Answer :
In Ward-Leonard control the lower limit of speed is imposed by residual magnetism of the generator.
asked
Mar 20, 2018
by
anonymous
Answer :
The main disadvantage of the Ward-Leonard control method is high initial cost, high maintenance cost, low efficiency at light loads.
asked
Mar 20, 2018
by
anonymous
Answer :
For constant torque drive armature voltage control speed control method is preferred.
asked
Mar 20, 2018
by
anonymous
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
asked
May 1, 2018
by
anonymous
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.
asked
Mar 20, 2018
by
anonymous
Answer :
The speed control of universal motor used for sewing machines is by varying the resistance.
asked
Mar 20, 2018
by
anonymous
Answer :
Series motor has the poorest speed control.
asked
Mar 20, 2018
by
anonymous
Answer :
Usually wide and sensitive speed control is desired in case of colliery winders.
asked
Mar 20, 2018
by
anonymous
Description : What are the speed control methods of dc motor?
Answer :
Field control of DC motor Armature control of DC motor
asked
Dec 16, 2017
by
anonymous
Description : speed control methods of three phase induction motor?
Answer :
Speed control of three phase induction motor
Description : Illustrate with neat wiring diagram a single lamp control by two point method.
Answer :
Single lamp control by two point method: This system is commonly used for stair case wiring. It consists of two way switches (the switch operates always in one of the two possible positions) the ... the person will change the position of switch S2, so that the lamp will be switched OFF'.
asked
May 3, 2020
by
anonymous
Description : Draw and explain bulk correction method for power factor & control.
Answer :
Bulk correction method for power factor & control: i) Here individual starter controls the capacitors located at distribution panel. ii) Centralized compensation is employed in large industrial plants where many ... capacitor units in steps to maintain P.F. more than preset limit (0.95).
asked
Sep 29, 2018
by
anonymous
Description : Write one advantage and one disadvantage each for spring control method and gravity control method.
Answer :
Advantages of Spring Control Method: 1) The spring-controlled meters may be used in any position. 2) In some instruments, springs can be used as current leads. 3) As springs are light in weight ... only. 2) Scale is non-uniform. 3) Control weights add to the weight of instrument.
asked
Sep 6, 2018
by
anonymous
Description : Explain spring control method with neat diagram.
Answer :
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 end of ... the springs are twisted in opposite direction to the motion of pointer and produce controlling torque.
asked
Sep 5, 2018
by
anonymous
Answer :
Ward-Leonard control is basically a voltage control method.
asked
Mar 20, 2018
by
anonymous
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.
asked
Oct 13, 2019
by
anonymous
Description : Explain the lighting scheme to be designed for each of the following: i) Special ward in hospitals ii) Dentist’s Cabin
Answer :
i) Special ward in hospital: For the patients in the wards, lighting should create a cozy and pleasant atmosphere. Lighting in the wards should be planned in such a way that it meets the specific ... we use such as cements and bonding agents that we use to restore your teeth back to health.
asked
May 3, 2020
by
anonymous
Description : The chief advantage of Ward-Leonard system D.C. motor speed control is that is 1. Can be used even for small motors 2. has high overall efficiency at all speeds 3. Gives smooth, sensitive and wide speed control 4. Uses a flywheel to reduce fluctuations in power demand
Answer :
The chief advantage of Ward-Leonard system D.C. motor speed control is that is Gives smooth, sensitive and wide speed control
asked
May 13, 2018
by
anonymous
Description : The fall in speed of a dc generator due to increase in load can be corrected by (1) cooling the armature.. (2) increasing the excitation. (3) reducing the load voltage. (4) increasing the input to the prime mover
Answer :
It can be corrected by increasing the input to the prime mover.
asked
May 1, 2018
by
anonymous
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
asked
Apr 28, 2018
by
anonymous
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
asked
Mar 20, 2018
by
anonymous
Answer :
The speed of a D.C. shunt motor can be increased by increasing the resistance in field circuit.
asked
Mar 20, 2018
by
anonymous
Answer :
The speed of a universal motor is usually reduced by using gearing.
