3rd 6 Flashcards
In a pneumatic system what provides the force that performs work?
compressed Air
How much work is done by a piston that exerts a force of 15lbs through a distance of 10in?
150 in-lbs
Heating a gas in a solid rigid container will ____ the ____ of the gas.
increase; pressure
Two cylinders having different diameters are connected by an air line. A force is applied to the smaller piston. The larger piston exerts a force on a load and moves it. The force on the load is ____ the force applied to the small piston, and the distance load moves is ____ the distance the small piston moves.
greater than; less than
When air flowing in a pipe reaches a section where the diameter is reduced, the speed of the air ____ and its pressure ____.
increases; decreases
A reciprocating compressor is one kind of ____ compressor
positive- displacement
In a typical reciprocating compressor, the intake valves are forced open by:
atmospheric pressure
The purpose of the intercooler between the two stages of a two stage compressor is to reduce the ____
power needed to run
The purpose of lubricating oil in a compressor is to reduce friction between the moving parts and:
improve the cooling of compressor
The advantage of unloading a compressor is to allow it to
Run without delivering air
Single-stage sliding- vane compressors can produce pressures up to
50 psi
Rotary screw compressors run at speeds ranging from ____ to ____ rpm
3,000 ; 12,000
Impeller compressors deliver air at ____ volume and ____ pressure
high; low
Compared to other compressors, centrifugal compressors
more power
Most effective way to reduce output of a centrifugal compressor is ____, but may not work if the reduction is too ____
speed variation; large
Water often collects in pneumatic systems because when air is compressed its ____ decreases
moisture capacity
Most common way to remove water vapor from the air leaving a compressor is to:
cool the air
Water cooled after coolers are typically used with ____ capacity compressors that run ____ hours a day
large; 10 or more
A desiccant removes water from air by ____ it.
absorbing
The main purpose of a receiver in a pneumatic system
maintain pressure during peak demand
The operation of an internal separator depends on
rapid change in the direction of air flow
Of the particles listed, the smallest are the ____ particles
aerosol
A filter can stop 100% of the particles down to a specific min size. Known as the filter’s ____ rating
absolute
An advantage of wetted filters over dry
can be cleaned many times
A fine mist lubricator should be used in a system if air flow is ____ and/or distance to the equipment is ____
intermittent; long
Laminar air flow in a system is made turbulent by
constrictions in pipe
Greater pressure losses occur if air is at ____ pressure, because of greater ____
low; friction
When used as a compressor discharge line, a pipe run should slope ____ in the direction of flow by 1in for every ____ ft
downward; 10
When should you use pipe joint compound in connecting NPT- threaded pipe?
Either
-if joint can’t be tightly fitted
Or
- never
[Never got the correct answer]
If an air hose is not completely depressurized when you disconnect it, the danger is a sudden
blowing of dust or chips
A four way valve has four
connecting ports
The ____ valve is a good throttling device and is suitable for high pressure service. It causes ____ pressure losses in the line
needle; high
The spool in a valve controls the flow of air by ____ from one piston to another. In a high pressure system, the spool is ____ to move
sliding; easy
An advantage of 4-way valves over 2-way and 3-way is that they
simplify controls
A valve has 5 connecting ports, 2 of which are exhaust ports. The valves is a
4-way
The cracking pressure of a simple poppet type relief valve is determined by the
spring adjustment
A diaphragm type relief valve responds very quickly to a pressure change because of its
larger pressure sensitive area
The only purpose of a pressure relief valve is to
prevent damage
An increase in pressure on a secondary side of a pressure regulating valve ____ the valve
slightly closes
The best way to guard against excessive pressure on the secondary side of a pressure regulator is
use a regulator with a built in relief valve
The thrust that can be applied when a rod of a single rod, double-acting cylinder is moving out of a cylinder is ____ the thrust that can be applied when the rod is moving in
greater than
An internal spring is sometimes used to return the piston in a ____-acting ____ rod pneumatic cylinder
single; single
The main purpose of an exhaust flow control metering valve on a pneumatic cylinder is to
limit return stroke speed
A cylinder that must be free to pivot requires a(n) ____ mounting
trunnion or clevis
You can determine whether a control valve can deliver air enough for a cylinder by calculating the ____ required by the valve
capacity coefficient
The highest torque a pneumatic motor can exert on a load is its ____ torque
stalling
The HP of a pneumatic motor varies with the ____ and the ____ of the motor shaft
speed; torque
The highest power output of a pneumatic motor occurs when its speed is
medium
An axial-piston pneumatic motor transmits force from the piston to the output shaft by means of:
