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What is the primary method used to distribute energy aboard ship?
Electricity.
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What two types of AC Generators are used aboard ship?
- Rotating field - Stationary armature
- Rotating armature - Stationary field.
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Which type of AC generator is used on GAS turbine powered vessels?
Rotating field - Stationary armature.
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What are two major components of a rotating field - stationary armature generator?
Stator and rotor.
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The stator is also known as what on a rotating field - stationary armature generator?
The armature.
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The rotor (field) is the rotating part of a generator and is driven by what?
The prime mover.
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What is used as the generator prime mover aboard ship?
Either a diesel engine or a Gas turbine engine.
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How is direct current induced into the generator rotor?
By a voltage regulator.
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What determines the number of magnetic poles required on the rotor and the frequency output?
The design speed of the generator.
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Field excitation in a brush-type generator is provided by what?
Either slip rings or brushes.
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Newer Brushless generators use what to induce field excitation?
A silicon rectifier assembly.
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What allows for the transmission of energy from the rotor to the stator?
The magnetic field.
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Varying current to the rotor allows you to control generator?
Output voltage and reactive load (amperage).
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What type of generators are used in the fleet for snip's service and emergency power?
Brushless AC generators.
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What advantage do brushless type AC generators have over brush-type AC generators?
Simplex design, Compact, Free of sparking, Reduced maintenance.
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What is the function of a silicon rectifier?
To furnish Direct Current to the AC generator rotor field.
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Prime mover speed is controlled by what?
A installed governor.
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What NSTM contains general information on AC generators?
NSTM310.
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What is used to adjust the compounding effect of the series field winding and the voltage regulation on a DC generator?
A shunt or diverter. . .
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What is an equalizer connection?
Connects two or more compound wound generators which are to operate in parallel.
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What is another name for a commutating pole?
Interpole.
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Commutating windings serve what function?
To correct flux distortion caused by armature reaction.
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Diesel engine driven generators operate within what speed range?
400 to 1800 RPMs.
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What are two different modes of DC generator speed control?
Speed governor and manual voltage control (rheostat).
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What device is provided on a turbine-driven DC generator to trip the generator circuit breaker when the throttle valve is tripped closed?
A shunt trip switch.
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Generator overspeed trip set points are verified IAW what directive?
The Planned Maintenance System (PMS).
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When conducting generator overspeed trip testing, how many means of measuring speed are required?
Two independent means and one must be a non-stroboscopic tachometer.
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How often are Turbine-driven generator overspeed trip tests conducted IAW PMS?
Quarterly.
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What action must be taken if a generator set inadvertently overspeeds?
Trip the manual shutdown and trip the generator circuit.
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When checking brush clearance on a newly overhauled AC generator, what should the brush pressure be when no pressure can be found in a technical manual?
2 PSI of brush area.
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Blackening on all bars of a DC generator commutator indicates what?
Incorrect brush pressure.
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Generator collector rings that are blackening on a DC generator is an indication of what?
A unbalanced rotor.
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What type of cloth is recommended when removing blackening from a DC generator?
Canvas.
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What reference is used to determine commutator/slip ring gap?
NAVSEA Handbook S9310-AC-HBK-010 (Commutator/Slip ring maintenance handbook).
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What is an indication of a open or loose connection in the armature?
A bright spark which appears to pass completely around the commutator.
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What is indicated by a bright spark each time the contact passes under a brush?
A loose soldered connection between the commutator risers and armature coils.
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What is the no-load neutral point on a commutator?
The point at which minimum voltage is induced between adjacent commutator bars when the machine is running without load and with only the main pole field winding excited.
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How does the manufacturer mark the neutral point?
By a chisel mark or an arrow on a stationary part of the machine.
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What are three methods used to determine the neutral point?
Mechanical, reverse rotation and the kick method.
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What method of determining the neutral point involves turning the armature until the two coil sides of the same armature coil are equidistant from the center line of one main field pole?
