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How do you measure the speed of a motor?

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Description : Which motor has the best speed regulation?

Description : The synchronous speed of an 8 pole induction motor supplied power from a 50 Hz source will be ?

Answer : Ns         equals        f/pair pole 50/4      - 12.5

Description : Speed control of the motor using TRIAC

Answer : Speed control of the motor using TRIAC:  This basic phase triggering circuit uses the triac in series with the motor across an AC sinusoidal supply. The variable resistor, VR1 is used ... meaning that it may not trigger at the exact same point for each positive and negative half cycle.

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 : A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The net Voltage across armature resistance at the time of plugging will be

Answer : A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The net Voltage across armature resistance at the time of plugging will be 474 V

Description : The speed of a three-phase induction motor is controlled by variable voltage variable frequency control (i.e. keeping V/f constant). As the frequency is reduced, the slip at maximum torque  (1) Decreases (2) Increases (3) Remains constant (4) None of the above

Answer : The speed of a three-phase induction motor is controlled by variable voltage variable frequency control (i.e. keeping V/f constant). As the frequency is reduced, the slip at maximum torque Increases 

Description : The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ (A) directly proportional to α and Φ (B) ... proportional to α and inversely proportional to Φ (D) directly proportional to Φ and inversely proportional to α

Answer : The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ directly proportional to α and inversely proportional to Φ

Description : The speed of a 2-pole, 3-phase stepper motor operated by 1200 pulses/min (A) 100 rpm (B) 200 rpm (C) 400 rpm (D) 800 rpm

Answer : The speed of a 2-pole, 3-phase stepper motor operated by 1200 pulses/min 200 rpm

Answer : In variable speed motor a weaker commutating field is needed at low speed than at high speed.

Answer : If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will increase.

Answer : Series motor has the poorest speed control.

Description : The speed of a D.C. motor can be controlled by varying  1. Its flux per pole 2. Resistance of armature circuit 3. Applied voltage 4. All of the above

Answer : The speed of a D.C. motor can be controlled by varying  1. Its flux per pole 2. Resistance of armature circuit 3. Applied voltage 4. All of the above

Answer : The speed of a D.C. shunt motor can be increased by increasing the resistance in field circuit.

Answer : As the load is increased the speed of D.C. shunt motor will reduce slightly.

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

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

Answer : In a D.C. shunt motor, speed is independent of armature current.

Answer : The speed of a universal motor is usually reduced by using gearing.

Answer : Speed control of a universal motor is achieved by varying field flux with tapped field windings, connecting rheostat in series, applying variable voltage by means of silicon controlled rectifier, applying variable voltage by means of variable auto-transformer.

Answer : In case of a reluctance motor, when the load is increased so that it cannot maintain synchronous speed the motor will run as induction motor.

Answer : Centrifugal switch disconnects the auxiliary winding of the motor at about 70 to 80 percent of synchronous speed.

Answer : The speed/load characteristics of a universal motor is same as that of D.C. series motor.

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

Answer : If the centrifugal switch does not open at 70 to 80 percent of synchronous speed of motor, it would result in damage to the starting winding.

Answer : The speed control of universal motor used for sewing machines is by varying the resistance.

Answer : The speed of a universal motor is generally reduced by using gear trains.

Answer : The operating speed of a synchronous motor can be changed to new fixed value by changing frequency.

Description : If we change the excitation of synchronous machine will it affect on motor speed?

Answer : No, If we change the excitation of synchronous machine it will not affect on motor speed.

Description : An electric motor in which both stator field and rotor rotates with same speed is called?

Answer : An electric motor in which both stator field and rotor rotates with same speed is called synchronous motor.

Description : Synchronous motor always runs at which speed?

Answer : Synchronous motor always runs at synchronous speed.

Description : Why the speed of synchronous motor is constant?

Description : What are the speed control methods of dc motor?

Answer : Field control of DC motor Armature control of DC motor

Description : speed control methods of three phase induction motor?

Answer : Speed control of three phase induction motor

Description : How do you measure power factor?

