To prevent over fluxing of transformers or generator.
Emf = 4.44 f φ Z A
If f frequency is reduced due to less speed,
φ = V / f Z A
And flux will be more to saturate the core of transformers or generator.
Description : Can we trip GFB from control room during unit operation?
Last Answer : No only if generator breaker is off.
Description : The closed circulatory system is more efficient. Since blood circulates only inside blood vessels it can do it with more pressure reaching farther distances between the organs where hematosis ... exchange independently from the circulation) are generally slower and have a low metabolic rate.
Last Answer : What is the difference between octopuses and mussels regarding their circulatory systems?
Description : A single-phase induction motor will only start if you spin the rotor rapidly with the line switch closed. After starting, its speed fluctuates between very slow and half-speed. The problem ... in the ________. A. starting winding B. centrifugal mechanism C. centrifugal switch D. running winding
Last Answer : Answer: D
Description : Two cyclists began a training run, one starting from Moscow and the other starting from Simferopol.When the riders were 180 miles apart, a fly took an interest. Starting on one cyclists shoulder, the fly flew ... was 30 mph. Each cyclist speed was 15 mph.How many miles did the fly travel? -Riddles
Last Answer : The cyclists took 6 hours to meet. The fly traveled 6*30=180 miles.
Description : A turbogenerator has a rated output of 1200 KW at 60 Hertz, with a no load frequency of 61.5 Hertz. What is its speed droop? A. 1.03% B. 1.50% C. 2.44% D. 2.50%
Description : A single-phase induction motor starts, comes up to about 75% rated speed, slows down to a lower speed, and accelerates again. The problem is most likely in the ____________. A. starting winding B. running winding C. starting capacitor D. running centrifugal switch
Last Answer : Answer: B
Description : A split-phase induction squirrel-cage motor will not come up to speed, even though the rated voltage, rated frequency, and rated load are applied. The suspected trouble could be due to _____________. A. a faulty centrifugal switch B. broken rotor bars C. worn bearings D. all of the above
Description : If the centrifugal switch or relay used for cutting out the starting winding of a split-phase induction motor fails to open once the motor is in operation, the _____________. A. motor will overspeed B ... C. motor will immediately stall under load D. motor torque will be above normal at rated speed
Description : In the illustrated motor controller circuit, which statment is true? EL-0023 A. The high and low speed lights operate at less than line voltage with a resistor in series. B. This controller can be ... . The wattage of the high speed light must be greater than the wattage of the low speed light.
Last Answer : Answer: A
Description : The power factor of an AC generator operating singularly is determined by the __________. A. connected load B. prime mover speed C. field excitation D. generator's rated voltage
Description : The power factor at which a paralleled AC generator operates is usually adjusted by the _____________. A. connected load B. prime mover speed C. field excitation D. generator's rated voltage
Last Answer : Answer: C
Description : As shown in the illustration, when the 'speed control' system is in 'SPLIT' _______________. EL-0096 A. Relays #1, #5 and #8 are not used B. the 'slew rated controller' is grounded through Relay ... E/P converters' are bypassed and air is fed directly to the governors via the 'load sharing valve'
Description : The counter EMF of a DC motor is maximum when the _________. A. motor is at rated speed B. armature is not turning C. motor is almost up to rated speed D. armature has just begun to turn
Description : The counter EMF produced in the windings of a DC motor is 'zero' when the ____________. A. armature has just begun to turn B. armature is not turning C. motor is almost up to rated speed D. motor is at rated speed
Description : If an induction motor were to be operated at 90% rated voltage, _____________. A. there would be an increase in starting torque B. starting current would increase slightly C. synchronous speed would decrease slightly D. the slip would increase
Description : The full load torque of an electric motor is the __________. A. minimum torque developed by the motor accelerating from stop to full speed B. turning moment exerted by the motor at rated load ... and frequency D. turning moment exerted by the motor from any rotor angular position at any load
Description : What are the possible reasons for not coming of rated speed during start?
