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When a D.C. series motor is connected to A.C. supply, the power factor will be low because of high inductance of field and armature circuits.

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Description : State the modification to be done in dc series motor to work satisfactorily as ac series motor. State applications of ac series motor.

Answer : Modifications are necessary in a dc series motor so that it operates satisfactorily on ac supply. The modifications are as follows:  1) AC series motor is built with a few field turns as ... and grinders 5) High speed vacuum cleaners 6) Sewing machines 7) Food processors 8) Drilling machine 

Answer : If a D.C. series motor is operated on A.C. supply, it will spark excessively, have poor efficiency, have poor power factor.

Answer : The power factor of a single-phase induction motor is usually lagging.

Answer : In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to 25% of the previous value.

Description : At which time power factor of the induction motor is low?

Answer : The power factor of the inducction motor is low at the time of starting as compare to while the induction motor is running.

Description : If the field of synchronous motor is under excited, power factor will be?

Answer : If the field of synchronous motor is under excited, power factor will be lagging.

Description : If the load of the normally excited synchronous motor is increased the power factor will?

Answer : If the load of the normally excited synchronous motor is increased the power factor will become lagging.

Answer : The direction of rotation of a D.C. series motor can be changed by interchanging field terminals.

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 :

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 : Why dc series motor should not be started at no load?

Answer : A.C. series motor as compared to D.C. series motor has smaller brush width, less number of field turns, more number of armature turns, less air gap.

Description : A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because?

Answer : A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because stator supply is not required to produce magnetic field.

Answer : The speed of a D.C. series motor is inversely proportional to the armature current.

Answer : A D.C. series motor is that which has its field winding consisting of thick wire and less turns.

Answer : An induction motor has relatively high power factor at near full load.

Description : The synchronous motor which works on leading power factor and does not drive any mechanical load is called?

Answer : The synchronous motor which works on leading power factor and does not drive any mechanical load is called synchronous condenser.

Description : How can we improve power factor using synchronous motor?

Answer : Yes, we can make the power factor of synchronous motor leading by adjusting its excitation.

Answer : In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be more than full-load current.

Description : Brake test on DC series motor

Answer : .embed-container { position: relative; padding-bottom: 56.25%; height: 0; overflow: hidden; max-width: 100%; } .embed-container iframe, .embed-container object, .embed-container embed { position: absolute; top: 0; left: 0; width: 100%; height: 100%; }

Description : Describe the reason of using dc series motor for electric trains.

Answer : Electric trains require an inverse torque speed characteristics for proper operation. That is a higher torque is required at start (when speed is nil or low) and as the train picks up ... torque - speed characteristics of DC series motors match, these motors are suitable for electric trains

Description : What are the advantages of DC series motor?

Description : Why a dc series motor has a high starting torque?

Description : The power factor of a D.C. circuit is always?

Answer : The power factor of a D.C. circuit is always unity.

Description : Two 100W, 200V lamps are connected in series across a 200V supply. The total power consumed by each lamp will be in Watts

Answer : 4800

Answer : The primary reason for low power factor is supply system is due to installation of induction motors.

Answer : For high value of diversity factor, a power station of given installed capacity will be in a position to supply more number of consumers.

Answer : In a low power factor wattmeter the compensating coil is connected in series with pressure coil.

Answer : In a low power factor wattmeter the pressure coil is connected to the load side of the current coil.

Answer : In A.C. series motor compensating winding is employed to reduce sparking at the brushes.

Description : We connected a 35V dc supply to a resistance of 600 Ohm in series with an unknown resistance R.A. voltmeter having a resistance of 1.2 kOhm is connected across 600 Ohm resistance and read 5v. The value of resistance R will be

Answer : We connected a 35V dc supply to a resistance of 600 Ohm in series with an unknown resistance R.A. voltmeter having a resistance of 1.2 kOhm is connected across 600 Ohm resistance and read 5v. The value of resistance R will be 2.4 kOhm

Answer : When two D.C. series motors are connected in parallel, the resultant speed is normal speed.

Answer : If a D.C. motor is connected across the A.C. supply it will burn due to heat produced in the field winding by eddy currents.

Answer : In a A.C. series motor armature coils are usually connected to commutator through resistance.

Answer : The value of starting capacitor of a fractional horse power motor will be 300 uF .

Description : Why does the speed of a DC shunt motor decrease as the load increases?

Answer : Because if the load is increasing then the torque must also be increase. If not then the speed of motor will decrease.

Description : Is the power line voltage available in our homes a dc or an ac voltage?

Answer : The power line voltage available in our homes is AC. Mobile dwellings are the most commonly DC-supplied homes and even then they tend to include AC supply for heavier loads.

Description : State the effects of low power factor on efficiency and voltage regulation of short transmission lines. 

Answer : i) Effect of Low power factor on efficiency:- When power factor of load reduces current drawn by transmission line increases so copper losses in transmission line increases, hence transmission ... increases, so voltage drop in transmission line increases so regulation increases. (Become Poor) 

Answer : The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is 0.5.

Description : A DC voltage source is connected across a series RLC circuit. Under steady-state conditions, the applied DC voltage drops entirely across the

Answer : A DC voltage source is connected across a series RLC circuit. Under steady-state conditions, the applied DC voltage drops entirely across the C only

Answer : In case the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be less than 50%.

Answer : If  equalising bar is connected to the 2 DC generators  the current will be equal in 2 generators irrespective of parallel connection so that we connect equaliser bar

Description : Write two applications of D.C. series motor. 

Answer : The applications of D.C. series motor: 1. Cranes 2. Hoists 3. Trolley and cars 4. Conveyors 5. For traction work i.e. electric locomotives 6. Elevator 7. Air compressor

Answer : Power plant having maximum demand more than the installed rated capacity will have utilisation factor more than unity.

Description : If we change the excitation of synchronous machine will it affect on power factor?

Answer : Yes, If we change the excitation of synchronous machine it will affect on power factor. If the synchronous motor is overexcited then it will have leading power factor and if the motor is underexcited then it will have lagging power factor.

Answer : At the instant of starting when a D.C. motor is put on supply, it behaves like a low resistance circuit.

Description : A transformer has negative voltage regulation when its load power factor is   (1) Zero (2) Unity (3) Leading (4) Lagging

Answer : Leading

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

Description : Minimum voltage regulation occurs when the power factor of the load is?

Answer : Minimum voltage regulation occurs when the power factor of the load is leading.

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