Last 6th Month Flashcards
The rotating weight of the unit is transferred through the thrust bearing, through the upper bridge, and through the______ ______ to the foundation
Stator frame
On an umbrella unit, the thrust bearing is located:
Below the rotor
The three typical types of thrust bearings are.
adjustable shoe, self equalizing and spring loaded
The adjustable shoe thrust bearing uses a_______ under each of the shoes for adjusting the height and loading of the shoes.
Jack screw
To install the thrust block, it is heated to a predetermined temperature and lowered over the shaft, again with the unit on jacks. The block is set on the________ the rigging removed, and the radial keys and keeper installed.
Thrust shoes
With the thrust block still hot and installed on the shaft, the jacks are released to
allow the full weight of the unit to set the block in place against the keys
Using the thrust bearing high pressure lubrication system, allows for both________and________ movement required during the alignment process.
Rotational; lateral
As alignment deviates, loading on the guide bearings wil increase as wil_______ levels
Vibration
Any increase in vibration from misalignment will decrease the_______ factor of operation in severe circumstances
Safety
The concentricity of the stationary components can be checked by.
hanging a single tight wire to check plumb reference
The tolerance for plumb of center of shaft run-out is_______ multiplied by the length of the shaft from the highest plumb reading to the lowest plumb reading in inches.
0.000025
The tolerance for shaft straightness should not be more than______ inch from a straight line connecting the top and bottom reading point.
0.003
The parallel misalignment between two shafts that occurs at the coupling between the generator and turbine shaft is called.
Offset
Shaft dogleg is
angular misalignment of the turbine and generator shafts
Plumb wires should be hung______
apart.
90° 
The first preliminary check during the alignment process, is to loosen the mounting bolts on each leg of the upper bridge to check for
Soft foot
One of the most important things to check before taking alignment readings is to make sure the
Shaft is free
The procedure that is particularly useful during major overhauls is to temporarily install the upper and lower bridges and the head cover to check the concentricity of the stationary components with a single plumb wire and a(n):
Electric micrometer
When the unit is centered the concentricity can be checked by taking______ readings at the turbine guide bearings, seal rings, generator air gap, etc.
Clearance
Correcting dogleg between the generator and turbine shafts requires installing a shim pack between the
Coupling faces
The second method used for aligning Hydrounits with Adjustable Shoe Thrust Bearings is using the adjustable feature of the shoes only to achieve equal:
Loading
On Self Equalizing Thrust Bearings, one step in the procedure is to center the shaft in the_______ ________ housing and move the______of the shaft to make plumb.
Turbine bearing; top
The final step in the alignment process is the installation and adjustment of the
Guide bearings
To make the generator guide bearings concentric to the turbine guide bearing, the________ is used as a Reference
Shaft
When installing the turbine bearing, several______are used to prevent lateral movement.
Dowels
Although vertical Hydro-unit machines may be extremely large:
Close tolerances must be maintained
The vertical Hydro-unit machine that has the thrust bearing and upper guide bearing located above the rotor is called
Suspended type
On large low-speed vertical hydro-unit machines, the rotor poles are secured to the rim by
Driven tapered keys
On an adjustable-blade pump or propeller (Kaplan) type turbine, a hollow shaft is required on the electrical machine to
allow oil pipes to be carried through the shaft from the oil head at the
top of the unit to the turbine servomotor
On guide bearings, lubrication arrangements eliminate the need for an oll circulating system.
The designated oil level is usually about______
the length of the bearing above its lower end
1/3
Brakes are usually operated by compressed air at________ psi. When used as jacks, the brakes are operated by an oil pressure of_________psi
75-100; 1000-3500
High-pressure bearing lubrication is frequently used to reduce:
Breakaway torque
The high-pressure bearing lubrication pump assembly uses a_________ to prevent starting the machine (hydro-unit) until the pressure is approximately 1000 psi.
Pressure switch
Prior to erection of the unit, the turbine or pump runner and shaft are centered and supported in a position at a specified distance usually_______inch below the correct operating position.
1/4 to 3/4
During the alignment process, fins should be provided on the plumb bob to allow it to hang in a pail of heavy oil to dampen any swings and protect the plumb line from:
all strong air currents
Electric welding on any part of the machine is a serious hazard to bearings. A bearing surface can be damaged:
rapidly if welding current passes across it
In regards to Hydro-units, if possible all electric welding should be done
before bearings are assembled
The thrust bearing tub cooling coil should be water-tightness tested to a water pressure of ______% of normal working pressure.
150
Precautions should be taken during assembly of the thrust bearings to avoid:
All of the above
Segmental bearings made up of independently adjustable segments must be set to:
Proper elevation and clearance
To eliminate the possibility of shaft current. bearings and other parts should be;
Insulated
Check the insulation with a______
volt insulation meter, if the resistance is less than_______ohms inspect the insulation and make necessary corrections.
