3rd 6th months Flashcards
Deceleration valves are usually used in meter-out configuration.
True
Accumulators may be installed in a system to absorb
shock
What is the purpose of the blast valve
the blast valve allows air to pass through the orifice plate and orifice ring. this air blows the arc from the stationary fingers to the arcing probe. it also cools and lengthens the arc so it will be extinguished at the next current zero.
What are the links in the power system chain
generator power transformers switchgear transmission lines distribution circuits utilization apparatus
Compared to a pressure regulator, a pressure-relief valve normally
protects the system from damage
Volumetric efficiency is equal to actual output divided by the _____ output.
theoretical
A line designed to return a fluid back to a piece of equipment in order to maintain a desired fluid level, temperature, pressure, or flow
recirculating line
A single-stage sliding vane compressor normally can produce a pressure of up to
50psi
The conservator system is used on transformers to
preserve the dielectric strength of the transformer oil
The most common way to remove water vapor from the air leaving a compressor is to
cool the air
Pressure reducing valve with internal check valve permits _____ free flow
reverse
Most fixed displacement vane pumps utilize the ______ cartridge design
balanced
How is the air for breaker operation dried
By conducting the air up through an automatic drying system. As the air reaches the top of the dryer it reaches its final dryness.
Of the following statements concerning mercury control switches, the one which is most nearly not correct is:
they are generally used only where circuit voltage is 120 volts or less
An axial-piston motor transmits force from the piston to the output shaft by means of
a cam plate and gears
plastic lined pipe would most likely not be used for the transfer of
oils
Greater pressure losses occur in a pneumatic system if the air is at ____ pressure, because of greater____.
low
friction
Steel pipe is used more extensively than any other type of pipe for penstock construction because:
of the degree of flexibility it offers in satisfying design criteria in all of the above areas
The main purpose of an exhaust-flow control metering valve on a pneumatic cylinder is to
limit the return-stroke speed
Pressure reducing valves are always drained
externally
Vacuum gauges are calibrated in inches of
mercury
How is the interrupter classified
the interrupter is classified as a multi-break double pressure unit.
Protective relay zones of protection are overlapped to
avoid leaving unprotected areas
A four-way valve may have how may ports
four or five ports
A transformer developed 120v in its secondary when a 2400v source was connected across its primary. assuming a primary current of .25 amperes the secondary current is
5 amps
2500v.25a=120vI
Transformer oil will lose its dielectric strength rapidly when
exposed to air or moisture
Federal law requires that pressure regulators for air hoses used for blowing chips have a maximum setting of
29psi
the closing time of an OCB becomes more important when it is considered from the standpoint of
synchronizing generators
A four-way valve has four
connecting ports
The point at which a relief valve first opens is called its ____ pressure
cracking
A 34.5kv circuit breaker has a rated interrupting capacity of 25000 amperes. what will be its approximate interrupting capacity when used on a 20kv circuit
25000 amps
amps@operating volt= amps @ rated volt * rated volts / operating volts
In a transformer, excluding the small amount of losses, the induced voltage per turn in the secondary winding is
equal to the voltage across each turn of the primary winding
the device used to boost pressure is called an
intensifier
Most water-coolers are designed for
great structural strength
Strainers that are used to automatically strain raw water to remove silt and debris are
self-cleaning
in many pipe systems, large pipe loops are used to
permit pipe expansion
The highest power output of a pneumatic motor occurs when its speed is
medium
A device by which contacts in one circuit are operated by a change in conditions in the same or another circuit is called a
relay
Of the particles listed below, the smallest are ___ particles.
aerosol
When the unloading valve is ____ operated, the spring force and pressure in the primary port are independent of each other
remotely
A device used to store fluid under pressure is called an
accumulator
Pressure switches on sf6 breakers are temperature compensated. why?
all pressure switches are temperature compensated in order to maintain a constant gas density.
