results in (A) voltage notching (B) harmonic distortion (C) voltage sag (D) voltage swell

**Answer** : In a 3-phase converter circuit during commutation when one SCR in one phase is turned on to turn-off an SCR in another phase, results in voltage notching

Description : The armature current on symmetrical 3 phase short circuit of a synchronous machine (salient pole) (A) has q -axis current only (B) has d -axis current only (C) has both d and q axis currents (D) cannot be divided between q and d axis currents

**Answer** : The armature current on symmetrical 3 phase short circuit of a synchronous machine (salient pole) has d -axis current only

**Answer** : Starting winding of a single phase motor of a refrigerator is disconnected from the circuit by means of a magnetic relay.

Description : Briefly explain how the power factor of an inductive circuit can be improved.

**Answer** : As we know that power factor should be corrected to ensure that the current supplied is cost friendly. Meaning the power factor should be around one but not greater than one(0.8-0.9) in a ... an inductive circuit due to the inductive reactance which oppose the change of current in the ac circuit.

**Answer** : In a single phase power factor meter the phase difference between the currents in the two pressure coils is exactly 90°.

Description : In an alternator at lagging power factor the generated voltage per phase as compared to that at unity power factor?

**Answer** : In an alternator, at lagging power factor the generated voltage per phase as compared to that at unity power factor must be more than terminal voltage.

Description : State any two disadvantages of one wattmeter method of measurement of 3 phase power.

**Answer** : State any two disadvantages of one wattmeter method of measurement of 3 phase power. Disadvantages of one wattmeter method:- 1. Only used for balanced load 2. It can not be used for ... connection then neutral point must be available 4. Delta connection must be opened to connect current coil.

Description : What is the power factor when a single phase watt meter operating on 200 V and 5 A for 5 hours makes 2016 revolutions and the meter constant in revolution is 420? A) 0.04 B) 1.04 C) 0.96 D) None of these

**Answer** : What is the power factor when a single phase watt meter operating on 200 V and 5 A for 5 hours makes 2016 revolutions and the meter constant in revolution is 420? A) 0.04 B) 1.04 C) 0.96 D) None of these

**Answer** : The power factor of a single phase load can be calculated if the instruments available are three ammeters or three voltmeters.

Description : In a pure resistive circuit, the average power Pavg is ______ the peak power Pmax. (1) Double (2) One-half of (3) One-fourth (4) Equal to

**Answer** : In a pure resistive circuit, the average power Pavg is One-half of the peak power Pmax.

Description : In an A.C. circuit power is dissipated in?

**Answer** : In an A.C. circuit power is dissipated in resistance only.

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?

**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 : The power factor at resonance in R-L- C parallel circuit is?

**Answer** : since a rlc circuit at resonance behaves like a pure resistive circuit, i.e there is no phase difference between current and voltage, hence the power factor is unity.

Description : Power factor of an inductive circuit is usually improved by connecting capacitor to it in?

**Answer** : Power factor of an inductive circuit is usually improved by connecting capacitor to it in parallel.

Description : How do you find power in a circuit?

**Answer** : Power can be find in a circuit by the means of meters .if an individual want to check for a power in a circuit he/she Calabria the meters on a high voltage range and put the meters Lee in parallel with the circuit he /she will know the amount of power within that circuit .

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