cam plate and gears
Air pressure of 100psi can create hydraulic pressure of 1000psi if the air piston drives a ____ hydraulic piston
smaller diameter
The designation 52Y indicates the device is a ____
circuit breaker, anti-pump auxiliary
The accepted industry standard for showing relay contacts on circuit diagrams is to show the contacts assuming the relay is
de-energized
Protective relay zones of protection are overlapped to:
avoid leaving unprotected areas
A well designed protective relay system should provide 3 basic operational characteristics
all above
The method of symmetrical components consists of reducing any unbalanced 3 phase system of vectors in 3 ____ systems
balanced
In high current arcs in excess of 100 amps, the voltage across the arc is nearly constant at an average of around ____ volts per foot
400
Open circuits on power occur more frequently than short circuits
T or F
False
The current flowing out at the polarity marked terminal on the secondary side is substantially in phase with the current flowing in at the polarity marked terminal on the primary side
T or F
True
The ground and neutral point on a 3 phase system are on the same point
T or F
False
Circuit diagrams show ____ of the currents and voltages. [Eliminate 1]
magnitude
Plasma is defined as the state of matter in which electrons are removed from atoms or molecules, creating electronically conducting gas
T or F
True
The plasma performs what function when breaking a circuit?
flow between two open circuits
Why must air in the breaker’s high air pressure system be very dry?
because it is the insulating medium between contacts
What is the purpose of SF6 gas in air blast circuit breakers?
insulate the support column current
The purpose of the blast valve is to blow the arc from the stationary to the arcing probe. It also cools and lengthens the arc so it will extinguish at the next zero current
T or F
True
Which element is used as a time delay?
disk
Relays reduce the number of alternate links to avoid equipment damage or limit damage to a single unit
T or F
True
The links in a power system chain are: generator, power transformers, switchgear, transmission lines, distribution circuits and the utilization apparatus
T or F
True
What is the most vulnerable portion of the power system chain
transmission lines
Operating characteristic curves is a graph depicting the relationship of quantities that will cause the relay to operate
T or F
True
What is the advantage of the induction cap
instantaneous operating with ability to monitor several electrical quantities
What are the 4 basic types of electromagnetic relay operating elements
All above
A device when energized by suitable currents, voltages, or both, responds to magnitudes and relationships of those values to indicate or isolate an abnormal condition. This best describes protective relays
T or F
True
The difference between primary and backup relaying is that the primary is the SECONDARY defense and isolates a greater portion of the chain
T or F
False
Speed of an actuator may be regulated with a
flow control valve
When the flow control valve controls the amount of oil going in the actuator, the application is
meter-in
In applications where the load might tend to “run away”, the flow control application should be
meter-out
When the flow control is teed off supply line from the pump and determines the actuator speed by metering a portion of the pump delivery to tank, the application is
bleed-off
The light spring in a bypass flow control valve holds the pressure compensator normally
closed
The light speed in a restrictor type flow control holds the pressure compensator normally
open
Flow through a pressure compensated flow control valve is subject to change with variations in oil ____
temperature
Deceleration valves are usually used in a meter-out configuration
T or F
True
The use of proportional valves requires the equipment contain ____ controls
electronic
This graphical symbol depicts what valve?
[Photo pending]
meter-in restrictor type valve
Pumps are generally rated by their maximum operating pressure capability and their output in ___ at a given drive speed
GPM
Pump ____ is expressed in cubic inches per revolution
displacement
Most pumps have a ____ displacement which cannot be changed easily
fixed
Volumetric efficiency is equal to actual output divided by ____ output
theoretical
High pressures at gear pump outlet imposes a(n) ____ load on the gears and bearings supporting them
unbalanced
Most fixed displacement vane pumps utilize the ____ cartridge design
balanced
Intra-vane pumps have holes drilled through the rotor segments to ____ pressure
equalize
The pistons in a(n) ____ piston pump are parallel to each other and to the axis of the cylinder block
axial
In a(n) ____ piston pump, the cylinder block and drive shaft are on the same centerline and the pistons retract parallel to the drive shaft
inline
In a(n) ____ piston pump the cylinder block turns with the drive shaft, at an offset angle
bent axial
A device used to store fluid under pressure is called a(n) ____
accumulator
Regardless of the percentage of fluid in a weight loaded accumulator, the pressure remains ____
constant
What type of gas is preferred for gas charged accumulators?