In a pt the voltage drop from the polarity to the non-polarity marked terminals on the primary side is substantially in phase with the voltage drop from the polarity to the non-polarity marked terminal on the secondary side.
true
According to the principles of pneumatic leverage, every force increase has a corresponding
travel decrease
IN a transformer a _______ must always exist between the primary and the secondary fields to maintain the required primary current to supply the transformer losses and secondary load.
balanced condition
The type of knife switch usually used to interrupt field current to generators and synchronous machines is a
field switch
Particles larger than 10u are classified as
dust particles
In most hydroelectric developments the head and water flow will
fluctuate
Air pressure of 100 psi can create hydraulic pressure of 1000 psi if an air piston drives a _____ hydraulic piston
smaller-diameter
A back pressure valve can also be used as a ______ valve
unloading
Eddy currents are circulating currents that cause
a loss of energy
Protective relays may be classified in all of the below ways except for:
a. construction
b. movement
c. contacts
d. manner
D. according to the manner in which they are connected in the circuit
What are the four basic types of electromagnetic relay operating elements?
plunger
hinged armature
induction disk
induction cup
When used as a compressor discharge line, a pipe run should slope 1 in. for every ____ ft of pipe.
10
The energy needed to rapidly open the contacts of most circuit breaker designs is usually provided by;
springs and gravity
The most distinguishing feature of pipe threads is their
taper
In a pneumatic system, what provides the force that performs work
compressed air
Transformers permit the transfer of electricity between two circuits which are:
completely insulated from each other
In a typical reciprocating compressor, the intake valves are forced open by the
atmospheric pressure
When used to support a load, the valve functions as a ____-
counterbalance
A fuse may serve the same purpose in isolating a fault as a
circuit breaker
How is clean oil made available for interruption in the general electric type fk ocb
by a spring-driven pump
Explain what is meant by operating characteristic curves.
Graph, depicting the relationship of quantities that will cause the relay to operate.
What force enables a pneumatic motor to begin rotation under full load?
starting torque
Of the following statements concerning OCB’s the one which is not correct is
the AC arc is always extinguished during the first current zero.
A line in a pipe system designed for routing the full system flow around a particular piece of equipment is called
by-pass line
Impeller compressors deliver air at ____ volume and ___ pressure
high
low
Negative water-hammer pressure is created by:
a sudden increase in the demand for water
An increase in pressure on the secondary side of a pressure-regulating valve _______ the valve.
slightly closes
IN applications where the load might tend to run away, the flow control application should be ______
meter-out
Increasing the rate of cooling on a transformer will increase its capacity.
true
Circuit breakers are generally classified by
a. continuous current rating
b. interrupting rating
c. the amount of current that they will carry for a period of four to five seconds
all the above
Open circuits on power systems occur more frequently than short circuit faults.
false
When you disconnect an air hose with quick-disconnect couplings
make sure to wear eye protection
Differential current relays are designed and installed to protect against
internal faults
when a transformer’s windings are connected wye
the line current will be the same as the phase current
Mechanical separators are used in a pneumatic system for the purpose of
moisture separation
A surge tank is normally designed to accommodate how much of the water load rejected by the turbines
all of the load rejected
The advantage of the unloading a compressor is to allow it to
run without delivering air
When a pressure reducing valve is vented its outlet pressure is at its
minimum pressure
Whenever a circuit which is carrying current is opened
the current tends to continue to flow across the contacts as they separate
Why must the air in the breaker low air pressure system be very dry
because it is used as the interrupting and insulating medium between the contacts
The induction-disc time overcurrent relay has which of the following characteristics
definite-time and inverse-time
The flow of air through a normally closed, direct-acting solenoid valve is shut off by
a spring-actuated plunger
To differentiate between pipes carrying different substances, pipe systems are often
color coded
The main purpose of an exhaust-flow control metering valve is to
restrict the flow of exhaust air
The best hydraulic rectangular cross-section occurs when
y=b/2
Speed is a desirable quality during the tripping operation of a circuit breaker to
make it less difficult to extinguish the arc, reduce the damage which could be caused by a fault, and protect equipment not directly involved in the fault area.
An advantage of wetted filters over dry filters is that wetted filters
can be cleaned many times
Flow through a pressure compensated flow control valve is subject to change with variations in oil ______
temperature
Small ice needles which form at the bottom of fairly quiet, shallow bodies of open water are called
anchor ice
Compared to the secondary of a loaded step-down transformer, the primary has
higher voltage and lower current
in a core-type transformer
a section of the primary and secondary windings are wound around each leg of the core
Cracking pressure of a simple poppet-type relief valve is determined by the
spring adjustment
All protective relaying may be classified according to the
function they perform
A device used to check oscillation or level out the movement of the fluid in a pipe system is called a ____
snubber
Compared to other kinds of compressors, centrifugal compressors
require more power
The high dielectric strength of gases, such as sf6, under static conditions is maintained by
pressurizing
If an air hose is not completely depressurized when you disconnect it, the greatest danger to you is a sudden
blowing of dust or chips
When the flow control valve controls the amount of oil going in to the actuator, the application is_____
meter-in
When is the breaker trip-free
when it is closed to a fault or when the control switch is held in the trip position after a closing operation is completed.