Answer : P= 1.83*V*I*[email protected] where P is power           V is voltage            I is current           COS @ is P.F [email protected]= P/(1.83*V*I)  in other way cos @ = true power/apparent power

Description : Explain the term reactive power. Why it is sometimes essential to measure reactive power?

Answer : Reactive power: The reactive power (Q) is defined as the product of voltage(V), current (I) and sine of angle between voltage(V) and current( I) Therefore Reactive power Q = V I ... power so that corrective measures can be taken accordingly to maintain systems power factor near to the unity.

Description : List any four measure knobs on front panel on CRO.

Answer : Knobs on front panel of CRO: 1. Power ON- OFF 2. Intensity control 3. Focus control 4. Astigmatism control 5. Volt/Div control 6. Vertical position control 7. Invert 8. Horizontal position control 9. Synchronization. 10. Channel selection.

Description : ‘PMMC instrument is not suitable to measure AC quantity’. State the reason.

Answer : The direction of force exerted on moving coil depends on the direction of current flowing through moving coil. If the direction of magnetic field is kept constant, it produces unidirectional torque if the current is ... on the coil in one cycle to zero. Hence the meter cannot read A.C. quantities.

Description : Name the method used to measure following resistances:- (i) Low resistance (ii) Medium resistance (iii) Insulation resistance (iv) Earth resistance.

Answer : Following are the methods used to measure resistances:-  (i) Low resistance: 1.Voltmeter-Ammeter Method 2. Kelvin's Double bridge Method  (ii) Medium resistance: 1.Voltmeter-Ammeter Method 2. ... of Charge Method  (iv) Earth resistance : 1. Fall of Potential Method 2. Earth tester

Description : What are ways we can measure the flow of electrons?

Description : Under constant load conditions, the speed of a d.c. motor is affected by?

Answer : Under constant load conditions, the speed of a d.c. motor is affected by field flux.

Description : Draw venture meter and write steps to measure flow rate.

Answer : Venturi meter consists of three sections that is converging section, throat section and diverging section. The flow is introduced to the meter through the inlet with diameter D' . The inclined angle ... to 15o . Flow rate is proportional to the square root of the differential pressure.

Description : A _________ is used to measure the stator % winding temperature of the generator.  (A) Thermocouple (B) Pyrometer (C) Resistance thermometer (D) Thermometer

Answer : A Resistance thermometer is used to measure the stator % winding temperature of the generator. 

Description : A Pyrheliometer is an instrument to measure :  (A) temperature of solar photovoltaic cell  (B) intensity of direct solar radiation at normal incidence  (C) intensity of indirect solar radiation  (D) efficiency of a solar photovoltaic cell

Answer : A Pyrheliometer is an instrument to measure : intensity of direct solar radiation at normal incidence 

Description : Piezoelectric Transducer is used to measure  (1) displacement (2) resistance (3) current (4) temperature

Answer : Piezoelectric Transducer is used to measure displacement 

Description : An unshielded moving iron voltmeter is used to measure the voltage in an AC circuit. The stray DC magnetic field having a component along the axis will be  (1) unaffected (2) decreased (3) increased (4) either decreased or increased depending on the direction of the DC field

Answer : An unshielded moving iron voltmeter is used to measure the voltage in an AC circuit. The stray DC magnetic field having a component along the axis will be either decreased or increased depending on the direction of the DC field

Description : Which of the following can be used to measure the capacitance of a capacitor? A) Rheostat B) Schering bridge C) Wheatstone bridge D) None of these

Answer : Which of the following can be used to measure the capacitance of a capacitor? A) Rheostat B) Schering bridge C) Wheatstone bridge D) None of these

Answer : To measure a resistance with the help of a potentiometer it is not necessary to standardise the potentiometer.

Answer : It is required to measure the true open circuit e.m.f. of a battery. The best device is D.C. potentiometer.

Answer : Integrating instruments are those which measure the total quantity of electricity delivered in a particular time.

Description : An open-circuit test on a transformer is conducted primarily to measure?

Answer : The open-circuit test in a transformer is used to measure

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