# In variable speed motor?

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

## Related questions

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 : In a self-controlled synchronous motor fed from a variable frequency inverter  (1) the rotor poles invariably have damper windings  (2) there are stability problems  (3) the speed of the rotor decides stator frequency  (4) the frequency of the stator decides the rotor speed

Answer : In a self-controlled synchronous motor fed from a variable frequency inverter the frequency of the stator decides the rotor speed

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

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 : 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.

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

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 : 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 : 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 : 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

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

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 : Synchronous motor always runs at which speed?

Answer : Synchronous motor always runs at synchronous speed.

Description : Which motor has the best speed regulation?

Description : How do you measure the speed of a motor?

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 : Advantages of Variable Frequency Drive (VFD)

Description : Explain following techniques related to energy conservation in transmission and distribution system. (i) By balancing phase currents (ii) Variable technical losses (I2R losses).

Answer : (i) Balancing Phase currents: Proper (healthy balanced) three phase loads always draw equal currents in all lines but single phase loads in the 3 phase 4 wire system or loads connected between two ... . 11) Minimize I2R losses. 12) Balance the load currents. 13) Regulate the system voltages.

Description : With sketch, justify use of Variable Geometry Turbocharger as compared to fixed geometry turbocharger.

Answer : Variable Turbine Geometry technology is the next generation in turbocharger technology where the turbo uses variable vanes to control exhaust flow against the turbine blades. The problem with the ... The angles of the vanes vary throughout the engine RPM range to optimize turbine behaviour.

Description : List variable flow meter.

Answer : 1. Variable area : Rotameter 2. Variable head : a) Venturi b) Orifice c) Pitot tube d) Nozzle

Description : Define resistor and draw symbol of variable resistor.

Answer : Resistor: A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Symbol of variable resistor:

Description : Compare variable head flow meter with variable area flow meter.

Answer : Parameter Variable head flowmeter Variable area flowmeter Working principle Restriction or obstacle is placed in the path of flow to create a differential Pressure. The pressure ... viscous fluid slurries and dirty fluids. In laboratories and testing and production lines.

Description : Compare variable reluctance and permanent magnet motors.

Answer : Variable reluctance Motor  Permanent magnet motors   The rotor is not magnetised The rotor is magnetised  High torque to inertia ratio  Low torque to inertia ratio  ... rotor has salient pole construction The rotor has mostly smooth cylindrical type of construction.

Description : With the knowledge of the state variable representation of a plant the transfer function of the plant

Answer : With the knowledge of the state variable representation of a plant the transfer function of the plant can be determined completely

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.

Answer : Usually wide and sensitive speed control is desired in case of colliery winders.

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.

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

Answer : Speed control by Ward Leonard method gives uniform speed variation in both directions.

Description : In a 3-phase slip-ring induction motor, the slip at some speed is 0.05. The speed is reduced by inserting an external resistance in the rotor circuit and the slip is 0.15. If the rotor winding resistance per phase is 0.2 Ω, the external resistance is (A) 0.2 Ω (B) 0.3 Ω (C) 0.4 Ω (D) 0.5 Ω

Answer : In a 3-phase slip-ring induction motor, the slip at some speed is 0.05. The speed is reduced by inserting an external resistance in the rotor circuit and the slip is 0.15. If the rotor winding resistance per phase is 0.2 Ω, the external resistance is 0.3 Ω

Answer : In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will remain unchanged.

Description : A 3-phase, 4-pole, 50Hz induction motor runs at a speed of 1440 rpm. The rotating field produced by the rotor rotates at a speed of ________ rpm with respect to stator field. (A) 1500 (B) 0 (C) 1440 (D) 60