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Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of D.C. series motor.

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

Description : Why high starting torque is required?

Answer : For the same H.P. rating and full load speed, following motor has poor starting torque differentially compounded.

Description : In a double squirrel cage induction motor, good starting torque is produced as (A) Large current flows through the outer high resistance winding. (B) Large current flows through the inner high ... the outer high resistance winding. (D) Large current flows through the inner low resistance winding.

Answer : In a double squirrel cage induction motor, good starting torque is produced as Large current flows through the outer high resistance winding.

Answer : The ratio of starting torque to full-load torque is least in case of shunt motors.

Answer : Capacitor start motor has high torque in starting

Description : Why does induction motor have high starting current?

Answer : In induction motor , the flux produce is quadrature to the applied voltage. Since when we are going to start motor , there is no flux present inside . So in order to lets say compensate it ... times of current to further increase flux. So that is reason for high starting current in induction motor

Answer : The starting resistance of a D.C. motor is generally low.

Answer : A direct online starter is used for starting motors up to 5 H.P.

Answer : For starting a D.C. motor a starter is required because it limits the starting current to a safe value.

Answer : The starting winding of a single-phase motor is placed in stator.

Answer : If starting winding of a single-phase induction motor is left in the circuit, it will draw excessive current and overheat.

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

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 : Is induction motor is self starting?

Answer : Single phase induction motor is not self starting. Three phase induction motor is self starting.

Answer : D.C. Series motor is generally preferred for cranes and hoists.

Description : Torque developed by a three-phase, 400V, induction motor is 100 N -m. If the applied voltage is reduced to 200-V, the d'veloped torque will be

Answer : Torque developed by a three-phase, 400V, induction motor is 100 N -m. If the applied voltage is reduced to 200-V, the d'veloped torque will be 25 N -m

Description : Torque angle for the synchronous machine is the angle between (A) stator magnetic field and rotor magnetic field (B) stator magnetic field and net magnetic field in the air gap (C) rotor magnetic field and net magnetic field in the air gap (D) excitation voltage and impedance voltage drop

Answer : Torque angle for the synchronous machine is the angle between rotor magnetic field and net magnetic field in the air gap

Description : The torque developed by any 3-phase induction motor at 0.8 p.u. slip is (A) Full-load torque (B) unstable torque (C) starting torque (D) break down

Answer : The torque developed by any 3-phase induction motor at 0.8 p.u. slip is unstable torque

Answer : The armature torque of the D.C. shunt motor is proportional to armature current.

Answer : Speed torque characteristic of a repulsion induction motor is similar to that of a D.C. compound motor.

Answer : In repulsion motor, maximum torque is developed when brush axis is at 45° electrical to the field axis.

Description : What is the formula of torque?

Description : State the advantages of use of high voltage in transmission of Electric power. 

Answer : Advantages: 1. As Transmission voltage increases, current decreases. 2. As current decreases, cross section of conductor decreases. 3. As cross section of conductor decreases, its ... high voltage transmission line, successful interconnection of transmission line is possible than low voltage. 

Description : Wire-wound resistors are unsuitable for use at high frequencies because they?

Answer : Wire-wound resistors are unsuitable for use at high frequencies because they exhibit unwanted inductive and capacitive effects.

Answer : For measurement of inductance having high value, we should use Hay's bridge.

Answer : For measuring a very high resistance we should use Meggar.

Answer : For measuring current at high frequency we should use thermocouple instrument.

Description : Which rotor is use for high speed in turbo alternators?

Answer : Non-salient pole rotor is used for high speed in turbo alternators.

Answer : In a capacitor start motor, the phase displacement between starting and running winding can be nearly 90°.

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 starting system in diesel electric power plant.

Answer : Starting system in Diesel Electric Power Plant: It includes Storage battery, compressed air tanks, self-starter etc. The purpose of engine starting system is to rotate the engine initially while ... as Ammeters, Voltmeters, Wattmeters, Thermometers, Pressure gauges, Visible and audible alarm etc.

Description : State the functions of following elements: i) Diesel engine system ii) Air intake system iii) Engine exhaust system iv) Engine starting system.

Answer : i) Diesel engine system:-  Four strokes Two strokes ii) Air intake system:- Air intake system is provided to supply air to engine cylinder for fuel combustion.  iii) Engine exhaust system ... provided to rotate the engine initially until the firing starts and engine run under its own power. 

Description : In a 741 Op-Amp, there is 20 dB/decade fall-off starting at a relatively low frequency. This is due to the (A) applied load (B) internal compensation (C) impedance of the source (D) power dissipation in the chip

Answer : In a 741 Op-Amp, there is 20 dB/decade fall-off starting at a relatively low frequency. This is due to the internal compensation

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

Answer : A centrifugal switch is used to disconnect starting winding when motor has picked up about 50 to 70 per cent of rated speed.

Answer : The rotor developed by a single-phase motor at starting is zero.

Description : A synchronous motor can be made self starting by providing?

Answer : A synchronous motor can be made self-starting by providing damper bar.

Description : Why starter is required for starting an induction motor?

Description : Name the different torque and their function in measuring instrument.

Answer : List of torques in analog instruments:  1. Deflecting torque  2. Controlling / restraining torque.  3. Damping torque.  1. Deflecting torque:  - To create deflection of pointer ... .  - Bring the pointer to standstill quickly.  - To minimize oscillations about final position. 

Description : DC motor gross torque example

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 spring control method of producing controlling torque in measuring instrument. Write any two properties required for spring material.

Answer : A)Spring control method: As shown in the figure, the inner ends of the both springs are attahced to the spindle, while outer end of upper spring is attached to the lever and outer ... of spring material: 1.Non Magnetic material 2.Low specific resistance 3.Low temperature coefficient of resistance

Description : State the function of controlling torque in electrical measuring instrument.

Answer : Function of controlling torque  1. The function is to opposes the deflection force and increases with the increase in the deflection of the moving system, to limit its movement. 2. and brought ... set a position where the two opposing forces i.e. deflection and controlling forces are equal. 

Description : List the different methods to produce damping torque.

Answer : Methods of providing damping torque in indicating type instruments: 1) Air friction damping. 2) Fluid friction damping. 3) Eddy current damping.

Description : State the function of controlling torque. Write two types of it.

Answer : Function of Controlling Torque:  To restrict the motion of pointer / spindle and stop the pointer at the relevant position to get correct reading.  To bring back pointer to zero ... measurement is removed.  Types of Controlling Torque: 1. Spring control method 2.Gravity control method 

Description : Ideally, the damping torque should be  (1) Proportional to velocity of the moving system and operating current.  (2) Proportional to the velocity of the moving system but independent of operating ... operating current.  (4) Independent of the velocity of the moving system and operating current.

Answer : Ideally, the damping torque should be Proportional to the velocity of the moving system but independent of operating current. 

Description : The meter which does not have any component in it to provide control torque is (A) Electrodynamometer for current measurement (B) Electrodynamometer for voltage measurement (C) Electrodynamometer for power measurement. (D) Electrodynamometer for power factor measurement.

Answer : The meter which does not have any component in it to provide control torque is Electrodynamometer for power factor measurement.

Description : The torque produced in wattmeter is proportional to

Answer : A

Description : The shaft torque of a d.c. motor is less than its armature torque because of .......... losses.

Answer : The shaft torque of a d.c. motor is less than its armature torque because of rotational losses.

Description : The maximum torque of d.c. motors is limited by?

Answer : The maximum torque of d.c. motors is limited by commutation.

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