Generators, motors, thermocouples and tachometers Flashcards
Current of each leg of delta and Y-Connected generator is divided by?
1.73
Equation for finding out (F) Hertz
F = # of poles x RPM / 120
Fuck = nopR 120
What is the horsepower equation?
[2π(rpm)(torque)]/33,000
What is an electric brake?
A device operated by electromagnetic means which functions to bring a load to rest mechanically and hold it at rest.
What are the 2 types of rotors in generators?
Salient pole and cylindrical types.
For synchronous speeds of 1,800 RPM’s and lower you will use a ______________ rotor.
Salient pole
For synchronous speeds of 3,600 RPM’s and higher you will use a _____________ rotor.
Cylindrical
What piece of equipment is an instrument capable of generating, transmitting and indicating information that can be converted into a measurable of rotational speed?
Tachometer
Where do you compare proper operation of rotating equipment RPM?
Name data plate
Equation for finding RPM?
120 x F / # of poles
What are the 3 types of hand held tachometers?
Centrifugal, Photo Electric and Chronometric
A sensor that converts a measurable pressure into an electrical output signal that is proportionate to the input pressure is?
Pressure transducer
What are the 2 types of pressure transducers?
DC 2 wire system and AC 4 wire system.
What is max length cable for 0-5VDC pressure transducer system?
100 feet because of interference
What’s a common problem in pressure transducers?
Moisture inside of it
Kings Nitronic pressure transducer uses what gas?
Nitrogen
When replacing transducer make sure what?
Right wire size…
What is an RTD?
Resistance Temperature Detector
What are the 2 types of elements of RTD’s?
Nickel 40-400 degrees
Platinum 40-1,100 degrees
2 wire RTD colors are?
1 red and 1 white
3 wire RTD wire color is?
2 white and 1 red
What does positive temperature coefficient mean?
As temperature raises so does resistance
What are the 3 types of configuration of RTD’s?
Thermowell, Bare Bulb, Embedded
What is a thermocouple?
A device used to measure temperature.
K Type thermocouple is made up of?
Chromel (Yellow +) and Alumel (Red -)
J Type thermocouple is made up of?
Iron (white +) and constantan (red -)
Air gap through the distance and thousands of an inch between the _________ and __________?
Stator and rotor
Air gap should be within _____% tolerance.
10%
Air gaps are measured with a ________________________?
Feeler Gauge
2 ways for installing bearings?
Arbor press and heat method
Preferred seating method is using what grit sand paper?
80
The mag pickup is used to detect the speed of the _________?
Prime mover
Forcing to much grease into a bearing may cause _______ and eventually _________ to the bearing.
Overheating and destruction
Chattering of a contactor may indicate what?
Rusty or pitted surface of the contacts
What are the 2 procedures for checking the temperature of windings?
Thermometer method or resistance method
Portable power tools must be checked?
Quarterly
What must never be used to clean contacts of a contacter?
Emory cloth
The gap reading between mag pickup and the gear should be ______ inches
.01-.04
What component accomplishes speed in phase matching up generators?
Synchronizer
One of the more common malfunctions of a synchronizer is no _________ control.
Governor
What component senses the output voltage of the generator compares a sample of that voltage with a reference voltage and supplies the field power necessary to maintain the predetermined ratio between the generator voltage and the reference voltage?
Voltage regulator
One of the most common problems of a voltage regulator is?
Over voltage
Why do you check windings temperatures on motors and generators?
To compare insulation resistance
The purpose of the polarization index test is to determine the condition of the?
Generator windings
If soft foot hasn’t improved in ____ corrective attempts, a bent foot condition may exist.
2
As the ambient air temperature changes, the cold junction will begin to produce its own electrical potential. This would cause an erroneous reading of the actual thermocouple. What is this called?
Cold junction compensation
A thermocouple is a key sensing component of a _______?
Pyrometer
What type of tachometer is used if the rotating shaft is not readily accessible?
Resonant
The prime mover stabilized using various types of?
Feedback
Brush holders are reaction type with 2 brushes inclined __________ ___________ at 35 degrees?
Against rotation
What is a generator heated with?
Stand-by exciter
What is the function of the reverse power relay?
Circuit protection for the prime mover
What type of adjustments can be made to the reverse power relay?
Time delay and a set point adjustment
An electrical motor that turns a generator to supply the closely regulated type III electrical power is known as an _______________?
Motor generator set
Motor insulation temperature of 10°C or higher than the manufactures recommendation will shorten the insulation life by how much?
Half
What is the distance of the mag pick up from the gear?
.25 and 1.02mm
Or
.010 and .40”
What item will shut the prime mover down if the magnetic pickup signal fails?
Speed sensing failsafe
What is the purpose of the magnetic pick-up?
Used to detect the speed of the prime mover.
The 2301a electric control requires a minimum output of how many volts from the magnetic speed pickup at the lowest control setting?
1.5 volts
What item generates an AC voltage whose frequency is proportional to the prime mover types and sizes?
2301 control, mag pick-up, current transformers.
Soft foot is corrected by adding what?
Shims
A condition that exists when the bottom of all 4 feet of a machine are not on the same place is called what?
Soft foot
Why are brushes on motors adjusted?
To keep brush pressure constant.
The woodward PGA-EG governor/actuator is designed specifically for marine applications requiring ______ control and ______ backup?
Electronic control and Mechanical backup
What interface is used to make adjustments to the 723plus electronic governor control unit?