500; 20,000
Before drawing the couplings together, their mating surfaces must be in alignment, parallel, clean and free from burrs. The couplings must be drawn up:
Evenly to prevent distortion
Coupling bolt tension can be determined by an accurate measurement of the bolt:
Elongation
To prevent plumb wires from swaying and twisting, the finned weights should be immersed in pails of:
Oil
Check commutator________with a dial indicator rather than by visual observation
Run-out
Various instruments and relays and their associated equipment, wiring, piping and conduit should be carefully installed, making sure that it does
Not short-circuit the bearing insulation
The rotating parts of the machine must be in______ balance and may require the addition of weights to the rotor.
Dynamic
Before connecting the generator to the power system check.
Phase sequency
If an operational check of the shaft run-out is required, make it after the generator:
Is operating under full load
The best way to determine the correct running clearance in a plain-bearing installation is to
Consult manufacturer’s charts and tables
The ability of bearing material to dissipate excessive heat generated during operation is called
Thermal conductivity
The ability of bearing material to flow slightly when loaded is called
Conformability
An advantage of grease compared to oil in lubricating a plain bearing is that
Newly applied grease forces old lubricants out
Discoloration in plain bearings is generally a symptom of
Excessive heat
Which of the following should be used to measure the running clearance of a plain bearing?
Feeler gauge
Which method should be used to remove moisture from a bearing shell after it has been cleaned?
Preheating
When building a plain bearing liner, coat the mandrel with_______ to keep molten babbit from clinging
White lead
What is the purpose of the grooves cut into a plain bearing liner?
Circulate lubricant
Which is the most likely cause of screeching from a plain bearing during operation?
Clearances are too tight
If you must leave your workplace temporarily, what care should you give a new, unmounted antifriction bearing?
Wrap it in oil-resistant paper
To prevent creeping of an inner bearing ring around the shaft, you should mount the inner ring with a(n)______fit
Interference
You can force an antifriction bearing into position on the shaft by using an arbor press or by impact, if the bearing has an O.D. Of
4in or less
A bearing is driven up a split tapered adapter by
Tightening a heavy-duty locknut
At approximately what temperature should you begin to suspect a bearing problem?
200° F
You clean an antifriction bearing before installation if it
Will be lubricated by automatic oil-mist
If the shoulder is too low when seating an antifriction bearing on the shaft the
Inner ring may distort
When inspecting a tapered shaft by blueing the gauge bore a(n)_______ % blueing transfer is acceptable.
80
When cold mounting an antifriction bearing, you must
lubricate the bearing bore and shaft with light oil
Which of the following is not an approved way to heat a roller bearing for a temperature mount?
Gas-operated torch
What is the correct tool to use when removing a locknut from an antifriction bearing installation?
A spanner
When you use a puller to remove a taper-mounted bearing, what should you do with the locknut?
Back the nut off several turns
An aluminum heating ring is designed for mounting and dismounting the inner rings of a_______bearing
Cylindrical roller
When you use an aluminum heating ring to expand a bearing, heat the ring to
500 °F
If you have cleaned and inspected an antifriction bearing but do not intend to reuse it immediately, how should you treat it before wrapping it in oil-resistant paper and storing it?
Fill it with grease
The two main methods of removing antifriction bearings are
Impact and heating
Which of the following is a correct way to remove an antifriction bearing with a diameter smaller than 4 in.?
Arbor press
The two important dimensions of a bearing puller are spread and
Reach
To remove a bearing, a splitter may be used with a(n)
Mechanical puller
Which of the following should not be used to clean an antifriction bearing when inspecting it?
Steam
Which type of bearing seal keeps out water, dirt, and contaminants most effectively?
Contact seal
Which type of antifriction bearing can tolerate the most internal misalignment?
Spherical roller bearing
The correct tolerance range for shafts from 2 to 4 in. in diameter is nominal to
-0.001in
When you lubricate bearings with grease, the actual lubricant is_______ which is held in suspension
Mineral oil
As a rule, the interval between lubrication renewals is cut in half for every 27° F increase in temperature above
160 °F
A special type of pillow block sometimes used on belt conveyors is called a
Takeup
To find the takeout amount needed to calculate final clearance when installing a bearing, refer to the
Manufactures chart
Which type of lubricant increases the effectiveness of a labyrinth seal?
Grease
Bearing temperature is typically________to_________ °F higher than the temperature of the housing
15;25
The threads of an acme screw are
Squared off and thick
Ball bearing screws are designed to
Move loads vertically and horizontally
The screw in a ball bearing screw is supported by
Standard ball bearings
In a contact seal, what forms the actual seal?
A thin film of oil
Before you install a lip seal, chamfer the end of the shaft and the leading edge of the housing bore at an angle of_______to______degrees.
15;30
The rolling contact of a ball bearing screw is_______% efficient.