asked
Mar 20, 2018
by
anonymous
Answer :
Plugging method of braking is generally used in elevators.
asked
Mar 20, 2018
by
anonymous
Answer :
The armature voltage control of D.C. motor provides constant torque drive.
asked
Mar 20, 2018
by
anonymous
Description : Armature control of DC motor
Answer :
Armature control of DC motor
Description : Field control of DC motor
Answer :
Field control of DC motor
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
asked
Sep 6, 2018
by
anonymous
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
asked
May 8, 2018
by
anonymous
Answer :
In variable speed motor a weaker commutating field is needed at low speed than at high speed.
asked
Mar 20, 2018
by
anonymous
Answer :
As the load is increased the speed of D.C. shunt motor will reduce slightly.
asked
Mar 20, 2018
by
anonymous
Answer :
For the same H.P. rating and full load speed, following motor has poor starting torque differentially compounded.
asked
Mar 20, 2018
by
anonymous
Answer :
The speed of a D.C. series motor is inversely proportional to the armature current.
asked
Mar 20, 2018
by
anonymous
Answer :
In case of D.C. shunt motors the speed is dependent on back e.m.f. only because flux is practically constant in D:C. shunt motors.
asked
Mar 20, 2018
by
anonymous
Answer :
In a D.C. shunt motor, speed is independent of armature current.
asked
Mar 20, 2018
by
anonymous
Answer :
When two D.C. series motors are connected in parallel, the resultant speed is normal speed.
asked
Mar 20, 2018
by
anonymous
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.
asked
Mar 20, 2018
by
anonymous
Answer :
Centrifugal switch disconnects the auxiliary winding of the motor at about 70 to 80 percent of synchronous speed.
asked
Mar 20, 2018
by
anonymous
Answer :
The speed/load characteristics of a universal motor is same as that of D.C. series motor.
asked
Mar 20, 2018
by
anonymous
Answer :
Speed torque characteristic of a repulsion induction motor is similar to that of a D.C. compound motor.
asked
Mar 20, 2018
by
anonymous
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.
asked
Mar 20, 2018
by
anonymous
Description : Why the speed of synchronous motor is constant?
asked
Mar 15, 2018
by
anonymous
Description : Explain energy conservation method in lighting system by using installation of separate transformer / servo stabilizer.
Answer :
Energy conservation techniques by installation of separate transformer / servo stabilizer: The luminous efficiency of lamps depends upon the voltage applied across the terminals. It gives its best ... the voltage constant in that installation for giving best luminous efficiency of lamps.
asked
Sep 22, 2018
by
anonymous
Description : With neat diagram explain calibration of energy meter by direct loading method.
Answer :
Calibration of Energy Meter by Direct Loading Method: There are three methods for testing/calibration: 1. Long period dial test 2. Using rotary sub- standard meter 3. Using precision grade instruments All ... of substandard meter in kWh Then % error = [(D - DS)/DS] x 100
asked
Sep 6, 2018
by
anonymous
Description : The power consumed by a balanced 3-ph load is measured by two-wattmeter method. The meter readings are 8 kW and 4 kW. The power factor of the load is (A) zero (B) 0.5 (C) between zero and 0.5 (D) between 0.5 and unity
Answer :
The power consumed by a balanced 3-ph load is measured by two-wattmeter method. The meter readings are 8 kW and 4 kW. The power factor of the load is between 0.5 and unity
asked
Apr 28, 2018
by
anonymous
Answer :
Annual depreciation as per straight line method, is calculated by the capital cost minus the salvage value, is divided by the number of years of life.
asked
Mar 20, 2018
by
anonymous
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.
asked
Mar 26, 2018
by
anonymous
Answer :
The speed of a locomotive is controlled by gear box.
asked
Mar 22, 2018
by
anonymous
Answer :
The speed of a universal motor is generally reduced by using gear trains.
asked
Mar 20, 2018
by
anonymous
Answer :
The operating speed of a synchronous motor can be changed to new fixed value by changing frequency.
asked
Mar 20, 2018
by
anonymous