Watch Windows
In a governor control system, the prime mover is stabilized by using various types of ______?
Feedback
On modern commutating equipment, under what condition is some sparking under the brushes considered normal?
At high speeds
Rated frequency of a motor or a generator can be found?
On the machines nameplate data
What information is found on a hand held tachometer?
Calibration date and due date
Thermocouples will produce what type of electrical output?
Millivolts
Motor insulation temperature of 10 degrees C or higher than the manufacturer’s recommendation will shorten the insulation by ?
1/2
Why do you check winding temperatures on motors and generators?
To compare insulation resistance measurements
What chart must be used to correct insulation resistance measurements to 25°C
Insulation resistance-temperature nomograph
What are the 2 methods for checking winding temperatures?
Thermometer method and resistance method
The purpose of the polarization index test is to determine the condition of the _______?
Generator windings
What is the purpose of checking the air gaps of motors and generators?
To monitor the equipment for abnormal conditions
Checking the phase balance and rotation on motors and generators prevents ______ for occurring?
Decreased efficiency
What indication would you see if a motor or generator was out of phase?
Decrease if the efficiency
What are the 2 acceptable methods for installing bearings?
Arbor press and the heat method
Brush holders distance from the commutator should be not more that _____ and no less than _____ of an inch.
1/8 and 1/16
What method do you use to fix staggered brushes and what does this prevent?
Wrap 80 grit sand paper around collector and manually rotate it 5-6 times.
This prevents curving of the commutator.
Why must 2 machines be aligned?
To prevent premature machinery failure
What tolerances are checked when aligning the pump and the motor shaft?
In service and caution tolerance
If a soft foot condition has not improved after 2 correction attempts, a ________ exists?
Worn foot
What is the preferred method for checking pump shaft alignment?
Indicator reverse method
The difference between rated speed and synchronous speed is called?
Slip
The percentage of a motor can be overloaded for a short period of time is called?
Service factor
Which type of overload device is heat sensitive and connected in series with a motor load circuit?
Thermal overload
What are the 2 types of contacts on motor controllers called?
Main and Auxiliary
What % over the load should fuses be in transformer and inductive load circuits?
125%
what motor component sustains the weight of the rotor and keeps it precisely centered within the stator?
End bells
What indicates the period of time in which the motor will run fully loaded at rated speed without overheating and exceeding a predetermined temperature rise?
Duty
What is the reference for the resistance test record card?
NAVSHIP Form 531
How long do megger cards stay onboard?
The life of the equipment being tested, if equipment is removed off the ship, the cards go with it.
What are 3 types of overload relays designed to interrupt the motor circuit and prevent damage to the windings and insulation?
- Thermal
- Magnetic
- Electronic overloads
Which component of an electric motor causes current to lead voltage, thus increasing torque during start up?
Capacitor
On NAVSHIP form 531, each vertical line represents _____ days?
5
Magnetic pickup voltage _________ as the air gap is _________?
Decreases
Increases
Motors and generators used on propulsion plants are usually insulted with class ___ insulting material?
B
Generators and propulsion equipment should be cleaned?
Monthly
When 2 or more DC generators are connected what device disconnects a generator from the line if the generator starts drawing from the line?
A reverse CURRENT relay
How do you clean the contacts of a contactor?
You don’t. They are self cleaning
When a motor or generator is submersed in salt water, what should you do to fix it?
Flushed out with fresh water and let it dry. Never let the equipment dry before flushing it with fresh water.
What motor is the most used aboard ships?
Polyphase induction AC motor
What rule should you use to determine the direction of the induced EMF coil?
The left handed rule
What is the purpose of slip rings?
To conduct the currents induced in the armature to an external load.
What component causes a generator to produce DC voltage rather then AC voltage at its output terminals?
The commutator
What causes sparking between the brushes and the commutator?
Improper commutation
Magnetic induction occurs when there is motion between what 2 elements?
Conductor and the magnetic field
The part of the alternator in which the output voltage is generated is?
Armature
What does the term single phase mean?
One voltage or one output
What determines the phase relationship between the voltages in a 2 phase AC generator?
Placement of the armature coils
In 3 phase motors what is the phase relationship between individual output voltages?
Each phase is displace 120 degrees from the other 2
What are the 2 ways of connecting the outputs from a 3 phase alternator?
Wye and Delta
What transformers and connectors are used to convert 450/3 phase to 115 volt single phase?
3 single phase, delta-delta, step down transformers.
What are the 3 types of AC motors?
Series, synchronous, induction
Series motors generally operate what type of equipment?
Small appliances
Why are series motors sometimes called universal motors?
The can operate at either AC or DC voltages
Angular displacement between field poles in a 2 phase motor are how many degrees?
90
Major difference between 2 and 3 phase motors?
Number and location of the field poles
What requirements is the synchronous motor specifically designed to meet?
Constant speed required by some loads
Why are induction motors used most often?
The are simple and inexpensive to make
What determines the amount of slip in a motor?
The load
When seating brushes 100%, brushes are?
Glossy with no distinct lines
Brush pressure should be _____ lb/in is the manufacture tech pub isn’t available?
2 - 2-1/2 lb/in
A power factor meter connected to measure the phase relation between the generator and bus bar voltages, the moving element is free to rotate continuously.
This defines?
Synchroscope
What is the voltage and frequency variation on motors installed on ships?
10% +/- voltage
5% +/- frequency
