Generation / Motors / Pumps / Tanks
Questions and Answers
- 1.
In a synchronous generator, which of the following will have the greatest effect on the short circuit current impulse during a fault situation
- A.
Synchronous reactance
- B.
Subtransient Reactance
- C.
Inductive reactance
- D.
Sub inductive reactance
Correct Answer
B. Subtransient ReactanceExplanation
In particular, generators are dominated by inductive reactance which involves energy stored in a magnetic field proportional to the square of the current.
A three phase symmetrical fault has three specific time periods of concern: Subtransient, Transient, Steady State. During the Subtransient period which only lasts a few cycles, the current rapidly decreases and the synchronous reactance Xs changes to the subtransient reactance X’’d.Rate this question:
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- 2.
A Generator is being run at synchronism with the voltage slightly below system voltage to meet operational needs of the system. To maintain stability what should be done:
- A.
Over excite the generator
- B.
Increase the torque from the prime mover
- C.
Apply the governor to increase the rotational speed
- D.
Under excite the generator
Correct Answer
D. Under excite the generatorExplanation
In technology, a device that automatically maintains the rotary speed of an engine within reasonably close limits regardless of the load. A typical governor regulates an engine's speed by varying the rate at which fuel or working fluid is furnished to it. Nearly all governors work by centrifugal force and consist of a pair of masses rotating about a spindle driven by the engine and kept from flying outward, usually by springs. With an increase in speed, the controlling force of the springs is overcome and the masses move outward, opening valves supplying the engine with its working fluid or fuel. Modern governors are used to regulate the flow of gasoline to internal-combustion engines and the flow of steam, water, or gas to various types of turbines.
If the amount of torque being applied by the prime mover to the generator rotor increases, the tendency is for the speed to increase, but if the generator is being operated in parallel with other generators on a grid with a stable frequency, then the speed of the generator cannot increase and the increased torque will be converted by the generator into amps. More torque, more amps. Less torque, less amps.
If the amount of torque being applied to the generator by the prime mover is less than that required to keep the generator rotor spinning at synchronous speed, and if the generator is being operated on a grid with a stable frequency in parallel with other generators, the tendency would be for the speed to decrease. But the speed cannot decrease and amps begin to flow into the generator and it actually becomes a motor to keep the prime mover spinning at synchronous speed. (This is called "reverse power", or "motorizing the generator", and it's usually not good for most prime movers and can sometimes result in catastrophic failure of some prime movers.)
10,000 KWH is equivalent to:
1 Watt = 60 Joules
1Watt hr = 3600 joules, 1kWh = 3,600,000 joules
1BTU = 1055 Joules
1kWh = 3412.14163 BTU
10,000 kWh = 3.6*10^10 Joules
10,000 kWh = 34131416.33 BTU
10,000 BTU = 1.055810^7 JoulesRate this question:
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- 3.
What is the most efficient cycle?
- A.
Carnot
- B.
Diesel
- C.
Otto
- D.
Rankine
Correct Answer
A. CarnotExplanation
The Carnot Cycle can be shown that it is the most efficient cycle for converting a given amount of thermal energy into work.
Every single thermodynamic system exists in a particular state. When a system is taken through a series of different states and finally returned to its initial state, a thermodynamic cycle is said to have occurred. In the process of going through this cycle, the system may perform work on its surroundings, thereby acting as a heat engine. A system undergoing a Carnot cycle is called a Carnot heat engine, although such a 'perfect' engine is only a theoretical limit and cannot be built in practice
The Carnot cycle when acting as a heat engine consists of the following steps:
1. Reversible isothermal expansion of the gas at the "hot" temperature, TH (isothermal heat addition or absorption).
2. Isentropic (reversible adiabatic) expansion of the gas (isentropic work output).
3. Reversible isothermal compression of the gas at the "cold" temperature, TC. (isothermal heat rejection)
4. Isentropic compression of the gas (isentropic work input).
The Rankine cycle is a mathematical model that is used to predict the performance of steam engines. The Rankine cycle is an idealised thermodynamic cycle of a heat engine that converts heat into mechanical work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid. The Rankine cycle, in the form of steam engines generates about 90% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants.
• Process 1-2:The working fluid is pumped from low to high pressure. As the fluid is a liquid at this stage the pump requires little input energy.
• Process 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapor. The input energy required can be easily calculated using mollier diagram or h-s chart or enthalpy-entropy chart also known as steam tables.