The device designation 52y indicates the device is a ____
circuit breaker anti-pump auxiliary
A centrifugal compressor that can deliver 150000 cfm at 150+ psi typically has all the following advantages EXCEPT:
A. delivery of oil-free air
B. nearly constant discharge pressure
c. low floor area requirement per cfm delivered
D. low horsepower requirement per cfm delivered.
d.
Wood-stave pipe would probably not be used for
heads above 500 feet
Protective relays may be classified in all of the below ways except for:
A. according to their construction
B. according to their type of movement
C. according to their contacts
D. according to the manner in which they are connected in the circuit
d
Water often collects in a pneumatic system, because when air is compressed its _____ decreases
moisture capacity
A pipe fitting used to join lengths of pipe to permit easy opening of a line is called a
union
A fine-mist lubricator should be used in a pneumatic system if the air flow is _____ and/or the distance to the equipment is ____
intermittent
long
If a sequence valve is installed in a cylinder line it should contain a
check valve
Bushings are used on transformer to
serve as entrances into the transformer for the main leads
The conditions that must be met when transformer are operated in parallel are
a. ratio of transformation approximately the same
b. voltage rating approximately the same
c. polarity must be the same
Of the following statements concerning mercury control switches, the one which is most nearly not correct is:
A. they are silent operating
B. they may be provided with single or double throw action
C. they are generally used only where the circuit voltage is 120 volts or less
D. they are maintenance free
c
Which type of positive-displacement compressor does not need timing gears to drive the compressor lobes
wet screw
Polyphase rotating equipment may be protected against single phase operation by using a
phase-balance relay
An internal spring is sometimes used to return the piston in a _____-acting, ______-rod pneumatic cylinder
single
single
The head obtained by subtracting the head loss from conveyance of the water to the turbine by conduit, through the turbine and back to the river, subtracted from the gross head is called
effective head
A valve has five connecting ports, two of which are exhaust ports. this valve is a ___ valve
four-way
A brake valve is used to prevent
overspeeding and excessive pressure
Current transformers are used with: A. ammeter B. watt meters C. protective relays D. all of the above
d
plasma is defined as
the state of matter in which electrons are removed from atoms or molecules, creating an electrically conducting gas.
The current flowing out at the polarity marked terminal on the secondary side of a current transformer is substantially in phase with the current flowing in at the polarity marked side or terminal on the primary
true
pneumatic cylinders differ from hydraulic cylinders mainly by
needing no return lines
hysteresis can be explained as
friction of the molecules due to alternating current
Where frequent cleaning is necessary, it is best to use
duplex strainer
Applying heat to a specific volume of gas in a closed container will
increase gas pressure
The primary reason for not replacing a blown fuse with a piece of copper wire is because
the desired circuit protection against overload may be lost
Rotary-screw compressors run at speeds ranging from ____ to ____ rpm
3000
12000
A back pressure type valve is normally
open
Most pipe is generally coated on the outside with paint, galvanize, or insulation to prevent
corrosion, condensation, and heat loss
A blowout coil would most likely be found in
an air magnetic circuit breaker
A well designed protective relay system should provide three basic operational characteristics. what are they
reliability
selectivity
speed
A diaphragm-type relief valve responds very quickly to a pressure change because of its
large pressure-sensitive area
Penstock velocities may range from
6 to 20 ft/sec
The relay-time setting is adjusted by means of
time-index lever
Limiting compressor output with a pressure-control valve may be accomplished by
holding open the valve ports
The minimum velocity of water in a power canal to prevent the deposit of silt is
2 to 3 feet per second
A diaphragm-type relief valve responds very quickly to a pressure change because of its
large pressure-sensitive area
The light spring in a restrictor type flow control holds the pressure compensator normally___
open