nitrogen
Two principal types of pressure gauges are the Shrader and ____
Bourden
Vacuum gauges are calibrated in inches of ____
mercury
The gas precharge pressure in an accumulator should never be less than ____ the working pressure
1/4th
The device used to protect a pressure gauge from surges is called a ____
snubber
Accumulators may be installed in a system to absorb ____
shock
The device used to boost pressure is called ____
intensifier
Converts a pressure signal into an electrical signal:
pressure switch
The most distinguishing feature of a pipe thread is the ____
shape
Which metal is least affected by corrosion?
stainless steel
____ strainers are commonly used where frequent cleaning is necessary
duplex
Female end pipe fitting used for joining 2 lengths of pipe:
coupling
Pipe supports are used to:
All above
Pipe less than 12” in diameter is usually designated by its ____ diameter
inside
For low pressures and cold services, ____ gaskets are generally used
rubber
The pipe fitting used to join lengths of pipe to permit easy opening of a line:
union
All pipe systems should be installed in accordance with the ____
ASCPP
Warm up or ____ lines reduce wear and make large valves easier to open
pressure equalizing
Pipe is coated on the outside with galvanizing, paint, insulation, or some other material to prevent:
All above
____ strainers are used to automatically strain raw water to remove silt and debris
self- cleaning
A ____ line is a line used to control the concentration of impurities in a pressure vessel
blow down
Plastic pipe is not normally used to transfer ____
oil
To differentiate between pipes carrying different substances, pipe systems are often ____
color coded
Pressure reducing valves are always drained ____
externally
If the vent connection of a relief valve is opened to tank the pump is said to be ____
unloaded
If operations take place in a certain order they are done in ____
sequence
A sequence valve should contain a ____
check valve
A back pressure valve is normally ____
open
If flow from secondary to primary is required, the unloading valve control pressure should be ____ above the spring setting
150 psi
When used to support a load, the valve functions as a ____
counterbalance valve
Pressure in the outlet part of an internally drained sequence valve adds to the ___ setting
spring
Pressure reducing valves with internal check valves permit ____ free flow
reverse
When the unloading valve is ___ operated, the spring force and pressure in the primary part are independent of each other
remotely
A brake valve is used to prevent:
Both A and C
A brake valve is used in the ____ line of a hydraulic motor
exhaust
When a load is being accelerated, pressure is maximum at the motor ____
inlet
A back pressure valve can also be used as a ____ valve
unloading
A relief valve is normally ___
closed
The point at which a relief valve first opens is called its ____ pressure
cracking
A relief valve limits the ____ pressure in a hydraulic system
max
The difference in pressure between the points where a relief valve first opens and passes full pump delivery is sometimes called ____
override
When the chamber above the balanced piston at a relief valve is opened to tank, it is said to be ____
vented
The best hydraulic formula:
Y = f/2
When a pressure reducing valve is vented, its outlet pressure is at its ____
minimum pressure
Penstock velocities may range from:
6 to 20ft per sec
A partially clogged trash rack will:
cause a decrease in effective head
The most advantageous form of cross-section to use from a hydraulic point of view would be that which provide the:
smallest wetted perimeter
Wood-stave pipe is not used for:
heads above 500ft
In hydroelectric developments the head and flow may be subject to continuous ____
fluctuations
The pumped storage type of development implies a capability of ___
All 3
Negative water hammer pressure is created by
a sudden increase in demand for water
Intake design has a large effect on ____
All 3
Which would not cause water level in the riser to fall?
load rejection
The efficient type of high-line conduit is that type which
has the greatest effect on the available head
Steel pipe is probably used more extensively than any other type because of the degree it offers in satisfying service criteria….
In all above areas
An open conduit system implies
the presence of a free surface
The advantage of using a pressure tunnel in a power conduit
permits full use of available head
The simplest means of eliminating positive water hammer pressure is:
any above
Transformers permit the transfer of electricity between two circuits which are:
completely insulated from each other
In a transformer the winding which receives the energy inductively is called the:
secondary winding
A power transformer transfers electrical power from one circuit at a certain frequency and voltage, to a second circuit at:
a DIFFERENT voltage and SAME frequency
Transformers are classified as static AC machines
T or F
True
A transformer developed 120V in its secondary winding when a 2,400 source was connected across the primary winding. Assuming a primary current of .25 Amps, the secondary current is:
5 Amps
When the number of turns or voltage on the secondary winding of a transformer is greater than that of the primary, it is known as a:
step-up transformer
Transformers only having ONE winding are called:
autotransformers
The secondary of a potential transformer should never be
short circuited to remove the device it operates from service
What is the induced secondary voltage of a transformer having a primary winding of 3,000 turns and a secondary winding of 300 turns, when connected to a 2,400V source?