• Process 3-4: The dry saturated vapor expands through a turbine, generating power. This decreases the temperature and pressure of the vapor, and some condensation may occur. The output in this process can be easily calculated using the Enthalpy-entropy chart or the steam tables.
• Process 4-1: The wet vapor then enters a condenser where it is condensed at a constant pressure to become a saturated liquid.
An Otto cycle is an idealized thermodynamic cycle which describes the functioning of a typical spark ignition reciprocating piston engine,[1] the thermodynamic cycle most commonly found in automobile engines.
The Diesel cycle is the thermodynamic cycle which approximates the pressure and volume of the combustion chamber of the Diesel engine,Rate this question:
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- 4.
The Rankine Thermal Dynamic Cycle is used ____________?
- A.
Diesel engine
- B.
Gas engine
- C.
Steam Power Plant
- D.
Hydro
Correct Answer
C. Steam Power Plant -
- 5.
The Rankine cycle is used primarily in the design of:
- A.
Gasoline engines
- B.
Diesel engines
- C.
Hydroelectric plants
- D.
Steam turbines in power plants
Correct Answer
D. Steam turbines in power plants -
- 6.
Adding an overexcited generator to the system is the same as
- A.
Adding shunt reactors
- B.
Adding shunt capacitors
- C.
Adding series reactors
- D.
Adding series capacitors
Correct Answer
B. Adding shunt capacitors -
- 7.
The main purpose of the exciter is to provide
- A.
Alternating current for the stator
- B.
Direct current for the generator rotating field
- C.
Aid in synchronizing the unit
Correct Answer
B. Direct current for the generator rotating fieldExplanation
The process of generating a magnetic field by means of an electric current is called excitation.
Alternating current is supplied to the stationary stator windings. DC current is applied to the field windings in the rotor. The field current interacts with the stator field causing the armature to turn. The power factor can be adjusted by varying the field current.
Unity power factor occurs with normal excitation. Leading power factor occurs with over excitation. Power factor is lagging with under excitation.Rate this question:
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- 8.
Increasing the voltage on the stator of an induction motor by 10% will change the output power by
- A.
Less than 5%
- B.
Greater than 5%, but less than 15%
- C.
At least 15%, but less than 25%
- D.
At least 25% or greater
Correct Answer
B. Greater than 5%, but less than 15%Explanation
Assuming you are changing the magnitude of the voltage and not the voltage angle or power factor:
output power is
P=V*I*sqrt(3)*cos(theta)Rate this question:
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- 9.
Speed droop of a hydrogenerator is defined as:
- A.
The percentage of speed change from zero gate to full gate
- B.
The percentage of speed change necessary to get governor action
- C.
The percentage of speed change from normal speed at no load to full load
- D.
The percentage of speed change resulting from changes in head and temperature
Correct Answer
B. The percentage of speed change necessary to get governor actionExplanation
Droop speed control is the primary instantaneous system using net frequency deviations to distribute with stability load changes over generating plants. For stable operation of the electrical grid of North America, power plants operate with a five percent speed droop. Adjustments in power output are made by slowly raising the droop curve by increasing the spring pressure on a centrifugal governor or by an engine control unit adjustment.Rate this question:
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- 10.
When adding a generator into an existing electrical system, which of the following does not belong in the sequence
- A.
Adjust the governor on the generator
- B.
Adjust the voltage of the generator to match the bus voltage
- C.
Check the lubrication of the ball bearings on the generator
Correct Answer
C. Check the lubrication of the ball bearings on the generatorExplanation
The standard power plant method of synchronizing two generators is to use a synchroscope. This instrument indicates whether the incoming generator is faster, slower or in phase with the bus.
Manipulate the throttle of the incoming generator which ever direction is
necessary to slow the flickering. As the speeds become almost equal, the lamps will stay off for a long period of time and then slowly start lighting, slowly get fully bright and then slowly dim again. You want to manipulate the throttle until the lamps are off for as long as possible. You want to close the breaker when the voltage between the generator is the least. Since the lamps will go out before the voltage reaches zero, you'll want to mentally time the period between going out and coming back on again and close the switch about in the middle.Rate this question:
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- 11.
Which of the following elements is not part of the High Pressure Steam Generation (HPSG) system?
- A.
Economizer
- B.
Catalyst
- C.
Evaporator
- D.
Condenser
Correct Answer
B. Catalyst -
- 12.
Which of the following is correct about hydrogen cooled generators:
- A.
Used for smaller generators
- B.
Are less efficient than air cooled generators
- C.
Require fewer auxiliary than air cooled generators
- D.