Last Answer : In case motor does not come to its rated speed then following could be the probable causes. a. Starting load is too high. b. Broken rotor bars (look for cracks near rings). c. Open primary circuit. d. Voltage is too low.
Description : A dc cumulatively compounded motor delivers rated load torque at rated speed. If series field is short circuited, then the armature current and speed will a) Both increases b) Both decreases c) Increases and decreases d) Decreases and increases
Last Answer : Ans: Both increases
Description : A 3-phase, 400 votts, 50 Hz, 100 KW, 4 pole squirrel cage induction motor with a rated slip of 2% will have a rotor speed of (A) 1500 rpm (B) 1470 rpm (C) 1530 rpm (D) 1570 rpm
Last Answer : Ans: B N = NS (1-S) and NS =120 f / p =120 x 50 /4 = 1500 rpm ∴N= 1500 (1-0.02) =1470 rpm
Description : The speed of a d.c. shunt motor at no-load is (A) 5 to 10% (B) 15 to 20% (C) 25 to 30% (D) 35 to 40% higher than its speed at rated load.
Last Answer : (A) 5 to 10%
Description : A balanced three-phase, 50 Hz voltage is applied to a 3 phase, 4 pole, induction motor. When the motor is delivering rated output, the slip is found to be 0.05. The speed of the rotor m.m.f. relative to the rotor structure is (A) 1500 r.p.m. (B) 1425 r.p.m. (C) 25 r.p.m. (D) 75 r.p.m.
Last Answer : (D) 75 r.p.m.
Description : In the illustration, the contacts between terminals 26 and 27 should be closed when _________. EL-0046 A. using one generator in isochronous mode only B. using two or more generators in ... through varying loads in parallel or single operation D. the circuit breaker is closed for that generator
Description : The average speed of a bus in the upward journey is 50% more than that in the return journey. The bus halts for 2 hrs on reaching the destination. The total time taken for the complete to and from trip is 34 hrs ... speed of the bus in the upward journey is. a) 63.24 b) 65.67 c) 63.49 d) 62.49
Last Answer : D Let the speed in return journey be x km/hr Then speed in upward journey = 150 /100 x = (3/2 x)km/hr Average speed = (2*3x/2*x) / (3x/2 +x) =3x2 / (5x/2) =6x2 / 5x =6x/5 km/hr Therefore (1600 ... 192x = 8000 X = 41.66 Speed in upward journey = (3/2 x ) km/hr =(3/2*41.66) =62.49 km/hr
Description : Fuses are usually rated in _____________. A. watts B. amps only C. volts only D. amps and volts
Description : Which of the following statements is true concerning a polyphase synchronous propulsion motor? A. The motor is started as an induction motor. B. Resistance is gradually added to the rotor circuit. C. ... is held below the rated current. D. The field winding is energized for starting purposes only.
Description : The power factor of a squirrel cage induction motor is (A) low at light load only. (B) low at heavy load only. (C) low at light and heavy load both. (D) low at rated load only.
Last Answer : (A) low at light load only.
Description : In the illustration, moving the engine room reference in the direction indicated will _________. SE-0002 A. cause a positive signal to be sent to the ahead function generator creating a more ... the ahead valve to open until the negative signal exceeds the low lube oil pressure override signal
Description : A single-phase induction motor fails to start. The rotor is spun rapidly with the line switch closed. Having started by this method it is noted that the motor fluctuates between a very slow ... lies in the ______ A. starting winding B. centrifugal mechanism C. centrifugal switch D. running winding
Description : Home buyers, what was your experience like after reaching an agreeable offer with the seller?
Last Answer : The home inspection and the termite inspection are usually the places where the big surprises lurk.
Description : Do Volcanic necks and dikes form when magma cools and hardens into rock after reaching the surface?
Last Answer : No, these features form when magma cools into rocks BEFOREreaching the surface.
Description : Plants that flower after reaching a certain stage of development irrespective of the day length are called: (a) Day-neutral plants (b) Long-day-short-day plants (c) Negatively phototrophic plants (d) Long-day plants
Last Answer : Ans:(a)
Description : Which of the following precautions should be taken when a blown fuse, rated at 10 amperes, is replaced? A. Short out the fuse before removing it from the circuit. B. Use needle-nose pliers to ... D. Fuses of 10 ampere rating and less are virtually harmless when energized and may be handled freely.