240V
In a core-type transformer:
A section of the primary and secondary windings are wound around each leg of the core
Current transformers are instrument transformers use to:
step current down
Hysteresis can be explained as
friction of the molecules due to alternating current
When a transformer’s windings are connected in WYE:
the line current will be the same as the phase current
A series street lighting system requires what type of transformer?
a constant current transformer
The rating of a transformer is usually given in:
all above
Bushings are used in transformers to:
serve as entrances into the transformer for the main leads
The conservator system is used on transformers to:
preserve the dielectric strength of the transformer oil
The secondary of a current transformer should never be
opened to remove the device it operates from service
In an energized transformer iron losses are present even if there is no load on the secondary.
Tor F
True
In a transformer a ____ must always exist between the primary and the secondary fields to maintain the required current to supply the transformer losses and secondary load.
balanced condition
Whenever a circuit which is carrying current is opened:
the current tends to continue to flow across the contacts as they separate
The initials TPDT would normally be used to identify a type of:
knife switch
The type of switch usually used to interrupt field current to generators and synchronous machines is a:
field switch
Disconnect switches are commonly used on 440 Volts or higher circuits to:
isolate the electrical equipment or circuits not in service
Of the following statements concerning mercury control switches, the one which is most nearly not correct is:
they are generally used only when the circuit voltage is 120 volts or less
The main difference between a circuit breaker and other kinds of electrical switches is that circuit breakers:
open automatically when the current exceeds a predetermined limit
Which of the below statements does not correctly describe a means or method for quenching an arc?
reducing the reluctance across the contacts
A blowout coil would most likely be found in:
an air-magnetic circuit breaker
of the following statements, the one which most nearly describes what is meant by trip-free operation is:
the precedence which takes place over any closing operation
A trip-free operation takes place if:
the circuit breaker is closed while the protective relay is energized
Circuit breakers are generally classified by:
all the above
Speed is a desirable quality during the tripping operation of a circuit breaker to:
all the above
The energy needed to rapidly open the contacts of most circuit breaker designs is usually provided by:
springs and gravity
Of the following statements concerning OCBs the one which is not correct is:
The AC arc is ALWAYS extinguished during the first zero current
The closing time of an OCB becomes more important when it is considered from the standpoint of:
synchronizing generators
A fast realistic circuit breaker opening operation (arc-out) time would be:
three to four cycles
The high dielectric strength of gases, such as SF6, under static conditions is maintained by:
pressurizing
A 3 phase 138kV circuit breaker can interrupt 12,000 amps. What is its interrupting capacity in MVA?
1656 MVA
A 34.5kV circuit breaker has a rated interrupting capacity of 25,000 amps. What will be its approximate interrupting capacity when used on a 20kV circuit?
25,000 amps
A 4.58kV circuit breaker has an interrupting rating of 30,000 amps. What is its interrupting capacity when used at 5.1 kV?
28,235 amps
In fig 28, which is not true?
the pallet switches indicate that the OCB is in a closed position
Concerning fuses, which is not true?
they are all non-repetitive in design
Fuses serve the same purpose as:
circuit breakers
A ____ is a device which functions when the circuit admittance, impedance, or reactance increases or decreases beyond predetermined limits
distance relay
The reason for not replacing blown fuses with copper is:
the desired circuit protection against overload may be lost
____ is adjusted separately for the degree of overcurrent at which it operates and also for the amount of time delay.
induction disk time-relay
the term zones of protection applies most nearly to the isolation of faulted equipment:
throughout the entire power system
The induction-disk time overcurrent is:
both A and B
A device by which contacts in one circuit are operated by a change in conditions in the same or another circuit is:
a relay
Protective relays must be able to:
all the above
Relays may be classified in a number of ways except:
the manner in which it is connected in a circuit
Differential current relays are designed to:
protect against internal faults
When CTs are used with protective relays the direction of current flow in the transformer windings (polarity marks) :
must be carefully observed for relay types which depend on the interaction of 2 currents for their action.
____ are used to protect polyphase rotating equipment from single or unbalanced phase operations:
phase balance relays
The protective device for motor branch circuit should:
not be of the instantaneous type
