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In Ward-Leonard control the lower limit of speed is imposed by residual magnetism of the generator.

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Answer : The main disadvantage of the Ward-Leonard control method is high initial cost, high maintenance cost, low efficiency at light loads.

Answer : Ward-Leonard control is basically a voltage control method.

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

Answer : For constant torque drive armature voltage control speed control method is preferred.

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 

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

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

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.

Answer : Series motor has the poorest speed control.

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 : 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 

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 : 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.

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

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'.

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.

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 : The speed of a locomotive is controlled by gear box.

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

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 : Write function of control rods in nuclear power plant.

Answer : Function of control rods in nuclear power plant: The function of control rod is to control the chain reaction in reactor core by adjusting its height.

Description : State the function of former and control spring in PMMC instrument.

Answer : Function of Former: To support the coil and provide eddy current damping.  Function of Control Spring: To provide control torque or force and in some instruments springs can be used as current leads.

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 : A differentiator is not usually used in control system, because it : - (A) reduces damping  (B) increases error  (C) reduces gain margin  (D) increases input noise

Answer : A differentiator is not usually used in control system, because it : - increases input noise

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 : Regulating-transformers are used in power systems for control of

Answer : Regulating-transformers are used in power systems for control of power flow

Description : Negative feedback in a closed-loop control system DOES NOT (A) reduce the overall gain (B) reduce bandwidth (C) improve disturbance rejection (D) reduce sensitivity to parameter variation

Answer : Negative feedback in a closed-loop control system DOES NOT reduce bandwidth

Description : The standard for long distance analog signal transmission in process control industry is (A) 4-20 mV (B) 0-20 mA (C) 4-20 mA (D) 0-5 V

Answer : The standard for long distance analog signal transmission in process control industry is 4-20 mA

Description : What are the electromagnetic waves used in remote control?

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Description : Draw the labeled block diagram of process control system and explain each block.

Answer : Explanation - Process control system consists of process or plant, sensor, error detector, automatic Controller, actuator or control element. 1) Process or plant- process means some manufacturing sequence ... process which changes the process variable. Output of this block is denoted by u .

Description : State the purpose of lighting control. List the different types of dimmer.

Answer : Purpose of Lighting Control:- 1. To turn ON or OFF the lamps 2. For dimming: The dimming control permits the adjustment of lighting over a range. 3. For changing the lighting levels ... operated dimmer 6) Triac operated Dimmer 7) PWM (Pulse width modulation) Controlled technique.

Description : Define the following terms : (i) Base Station (ii) Control Channel (iii) Mobile Station (iv) Page 

Answer : i) Base Station: - A fixed station in a mobile radio system used for radio communication with mobile stations. Base stations are located at the center or on the edge of a coverage region ... the page throughout the service area using base stations which broadcast the page on a radio carrier.

Description : What are the disadvantages of Open loop control system?

Answer : Open loop control system are less reliable. In open loop control system Optimization is not possible. Open loop control system are less accurate.

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). 

Description : State the function of following components of a nuclear power station: i) Moderator ii) Shielding iii) Control rod iv) Coolant 

Answer : i) Function of Moderator :- Moderator is to moderate or reduce the speed of fast neutron to help the fission process.  ii) Function of sheilding : Shielding is to protect environment, ... from reactor core and transfer it in heat exchanger for producing steam at high pressure and temperature. 

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.

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.

Description : Quality control is aimed at: a. Maintaining the desired quality b. Exceeding the desired quality c. Continuously improving the quality d. Following the quality

Answer : Quality control is aimed at: a. Maintaining the desired quality b. Exceeding the desired quality c. Continuously improving the quality d. Following the quality

Description : A control system having unit damping factor will give  (1) Oscillatory response (2) Undamped response (3) Critically damped response (4) No response

Answer : 1

Description : A unity negative feedback control system is found to have a gain margin of 20 dB. The Nyquist plot of the system (A) crosses the real axis at +0.1 (B) crosses the real axis at -0.1. (C) crosses the imaginary axis at -0.1 (D) crosses the imaginary axis at +0.1

Answer : A unity negative feedback control system is found to have a gain margin of 20 dB. The Nyquist plot of the system crosses the real axis at -0.1.

Description : Precise control of reactive current flow entering the transmission and distribution systems can be minimized by using (A) synchronous condenser (B) static VAR capacitor (C) capacitor bank (D) thyristor switched reactor in parallel with capacitor

Answer : Precise control of reactive current flow entering the transmission and distribution systems can be minimized by using (A) synchronous condenser (B) static VAR capacitor (C) capacitor bank (D) thyristor switched reactor in parallel with capacitor

Answer : The armature voltage control of D.C. motor provides constant torque drive.

Description : What is a phase control thyristor?

Description : Explain series switching control of AC load. Single phase resistance load - Integral half cycle control Phase control - Resistance load

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