More reliable than air cooled generators
Correct Answer
D. More reliable than air cooled generatorsExplanation
hydrogen-cooled turbo generator is a turbo generator with gaseous hydrogen as a coolant. Hydrogen-cooled turbo generators are designed to provide a low-drag atmosphere and cooling for single-shaft and combined-cycle applications in combination with steam turbines. Because of the high thermal conductivity and other favorable properties of hydrogen gas this is the most common type in its field today.
Generally, three cooling approaches are used. For generators up to 300 MW, air cooling can be used. Between 250-450 MW hydrogen cooling is employed. For the highest power generators, up to 1800 MW, hydrogen and water cooling is used; the rotor is hydrogen-cooled, the stator windings are made of hollow copper tubes cooled with water circulating through them.
Hydrogen is 7-10 times better at cooling than air. Another advantage of hydrogen is its easy detection by hydrogen sensors. A hydrogen-cooled generator can be significantly smaller, and therefore less expensive, than an air-cooled one. For stator cooling, water can be used.
Hydrogen is often produced on-site in electrolyzers, as this reduces the need for stored amount of compressed hydrogen and allows storage in lower pressure tanks, with associated safety benefits and lower costs. Some gaseous hydrogen has to be kept for refilling the generator but it can be also generated on-site.Rate this question:
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- 13.
In a large rotating motor the DC winding should be grounded to the frame for at least 10 minutes prior to measuring the rotor resistance with a megaohmeter to avoid?
- A.
Injury to the employee
- B.
To eliminate the possibility of any stored charge in the rotor
- C.
To measure winding resistance
Correct Answer
B. To eliminate the possibility of any stored charge in the rotor -
- 14.
Before measuring the DC resistance of a winding, the windings are grounding because:
- A.
Safety to employee
- B.
Remove excess amperage in the windings
- C.
Protect the megohometer
- D.
To get higher resistance read
Correct Answer
B. Remove excess amperage in the windingsExplanation
Before testing lift the rotor brushes, ground the starter terminal and frame and ground the motor shaft. Discharge the field winding by grounding. Then remove the field winding from ground and connect to the (-) Line connection on the megohmmeter. Connect the (+) Earth terminal to ground. The stator winding may also be measured in a similar manner.Rate this question:
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- 15.
Which diagram represents a series DC motor?
- A.
![Generation / Motors / Pumps / Tanks - Quiz]()
- B.
![Generation / Motors / Pumps / Tanks - Quiz]()
- C.
![Generation / Motors / Pumps / Tanks - Quiz]()
- D.
![Generation / Motors / Pumps / Tanks - Quiz]()
Correct Answer
A. -
- 16.
Which diagram represents a shunt DC motor?
- A.
![Generation / Motors / Pumps / Tanks - Quiz]()
- B.
![Generation / Motors / Pumps / Tanks - Quiz]()
- C.
![Generation / Motors / Pumps / Tanks - Quiz]()
- D.
![Generation / Motors / Pumps / Tanks - Quiz]()
Correct Answer
B. -
- 17.
Which diagram represents a synchronous motor?
- A.
![Generation / Motors / Pumps / Tanks - Quiz]()
- B.
![Generation / Motors / Pumps / Tanks - Quiz]()
- C.
![Generation / Motors / Pumps / Tanks - Quiz]()
- D.
![Generation / Motors / Pumps / Tanks - Quiz]()
Correct Answer
C. -
- 18.
Which diagram represents a induction motor?
- A.
![Generation / Motors / Pumps / Tanks - Quiz]()
- B.
![Generation / Motors / Pumps / Tanks - Quiz]()
- C.
![Generation / Motors / Pumps / Tanks - Quiz]()
- D.
![Generation / Motors / Pumps / Tanks - Quiz]()
Correct Answer
D. -
- 19.
More torque on a generator equals less amps
- A.
True
- B.
False
Correct Answer
B. FalseExplanation
If the amount of torque being applied by the prime mover to the generator rotor increases, the tendency is for the speed to increase, but if the generator is being operated in parallel with other generators on a grid with a stable frequency, then the speed of the generator cannot increase and the increased torque will be converted by the generator into amps. More torque, more amps. Less torque, less amps.Rate this question:
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- 20.
If the amount of torque being applied to the generator by the prime mover is less than that required to keep the generator rotor spinning at synchronous speed it becomes a motor.
- A.
True
- B.