Description : An open shunt field in a direct current machine may be located by connecting the field circuit to an external power source, equal to the rated field voltage or less, and tested with a voltmeter from ... C. any suitable ground to any available line lead D. any field pole to each field coil lead
Description : A vessel is equipped with two ship's service generators. Generator #1 is rated at 900 kw and generator #2 is rated at 600 kw. During parallel operation, with a hotel load of 1,000 kw, what should be the kw load on generator #2? A. 100 kw B. 400 kw C. 500 kw D. 600 kw
Description : A circuit breaker for a 300 KW alternator is rated at 470 amperes of full continuous load. The amount of overcurrent allowed is 125%. Which of the following conditions will trip the breaker? A. ... 10 minutes. C. Momentary starting load of 550 amperes. D. Sustained current flow of 590 amperes.
Description : Electric motors intended for use outside the engine room and boiler room are frequently rated to run at a designed ambient temperature of 40°C. What is the equivalent temperature in degrees Fahrenheit? A. 54.2°F B. 72.0°F C. 104.0°F D. 129.6°F
Description : Two paralleled alternators are operating near rated load. If one trips out mechanically, which of the listed actions should be taken FIRST? A. Restart the tripped machine immediately. B. Strip the board ... circuits. C. Start the emergency generator. D. Transfer all vital loads to the emergency bus.
Description : A fuse will 'blow' if _____________. A. an electric motor is stopped suddenly by opening a switch B. the flow of current to the protection device is reversed C. the electrical current exceeds the rated value of the fuse D. unequal resistors are connected in parallel
Description : In the illustration, the purpose of part B is to _________. EL-0033 A. increase resistance in series with the contacts as they close to prevent arcing B. create a magnetic field in the steel ... event of an overload D. provide ventilation to the contact when the breaker is close to rated capacity
Description : During maintenance of circuit breakers, _______________. A. always smooth roughened contact surfaces with a file B. never pass more than rated breaker current through the overload heater element C. ... wear and misalignment of main contacts D. assume heater elements installed are of correct size
Description : In the illustrated circuit the voltage is 12 VDC and the resistance is 3 ohms. If the battery is rated for 120 amp-hours, how long before the voltage will drop to 1.75 volts per cell? EL-0018 A. 12 hours B. 1.75 days C. 30 hours D. 2.5 days
Description : When troubleshooting a motor controller, all indications are that a relay coil should be energized. If there were no magnetic pull, with rated voltage measured across the coil, the most probable cause ... open C. auxiliary contact in series with the coil is defective D. relay armature is stuck
Description : Periodic testing of circuit breakers is necessary to assure that a correctly rated and properly installed unit _________________. A. can trip faster as it increases in age B. will continue to provide ... not exceed its interrupting capacity D. be able to withstand at least 125% of applied voltage
Description : One method of testing for a reversed shunt field coil in a DC generator or motor is by connecting the field to a direct current source, at reduced field rated voltage, and test for ... placed near each field C. test lamp across adjacent fields D. copper jumper across the interpole connections
Description : Power transformers are rated in _____________. A. kilowatts B. ampere-turns C. kilowatt-volts D. kilovolt-amperes
Description : Fuses are rated in _____________. A. voltage B. amperage C. interrupting capacity D. all the above
Description : The torque produced by a motor when its shaft will not turn, even though rated voltage is applied to the stator, is known as _____________. A. locked-rotor torque B. pullout torque C. breakdown torque D. torque margin
Description : The rated temperature rise of an electric motor is the _____________. A. average temperature at any given latitude B. normal temperature rise above the standard ambient temperature at rated load ... D. permissible difference in the ambient temperature of the motor due to existing weather conditions
Description : What is the supply rated o/p if two single phase transformer connect to give three phase o/p from a three phase I/p?
Last Answer : A. Each transformer is only capable of supplying 86.6%of its o/p rating