90
Which of the following carries the load moved by a ball bearing screw?
Ways
When preparing a ball bearing screw for installation, use a_______ to expand the inner ring Og the bearings.
Hot-oil bath
Which seal is most effective when large quantities of contaminants are present close to the machinery?
V-ring
Which seal material works well for machines operating at extremely low temperatures?
Silicone
When using the grub screw method to hold a bearing in a pillow block, use
No collar
In planning a major overhaul of a hydroelectric unit, one of the best sources of information is.
Maintenance records
Determining the condition of the equipment should be done by performing a thorough inspection of the unit
6-12 months before the planned overhaul
A list of________ for all of the machine’s components should be made from the drawing information
Weights
If substantial welding is needed, then a_______for the required repairs should be
written and distributed to all personnel that will be involved in the welding.
Welding procedure
Units with replaceable seal rings should have a________onsite
Spare set
Shaft run-out readings, bearing temperatures, pressures and Permanent magnet generator (PMG) voltage are all part of
Pre-shutdown readings
Pre-teardown readings include.
Shaft alignment readings, guide bearing clearance, seal ring clearance, and generator air gap
To make sure parts are installed in exactly the same position from which they are removed, they should be ________prior to removal
Match marked
The rigging to lift the thrust block should include (a) _______ so that the block can be kept level to prevent binding when it is lifted off the shaft.
Turnbuckles
After removing thrust and guide bearings, minor scratches and even some deep gouges can be adequately repaired by________
the high spots from the babbitt surface.
Scraping
In most cases, the repair of_________
damage can be accomplished much more effectively with the runner removed from the turbine pit, as the runner can be positioned for easier access.
Cavitation
Operational readings should be taken once the unit has been determined to operate with no problems, they include:
Bearing heat run, shaft run-out readings, load rejection tests
To prevent the damage that could occur from circulating currents passing through them the following are insulated from the frame and should be checked with an ohmmeter prior to startup:
Upper guide bearing, thrust bearing,pmg
A very thorough inspection of the________ __________ and the _________ _________ should be made to check for any bolts, nuts, tools, etc.
Generator housing; spiral case
There should be________ leakage upon the initial startup after the installation of new turbine shaft packing. The packing gland should be________ evenly and in small steps until the leakage is reduced sufficiently.
Generous; tightened
When setting clearances on upper and lower guide segmented shoe bearings, install a feeler gage to check clearance by
inserting the feeler gauge so that it extends all the way through the
bearing
When working on wicket gate adjustment, the amount the servomotor travels after the gates contact each other is referred to as the________.
Squeeze
When aligning a unit, it is important to make the bearing centers all_________
the shaft must be perfectly plumb. This can be accomplished by installing the turbine bearing and shimming the shaft to center in the_______bearing(s).
Concentric; turbine
A more accurate method of measuring the preload of a coupling bolt is to measure the amount the bolt ________ as the nut is tightened.
Stretches
When doweled components are moved during the alignment process following the overhaul of a unit,________
is necessary
Re-doweling
Dowels have a very________ fit to prevent the components from shifting once the part is positioned.
Tight
To find the unit’s center, the upper bridge and head cover should be installed after all the _______ parts have been removed. A ________ wire should be hung through the unit and reference measurements taken from the stator, the turbine bearing housing, the packing box bore, and to trammel points in the draft tube
Rotating, single
Bearing cooling coils should be thoroughly inspected and ________ tested
Hydrostatically
The interior bore of the packing box can be built up with ________, as long as the box is structurally sound
Epoxy coating
Where an overlay of a dissimilar material is being used, such as stainless steel over mild steel, enough material should be removed to allow at least_______
weld passes to be made.
Three
The machine operator frequenty can give the troubleshooter
Valuable information
Mechanical, hydraulic and pneumatic systems all are worked on by the
Mechanical troubleshooter
The purpose of good maintenance is to
Keep machines and equipment working
Amantenance specialist reports to craft supervisors in all plant departments in a plan organized under
Central organization
In a large plant, the building-mantenance groups is most likely to be made up of.
Electricians, mechanics, plumbers, carpenters, and painters
All communication is essentially a cycle of ________ step(s).
Four
When you give a person a chance to express himself, you may
Find him easier to work with
Writing down an order
Helps prevent misunderstandings
Before you make a repair, you should
Find out what your responsibilities are
if you have a problem or complaint about your job, you should
Report it directly to your supervisor
If possible, you should schedule repair work for a time when
The machine is not in use
Before you can diagnose problems, you should
Be able to recognize normal operations
An ohmmeter measures
Resistance
Air supplies should be checked
When the machine is running
Your first duty in an emergency is
To protect workers from injury
Which of the following displayed symbols describes a flanged tee?
Given the drawing and information below, calculate the face-to-face distance between the fittings
5ft 4in