False
Correct Answer
A. TrueExplanation
the generator is being operated on a grid with a stable frequency in parallel with other generators, the tendency would be for the speed to decrease. But the speed cannot decrease and amps begin to flow into the generator and it actually becomes a motor to keep the prime mover spinning at synchronous speed. (This is called "reverse power", or "motorizing the generator", and it's usually not good for most prime movers and can sometimes result in catastrophic failure of some prime movers.)Rate this question:
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- 21.
When a system is taken through a series of different states and finally returned to its initial state, a thermodynamic cycle is said to have occurred
- A.
True
- B.
False
Correct Answer
A. True -
- 22.
The process of generating a magnetic field by means of an electric current is called
- A.
Excitation
- B.
Magnetic flux
- C.
Inducion resonace
- D.
Induction current
Correct Answer
A. Excitation -
- 23.
In a generator alternating current is supplied to
- A.
The stationary stator windings
- B.
The field windings
- C.
The armature
- D.
The field windings
Correct Answer
A. The stationary stator windings -
- 24.
For a table opertion of a power grid power plants operate with what perecnt speed droop
- A.
5%
- B.
2%
- C.
7%
- D.
1%
Correct Answer
A. 5% -
- 25.
Which of the following is not true for wiring diagrams?
- A.
A rear view is assumed if front or rear is not specified
- B.
It is drawn assuming the worker is facing the equipment when wiring
- C.
It is often used in connection with conduit and equipment drawings during installation
- D.
None of the above is correct
Correct Answer
A. A rear view is assumed if front or rear is not specified -
- 26.
Which of the following has the least effect on the efficiency of the compressor
- A.
Inlet air temperature
- B.
Altitude
- C.
Fuel type
- D.
Air filters
Correct Answer
C. Fuel type -
- 27.
Valve A, when open, can fill an empty tank in 50 Minutes. When valve B is open, the tank can be emptied in 80 minutes. How long does it take to fill the tank from empty when both valves are open
- A.
1/(1/50-1/80)
- B.
1/(180/50-50/80)
- C.
1/50/(1/50-1/80)
- D.
1/80/(1/50-1/80)
- E.
1/(1/80-1/50)
Correct Answer
A. 1/(1/50-1/80) -
- 28.
A tank prefilled with 9000 gallons of water. Water is coming in at a rate of 450 gallons/minute and is shut off after 15 minutes. Water is coming out at a rate of 500 gallons/minute. How long does it take to empty the tank
- A.
(9000-450) (15)]/500
- B.
(450-9000)(500)/15
- C.
(9000-500)(15)/450
- D.
(9000-450)(500)/15
Correct Answer
A. (9000-450) (15)]/500 -
- 29.
The number of poles and rotor speed determine the ____ of an alternator.
- A.
Frequency
- B.
Power
- C.
Speed
- D.
Current
Correct Answer
A. Frequency -
- 30.
The ____ controls the output voltage of an alternator.
- A.
Regulator
- B.
Stator
- C.
Rotor
- D.
Excitier
Correct Answer
A. Regulator -
- 31.
What do AC motors have a that DC motors do not?
- A.
Rotors
- B.
Armature
- C.
Commutator
- D.
Frame
- E.
Brushes
- F.
Brush holder
Correct Answer
A. Rotors -
- 32.
What do AC motors have a that DC motors do not?
- A.
Stators
- B.
Armature
- C.
Commutator
- D.
Frame
- E.
Brushes
- F.
Brush holder
Correct Answer
A. Stators -
- 33.
A 2 ½ horse power motor is supplied by 2200 ft-lb. What is the efficiency of the motor.
- A.
54%
- B.
85%
- C.
62.5%
- D.
42.25%
Correct Answer
C. 62.5%Explanation
Answer: 2.5*550/2200 = 62.5%.
Horsepower (hp) is the name of several units of measurement of power, the rate at which work is done
The mechanical horsepower, also known as imperial horsepower, of exactly 550 foot-pounds per second is approximately equivalent to 745.7 watts.Rate this question:
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- 34.
In a power sytem current ____ voltage____
- A.
Leads, lags
- B.
Lags, leads
- C.
Leads,leads
- D.
Lags,lags
Correct Answer
A. Leads, lags -
- 35.
In a synchronous generator, which of the following will have the greatest effect on the short circuit current impulse during a fault situation
- A.
Synchronous reactance
- B.
Sub sychronous Reactance
- C.
Inductive reactance
- D.
Sub inductive reactance
Correct Answer
B. Sub sychronous ReactanceExplanation
In particular, generators are dominated by inductive reactance which involves energy stored in a magnetic field proportional to the square of the current.