Mechanical method.
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What device is used to measure machine speed in the reverse rotation method of determining the neutral point?
A tachometer.
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What method of determining the neutral point is associated with initial settings?
The kick method.
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When performing the kick method, field current is reduced by what percentage of normal value?
10 percent.
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The commutator of a properly operating machine will have what appearance?
A uniform, glazed, dark brown polish where the brushes ride on it.
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What effect will an open circuit in the field winding have on a operating non-paralleled AC generator?
An immediate loss of armature voltage will occur with a subsequent loss of load.
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Where do open circuits in the field winding normally occur?
At the connections between poles.
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What is the most common cause of a short circuit in a brushless exciter?
A defective diode on the rotating rectifier.
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A desiccant bag that is designated as an eight unit bag, weighs what amount?
1 Pound.
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Desiccant must be replaced when the humidity card indicates what?
40 percent relative humidity.
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A satisfactory operating desiccant humidity indicator card will be what color?
Blue.
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What is the prefered method of removing loose particles from windings when stoning commutators?
By use of a vacuum placed adjacent to the commutator.
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What is the function of a brush sealer?
To ease the seating of brushes.
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What are three approved methods to determine correct neutral position when dealing with commutating pole machines?
- Mechanical
- Reversed rotation
- Inductive kick.
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What method of setting neutral position would be required on machines that rotate in both directions?
Reversed rotation method.
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An indication of improper commutation surface would have what appearance?
A nonuniform or bluish colored surface.
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A proper commutation surface will have what appearance?
A uniform glazed dark brown color.
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What is the most effective method of cleaning a collector ring?
By use of a canvas wiper.
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What is the maximum TTR for collector rings?
.001 - .002 inch.
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An AC stator winding that is suspected of a short circuit can be verified by testing for what?
An insulation resistance test of the windings.
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A bright spark which appears to pass fully around the commutator indicates what?
An open armature coil.
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What tool is used to conduct armature commutator radial checks?
A dial indicator.
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What cleaning method is used when compressed air and vacuuming fail to properly clean oil from the windings of a generator?
High pressure water spray.
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Who is the approval authority for using an alternate type of high pressure water sprayer?
NAVSEA.
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When using the high pressure water sprayer what is the required water temperature?
130 - 150 degrees F.
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The high pressure water sprayer is normally set at what pressure prior to use?
2500PSL
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Polyamide paper serves what function when dealing with windings?
Acts as an insulator.
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Why is a high potential test conducted on a reconditioned peice of equipment?
To test the insulation for weakness.
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What is the required clearance between the winding and the frame on a peiece of equipment?
1/8 inch.
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What is the reason that new or reconditioned windings are varnished?
To prolong service life.
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How is varnish applied to large, heavy generators used in propulsion applications?
By spraying using air drying varnish.
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Baking varnishes must never be stored were temperatures exceed what?
104 degrees F.
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When determining the proper thickness of a U-shaped cutter to repair commutator mica, what is the formula?
The thickness is equal to mica plus or minus .001 inch.
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After undercutting with a U-cutter always chamfer the commutator bar edges to what?
1/64 to 1/32 inches.
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What tool is used to chamfer the commutator bar edges?
A slotting file.
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How are small commutators undercut?
By use of a bench type undercutter.
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Defective commutator mica is removed and replaced by what?
Sodium silicate.
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What tool is used to indicate shorts and opens on the inside of stators?
Internal growler.
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When is core testing mandatory?
On all motors requiring rewind by an EVLA or depot.
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What is the proper brush pressure set to on a integral kilowatt machine when no technical manual is available?
A pressure of 2 to 2.5 Ib/in2 on contact area is used.
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When would hand stoning of a commutator surface be required?
When machine stoning cannot be accomplished.
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What type of commutator surface stoning is used in cases of eccentricity, high bars, or out of round conditions?
Fixed stoning.
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