A three phase symmetrical fault has three specific time periods of concern: Subtransient, Transient, Steady State. During the Subtransient period which only lasts a few cycles, the current rapidly decreases and the synchronous reactance Xs changes to the subtransient reactance X’’d.Rate this question:
-
- 36.
This is not a typical component of a Heat Programmed Steam Generator (HPSG)
- A.
Evaporator
- B.
Economizer
- C.
Condenser
- D.
Catalyst
Correct Answer
C. Condenser -
- 37.
Which of the following is correct about hydrogen cooled generators
- A.
Used for smaller generators
- B.
Re less efficient than air cooled generators
- C.
Require fewer auxiliary than air cooled generators
- D.
More reliable than air cooled generators
Correct Answer
D. More reliable than air cooled generators -
- 38.
A synchronous motor running idle with an overexcited field has the same effect as
- A.
A shunt reactor
- B.
A shunt capacitor
- C.
A series capacitor
- D.
A series reactor
Correct Answer
B. A shunt capacitor -
- 39.
Adding an overexcited generator to the system is the same as
- A.
Adding shunt reactors
- B.
Adding shunt capacitors
- C.
Adding series reactors
- D.
Adding series capacitors
Correct Answer
B. Adding shunt capacitors -
- 40.
Ordinarily the addition of an inductance load to an AC generator causes the
- A.
Armature flux to strengthen the rotating field flux
- B.
Armature flux to weaken the rotating field flux
- C.
Elimination of the armature flux by the field flux
- D.
Field flux to remain constant in inensity
Correct Answer
B. Armature flux to weaken the rotating field flux -
- 41.
The main purpose of the exciter is to provide
- A.
Alternating current for the stator
- B.
Direct current for the generator rotating field
- C.
Aid in synchronizing the unit
- D.
Energize the flux capacitor
Correct Answer
B. Direct current for the generator rotating field -
- 42.
Thermal plants on the departments system are usually operated to
- A.
Minimize fuel use
- B.
Maximize utility factor
- C.
Minimize the number of units online
- D.
Full capacity
Correct Answer
A. Minimize fuel use -
- 43.
Which of the following has the least effect on a compressor efficiency?
- A.
Air filter
- B.
Air density
- C.
Altitude
- D.
Inlet air temperature
Correct Answer
A. Air filter -
- 44.
The greater the rotor angle what happens to the electrical output?
- A.
Increases
- B.
Decreases
- C.
Stays the same they are not related
Correct Answer
A. Increases -
- 45.
In a generator direct current current is supplied to
- A.
The armature
- B.
Rotor body
- C.
The stationary stator windings
- D.
The field windings
Correct Answer
B. Rotor body -
- 46.
The generators output voltage is dependent on:
- A.
Number of turns in the stator
- B.
The DC field in the rotor
- C.
The number of poles
- D.
The heat rate of the plant
Correct Answer
A. Number of turns in the stator -
- 47.
The p.u. impedance value of an alternator corresponding to base values 13.2 kV and 30 MVA is 0.2 p.u. The p.u. value for the base values 13.8 kV and 50 MVA will be:
- A.
0.306 p.u.
- B.
0.33 p.u.
- C.
0.318
- D.
0.328
Correct Answer
A. 0.306 p.u.Explanation
Use the change of base formula:Rate this question:
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- 48.
The typical value of SCR for modern alternators is:
- A.
1.5
- B.
1.2
- C.
1.0
- D.
0.5
Correct Answer
D. 0.5Explanation
The Short Circuit Ratio (SCR) of a synchronous machine is defined as the ratio of the field current required to generate rated voltage on an open circuit to the field current required to circulate rated armature current on short circuit.
Short Circuit Ratio is an important factor of the synchronous machine. It affects the operating characteristics, physical size and cost of the machine. The Large variation in the terminal voltage with a change in load takes place for the lower value of the short circuit ratio of a synchronous generator. In order to keep the terminal voltage constant, the field current (If) has to be varied over a wide range.
Read more: http://circuitglobe.com/short-circuit-ratio-of-a-synchronous-machine.html#ixzz4OJY0S1NPRate this question:
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- 49.
In case of large size alternators the voltage control becomes serious if:
- A.
SCR is high
- B.
SCR is low
- C.
Voltage control is independent of SCR
- D.
None
Correct Answer
B. SCR is low -
- 50.
A large size alternator is protected against overloads by providing:
- A.
Overcurrent relays
- B.
Temperature sensitive relays
- C.
Thermal relays
- D.
A and b
- E.
B and c
Correct Answer
B. Temperature sensitive relays -
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Mar 21, 2022Quiz Edited by
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